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How can I check the accuracy of the odometer? The speedometer and my GPS disagree by 3 miles per hour. The GPS has been accurate in my last two cars. I have a lease for 15,000 miles per year.

3 MPH is within most fault allowances. Odometers measure distance, speedometers measure speed…odometers are regulated, and highly controlled but speedometers may disagree some. No biggie, really.

The only way to test it is by measured distance. However, comparing the speedometer to a GPS won’t give you accurate odometer readings.


I once figured out that my odometer is slightly off by using mile markers on an interstate highway. Of course, I have no idea how accurate those are. But basically, my odometer loses 1/10th of a mile about every 5 miles (at least that’s what I think it was).

You can’t do this over short distances. I tracked it for something on the order of 100 miles or so. And obviously you have to assume that the mile markers are reasonably accurate.

Oh, and there will be variances based on tire wear and tire size if different from standard.

Granted, wear variance will be minimal, but we’re talking about differences over hundreds of miles, really…and they’ll be fairly small.

I wouldn’t worry about your lease, and the odometer. It’ll be so close as not to make a difference in the end.


Modern GPS units (not the old ones) are very accurate and are likely correct. The odometer is likely intentionally adjusted to over report the car’s speed. They do this to prevent problems if there is an error and you end up driving faster than you intended and get a ticket or an accident.

Note: your GPS is likely more accurate than the odometer.

“The odometer is likely intentionally adjusted to over report the car’s speed.”