Truck and Barter: Does Driving Slower Save Gas?

Does Driving Slower Save Gas?

By Kevin

Michelle Singletary advises that to save on gasoline, we should, among other things, slow down.

Stop speeding. The faster you drive, the more gas you use, the more money you spend. Each 5 mph over 60 is equivalent to paying an extra 10 cents per gallon for gas....

Avoid aggressive driving and quick starts and stops. At highway speeds, you'll lower your gas mileage by about 33 percent. By maintaining a constant speed and driving sensibly, you could save as much as 50 cents a gallon.

I'm not going to discuss the time cost of slowing down. For arguments sake, assume that you're indifferent between sitting at home or sitting in your car. Is it true, regardless of your car make, model, and condition, that driving 65 instead of 60 increases average fuel cost by about 10 cents per gallon? I'd say yes, with anecdotal caution.

It seems about right, but only if gas prices are about $2.50 per gallon. This is confirmed by a casual analysis of the graphics provided by the government.

fueleconomy.gov reuses the following graphic without explanation of sources or methodology:

Assume this graph represents an average automobile. That line conveniently peaks at 55MPH, which seems to be the government's consensus estimate for "most efficient". But the government sometimes uses an extended graphic in it's reports:

This graph has the same long plateau, a drop in efficiency from 55 to 60, and a much smaller drop from 60 to 65. It looks to me like driving 60 MPH saves you 1 MPG compared to driving 65 MPH. 1 MPG/26 MPG = ~4% increase in efficiency, or about 4% less fuel needed to drive the same mile. At $2 a gallon, this saves us 8 cents per mile.

But including speeds from 0 to 15 on the left makes fast highway driving look very favorable to slow log-jam traffic. It's more fuel efficient to speed home early than to sit in rush hour parking lots.

But an honest examination of fuel efficiency must conclude that the optimum fuel efficiency speed is not easily calculated, although the "sweet spot" is usually somewhere between 40 and 60 miles an hour, depending on the type and configuration of each car, and weather conditions.

Confirming the chart's line: In my wife's Volvo V40, I averaged almost 30 MPG driving at 65 MPH up and down I-95. I found that there was no perceptible difference in fuel efficiency between cruising at 60 and cruising at 65.

-- June 24, 2004 4:10 PM | Permalink

Comments

John Doe wrote:

Driving fast imposes huge negative externalities on others. Tens of thousands of Americans are basically murdered by negligent drivers each year, yet we continue to call these homicides 'accidents.'

Perhaps black boxes in cars and 'smart road' technology will improve commuting. If driving speed and lane changes could be precisely controlled in key places at key times, perhaps road capacity would increase, while commute times and traffic fatalities decline. Pehaps 'smart lanes' could be built as toll lanes so the public would see them as a new choice and not an imposition.

-- June 24, 2004 6:02 PM ∞

gerald wrote:

In my car, on long interstate trips, I see no significant differences in mileage between going 70 and going 95. If anything, it may have been better.

I suspect that there is a *lot* of variability in different cars depending on engine size and torque, aerodynamics, and especially gearing. Perhaps the elevation at which I was driving also made a difference, as the higher-speed driving tended to be in the high west. Hmm. Maybe the air-conditioning was the main factor.

-- June 24, 2004 8:59 PM ∞

Ian Wood wrote:

"Stop speeding. The faster you drive, the more gas you use, the more money you spend. Each 5 mph over 60 is equivalent to paying an extra 10 cents per gallon for gas...."

This is nonsense.

If you pay $2.11 for a gallon of gas, you've paid $2.11 for a gallon of gas, whether you burn that gallon travelling ten miles or thirty miles.

You can save pennies per mile, but not pennies per gallon.

-- June 25, 2004 4:16 PM ∞

Eric Krieg wrote:

Okay, she's got the units wrong (you are paying more per mile, not more per gallon by speeding).

HOWEVER...

The physics are undeniable. Driving faster increases the drag force due to aerodynamics on your vehicle. The drag force increases at the square of your velocity, so driving twice as fast results in 4 times the drag force.

You WILL get better gas mileage at 60 mph (or even better, 55 mph) than at 95 mph. There isn't even an argument there. But you do need to determine how much your time is worth, as well as other factors like safety, blood pressure, etc. During my commute, I generally pump up the tunes, set the cruise control at 65, and park myself in the center lane. It takes me longer to get home, but it is a lot less stressful.

I'm a mechanical engineer, by the way. So I know what the heck I'm talking about on this subject.

-- June 28, 2004 12:48 PM ∞

Nicholas Weininger wrote:

To what extent does variation in engine design and gearing affect the placement of the efficiency peak, though? Drag force can't be the only relevant variable.

On a related note, does anyone know

-- what the highway speed used in determining the EPA highway mileage figures is?

-- same for the European "extraurban cycle" figure?

It seems intuitively likely that the Euro-cycle would use a higher speed, since Europeans drive much faster on their highways; and the Euro extraurban figures I've seen tend to be higher than the EPA highway number for the same car with the same engine.

-- June 28, 2004 7:55 PM ∞

Eric Krieg wrote:

There isn't a car sold in America that isn't in top gear by 55 mph. In fact, most automakers tune their transmissions to get them into top gear as soon as possible in order to save gas.

I'm not saying that slowing down is going to save a HUGE amount of gas for every vehicle. Some cars are more aerodynamic than others. Of course, SUVs, trucks and minivans will save the most money by slowing down.

But gas WILL be saved by slowing down in ANY car. Again, it is physics.

The EPA highway mileage is done at 55 mph. This is a huge bone of contention now that speed limits have been deregulated. It would be more realistic to do the test at 65mph, but that would lower mileage ratings and CAFE numbers. Car makers would have to sell more small cars, not a good thing for the bottom line.

-- June 29, 2004 8:57 AM ∞

Noah Yetter wrote:

Any car with a 6-speed can do 55 in 5th gear, and any car with a 5-speed can do it in 4th. In fact, a 6-speed Corvette can do 60 in *2nd* gear (hardly a typical example, just a striking data point).

The point is, Gear Ratios Matter. If an auto maker wanted, they could push the fuel economy peak to a higher speed. I would contend the demand really isn't there though...

-- June 30, 2004 3:39 PM ∞

Eric Krieg wrote:

Have you ever driven a 6 speed Corvette? It has a wicked annoying feature called a "skip shift". If you leave the stoplight in a leasurely manner, you can't shift from first to second (or third) gear. You have to go right to 4th gear!

This, of course, is a way to improve the 'Vette's mileage.

The 6 speed itself is a great way to save gas. The 'Vette is barely above idle at 55 mph in 6th gear. That is why the highway mileage of a 405hp Z06 'Vette still meets CAFE standards.

The point is that no one actually DRIVES a 'Vette that way. The point is that it CAN be driven that way during the EPA test, and the mileage that results meets CAFE standards.

Oh, and if $2.50 a gallon gas is getting you down, YOU can drive the 'Vette that way and get better mileage.

The fact that NO ONE is slowing down on the highway proves that, despite all the bitching, gas prices are not very high. If they were, people would slow down to get better mileage.

The best mileage will be achieved right at the point that the transmission gets into the highest gear and the torque convertor locks up (on an auto). This speed of course varies from car to car, but the ballpark is around 45mph.

-- July 1, 2004 9:07 AM ∞

Conan wrote:

The first comment is nonsense. Read this study. It shows that when they removed the national 55mph speed limit, fatalities went down.

http://www.safespeed.org.uk/speed-doesnt-kill.pdf

-- July 16, 2004 3:18 PM ∞

anon wrote:

Just an addon. With my 98 escort zx2, JBA header, Pacesetter 2.25 exhaust, .405/242 intake cam, intake Cam gear set at +2, Stock ride hieght,stock computer, 3 inch Aluminum intake, 60mm TB, stock rims and tire size. I got 40mpg at 60mph, 70mph, 80mph, and 90mph but once I got above 93 my gas mileage went progessivly down to no lower than 33mpg which is still higher than the EPA tested 27mpg I'm supposed to get.

-- March 23, 2005 2:09 AM ∞

Bluegrass Audio wrote:

I wonder how many of you smart alecs are slowing down now ...?

FACT: The speed limit is the LAW. Obey it! The life you save could be mine.

"The fact that NO ONE is slowing down on the highway proves that, despite all the bitching, gas prices are not very high. If they were, people would slow down to get better mileage"

-- April 6, 2005 1:50 PM ∞

Larry wrote:

I have a 2003 Dodge Caravan with 6 cyl. I typically drive 60mph on 120 daily round trip to work. I was getting 24.7 mpg at 60 mph and am now getting 28 mpg (over last two tanks of gas) at 55 mph on the tollway and being VERY gentle on accelleration and braking when not. About 11% savings. If we are dumb enough to pay the high prices without doing something proactive, the oil companies will surely oblige us.

-- April 8, 2005 10:07 AM ∞

Joesph Xavier wrote:

When you are in top gear, the only variable becomes drag. The amount of gas you use depends on the RPM of the engine (thusly, driving 35 mph in 2nd or 5th in a manual will produce a dramatic effect on mileage [and engine life...]), which then goes through the transmission (the only variable reducer for engine speed), then to the axle ratio. From there, the wheels turn, and you move the diameter of the tire times pi (circumference) inches. Done many consecutive times quickly, these inches constitute a readable MPH.

As speed increases, the force of air slowing you down increases. What can happen as the speed increases to a point different for each car is that the engine is working enough so that it would be going 75 mph for examle, yet you're only going 70mph. I don't know what the actual effect of drag is, just that its there and thats how it would end up.

If you really want to find out the effect of drag, its kind of simple, really. The formula to find out how fast you SHOULD be going is as follows:

MPH = (Engine RPM * Tire Diameter * pi) / (Gear Ratio of gear for tranmission * Axle ration [final drive] * 1056)

The tire diameter is (the width of the tire in mm * the profile / 50)/25.4 + rim size = tire diameter in inches.

For example, my tires are 235/45R17. (235*45/50)/25.4 + 17 = 25.33 inches.

Given this, and a transmission that has the following gears I - 3.42 II - 2.14 III - 1.45 IV - 1.00 V - 0.70, and a final drive of 4.06, I can do a little test. (If this seems high to you, well, it kind of is, it can easily start in 2nd. BTW, I average about 22mpg city, 28 highway, and its a 170hp 165ft-lb V6 on a 2800lb car).

At 65mph in 5th, I should have 2451RPM. At 65mph in 3rd, I should have 5077RPM. Since it redlines at 7000, I can safely do 65 in 3rd. If I enter the highway in 3rd, and keep it there until I reach 65, I should have 5077RPM, sort of hard to measure, maybe a little more than 5000. If I notice that it is somewhere else, like 5300RPM or 5500RPM, then I know the effect drag has. If it reads 5500, then I should be doing 70.4MPH, but I'm only doing 65.

If you have a manual, then this is an easy test.... In a 4spd auto, my 3rd is like your 2nd, and most autos have OD, D, 1, thus, 4-3-1, no way to select 2. You could try it with OD and D, though. Or if you have a manumatic or SMG, well, thats a given.

If you actually try this, your peak efficiency (100% in a vaccum) will be when your calculated speed for the RPM your enging is turning divided by the actual speed is highest. I don't think it would ever actually be 1.00, though. (If I am going 65 and should be going 70.4, then the efficency would be 92.3%). Be interesting to see the difference in efficiency at 35 and 70. We all know city MPG is lower because of stop and go. This introduces idle, which gets 0MPG, and time in lower gears.

For anyone with a manual, I've done this before and it works fairly well, perhaps you have as well. If I'm going reasonably fast, atleast 35, works real well at 45, and theres a point that I'll have to stop at, maybe 1/4 mile away or a little less, I can shift into neutral or hold the clutch in, and since that lowers my RPM to 600RPM, and I'm still moving, the gas mileage for that little bit of roadway goes up really high. It's actually amazing how much kinetic energy is in a 2800lb vehicle moving 45mph. It can easily send you to that stop sign from 1/4 mile away, and you'll actually have to brake, its not a slow rolling stop. Anyways, done enough times, this can increase mileage (for example, done from 1/4 mi away four times, and if you drive around at 2500RPM average (maybe a little high, but I do get 24mpg driving with 2500RPM in 4th; sending it to 5th puts the RPM around 1800, and there isnt enough torque) but now are doing 600RPM and you got 24mpg average, now you should have 24 * 2500/600 MPG, or better known as, 100MPG. Remember, though, that 100MPG is only when moving from speed. Moreover, if you do that four times per trip, from 1/4 mile, on a trip that is 20 miles, the effect that 100MPG has on the average ends up being less so. If it were in a 10 mile trip, it would be more so. (E.G., 24mpg on 20 miles with this neutral thing for 1 mile, yields an actual MPG of (19*24+100)/20 = 27.8MPG, whilst on a 10 mile trip, (9*24+100)/10 = 31.6MPG.

Anyways, the only effect on mileage is drag once youre in top gear. If I swapped in a new final drive ratio of 3.33, my mileage would change accordingly (from 24 w/ a 4.06 to 29 w/ a 3.33), but I can't really do that. Driving slower should decrease the drag, by an amount that might or might not be significant (I'm taking physics in the fall and my high school physics teacher never got that far), thereby increasing the efficiency, thus making each gallon of gas go further. It's entirely possible that a car that is aerodynamically designed can get the same mileage at 100mph and 55mph. So, really, that graph is bull. Once you reach top gear, your mileage is at a general peak (if I can go fast enough to reach 5th, which is 35mph for me, I automatically get better mileage than the same speed in 4th). How fast do you have to go for drag to decrease it a noticeable amount? Depends on car design. I can tell you right now a boxy Astro van won't be able to go fast with the same mileage...maybe better luck with an Audi TT or Nissan Z, something a bit more aerodynamic.

-- April 23, 2005 5:37 PM ∞

sandra bigwoode wrote:

What I find interesting in these discussions of 55 saves gas is the time factor.

While I believe you will get better gas mileage in most cars at 55 than at 70 mph, it will take you 27% more time to travel the same distance.

Even though your engine is burning less fuel per hour due to the slower speed; it is running for 27% more time which has to be taken in account.

[I am not considering what your personal time is worth for sake of this example.]

Let's say you drive 60 miles at 70 mph at 30 mpg. You have used exactly 2 gallons of gas.

Now you drive 60 miles at 55 mph getting 35 mpg. You have used 1.714 gallons of gas but it took 27% more time [70/55]

What is your fuel savings?

-- May 19, 2005 2:26 PM ∞

Anonymous wrote:

Time is not a factor in fuel savings. You still get to the same place using less fuel, it just takes you longer at lower speeds.

-- August 24, 2005 1:46 PM ∞

T. M. Ross wrote:

In postwar (WWII) Germany, vehicles with carburetors were converted to burn wood, or more precisely wood fuel vapors. In other words the wood did not give of flames much but rather smoldered. I have been told that this was true by someone who was there at the time. It seems to be the case that these vehicles did not achieve the speeds to which we moderns are accostumed but they did "do the job". Is there a reader out there that knows something about this?

-- September 2, 2005 9:14 PM ∞

trey wrote:

if starting acceleration is conservative, it wont matter how fast you are driving because when you drive slower you are still driving for a longer period of time. Its a fact.

-- September 13, 2005 12:26 AM ∞

Rick wrote:

Time is not a factor, because if one person went 60 mph and another went 50 mph, the 60'er used more gallons of gas to get to the same point even though they were there before the 50'er. But that doesn't mean that it is not calculated into the miles/per gallon you get regardless of how far you go. The 50 mph probably got 25 mpg whereas the 60 mph got 24 mpg. But if a person went 40 mph instead of 50 mph they would probably get 25.2 mpg if looking at a graph because time of travel was already calculated in.

-- September 14, 2005 1:10 PM ∞

Zaphod wrote:

You should separate your ideology of slow driving for accident prevention from the engineering reality of driving faster for gas savings. It is a reality. The notion that faster driving uses more gasoline because of air resistance is false especially with modern wind-tunnel-designed cars, because faster driving reduces the throttling loss of a gasoline engine much faster than wind resistance increases. I tried this in real life about 30 years ago. A VW Beetle going no faster than 55 mph gets 29 mpg. According to all the nonsense I see on the net, going 70 to 75 mph should lower that to 24 mpg. Instead, it jumped to 31 mpg.

Get your butts back into classes where you can learn some engineering reality. A GASOLINE engine is more efficient at higher speeds. DIESEL engines are most efficient at the lowest speed that allows them to get into top gear.

-- September 19, 2005 3:02 AM ∞

Zaphod wrote:

To T. M. Ross--

You are interested in wood gasifiers used for fueling car engines. Use a search engine to look for gasifier, wood gasifier, charcoal gasifier, gengas, wood gas, there's plenty of information out there. Be sure to check out the Kalle gasifier.

-- September 19, 2005 3:15 AM ∞

Ron Beuke wrote:

Make it simple and informed!
Buy any motoring mag and you will find the small engined vehicles at 65 mph uses much MORE than a larger engine of the same type, the engine works much harder on these sub-compact's.

Although drag is a HUGE contributor in fuel consumption, aprox 35% of fuel used if my memory serves me correct, all engines have a torque and power curve, to which the manufacturer designs the gear ratio. Hence a small 4 at 65mph will use much more than a medium 6 or even 8Cyl at the same speed.

-- September 19, 2005 9:45 AM ∞

Kris Isaak wrote:

I have a question that maybe you guys can answer if I go from point A to point B at 35mph, then do the same at 100mph, wich speed would be less in gas, for me I would think that ut would be the same becouse it would take longer at 35mph and shorter at 100mph so I would think that it would turn out the same in gas consumption. Is this right or am i just being stupid. lol

-- October 1, 2005 11:29 PM ∞

Kevin Brancato wrote:

Your fuel economy (miles/gallon) depends on your driving speed (miles per hour). The distance you drive at that speed determines the amount of gasoline you use.

Take an example; say you want to drive 100 miles from A to B.

1) You drive 50 miles/hour, and at that speed your fuel economy is 25 miles per gallon. It takes you four gallons of gasoline in two hours.

4 gallons = (100 miles)/(25 miles per gallon)

2) You drive 100 miles/hour, and at that speed your fuel economy is 10 miles per gallon. It takes you ten gallons of gasoline (in one hour).

10 gallons = (100 miles)/(10 miles per gallon)

Time you travel = (distance traveled/speed)

Fuel you use = (distance traveled/fuel economy [given a set speed])

It's obvious that your fuel economy -- by itself -- doesn't change the anount of time it takes to get from A to B. The same principle says that the amount of time it takes to get from A to B -- by itself -- doesn't effect your fuel economy.

-- October 3, 2005 12:43 PM ∞

miles before I get there wrote:

Bitch, moan and complain about speed, time and the price of gas here but the simple fact is, we are wasting what little reserves (worldwide) that are left AND ignoring any kind of strategic backup. I'm doing 55 on my trips to town, 40 miles away, and I'm passed everyday by government vehicles like I'm standing still and it's like some "g" given right to waste. Let's look at the big picture here folks. Who wants to rein in the government at it's best, when it comes to waste? (keeping in mind I'M IN THE MIDDLE OF NOWHERE) Raise your hands? Its got to start somewhere.......N

-- October 27, 2005 7:53 PM ∞

Adebowale Adeleye wrote:

I do totally agree with you about the 55mph giving you the best gas milage but something happening with my car made me wonder. Two years ago in my BMW 328i, I decided to drive faster at about 90mph and I got the fastest mph I had ever in my care going from a 32mile per gallon rate at 55mph to 36 miles per gallon and I just couldn't explain it. Was a pretty new care then but now it just doesn't seem to do that anymore, so when I want to save gas, I go at 55mph with my windows up and my sunroof open.

-- November 4, 2005 6:03 PM ∞

Charles Simkins wrote:

Eric is basically on spot ( I am also a ME) but an additional factor is the speed and patterns of traffic. You will do best by not varying your speed when you drive. The government graph shows nothing about gear ratios, engine speeds, etc. at lower speeds. I drove half way across country a couple of years ago in a pickup truck. It had an automatic transmission and large V-8 engine. There was a marked drop in fuel mileage even when the speed increased by 5 mph due to the lack of significant streamlining of a pickup with a large frontal area. My wife's little BMW on the other hand gets pretty good fuel mileage even at fairly high speeds because it has good streamlining and a small frontal area. But the BMW does not suffer the drop in mileage proportionally to that of the pickup just because it is designed for less wind resistance. The drag factor is more proportional to the square of the speed difference in any case, not linear but more parabolic.

CBS

-- November 5, 2005 9:02 PM ∞

Erik A. Garland wrote:

Tractor Trailers....

Is there any evidence or data to support cruising behind tractor trailers. It's obviously dangerous to an extent but it dramatically reduces wind resistance without a doubt. Does anyone know how much doing this may increase your gas mileage??

-- November 6, 2005 1:26 PM ∞

miles before I get there wrote:

Eric,years ago, I traveled cross country and one morning hooked with a couple of truckers via the CB. They tucked me in the "cradle" (semi in front and in back)and the miles flew by! As I recall, I did get better gas milage that day and it was also great fun swapping stories over the CB and sharing a table at lunchtime with these guys!

-- November 7, 2005 9:26 AM ∞

Anonymous wrote:

Those graphs are pure bunk, how can a Hummer and a Geo Metro have the same curve! (I drove a Geo Metro for years, now I bike, it always got 45mpg combined city/highway and I drive FAST, over 80 on the highway usually. I'm a professional driver)
Also see all the other posts for people getting much BETTER fuel economy at higher speeds. I don't know why considering all the discussion about wind resistance, but maybe it has something to do with how engines are designed to perform better at higher speeds, emitting lower emissions, operating at higher, more optimal temperatures, not having to constantly fight inertia, etc. but there seems to be a lot of stories here and elsewhere of people finding that "55 saves fuel" is a total lie. Hmm, but our government would never lie to us and use faulty science, would they?
As for safety, most driving deaths are the result of drunk drivers. Deaths decrease when speed limits are higher!
Smart lanes will turn our highways into train rails, why not demand the real thing and destroy our bonds of slavery to maintaining our cars. Demand better rail service!
Don't forget the European emission standards are much different. They don't strangle their cars with all the emission reducing stuff that we do like catalytic converters, so their cars run a lot differently than ours.
Wood vapor engines sound cool, hemp would be perfect for that.
How come cars can't be geared higher to make them even more efficient at highway speeds? Sounds like they've been geared intentionally to run at 55, therefore all "scientific" date should be thrown out. I am very interested in studies of air resistance. If anybody can get me time on a state of the art wind tunnel program for free I have a number of ideas I'd like to test. Now the engineers all seem to agree that wind resistance is a major factor ONCE THE CAR GETS INTO TOP GEAR so what would be the result if there were say 7 speeds on a car instead of 5, 6 or 7? Wouldn't that place maximum efficient speed much higher? Why isn't that done? Is it really lack of consumer demand or just government mandated speed regulation and hence fuel inefficiency?
Glad to see at least Miles noticed shocking government waste!
As for "drafting" I once had to draft an 18 wheeler at very close proximity driving an RV up through Mexico in the middle of the night with no gas in sight. I got right on his tail and he literally pulled my hundreds of miles. I could actually see the dust kind of floating in my headlights between his tail and my nose, in other words there was no wind resistance, the dust wasn't blowing away, just kind of floating between us. What actually happens is that behind every vehicle pushing through air an air pocket forms behind the vehicle pulling it backwards. If you get behind a large vehicle, into his air pocket then he does all the work of tearing a hole in the air for you and then HIS engine must overcome the drag behind your vehicle where the new air pocket would be. This is similar to fluid dynamics like how fish tails, by swaying back and forth, disrupt the "drag" factor by basically swishing it away by their side to side motion. This may also be the theory behind rear spoilers, although I believe they are more to keep the car pressed tight to the road at high speed. I've envisioned cars with swishing tails, dimpled surfaces like a golf ball to help it "slip" through air, wedgeshaped projections protruding from front bumpers to rip a smaller hole in the air for the car behind it to slip through like on some fighter planes, and even wave generators using sound waves of something to rip through the air immediately in front of a car negating resistance like new super high speed submarines use, or reconfiguring tailpipe emissions to disrupt the airpocket of drag behind every car. Damn I need to get on that windtunnel program! Anyway, drafting definitely works great as long as the guy in front of you doesn't mind you tailgating.
After all that discussion coupled with the testimonies that higher speeds equal greater efficiency, for the MEs in the crowd, perhaps something happens at higher speed on the highway that disturbs that straight "The drag force increases at the square of your velocity, so driving twice as fast results in 4 times the drag force" or even "The drag factor is more proportional to the square of the speed difference in any case, not linear but more parabolic" could there be other forces in effect like headwind/tailwind, turbulence from other cars on the highway disrupting airflow, varying car aerodynamic designs being set up to be more efficient at higher speeds, higher speeds creating more "lift" on a car, thereby making it lighter which would increase fuel economy, hell, maybe even higher speeds equaling higher pressure tailpipe emissions which creates a rocket/thrust effect? Can somebody even more knowledgeable please do so research on the other factors involved that might comprehensively explain why people seem to consistently be getting BETTER fuel economy at higher speeds? And if somebody can explain that satisfactorily then maybe you can tell me where most of the energy is lost in a standard gas internal combustion car engine and contact me because if your answer agrees with mine I believe I know how to triple engine power AND efficiency at the same time. Thanks

-- November 7, 2005 3:20 PM ∞

Big Daddy wrote:

SUV design improvements here: http://www.suvsolutions.org/blueprint.html I spent an hour posting a comprehensive response, lost it, spent another hour retyping and lost it. I guess the powers that be don't want me to tell you about my myriad ideas for vehicle improvements to get well over 100mpg or the destruction of our rail system by GM or how hemp could be converted into methanol for cheap, clean burning fuel. Oh well. I'll just suggest common fuel saving strategies everybody should already be well aware of. 1. Inflate your tires to at least maximum inflation and check them every fill up. Max inflation is written on the sidewall of your tire in p.s.i. for pounds per square inch. This number is usually 35lbs/in but some tires are rated at 36, 45 or even 60psi. I'm a professional driver and I usually run my tires 15 pounds over that for even better efficiency, although it increases my stopping distance a little. 2. Change your oil! Every 3K miles or sooner (don't listen to automaker recommendations, remember, their job is to SELL NEW CARS!) Fuel efficiency is maximized by clean, viscous, good oil circulating through your engine. It reduces emissions too, acting as a medium to pull pollutants out of your combustion chamber and into your oil filter. Ask a very trustworthy mechanic what the best oil is for your particular car. As a mechanic 20 years ago I used Castrol GTX 20-50, but that was for an old big block, newer high revving cars may do better with 5 weight oil, high performance cars may do better with synthetic oil. It depends on your car, so ask a gearhead. 3. Tune up your car! Your car runs at max efficiency with a proper tune up, strong spark from clean plugs and wires, good connections in your distributor, good clean fluids, full all around, good belts getting a tight grip, clean breather elements and fuel filters, PCV valve etc. Plan on a full tune up about once a year for average use, once again nothing is more valuable to a car owner than a very trustworthy mechanic. Ask everyone you know to obtain one. 4. STOP TAILGATING and racing to red lights! You should never have to apply the brakes on the highway. You should always be looking AT LEAT 3 seconds ahead, count it out, and planning your "escape route" in the event the car in front of your slams on its brakes. No matter what your speed always keep at least 3 seconds between you and the car in front of you. If you must apply your brakes on the highway do it gently so as not to unduly decrease your momentum. Most energy is used up overcoming inertia (an object at rest tends to stay at rest and an object in motion tends to remain in motion unless acted upon by and outside force like gravity, friction, air resistance, etc.) stepping on the brakes hard might cause your car to downshift and force it to exert a lot of energy (fuel) getting back up to speed. That red light will still be red if you get there in 2 seconds or 10 seconds, and if not, then it will be green and you've just saved yourself from having to apply your brakes, decreasing your momentum and you've saved yourself a ton of fuel, not to mention that time in idle. If you have a good starting car and you are coming to a major intersection where you will be waiting for well over a minute, feel free to turn off your car. The fuel required to idle for 1 minute is the same amount required to start your engine. 5. Lighten your load if you can. A heavier car takes a lot more energy for your engine to push so don't carry around hundreds of pounds of junk in your car. Roll up your windows over 35 mph, most of your energy is converted to overcoming air resistance above that speed, so make yourself as streamlined as possible over that speed. 6. A good oil additive can definitely reduce the friction inside your engine making it more efficient. Lucas is a product that clings to engine walls like glue to ensure all engine parts are always well lubed and slippery. 7. Accelerate on a downhill or straightaway, maintain or decelerate on an incline. Accelerating uphill is a huge waste of fuel, just try to maintain your speed or gently decelerate when climbing and then maximize the help of the downhill to get your car zipping along again. Using this strategy to the extreme in an emergency I once squeezed over 75 miles out of a single gallon in a 1979 Monte Carlo. 8. COAST! When you reach your desired speed, take your foot off the gas! Let your car use its own inertia to coast as much as possible. I see a lot of people who think they either need to be pressing the gas pedal or the brake with no in between. Almost all your time if you're driving efficiently should be coasting. Keep your foot off the brake!
These have been a few common sense tips that I see ignored all the time. I listed them in order of importance for the most part. Tire inflation is certainly the most important thing to monitor regularly for best efficiency. I had previously interjected a lot of hypothesizing about new car designs to achieve over 100mpg but I figured best to educate you about what you have, not pipe dream about the car I hope to build someday. Automakers sell you the same recycled piece of crap car getting the same economy for the last 30 or even 50 years because you keep buying them. STOP and they will be forced to make more efficient cars. They have all the technology to do it easily. My cousin worked with a guy at Raytheon who found a chrystal that maintained an engine so efficiently that it got well over 100mpg consistently. The technology was bought by one of the majors, I think Toyota, and they just sit on it to keep the competition from getting it. This is how monopolies work. Think final scene, Raiders of the Lost Ark. Much, much better cars can be made, but the big guys won't let it happen. I hope gas goes up to $5/gallon so the mindless sheep will finally demand what they and Mother Earth deserves. The big automakers are some of the biggest gangsters and special interest lobbies. See Taken for a Ride to learn about how GM dismantled our national rail systems to market their new diesel engines to the detriment of humankind:
http://www.newday.com/films/Taken_for_a_Ride.html
My other favorite documented conspiracy is by another bunch of good old boys against hemp. Hemp could easily be turned into methanol and power all our vehicles cheaply and with no emmissions (water vapor and carbon dioxide only, which is what plants absorb). See many discussions of this reality with a simple googlesearch for hemp methanol:
http://www.google.com/search?client=opera&rls=en&q=hemp+methanol&sourceid=opera&ie=utf-8&oe=utf-8
Come on folks, race cars run on methanol, this is hardly new science! Demand more from YOUR government and your car. The only reason hemp is illegal is because in 1934 Popular Mechanics announced an invention that was going to revolutionize hemp processing and do for hemp what the cotton gin did for cotton, and who runs our country? Dupont had just figured out how to spin cotton into polyester, Hearst had huge timber holdings, RJReynolds, well you know about their self interest, pharmaceutical companies can't trademark a natural substance, etc. These people run OUR government. Do another simple googlesearch for hemp prohibition truth if you're interested:
http://www.google.com/search?client=opera&rls=en&q=hemp+prohibition+truth&sourceid=opera&ie=utf-8&oe=utf-8
Anyway, I have been a mechanic, an engineering student, a professional driver for probably over a million miles. Try my common sense tips and I think you'll be a lot happier with your fuel costs. If you want REAL CHANGE educate yourselves with a little fun Google reading and demand it!

-- November 7, 2005 3:22 PM ∞

Kevin Brancato wrote:

Sorry about the trouble you've had posting; I've published what you put in originally...

Anyway, since I originally wrote this post over a year ago, I've found the source data for the curves. Are they bunk? No, but they are not representative of 2005-6 automobiles either.

There were three studies done on fuel economy by speed: one in 1973, one in 1984, and the latest in 1997. Their results are available here (excel workbook).

Read chapter 4, pages 4-24 and on of the transportation energy data book (pdf) for specifications about which cars were tested, and for detailed results.

The bottom line is on table 4.25. The latest car tested was a 1997 Toyota Celica, which got better gas mileage (48.4 mpg) at 60 mph than at 55 (42.5 mpg), but all 7 other cars from the 1993-1995 era (and one 1988 Chevrolet Corsica!) showed a 1 to 2 mpg decrease in steady speed fuel economy at 60 mph compared to 55 mph.

-- November 7, 2005 4:47 PM ∞

Anonymous wrote:

on the topic of drag, skin friction drag isn't going to change with speed, just pressure drag. Feasibly, at some speed the boundary layer could be tripping from laminar to turbulent (its a function of RE), which delays seperation and causes a huge reduction in pressure drag at that point, then as the RE continues to increase the drag increases again. There are quite a few plots of drag vs RE on the web, try googline drag on a cylinder, sometimes those turn up sites

-- November 14, 2005 12:28 AM ∞

Dan wrote:

What in the world is that last comment by Sandra Bigwoode supposed to mean??? Honey, it does not matter one single bit in your scenario how long the engine has been running. You answered your own question...You will use 2 gals at 70 MPH and 1.714 at 55 MPH. That's it. Done deal. Fuel economy does not take time-running into consideration because it doesn't have to. It makes no difference at all. You either use 2 gals. or you use 1.714!

-- November 17, 2005 8:34 AM ∞

rene wrote:

Sir/Ma'am,

could you send me an x/y graph indication pounds per square inch vs. miles per hour of wind speed.

thanks,

rene

-- November 17, 2005 9:37 PM ∞

Big Daddy wrote:

hello? webmaster? how come my posts are always hung up?

-- November 27, 2005 2:49 AM ∞

Big Daddy wrote:

Hello, anybody home? The spam filter keeps blocking my posts for some reason. Please explain why so I can fix it. Is it because I include links? I've tried to post at least 3 times now and it won't let me.

-- November 28, 2005 3:45 PM ∞

Big Daddy wrote:

I'll try this in bites/bytes to see what happens since I'm not getting any response:
Thank you Miles. I was actually the Anonymous post immediately before that too. Unfortunately my first 2 attempts at a really long single post were lost and then I forgot to re-enter my name when my third post went through. My friend who is a mechanic was surprised that I hadn't mentioned how much power air conditioning robs from your engine, but it seemed to have been mentioned in earlier posts and I assumed it was common knowledge. If you never use your air conditioning, I even recommend removing the belt as it drags on your engine even when not in use, although if you intend to sell the car someday, realize that you should put your AC on once in a while to lubricate the compressor - this is why on many cars, especially old GMs, you must slide the climate control lever past the AC to reach the vent, defrost or heat, because in that half second pass over your compressor kicks in and lubricates itself. For more discussion of interesting power boosters/economizers I'd like to remind people of fender skirts. In my high school auto shop years, my very knowledgeable teacher told me that instead of putting on headers or bigger carburetors an equal boost in horsepower (around 5HP I believe on average) could be achieved by attaching rear fender skirts to reduce drag. I thought that was powerful information and am disgusted that every car today doesn't have them. I do note however that the Honda Insight, the highest efficiency car in the US in mass production, does indeed have fender skirts, along with very slim/low rolling resistance tires.

-- November 30, 2005 2:06 AM ∞

Big Daddy wrote:

Another mention should goto fuel atomizers which vaporize and pressurize fuel coming into an engine and its combustion chamber. There are other products like the Turbonator and fuel line magnets that claim to also make fuel burn better/cleaner/more efficiently. You might start your search here:
http://www.google.com/search?client=opera&rls=en&q=fuel+atomizer&sourceid=opera&ie=utf-8&oe=utf-8
Personally I put one of those atomizers advertised in the back of Popular Science 8 or 10 years ago. It claimed to be a miracle. I put it on my 1969 Delta 88 with a 455 Rocket engine. This car got 10 mpg until California "oxygenated" its gas and then it dropped to 8mpg. They all come with a satisfaction guarantee so I tried it. The company was great, sent me a second one really cheap with free sample bottles of "superlube" of some kind - an oil additive. Anyway, I think they were around 70$ or more. I put it on my 8mpg Delta and indeed it did increase my mpg back up to 10mpg, which was a pretty impressive (relatively) increase of 25%, so I couldn't really complain. Of course I'd been hoping to break 50mpg based on their claims, but 25% is certainly nothing to sneeze at! Anyway, I went to put the second one on my Geo Metro and guess what...there was an identical looking cylinder already mounted in the fuel line! So apparently the big guys are using old science technology to boost efficiency too. I just read one testimony of a Geo driver from the link above and apparently I should have put the second one on anyway as he's claiming a jump from 42mpg to 74mpg! Anyway, I recommend trying some of these who claim the biggest improvement and the longest trial period. They claim to clean your engine and reduce your emissions dramatically, boost your power/performance/horsepower, and of course save you a lot of gas. So if you plan on keeping your car for a long time, why not invest in improving its performance with a satisfaction guarantee. Maybe you'll be the lucky on who gets over 50mpg in your SUV! And considering the cost of many emission correcting repairs, why not try a multipurpose unit that may fix that problem for you at the same time?

-- November 30, 2005 2:09 AM ∞

Big Daddy wrote:

Anyway, I checked out Kevin's new information and found it interesting, although I still find myself craving more comprehensive descriptions of the tests and more comprehensive tests in general! Come on now, the most relevant test in my opinion was on a 1997 Toyota, which would probably come closest to today's cars, although still an antique, and that was already starting to disprove their older tests. How about if the government set a standard for testing fuel economy by speed each automaker had to abide by and test and provide results for? I'll bet the Honda Insight wouldn't be most efficient at 55mpg! And also, where are the more realistic test results for speeds over 75mph? I'm sure those results would be highly Illuminating! I tried to make sense of the RE vs drag graphs I found on Google, but they merely confirmed that each body has its own entirely unique drag characteristics, as far as I could figure, so I don't know how helpful that is to any kind of general drag discussion. I still have to guess that there are numerous highly efficient ways to reduce drag that nobody is applying because they require innovation and we've already established that is the last thing in the world the major automakers are interested in. But thank you very much for scientifically elevating the discussion for us with this commentary: "skin friction drag isn't going to change with speed, just pressure drag. Feasibly, at some speed the boundary layer could be tripping from laminar to turbulent (its a function of RE), which delays seperation and causes a huge reduction in pressure drag at that point, then as the RE continues to increase the drag increases again," which I'm afraid went a little bit over my head. But I do question if a "cylinder" is the best comparison. I always thought a bullet was the ideal aerodynamic shape (borne out in more than one Pinewood Box Derby I reached the finals of in my Cub Scout days:-) but I was also very intrigued by the one experiment with a sphere in water which benefitted dragwise from a rough patch of sand on its nose which created a beneficial turbulence which reduced drag if I read it right, and I think I did. So this again kind of supported my argument for a "dimpled" surface on car finishes to reduce drag I think. Do you really think the aerodynamic properties of a car are best matched to those of a "cylinder" Anonymous?

-- November 30, 2005 2:11 AM ∞

Big Daddy wrote:

Also, whatever happened to clean burning 2 stroke technology? It was supposed to provide more power with similar emissions, or most importantly the ceramic engines which require no lubricant and operate at much higher, more efficient temperatures. They use the carbon in the exhaust piped into the block or something to lubricate themselves with a graphitelike dust. Unfortunately (and suspiciously) the scientist who was working on this died right after the huge breakthrough about exhaust gases as lubricant. A ceramic engine could be much smaller and lighter and smaller means a much more streamlined/aerodynamic front facade to dramatically decrease drag. But alas, the research seems to have disappeared, just like the awesome potential of Kinetic Energy Batteries or even the Urine Battery - does anyone remember that one? Well, I just read some stuff here:
http://www.google.com/search?client=opera&rls=en&q=ceramic+engine&sourceid=opera&ie=utf-8&oe=utf-8
and apparently tolerances are so close and other reasons make any coolant or lubricant unnecessary, read this:
http://www.geocities.com/CapeCanaveral/1614/ceramic.html
for some pretty interesting background. They also emit virtually no heat or contaminants because they operate 3 times hotter than metal engines and so burn everything up internally.

-- November 30, 2005 2:16 AM ∞

Big Daddy wrote:

Also, whatever happened to clean burning 2 stroke technology? It was supposed to provide more power with similar emissions, or most importantly the ceramic engines which require no lubricant and operate at much higher, more efficient temperatures. They use the carbon in the exhaust piped into the block or something to lubricate themselves with a graphitelike dust. Unfortunately (and suspiciously) the scientist who was working on this died right after the huge breakthrough about exhaust gases as lubricant. A ceramic engine could be much smaller and lighter and smaller means a much more streamlined/aerodynamic front facade to dramatically decrease drag. But alas, the research seems to have disappeared, just like the awesome potential of Kinetic Energy Batteries or even the Urine Battery - does anyone remember that one? Well, I just read some stuff here:
http://www.google.com/search?client=opera&rls=en&q=ceramic+engine&sourceid=opera&ie=utf-8&oe=utf-8
and apparently tolerances are so close and other reasons make any coolant or lubricant unnecessary,

-- November 30, 2005 2:18 AM ∞

Big Daddy wrote:

read this:
http://www.geocities.com/CapeCanaveral/1614/ceramic.html
for some pretty interesting background. They also emit virtually no heat or contaminants because they operate 3 times hotter than metal engines and so burn everything up internally. Did anybody watch Beyond 2000 on the Discovery Channel years ago? I'm sure it was pulled off the air because they were educating the public scientifically too well. They presented the Urine Battery, based on a material discovered in South America that reacted with the minerals in urine to produce current. I was most fascinated by the Kinetic Energy Battery which I know for a fact, was commandeered by the military for its exclusive use. It was basically an alternator producing current from spinning, but with the moving parts suspended in a magnetic field so as to defeat gravity and in an evacuated (vacuum) chamber thereby negating friction/air resistance. In effect you could spin this thing up to high speed somehow, be it a drill, gravity, a bicycle, an engine, whatever, and it would continue spinning for days and weeks producing substantial current. I envisioned batteries for portable devices like cellphones or walkmans that could be recharged just by shaking them up! On Beyond 2000 they actually showed cars and boats running on this technology. I just found a link to the old show which was killed in 1999 despite: "Since 1985, Beyond 2000 has been the most successful series of its type in world television history." Here's the link:
http://www.beyond.com.au/television/catalogue/science_n_technology/1.html

-- November 30, 2005 2:19 AM ∞

Big Daddy wrote:

read this:
http://www.geocities.com/CapeCanaveral/1614/ceramic.html
for some pretty interesting background. They also emit virtually no heat or contaminants because they operate 3 times hotter than metal engines and so burn everything up internally.

-- November 30, 2005 2:20 AM ∞

Big Daddy wrote:

Did anybody watch Beyond 2000 on the Discovery Channel years ago? I'm sure it was pulled off the air because they were educating the public scientifically too well. They presented the Urine Battery, based on a material discovered in South America that reacted with the minerals in urine to produce current. I was most fascinated by the Kinetic Energy Battery which I know for a fact, was commandeered by the military for its exclusive use. It was basically an alternator producing current from spinning, but with the moving parts suspended in a magnetic field so as to defeat gravity and in an evacuated (vacuum) chamber thereby negating friction/air resistance. In effect you could spin this thing up to high speed somehow, be it a drill, gravity, a bicycle, an engine, whatever, and it would continue spinning for days and weeks producing substantial current. I envisioned batteries for portable devices like cellphones or walkmans that could be recharged just by shaking them up! On Beyond 2000 they actually showed cars and boats running on this technology. I just found a link to the old show which was killed in 1999 despite: "Since 1985, Beyond 2000 has been the most successful series of its type in world television history." Here's the link:
http://www.beyond.com.au/television/catalogue/science_n_technology/1.html

-- November 30, 2005 2:21 AM ∞

Big Daddy wrote:

I would be very interested to see a proper response to Rene's request for "an x/y graph indication pounds per square inch vs. miles per hour of wind speed" if anybody's got one laying around. Don't forget your Lucas next oil change. Miles, I also noted I think on the ceramic engine site, that metal internal combustion engines haven't really changed much in over 100 years, and why should they? We keep buying them and acting happy about it. Why should the big guys waste money on research and retooling when they can just sell us the same inefficient crap year after year and make billions doing it? Sure they give us tiny, incremental improvement, just enough to sell the new model year's crap. As for the new behemoth gas guzzlers, we backlashed back to speed and horsepower. We drove the "rice burners" and then decided we preferred to drive giant trucks that crushed rice burners with tons of horsepower to haul our briefcases around in. They made them cheap so we would buy and they kept gas cheap so we would enslave ourselves to their metal gas pump penises. The bigger and faster the car the bigger the penis, right? We are hugely wasteful overspenders. Japan was taking us in the right direction and they the megarich went after the high end market and Japan found out they could make more profit selling larger luxury sedans to them than selling Civics to the working man. They didn't want to get into a pissing contest with Yugos and Hyundais, so they went after Cadillac and Lincoln, who were pretty clueless anyway. They made billions on Lexus, Infiniti and Acura and ditched their economy markets and research. The American way is bigger is better, so we ate that right up. Rush out to buy a better car than our neighbors and now we're in Hummers. They're all in collusion (duh). More profits for everyone, the oil producers, tiremakers, roadbuilders, insurance companies. Why aren't we all using Kinetic Energy Batteries? I don't know who owns the battery companies, but I'm sure they have a huge lobby and monopoly. Does anybody know? Is it Dupont, who also owns most of Delaware? Whoever it is, I'd suspect they bought the technology for their military so we will be slaves to their batteries. Okay, enough of my delusional ranting, ahem, I mean shockingly clear, enlightening, Illuminating thoughts.

-- November 30, 2005 2:23 AM ∞

Big Daddy wrote:

bc's comments are interesting:
"Sandra Bigwoode's post on May 19 makes a lot of sense. Another thing to consider is the frictional force between the tires and the road which probably decreases with increase in speed."
I'm not sure what's so interesting about Sandra Bigwoode's post. Obviously she's right and it takes longer to get somewhere at lower speed, and if you use 2 gallons getting there at a higher speed and 1.7 gallons at a slower speed, then obviously you've used less gas at the slower speed and saved money if not time (and some consider time equal to money I concede), but other than stating the obvious, our argument/discussion here is focusing (with substantial digressions admittedly) on what is truly the optimal speed for a vehicle, or more specifically, the optimal speed for each individual vehicle which is entirely unique based on the vehicle. We're also discussing what factors are involved in determining those numbers and why they are important or in what hierarchy of importance they exist.
Personally I'm just trying to suggest strategies that I know are very effective at optimizing fuel efficiency with whatever vehicle you happen to be driving as well as begging discussion on other forces in effect like air resistance/drag and tire rolling resistance to try and find out from scientists and engineers out there what kinds of things might be possible with new car designs. Also, of those knowledgeable about cars, designs, aerodynamics, drag, friction, engines, energy, etc. I pose my question again: can anybody identify where the bulk of energy is lost in a standard internal combustion engine. If you can supply me with the correct answer I would like to discuss with you a design I've come up with to triple power AND efficiency at the same time based on eliminating this loss. I await your response.

-- November 30, 2005 2:39 AM ∞

greensmile wrote:

Everyone's personal data is anecdotal, gathering of data would have to get carefully designed and checked methodology to establish valid averages. Averages matter to policy making but I only save or lose money based on personal data.
Now that I have a hybrid, I am driving with a video game-like feedback in the form of a continuous and realtime gas milage performance meter in my face. It is working like a charm as a training vehicle. I have learned that at 40mph and lugging the poor little engine at around 1200 to 1500 rpm, I get a better-than-advertised 50 mpg average in the summer, a bit less as the weather cools.
At the least, hybrids are going to force corrections to the graph presented here.

-- December 1, 2005 9:03 AM ∞

Big Daddy wrote:

That's great feedback greensmile! While everyone's personal data is of course anecdotal, except for others with the same car, it is of course all that really matters to the individual. Just as Washington D.C. has no idea (or doesn't care) what is best for Florida, and Florida only has a vague notion (relative of course to the constituency of voters there and how much money they donate to the politician's campaign warchest) of what is good for Key West, so too can averages for national policymaking be of little value to the individual who just wants to maximize their particular fuel efficiency. For example, you yourself drive a hybrid and optimize efficiency at 40mph. This information is of little value since we don't know the specifics of what hybrid you drive, in what kind of climate/environment (cold/hot, dry/humid, flat/hilly) and of course this information is useless to those who might drive the same car but have to do it on a highway and maintain at least 55mph. I know from reading boards about it for instance that the Honda Insight does best when the driver gets to the highest, most efficient gear as quickly as possible. This means that hard fast acceleration to shift up through the gears ASAP is the optimal fuel efficiency driving model for that car, which is typically counter to what other cars might find most fuel efficient. Other particular/peculiar strategies for the Insight enable some owners to achieve upwards of 80 or 90 mpg, which again most likely has a lot to do with type of driving and environment. For example again the Insight shuts down at full stop (traffic signals) to conserve fuel and uses regenerative braking so I think it actually gets better economy in the city than on the highway if I recall correctly. So this is exactly what I'm pushing for: specifics for actual optimal efficiency testing and models for every car by either the manufacturer or an independent agency like Consumer Reports or something. I LOVE the idea of having a feedback indicator in every car that shows people clearly where/how they are driving to facilitate greater efficiency. Like while people might not be able to drive 40mph all the time they might find a sweet spot between 55-85mph somewhere as Anonymous points out above "Feasibly, at some speed the boundary layer could be tripping from laminar to turbulent (its a function of RE), which delays seperation and causes a huge reduction in pressure drag at that point" and of course there would also be adjustments to make according to tire pressure/tire type, load weight, wind speed and direction outside vehicle, other vehicles on the road affecting air flow/resistance, barometric pressures, wet or dry pavement, elevation, etc. So I love the idea of forcing this information into the cockpit to encourage more efficient driving.

-- December 1, 2005 8:43 PM ∞

Big Daddy wrote:

I guess our moderator has abandoned us to let the thread die with enhancements for the erectionally challenged.

-- December 6, 2005 2:50 PM ∞

Big Daddy wrote:

I guess our moderator has abandoned us to let the thread die with enhancements for the erectionally challenged. Kevin Brancato, where are you?

-- December 6, 2005 2:51 PM ∞

Kaitlin F wrote:

hello..we are doing our science fair project on this topic!! thanks for the posts!!

-- December 7, 2005 10:55 AM ∞

Big Daddy wrote:

What grade? What is your focus exactly?

-- December 7, 2005 4:04 PM ∞

Big Daddy wrote:

Damn filter is censoring me again! Where are all my scientists and engineers from above? I've repeatedly asked a question which should have a clear and simple answer. Where is most of the energy lost in a standard internal combustion car engine? Come on, this is not brain surgery. If you really understand the engine then answer please.

-- December 9, 2005 5:25 AM ∞

Big Daddy wrote:

I'm pretty apalled that in a world where cars have been produced for over 100 years, they have progressed very little in the last 50 or so. Really, how does a 57 Chevy differ from a large Chevy sedan today? Same engine block, wheels, braking system, suspension, exhaust, interior, battery, distributor, alternator, radiator, etc. We've finally advanced from carbeurators to fuel injectors for a little improvement. Tiny weight and effectiveness savings of front disc brakes over drums. Struts from shocks and springs. Catalytic converters which rob us of power. Sensors and hoses which get us infinitessimal improvements in performance during the brief periods that they are working and the "check engine" light isn't on. Is this the best "science" can manage in the last 50+ years for something so incredibly common, expensive and polluting? To believe that is foolhardy. To deny that there are those in power who would rape and pillage the earth to line their pockets with consumer's blood, sweat and tears is to live with one's head in the dirt. Personally I would never, ever buy a new car until technology impresses me. I'll buy a cheap, used, disposable car and save thousands on insurance thank you very much. I love the Geo Metros. You can buy a certified replacement engine from Japan for under $500 since their emissions standards are so far above ours. Of course those were too efficient and cheap, so they pulled them off the market. Perfect proof of their intentions. They didn't even bother to replace it with anything comparable. Does anybody even know how efficient solar photovoltaic cells are? I'm pretty sure that thanks to the negligible research and development done these days they have not improved more than a percent or 2 in the last quarter century, and last I heard they were barely 10% efficient. How pathetic. Were'nt we all supposed to be driving flying cars by now? Did you know that your right to drive and travel on public roads is guaranteed to you in the Constitution? It is not a privelege granted to you by the state. The only people who had to get licenses were driving professionals like taxi, truck and limo drivers. They slowly combined all the professional licenses into 1 and then somehow convinced stupid, arrogant early drivers to "sign up" for a license to prove their driving prowess (I'm a big shot because I've been licensed by the State to drive. I had a little trouble finding good info. This link (remove the (dotcom)
http://www.findarticles (dotcom) .com/p/articles/mi_qa3894/is_200310/ai_n9336353/pg_3
had a lot of good info, but a lot of the actual history I read elsewhere years ago is conspicuously missing. That article really gets rolling on page 3 although the author's agenda is clearly to "illuminate" us about the coming National ID. He refers to what sounds like a very good and interesting book Rose Wilder Lane's 1943 book, DISCOVERY OF FREEDOM. Anyway, he made a lot of good points and seems to admit when his facts or info are sketchy, which is kind of what I encapsulated above and extrapolated further to implicate auto manufacturers in the non-evolvement of transportation technology keeping us slaves to our gastanks and automobiles. Of course now that gas prices have dropped it seems virtually nobody is reading these posts anymore. Immediate crisis averted, back to the Hummers! I think it is very likely that the powers who run OUR government just jacked gas prices through the roof to gather data about our reaction to such major/catastrophic events. This is part of their construction of a giant algorithm, based upon all of our actions in response to numerous stimuli - how will the public react if fuel costs increase 50% - and compiling all of this data in new supercomputers with incredible data storage capabilities they will then finally be able to predict with great accuracy our behavior based on reactions to events which they manipulate, like Bush's collusion in the Sept 11 terrorism just like FDR knew about Pearl Harbor. There really doesn't seem to be any doubt about this. I won't put any more links in or my post won't post. Just do a simple googlesearch for Bush knew 9/11 or proof Bush knew 9/11. There are tons of results. Anyway, the goal for the "Illuminati" is to be able to predict our behavior based on say increases in fuel costs, increases in the cost of staples like beef or chicken, terrorist attacks, the erosion of personal rights and freedoms, the destruction of the Constitution, greater police presence, etc. ad infinitum. Then, when they can accurately predict the public's response to infinite minutiae they will effectively be able to control our every action and decision. Wow, I really need my own blog. Sorry for straying pretty far from cars, but I think that article I linked to above really made some strong points about how much power the Government wields over us through our vehicles. I guess I was getting at the fact that they have no interest in making cars more efficient as long as we don't make a fuss and they can manipulate us through our gas tanks. It would be a serious blow to their power and profits if people started driving solar cars, which don't need to be registered, insured or licensed. A "motor vehicle" being defined as one that is powered by and IC engine for the most part. There are many qualifiers which vary by state, but in general it is a good starting point for challenge and getting out from under those who exploit us and poison us. Demand better cars, better technology, alternative clean fuels, cheaper vehicles and costs. Stop being a slave to the establishment. Strive to be sand in the wheels.

-- December 9, 2005 5:27 AM ∞

Big Daddy wrote:

We've finally advanced from carbeurators to fuel injectors for a little improvement. Tiny weight and effectiveness savings of front disc brakes over drums. Struts from shocks and springs. Catalytic converters which rob us of power. Sensors and hoses which get us infinitessimal improvements in performance during the brief periods that they are working and the "check engine" light isn't on. Is this the best "science" can manage in the last 50+ years for something so incredibly common, expensive and polluting? To believe that is foolhardy. To deny that there are those in power who would rape and pillage the earth to line their pockets with consumer's blood, sweat and tears is to live with one's head in the dirt. Personally I would never, ever buy a new car until technology impresses me. I'll buy a cheap, used, disposable car and save thousands on insurance thank you very much. I love the Geo Metros. You can buy a certified replacement engine from Japan for under $500 since their emissions standards are so far above ours. Of course those were too efficient and cheap, so they pulled them off the market. Perfect proof of their intentions. They didn't even bother to replace it with anything comparable. Does anybody even know how efficient solar photovoltaic cells are? I'm pretty sure that thanks to the negligible research and development done these days they have not improved more than a percent or 2 in the last quarter century, and last I heard they were barely 10% efficient. How pathetic. Weren't we all supposed to be driving flying cars by now?

-- December 9, 2005 5:28 AM ∞

Big Daddy wrote:

so sad to see a meaningful discussion succumb to the lowest common denominator, I'm out.

-- December 12, 2005 4:11 PM ∞

Tim wrote:

I've driven my 97 VW Passat TDI Wagon across the country (3000+ miles) and also on a 1600 mile trip and this is the mileage I get based on filling up, driving with cruise control locked on one of these speeds for almost the entire tank, then filling up and checking mileage. Only a few rest stops along the way with minimal/no in-city driving.

55 mph: 56 mpg
65 mph: 49 mpg
75 mph: 42 mpg

At $2.50/gal I save about 35 cents per gallon by driving 55 instead of 65, so now when I'm on the freeway I get into the right hand land and set cruise control at 55. This car would be wonderfully paired with a 6 speed transmission instead of the 5 speed it has.

-- February 26, 2006 4:56 AM ∞

Sparkie wrote:

Solar cells are typically 15% effecient, dep. on temperature. Newer, much more expensive cells are closer to 20%. The solar car I'm working on at school has a 12 foot long by 6 foor wide array of cells and produces about 900W. That amount of energy is equiv to One (1) toaster oven, or about 1.3HP (yes, your toaster might be more powerful than a horse... who'd've thunk?)
figures i read in a motorcycle magazine indicated that a bike required 15HP@60MPH and a car required 25HP@60MPH to overcome dynamic losses and retain its speed.

As I recall, the typical gasoline engine is 25% effecient.

-- March 18, 2006 12:37 PM ∞

wwlin wrote:

Last Sat, April 14, 2006 at 7PM we have "special" FFI training session with FFI founder/owners Randy & Wendy Ray present. They flew in from Orlando, FL this past week to "kick-off" their California "campaign" and have been met with mobs of enthusiastic distributors with their prospective recruits. They have been able to answer the questions that we all needed to know which makes amazing sense and provide us the reasons our MPG tablets are so far superior and saver than other "foreign-produced" products. Be there!!

I just ran into a new MLM called "FFI", a company that started only 4 months ago in Florida, that sells "gasoline improvement tablets", i.e. tablets that you put in your gas tank which increases the mileage of your car by 30% average and increases your octane. and reduces pollution. The pill is to be put in into a virtually empty gas tank and then filled with up to 20 gallons of regular gas. I tried that with my car and I noticed that my car engine is stronger and more responsive and got 64 miles (= 32%) more in mileage. In today's age of rising gas-prices, this may become a huge money saver and this is not lost on the ordinary consumer of gasoline or energy: there is a universal need for these types of gadgets!! And there is little explanation required.

You can see how easy it is to sign up people underneath you. All that is required is for you to have a basic understanding as to where you put your "underlings" in your down line as FFI is using a "binary" system that I think Winny, my up line, can explain to you in her email to you. But you will get a website assigned to you under your name or an alias you choose. Like my alias is "savegas123" for my FFI website is www.savegas123.myFFI.biz. Go to my website and that explains to you a lot of things on this explosive MLM. We have a person, I think he is Canadian, who signed up 4 months ago and now is already earning $ 18,000/week and is now coming to Diamond Bar to address our group here in LA. As soon as this Canadian hits $ 25K/wk or $ 100K/month, FFI will give him another "position" on the FFI binary and so on, and so on!! My immediate up line Kim joined FFI 3 weeks ago and is already "splitting" $ 1000/day and soon will be surpassing my Canadian friend.

I think, this is a golden opportunity for you, where all you have to do is sign up on my website www.savegas123.myFFI.biz , order your $ 399 worth of "tablets" (you get 240 tablets) and start using yourself in your car and start giving "5 tablet" samples to other people and tell them to try it out themselves and if interested to go to your website to sign up etc. etc. A lot of people who sign up this way, you will not know, but you get their purchase commissions endlessly. As soon as I received my "samples", I will send you some.

Winny now will explain to you the workings of the "binary" system and how your commissions are calculated and disbursed weekly. International distributors will be paid through bank-issued ATM/debit cards.

Our next meeting is on Thursday 7PM at the same place, Denny's at Rosemead Bal. & Fwy 10. You can't miss it.

If you have any question, please contact me for discussion. And for more detail information of this product, please visit my website for review www.savegas123.myffi.biz.

Important Reference Information:

Products Liability Insurance Policy: http://www.savegas123.myffi.biz/en/pdf/ffi_insurance_policy.pdf

EPA Registered Info:

http://www.savegas123.myffi.biz/en/pdf/EPA_registration_info_pkge.pdf

Works with all types of fuels!

Gasoline

Diesel

Biodiesel

Ethanol-gasoline blends

Product Test Results

http://www.savegas123.myffi.biz/en/section_201.asp

Testimonials

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-- April 20, 2006 3:59 AM ∞

janet lapp wrote:

We have a new 2005 Dodge with only 13000 miles on it. We got between 30 to 31 miles to a gal THAN they had to replace the computer now we ge 22 miles to the gal. They put it on the scope and checks out find, What in the sam blazes is going on, my husband is having a fit

-- April 27, 2006 7:49 PM ∞

Tim wrote:

I agree, driving slower will save you fuel.
Another way to save 10% to 30% on your fuel
costs is with our 10 year proven fuel saver.

How much would you save on a monthly basis on
your fuel if you could reduce your fuel costs
by 10% to 30%???

Go to: http://www.gonow.cloud4.com

to see product product and to order product.

Watch News clips by NBC & Fox News and Corporate Video.

Go to: http://www.ethosfr.com

to see proven test in the inductry.

Works with all types of fuels:

Gasoline, Diesel, Biodiesel and Ethanol-gasoline blends.

Contact me off my website with any questions you have.

Bob

PS: Waste Management, an 8 Billion Dollar company with over 500
locations has been using our product for over 7 years with a 16%
savings on their fuel costs.

-- May 12, 2006 12:12 PM ∞

John_Thomas wrote:

Don't know if anybody's noticed this yet, but look at the graph: DRIVING FASTER SAVES GAS--at least up until ~55mph.

As for saving gas at higher speeds, I know the variable isn't per gallon, but let's assume the source adjusted for that. 10 cents saved per gallon. That'll save me roughly $3.40 on a full tank, $4 if I'm running on fumes. You think I care about saving $2-$4 on a $50+ fill-up. Totally negligible.

That's no excuse for speeding or driving recklessly, but let's not pretend there's some significant economic reason to drive slowly, because to an extent the opposite is true.

-- June 2, 2006 2:59 PM ∞

slick49 wrote:

Hey Anon,

It seems that your 98 Escort is not only equally efficient at any speed, but quite a chick magnet as well. They must swarm your car when you rev all that superheated muscle.

Quick question: why didn't you just buy a better car than putting all your (hard earned) money into an Escort (and a fade haircut)?

Slick

-- June 24, 2006 9:42 AM ∞

Michael wrote:

There are many considerations to take into account before just saying driving slower will save fuel it depends on the car.

If you want to find your best fuel/mileage rate you would need to monitor your car’s fuel consumption rate like is done on ocean going vessels. Pilots do this by finding the best adjustment of engine speed ,prop pitch and knots. They do this to save millions of dollars per year in fuel cost, the same can be done for cars.

One commonly over looked aspect is inertia. A body in motion tends to stay in motion until outside forces act on it.These forces are friction, air and surface friction to be exact.

To prove any of this first you would need to instrument your car with a few real-time gages. Your rate of fuel needs to be monitored at the fuel line not with the highly inaccurate gas gauge.

Using a percision fuel rate meter and Speedo you can start to test which driving method has the best mpg. Changing your Hiway driving style can yield huge increase in MPG, but just slowing down doesn’t always work like many people claim.

-- February 21, 2007 4:54 PM ∞

Jason wrote:

I have a Chevy Colorado, and I drive about 23 miles each way for work. I started driving 65 on the expressway instead of my usual 90. I averaged 20 mpg going 90. Since slowing down I now average 25 mpg. That's 5 extra miles per gallon, but when added up for a 19 gallon tank, that amounts to 95 miles more per tank, so if I take 95, divided by my regular mileage of 20 mpg, I get an extra 4.75 gallons, times the $3.25/gallon cost of gas, I squeeze $15.44 out of each tank. Also, if everyone slowed down (which it took a long time to get used to 65 mph and I don't blame people for not doing) the country's oil and gas consumption would drop. With my short commute on the expressway I only lose about 5 minutes of time. Its worth my time to save the money.

-- May 11, 2007 6:48 PM ∞

Roger wrote:

Anything like the turbonator or anything doesn't work, I tried it for shits and giggles, adds no horsepower or milage, if anything it hurt my horsepower since there was a chunk of metal in my intake, and it may give better milage because you arn't getting any air into the system so your EMU will automatically put less gas in the engine cause theres no air. Get cold air intake, look up velocity intake system, cheap and it works well.

-- September 30, 2007 7:22 PM ∞

Zaces wrote:

There is a lot of ...things going on in this thread.

I have done alot of monitoring of cars as they decel to model drag forces. The data aquisition was high speed and very accurate at determining the HP lost. This was verified by a Mechanical Engineering Friend.

One thing you guys are completely missing is that in virtually every car I have tried this the numbers are about the same. SUVs and Minivans aside. The point is that it will be about the same for most vehicles.

Why is 55 MPH important? That is the point where rolling friction and aero drag are approx equal. I think that has a huge deal with why 55 MPH is the best speed you can travel at.

Beyond 55 MPH it takes expontial HP to power the vehicle down the road. 55 MPH = 17HP, 80 MPH = 50HP.

The faster you go the more fuel it takes for second to run the vehicle.

Some of you might be saying sure because you are covering more ground it outweights the drag.

Well go plot this equation based on your engine's fuel consumption.

"{VSS.mph}/({INJFLOW.lbpm} * {IBPW1} * {RPM} * 4 / 6250)"

In fact I am going to go model that in Matlab right now!!

-- October 9, 2007 10:56 PM ∞

Susan wrote:

It seems the best way to save gas is to regulate the flow of traffic, by changing the times that people leave their jobs to go home or go to work, by eliminating bottle necks, traffic jams and limit the distractions along highways-sights and signs, etc. You can save more money by eliminating road rage, than saving pennies on gas because of different speeds. One person having a road rage attack sometimes has a domino effect.

-- January 2, 2008 7:41 PM ∞

TruthSeeker wrote:

For Sandra: The vertical axis of the graph is simply miles per gallon, NOT gallons per unit of time as I believe you are implying.

How much fuel your engine burns per hour is not a factor in this discussion, and no one is attempting to argue the obvious fact that driving slower requires more time spent driving.

-- April 7, 2008 12:10 AM ∞

TruthSeeker wrote:

For Sandra: The vertical axis of the graph is simply miles per gallon, NOT gallons per unit of time as I believe you are implying.

How much fuel your engine burns per hour is not a factor in this discussion, and no one is attempting to argue the obvious fact that driving slower requires more time spent driving.

-- April 7, 2008 12:12 AM ∞

Ernest wrote:

Tips to Save Gas

Here are simple tips to save gas. These tips will allow you to spend lesser amounts on gas. Ultimately, these tips can also save the environment as well.

Save gas by braking the correct way:

You can easily save at least 10% to 25% gas by braking the correct way. Especially when there is a traffic jam, try to press on the brakes as little as possible. This works because the vehicle consumes the most gas while accelerating than already moving. So by using this simple tip, you can save a considerable amount of gas.

Taken from:
http://www.tipstosavegas.com/

-- April 19, 2008 2:23 AM ∞

Shane wrote:

There's a site that has taken the studies into account and provided a calculator to determine what the real difference in MPG for each speed is for you - http://www.slowdowntosavegas.com/

-- May 28, 2008 4:45 PM ∞

Dr. Andrew wrote:

driving slower does NOT increase your gas milage by a noticable amount! what decides your effeciency at flat level crusing? RPMS of the motor? the lower they are, the less gas you would use? look it up yourself dont beleive what some guy on the internet says. BUT the slower you are going, the more time you spend on the road.Keep that in mind.The 300rpm difference between 55 and 70 is hardly enough to make up for the extra 10 minute you spend on the road, especially when you have hills to climb, the lower rmps will put a strain on your motor and eventually kick it into lower gear, while the higher speeds would have taken you over the hill by that time...most cars have an overdrive transmission anyways!...

if they are really worried about it on such a minute yet 'serious' level, then why arent we replacing every intersection with an overpass so we dont have to stop? stop letting the government fill your heds with shit to keep u within there fun little game.

the only way to improve your milage through driving habits is through proper stop-accelerate techniques, put the car in neutral down hills, dont start slowing down before you turn, put it in enutral,wait until you are right up on it and smash the brakes, makes drivers behind you happier because you are getting out of there way quicker so they dont have to slow down and speed back up. just make sure to use your turn signal.

-- June 3, 2008 10:21 PM ∞

KELLIE wrote:

SAVE GAS !!!!!!!!! RIDE A BICYCLE.... I HAVE TRIED EVERYTHING , CRUISE . WINDOWS UP . AIR OFF. BEHIND A BIG TRUCK. THE ONLY WAY I SEEM TO SAVE GAS IS TO STAY HOME.

-- June 24, 2008 8:13 PM ∞

me wrote:

I see only one govt cited source in this discussion and it appears outdated.
I would like to see alot more evidence on this subject before I consider it true.
I think there are too many factors involved than 55mph alone to affect gas mileage.
I agree drag is only one factor.
http://craig.backfire.ca/pages/autos/drag
See this section on Gas Mileage.

-- July 18, 2008 12:57 PM ∞

James wrote:

This thread has gone on for 4 years! HAHAHAHAHAHAHA!!!

-- October 10, 2008 11:41 AM ∞

archie four wrote:

Astonishing. Not one of you understands automobile engines. I guess cars are too complicated these days for the average joe to take an interest anymore. Maybe this is why the government runs over us like a bulldozer whenever we feel like it.

Facts:

1. Posted speed limited and fatalities, studied repeatedly, have no correlation, or a negative correlation. Speed limits line government coffers and pay for fun toys for police. That is their purpose. If we really wanted to save lives we would enforce NO TAILGATING laws, the number one cause of accidents. But that would require too much work on the part of the police, who again, are just try to make revenue and pay for cool new toys.

2. Decreasing speed limit increases time each car is on the road, increasing traffic density and traffic jams, which decrease gas mileage for everyone. (Think of it this way: at 100mph, you are on the road half as long as at 50mph, so is everyone else -- there are half as many cars on the highway at any particular time).

3. Internal combustion efficiency is NOT LINEAR, therefore it is common for a car to be more efficient at higher speeds than lower, and for an engine to be more efficient at higher rpms than lower.

-- October 12, 2008 7:18 PM ∞

Swaff wrote:

In response to Joesph Xavier:

Good math, but you've missed the point. Fuel consumption is not directly related to RPM. What is directly related to RPM is speed. If you are observing an RPM that is higher than what your calculations show it should be, then either your calculations are wrong, your tach is wrong, or your clutch/torque converter is slipping. Your engine speed is directly related to wheel speed, always. The effect of drag or another force of load on your car results in more fuel consumed to produce the same RPM, because there is more resistance to be overcome. Ever tromped on your accelerator with the car in neutral and noticed how easily and quickly the engine revs up? Its because there is no load. Increase the load and you need more fuel to maintain the same RPM because the piston, attached to the road through all the mechanisms you described, has more resistance to the explosion than before, therefore more fuel and a greater explosion is necessary to balance. If RPM always matched fuel flow, then it would be a lot easier to calculate and manage fuel economy. If you had a gauge to measure fuel flow or fuel mileage, you may notice that certain speeds (45mph maybe) will result in nearly the same amount of fuel consumption in either 4th or 5th gear, as fuel consumption is largely based on the load being moved, and not simply on RPM.

sandra bigwoode:

In response to your question of "What is your fuel savings?" the answer is: 2 - 1.714 = 0.286 gallons.

Fuel efficiency is measured in miles per gallon for the very reason you brought up. If it were measured in gallons per hour, then we wouldn't be able to reach a conclusion as to the total fuel consumed. But to drive 60 miles at 35 mpg will always consume less fuel than driving 60 miles at 30 mpg.

As for the cost of personal time, I figured out in my own car, a pretty efficient TDI Jetta, that by slowing from 100km/h to 90 km/h (62 - 55 mph) I save $10 worth of fuel, for every added hour of driving that results. Of course an SUV that consumes 3 times what my car does, would consume $30/hour more.

-- October 12, 2008 8:28 PM ∞

Jared wrote:

Complex physics at work here, and so far not one comment actually answers the issue:

In the city, driving 20mph is stupid in a 35mph zone. It causes frustration in other drivers, and you will be probably be in OD since most people don't put their cars in the proper gear for the speed they are at... Being in OD causes the engine to be 'luggin' as opposed to be running efficiently. As far as it being stupid, the savings are negligible, and will probably be negated since the driver floored it to get to 20mph. Now, those with variable transmissions, what gear your in doesn't matter anymore since the engineers designed the motor to cruise at optimal efficiency... but most of us don't have CVT trannies.

The main problem with fuel efficiency in the city is acceleration. The faster you accelerate, the less your efficiency will be. People floor it everywhere, follow to close - needing to surge as they are driving... among many other efficiency killing behaviors, are the root of the problem.

The best things drivers can do are, accelerate about 1/4 throttle (like a grandma for you teenagers out there), maintain the speed limit. On the highway, do 55-60. Doing 75 isn't efficient in any vehicle, but your efficiency (due to drag in this sentence), is exponential, not linear. Look up the efficiency curves for a CVT car with a constant throttle position. It will look like a parabola.

Do your selves a favor, calculate the time your actually saving by driving crazy and fast to get to work... I bet it is merely, 5-10% difference in time, and a hell of a lot safer. Worst case, you will at least save gas and your wear and tear on your car will decrease dramatically leading to a healthy life.

-- October 12, 2008 9:24 PM ∞

Van Dempsey wrote:

"FACT: The speed limit is the LAW. Obey it! The life you save could be mine."

Tell that to all the cops I see speeding every week, without lights and sirens.

Speed limits are not about saving lives - they're about rationalizing the municipal theft of millions of dollars from innocent citizens who have done no wrong.

-- October 12, 2008 9:53 PM ∞

Erik Martin wrote:

You cannot make any kind of generalization that driving 60 will use less fuel per mile than driving 65. I don't doubt that the graph represents a typical result, but as the link in the article discusses, every car design is going to be different. Depending on how the engine and the frame are designed, and their state of repair, your optimal speed could be 75, or it could be 30.

If you're that intent on improving your milage, maybe you should dimple your car like a golf ball. ;)

-- October 12, 2008 10:12 PM ∞

Dan wrote:

I understand that drag increases with speed. However, I measure my MPG with a device called ScanGauge and I have found that my MPG does probably peak at 55MPH, but it only drops less than 1 MPG up to 70 MPH. The difference in MPG between 55 and 75 MPG is less than 2 MPG. (I drive a Honda Odyssey and I average 24MPG.) Your mileage may vary differently with speed.

-- October 12, 2008 10:16 PM ∞

Common Sense wrote:

Speeding does not equal more traffic fatalities. The reason you get speeding tickets has nothing to do with safety and everything to do with increasing government revenue. It's pretty much a tax.

Europe currently has an ongoing laboratory that studies this "speeding kills" hypothesis.

http://en.wikipedia.org/wiki/Autobahn

Results? Fatality rates don't rise or fall. It's pretty much the same.
.

-- October 12, 2008 10:28 PM ∞

Anonymous wrote:

No.

Driving slower pisses everyone off.

Take the bus if you insist on driving more than 30 MPH under the posted speed limit.

-- October 12, 2008 11:06 PM ∞

Tobias d. Robson wrote:

I have a new car that calculates, and displays, my mpg (momentary, and average for the trip). A lot of you must have cars with similar gauges. When I have the opportunity to do a long distance drive, I'm going to let my car tell me what my mpg is at 55, 60 and 65. Why don't some of you do the same and report? Let the car's computer do the talking.

Oh, and if I turn the A/C off at 60 mph, what difference will that make?

-- October 12, 2008 11:10 PM ∞

Tobias d. Robson wrote:

I have a new car that calculates, and displays, my mpg (momentary, and average for the trip). A lot of you must have cars with similar gauges. When I have the opportunity to do a long distance drive, I'm going to let my car tell me what my mpg is at 55, 60 and 65. Why don't some of you do the same and report? Let the car's computer do the talking.

Oh, and if I turn the A/C off at 60 mph, what difference will that make?

-- October 12, 2008 11:11 PM ∞

Anonymous wrote:

"FACT: The speed limit is the LAW. Obey it! The life you save could be mine."

And why do you think that law is in place? If you say safety, try again. It's called revenue generation. Montana had no daytime speed limits for a while, and accident rates went DOWN - *gasp*!

Drive 55mph out here in the American west. You'll quickly understand that 75mph is not at all unreasonable.

Drag coefficients play a part, yes. Gearing and power delivery also play a HUGE part. My '04 Cadillac CTS V6 gets 29mph on the highway - 65, 75, or 85 mph, on a 500-mile trip to Denver, CO from Wyoming.

My wife's Toyota only varies 2mpg between 55 and 80 - I'll take a 2mpg hit for 25mph. My time is worth that, easily.

"Our gas has been too cheap"?? Shut up, you socialist idiot. It's called the Free Market, and the blind acceptance of people like you are why it's being swallowed at $4/gal. Drive what you like. If you can't afford it, OK. You'll drive a Prius. If you can, you'll drive a larger vehicle. At some point, it all runs out - and that's the real solution, not artificial price inflations to enforce the economy of a resource that is required for the entire world.

-- October 12, 2008 11:42 PM ∞

bryan wrote:

Your time savings in the above example is actually 22%, not 27%. You are basing your conclusion on the premise of speed when you should be using time instead (R * T = D).
1. 55(T) = 60; T= 1.09
2. 70(T) = 60; T=.86

.86/1.09 is approximately 78%, or 22% savings.

-- October 13, 2008 12:03 AM ∞

Ray wrote:

Actually, in top gear air resistance isn't the *only* factor to consider, though for most cars it is. The fact is, though, that different ICEs have their thermal efficiency peak at different power outputs.

And, in fact, at various speeds, top gear isn't the most efficient gear either. It really is a curve that's different for every car.

The reason 55 is the most efficient is that the EPA test tests at 55, so cars are designed for it.

Most of them, anyway...

A Prius, for example, has an entirely different looking curve: its most efficient speed is at something like 45, and is much flatter heading down towards 0 (and upwards as well, staying pretty high up to around 65, at which point you're getting beyond the engine's thermal efficiency peak and air resistance takes over).

-- October 13, 2008 12:39 AM ∞

Tahoe Driver wrote:

Greetings, I happen to own a 1997 Chevy Tahoe 4x4, and i drive 53 miles each way to and from work. for the first month, i drove observing the posted speed limit(55 mph) i averaged 16.8 mpg. In the last two months i have increased my speed to 69mph(70+ becomes 20 over speed limit, and is considered reckless endangerment), and my mpgs has risen to 18.1 mpg.

also, for comparisons, while i do not remember the RPMs at 55 mph, at 69 i am right around 2k RPM

-- October 13, 2008 1:59 AM ∞

Joel Odom wrote:

I've measured my SUV's highway gas mileage at about 24 mpg at 55 mph and about 17 mpg at 70 mph. My sedan, which is more aerodynamic, does not have such a drastic change, but the difference is not as dramatic.

In regards to the time factor that the previous poster discusses, we're talking about "miles per gallon." This is the amount of fuel it takes to travel a certain distance, regardless of how long it takes you to get there.

Driving about 55 saves a significant amount of gas.

-- October 13, 2008 7:23 AM ∞

Robert Cole wrote:

sandra: Your fuel savings is 2 gal - 1.714 gal = 0.286 gal. Just because your engine was running for 27% longer, it doesn't mean that it used more gas. The key here is the *distance*. If you were gauging gasoline usage on a basis of gallons per hour, then yes, you'd have to take the time factor into account.

Example (using your numbers):
60 miles @ 70mph @ 30mpg
60 mi / 70 mph == 0.857 hr
Gasoline usage @ 30mpg = 2 gal
2 gal / 0.857 hr = 2.333 gal/hr

60 miles @ 55 mph @ 35 mpg
60 mi / 55 mph == 1.091 hr
Gasoline usage @ 30mpg = 1.714 gal
1.714 gal / 1.091 hr == 1.57 gal/hr

Therefore, with a time factor, your gas usage has increased 48%.

This wouldn't matter for any real world examples though, because you don't travel based on time, you travel based on distance. One doesn't go arbitrarily an hour to get somewhere, rather a set distance.

Now, what you pointed out is the time cost of travelling, which DOES matter. For instance, say I am getting paid $25/hr. If I set my personal time cost of travel to my wages, then it's $25/hr for travel time. That means that the difference in driving 70mph vs. 55mph is 0.234 hr, and a savings of $5.88.

Therefore, my bad habit of speeding to work didn't cost me more, because at $4/gal for gasoline it may have cost me 0.286 gal = $1.14. That means I actually saved $3.74 by speeding.

The only time speeding *doesn't* save you money is if your time is considered to be almost equal to the cost of a gallon of gas. Personally I don't know anyone who would work for $3 to $4 per hour, or consider their time to only be worth that much.

-- October 13, 2008 8:06 AM ∞

vnutz wrote:

For a related and detailed analysis of wind resistance, out-of-gear consumption comparisons and graphs on other fuel efficiency elements of driving habits, please read Improve MPG: The Factors Affecting Fuel Efficiency hosted on OmniNerd. The study was conducted by sampling data directly from a Jeep Wrangler's engine computer via the OBDII interface in order to determine how different driving habits influence fuel efficiency. An additional aspect that is important to consider (from those on this page) are acceleration, use of air-conditioning and cruise-control.

-- October 13, 2008 8:52 AM ∞

silven wrote:

"When you are in top gear, the only variable becomes drag. The amount of gas you use depends on the RPM of the engine."

That is so wrong I can't believe you posted that. Hills, Road surface, wind speed, direction there are many variables. Parasitic drag does affect cars, especially at higher speeds (meaning over 70), but the difference in wind induced drag between 45 and 55 is negligible. Especially in higher powered cars.

"Anyways, the only effect on mileage is drag once youre in top gear."

That's absolute crap too. If you're in top gear, but at low rpm/low torque and have the throttle wide open the engine is using more gas than if you were a gear lower and the throttle eased back.

If you want decent gas milage, get your tire pressues correct, check them often, get a manual transmission car, understand how an engine works, and be intelligent and conscious of your usage and shifting. There is no magic "if you drive X speed" you will get better milage.

As far as drag goes, in most recent and reasonably aerodynamic cars with decent engines, anything below 60 drag is negligible. It's a factor, but with so many other factors that affect gas milage in greater ways, trying to figure out miniscule factors like drag between 45 and 50 is mental masturbation.

-- October 13, 2008 8:58 AM ∞

jm wrote:

The engineers here claiming the only important factor is aerodynamic drag on the car body need to take a course in combustion engine design.

The most important additional factor is pumping losses in the engine intake and exhaust systems. Even in a fuel-injected gasoline engine, there is a throttle that presents a variable restriction to the intake air, the restriction being greater the lower the power output. And the efficiency of air and exhaust gas movement past the intake and exhaust valves and through the manifolds varies with engine RPM (especially in "tuned" intake and exhaust systems.

The main reason why smaller engines give better fuel mileage even at high speeds is that they are running more nearly at "full throttle" -- i.e., with the throttle fully open and presenting minimum restriction to air flow, and thus minimizing the horsepower expended to pump intake air past it. This is why if you rent a 7-Series BMW in Germany you may find it has a 1.8-litre engine (my experience in 1999); although the acceleration is leisurely, it will get the car to autobahn speeds and yet give good gas mileage because it's running with a very open throttle.

This is also the underlying factor that has led some automakers to introduce engines in which some of the cylinders close up completely in cruising mode. With the valves closed, though there are still more frictional losses than in a smaller engine, no power is wasted pumping air in and exhaust out.

Because most American vehicles have engines far larger than are needed to drive them at highway speeds, they are usually running with nearly closed throttles and pumping losses so high that they offset the savings from lower car-body aerodynamic drag at low speeds.

-- October 13, 2008 10:19 AM ∞

European wrote:

Reading through these comments, it seems to be true most Americans fail at basic physics and lack the ability of logical thinking...

-- October 13, 2008 10:32 AM ∞

gina wrote:

At 55 mph on a trip from eastern Ct to Scranton Pa i got 64 mpg round trip the same trip at 70 returned 48 mpg the time difference was not all that bad. Consider that to cut the trip time in half you must double the speed can you afford the speeding ticket and insurance cost jump when you get caught

-- October 13, 2008 10:46 AM ∞

William Mitchell wrote:

The federal calculation ignores that higher freeway speed limits reduce traffic jams.

Why? It's a capacity utilization problem. Traffic jams appear as utilization approaches 100%. Utilization is a function of the number of cars you can push past a certain location in a certain time. The higher the limit, the higher the average throughput. You can show this to be true in 3 ways: experimentally, or with partial differential equations, or with computer modeling. All show the same result.

Thus, even if 55mph were the optimal speed, it can be better achieved on AVERAGE with an 85mph limit than with a 55mph limit. If you set the limit at 55, then the average will always be lower than that, due to traffic. Especially here in Los Angeles!

-- October 13, 2008 11:05 AM ∞

Scott Wilkins wrote:

I have a 2000 Buick LeSabre. On the highway, I have worked out that 49-50 mph give me my Maximum MPG. At 49-50 mph, I get between 40-46 MPG.

-- October 13, 2008 11:09 AM ∞

wra wrote:

"Driving fast imposes huge negative externalities on others. Tens of thousands of Americans are basically murdered by negligent drivers each year, yet we continue to call these homicides 'accidents.'"

Driving slow imposes more negative externalities on others than driving fast. I'm sick and tired of getting stuck behind smug, self absorbed, do-gooders driving 3-5 under the posted limit. Speed has very little to do with collisions. Collisions are caused by inattentive driving. To blame collisions on speed is to buy into the government's propaganda without doing any critical thinking of your own.

-- October 13, 2008 11:17 AM ∞

Richard Ward wrote:

Exactly. Sandra for the win on this one. Going slower will get you better gas mileage, however you're driving longer to reach the same destination, causing you to run your car longer to go the same amount of miles. Regardless of how many MPG you get -- when your motor is running it's using gas. Bottom line.

-- October 13, 2008 11:18 AM ∞

mark gross wrote:

I call bullshit!

there is no way I get better gas mileage at 75 than 50.

Wind resistance goes up linearly with the speed. These graphs where probably generated in a lab with the car sitting on a dino. Not an open track where the wind is a factor.

-- October 13, 2008 1:20 PM ∞

Matteo wrote:

Sandra, the time facto makes no difference in amount of fuel used. In your example the savings would be 2 - 1.7 = 0.3 gallons. The time enroute makes no difference to total fuel consumed.

The main consideration is this: energy = force * distance. The drag force is higher for higher speeds, but the distance is the same in both cases. Therefore, total energy used is higher for higher speeds. And total energy used is proportional to gas used.

According to the logic I'm getting from your statement: "Even though your engine is burning less fuel per hour due to the slower speed; it is running for 27% more time which has to be taken in account," it seems like you might advocate "flooring it" to get to the next gas station when you're getting close to empty, in order to get there before the tank goes dry. But all that would accomplish is having you run out of gas further from the gas station than otherwise...

-- October 13, 2008 1:32 PM ∞

Matteo wrote:

Joseph Xavier,

You said: "At 65mph in 5th, I should have 2451RPM. At 65mph in 3rd, I should have 5077RPM. Since it redlines at 7000, I can safely do 65 in 3rd. If I enter the highway in 3rd, and keep it there until I reach 65, I should have 5077RPM, sort of hard to measure, maybe a little more than 5000. If I notice that it is somewhere else, like 5300RPM or 5500RPM, then I know the effect drag has. If it reads 5500, then I should be doing 70.4MPH, but I'm only doing 65."

Assuming there is no slippage in the transmission, this statement makes no sense. You will actually be doing the same RPM at a given road speed, regardless of the drag on the vehicle. The difference will be in the fuel flow, not the RPM.

Mark Gross, air resistance increases as the square of the speed, not linearly with speed.

-- October 13, 2008 1:38 PM ∞

ahmosis wrote:

I agree this is not that easy to figure out.

another factor: engine has a diferent hp at diferent RPM

-- October 13, 2008 2:06 PM ∞

jerry wrote:

Parasitic Losses. The reason why faster is sometimes better milage than slower. Your engine has a number of parasitic losses, these losses generally take the form of Joules/Hour. If you go faster, there is less parasitic loss per mile, and this can offset the reduced drag in some speed ranges. The speed where this tips and favors slower is going to vary from design to design.

Death. Death is a normal function of all living things. Anytime you combine an examination of human experience and time, you are going to get a death rate. This is true for ALL forms of human experience, including obviously driving. Factors that impact the rate are certainly speed. But safety aspects of modern cars are so numerous that determining key causes is dubious at best. Certainly, however, the statistics that show that the death rate on expressways is low per passenger mile as compared to other roads, shows that speed must likely be a minor factor in over death rate from transpertation. Also the factor that the death rate on expressways is lower than other roads combined with the fact that higher expressway speeds could redirect traffic from more dangerous roads could offset the death rate in a manner sufficient to make an increase in expressway speeds actually make the overall transpertation system SAFER. Like I said, numerous factors to consider, simplistic approaches will always be dubious.

Regards.

-- October 13, 2008 2:09 PM ∞

Ron wrote:

It's absolutely going to depend on the car!

For example, My 1993 Honda Accord has much longer gearing than my 1997 Honda Prelude. 80MPH in the Accord comes in around 3000 RPM. The Prelude 80MPH is at 4000 RPM. Combine that with the larger injectors for the higher compression and premium gas it requires and doing 60 which drops the RPMs more than doing 60 in the Accord would will make a big difference in cost per mile.

55, 60, or 65 won't make much difference in the Accord at all (and infact it doesn't as I do a lot of highway driving and know in around any of those speeds I get right around 450 to 460 MPG on the ~17 gallon tank. The Prelude on the otherhand will make a big difference. While 80 @ 4000 and it tops out at 160 @ 8000 RPM, so 55mph = 2750RPM and 65mph = 3250. Those 500RPM on with the fuel flow it has on premium will surely add up higher than the smaller RPM change on the lower fuel demanding accord motor. (And yes, both motors are 2.2 liter)

-- October 13, 2008 2:38 PM ∞

David wrote:

Kevin wrote, "It looks to me like driving 60 MPH saves you 1 MPG compared to driving 65 MPH. 1 MPG/26 MPG = ~4% increase in efficiency, or about 4% less fuel needed to drive the same mile. At $2 a gallon, this saves us 8 cents per mile."

WRONG... I can't believe nobody called you on this, because the correct math is pretty simple.

At 25 MPG and $2 per gallon, your fuel cost to drive one mile is 8 cents. At 26 MPG and $2 per gallon, your fuel cost to drive one mile is 7.69 cents.

So, if slowing down from 65 to 60 MPH causes your fuel economy to improve from 25 to 26 MPG, you have saved 0.31 cents per mile. (Because 8 - 7.69 = 0.31.) That's a far cry from saving 8 cents per mile.

-- October 13, 2008 4:31 PM ∞

Tom Shillock wrote:

Does the government's graph which shows much lower fuel efficiencies at lower speeds reflect efficiencies at constant speeds or the cost of efficiency due to acceleration up to a given speed? If the latter then I understand it because F=MA.

-- October 13, 2008 5:07 PM ∞

Old Bogus wrote:

I have found that only going downhill increases my gas mileage by 20%. Unfortunately I live on a hill 4000' above the flatlands where the groceries are.

-- October 13, 2008 9:42 PM ∞

chef wrote:

"[I am not considering what your personal time is worth for sake of this example.]
Let's say you drive 60 miles at 70 mph at 30 mpg. You have used exactly 2 gallons of gas.
Now you drive 60 miles at 55 mph getting 35 mpg. You have used 1.714 gallons of gas but it took 27% more time [70/55]

What is your fuel savings?"

Um.. trick question? Looks like 0.286 gallons. As you said, you're not considering what time is worth. However, slowing down reduces risk of fatalities (and conversely, speedin up increases risk), so the time saved by speeding could cost you your life.

-- October 13, 2008 10:29 PM ∞

Nick wrote:

Your savings is 0.286 gallons of gas. Miles per gallon has nothing to do with the amount of time your engine is running for; if you get 60 mph going 60mph, and 60 mph going 30 mph, then you use the same amount of fuel to go any distance.

Aside from the consumption of personal time (gas is still cheap enough that burning more per mile to go faster probably still pays for itself if you use the time you save to work), I don't see why running longer causes more maintenance expenses. Assuming you are in the highest gear your car has on the highway, then your RPM (And therefore the number of wear-causing cycles every engine part goes through) is proportional to speed, so your engine turns the same number of times for a given distance. The forces on engine components will be higher at higher RPMs, and temperature will be higher due to higher power consumption to go fast. This is a mixed blessing, in extremely cold weather keeping the moving parts of your car warm will reduce wear, so running everything faster will keep all the moving parts in your car warmer in the winter, which might offset the increased wear due to the low temperature.

I think that driving faster is still ultimately wasteful unless you are using the time to work; the cost of the fuel you burn going faster is not the only cost of going faster; speeding tickets aside your car will suffer more wear and tear due to increased forces in the engine and higher temperatures.

However, people who drive slower than the speed limit (except of course on the highway), are most likely wasting fuel, or at least wasting time.

That being said, slowing down to 55mph on the highway is a good thing, but it is not nearly as important as avoiding hard acceleration and braking in the city. That wastes a lot of fuel and is very hard on the car compared to driving 10-20 mph too fast on the highway.

It is also safest to go the same speed as everyone else on the highway, which is important to consider.

Personally I drive the same speed as everyone else in the slow lane, which, where I live usually is 55-65 mph.

-- October 14, 2008 10:13 AM ∞

Patti Robinson wrote:

I have a Toyota Yaris. I added the ScangaugeII. I get the best gas going between 35mph and 40 mph. Above that the gas mileage falls. When driving 40 in fifth gear I watch the gauge and it stays around 60 mpg. If I go a 20 mile stretch at 40mph (up and down small hills with curves and corners) I average about 55. If I increase to 45mpg, I average less than 50mpg. When I am forced to go 60mph on the highway, I average 43mpg. Yes, slowing down helps with a car that is made for efficiency. In my Mits. 3000gt, I get the best gas mileage at 65mph.

-- October 14, 2008 12:53 PM ∞

Tim wrote:

heh, no one has commented here in a while but i can't resist.

Now the fact of the matter is that in a vacuum the faster you were going, assuming you could continually better your gearing ratio to keep you rpm's down, the better your fuel efficiency would be. However, we do not live in a vacuum. Thus it follows that friction, most specifically air friction, better known as drag force becomes a factor. Now i won't bore you with the technical details but drag force increases dramatically with velocity, i believe its a squared proportionality. Anyway the fact of the matter is that at a point, between 50 and 60 mph in most vehicles, the drag force acting on your car is negating the theoretical fuel economy of driving faster. Its a matter of how much energy does it take to do the same amount of work. Now because of gearing your fuel economy will be increasing until in a jagged upward climb until you hit the spot where drag force is too much, thus driving slower than that speed will actually decrease your fuel economy just as driving faster than it will. Now as i've already said this speed is usually around 55 mph, however if you are thinking that driving a super areodynamic vehicle is going to allow you to drive 70 mph and get the same economy as 55 your mistaken, as a general rule i would say you are going to be sitting within 10 mph of 55 on either side depending on the vehicle. Now as to the matter of time, since we measure fuel economy as a function of mileage, whether it took you 1 hour or 2 to go sixty miles makes no difference, the time the engine is running makes no difference, however the time does say something about your velocity which in turn says something about you fuel economy, but im afraid the guy going 60 instead of thirdy wins, however the guy going 120 loses real bad. If you want to know more about drag im sure there is a good wiki on the subject.

-- October 14, 2008 6:30 PM ∞

Taylor wrote:

I would imagine that every vehicle would have a different graph, some hugely different than the one shown. Much would depend on where the manufacturer decided the best mileage should be.

Each engine operates the most efficiently at a different RPM. That coupled with the ratio of the top gear would determine the most efficient speed for that vehicle.

In short, A VW bug is winding out and well over it's most efficient speed by 65, where a Porsche is likely just reaching it's optimum level.

-- November 14, 2008 3:53 PM ∞

i can't remember it wrote:

i don't understand anything anyone is talking about

-- February 3, 2009 9:30 AM ∞

i can't remember it wrote:

i don't understand anything anyone is talking about

-- February 3, 2009 9:31 AM ∞

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Does Driving Slower Save Gas?

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