Truck and Barter: On the Accuracy of Odometers

June 18, 2004

On the Accuracy of Odometers

By Kevin

All instruments have measurement error, independent of a human misreading their output. No yard stick is exactly a yard, no reasonably priced bathroom scale measures to the quarter pound, no chem lab balance is accurate to the microgram. Similarly for an odometer, which measures distance traveled.

Correct me if I'm wrong, but the United States has no federal or state regulation about speedometer or odometer accuracy; of course it is illegal to shift the odometer without posting a notice of having done so--even if the original odometer was reading wildly outside the design tolerance of the manufacturer. (Here are the federal regs.)

Tampering with automobile odometers is an extraordinarily costly problem. A while back the NHTSA studied 10,000 randomly selected automobiles to figure out how frequently used autos have their odometers rolled back.

NHTSA's study was requested by Congress and examined the title transfers of 10,000 vehicles and its own database of known odometer fraud. The researchers calculated that 3.47 percent of vehicles less than 11 years old have had their odometers rolled back, or about 452,000 vehicles sold each year.

From the full report:

The increased cost consumers pay to purchase passenger vehicles with odometer rollback of $1,056 million per year makes odometer fraud one of the top crimes against property in the United States. By comparison, the Federal Bureau of Investigations estimated that in the year 2000, auto theft resulted in direct losses of $2,900 million, arson $760 million, burglary $3,000 million, and shoplifting $200 million.

Even if you're buying a used car from a reputable person or dealer, there is still a very good chance that the odometer meter is wrong, even if it has not been tampered with. But the question when dealing with either an honest man or a crook is not "is the odometer wrong?", the question is "how wrong is the odometer?"

Even non-tampered odometers may wrong by a large amount, as tolerance levels for manufacturers differ; a consumer should know how this error tolerance effects their valuation of the car.

According to one calibrator merchant:

The speedometers and odometer on.... modern cars, are calibrated from the factory with a plus 1-2 percent error. This means that actual speed or recorded mileage is actually lower than that indicated on the speedometer and odometer.

Some organizations, when testing out cars, will examine speedometer/odometer error. Here are 5 foreign models tested in 2001:

Subaru Impreza WRX 3.2%
Ford Focus 2.1%
Chrysler PT Cruiser 1.07%
Toyota Condor 2400 1.54%
Volvo V70 T5 0.14%

One man claims the Porsche told him that 10% over (for a speedometer and apparently odometer) was with design tolderance. Another has a 2% overage.

Hence, if you're buying a car with 50,000 miles on it, the actual mileage can legitimately be 1,000 miles or more less than the odometer reads. Perhaps it's sellers, not buyers, who should be most concerned about this.

If this has amused you, see this longish treatment of mechanical and digital odometers.

Also note that the Iron Butt Association brings together those who motorbike long distances in short times--say 10,000 in ten days.

Their stringent rules require that applicants know their odometer error. One milestone has the following requirement:

WARNING: Unless your speedometer has been calibrated, do NOT depend on your own odometer readings for official readings! Most Japanese motorcycles register five to ten percent more kilometers than actually traveled. Over the course of a 24 hour period, this error can be quite severe - as much as 200 kilometers. IN ALL CASES, mileage will be verified with either paper or computer maps of the country you live in.

This man notes that race courses measured by auto odometers will be too short, yielding a who bunch of angry runners who really hadn't made personal bests...!

Posted at June 18, 2004 03:33 PM

Comments

The Odometer of my new 2004 Chevy Malibu registers approximately 3.5% more miles than accually driven. Over a 200 mile stretch on Interstate 35 (using the mile markers for reference) the odometer indicated I drove almost 207 miles.

Because some Chevy/GM Tech Rep has stated "a +/- 4% error factor is acceptable, I have been told by the GM Customer Service people that I will have to live with situation.

Curious if any other GM/Chevy owners have experienced a similar situation.

Thanks, Wayne B., San Antonio, TX

Comment by Wayne B at October 22, 2004 12:47 PM | Permalink

My Audi TT odometer is off by an unfavorable 2.6% with sample data taken over 1,600 miles using GPS and mile markers. Over the life of the vehicle, I calculate that this error will cost owners $1,233/vehicle. I called Audi customer service about this issue and they informed me that odometers can vary in accuracy and that 2.6% is within manufacturing specifications (but they wouldn't tell me the actual tolerances)! I then sampled a friends Audi TT over about 300 miles and concluded that the odometer was off by 2.5%. Funny how a German company, known for engineering excellence, can be off by such a consistent amount. No wonder fuel efficiencies are so high!

Comment by Tom L at January 24, 2005 09:08 AM | Permalink

I have a Audi A4 1.9tdi, it seems to be out between 8 and 10%, unfortunately I didn't have the functionality to test it against a GPS, but Audi did a few comparisons and found first found the problem when comparing it to a Volkwagen and the denied a problem when they compared it to an other A4. Thus all the A4 units are out with this much!

Comment by Johan at February 18, 2005 03:27 AM | Permalink

I have an '03 Acura TL. My father taught me as a young driver to check the accuracy of the spedometer and odometer using the 1-minute, 60MPH, mile marker formula. This car consistently adds .02 to every 5 miles travelled. I have also compared it with 3 different cars that were able to follow the same route directly behind with synchronized trip-odometers -- each time there was a significant difference. The dealer claims that they have road tested it against other '03 TLs and found no discrepancy (are they all off?, is it a plot???). I have asked them repeatedly to test it against a different make for at least a ten mile highway trip. No luck. Also, Acura customer service says it's an acceptable discrepancy. Since this is a lease, we are going to end up paying in the end for miles we didn't travel. Does anyone know how I can have the accuracy officially documented so I don't end up paying these theives extra money?

Comment by Cleo Z at February 22, 2005 03:09 PM | Permalink