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...!
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