Originally Posted by
paulrad9
That sounds about right as car odometers are often a bit optimistic when displaying velocity/distance
If you really want to measure the distance, calibrate a bicycle computer and ride the distance or get a paper map with a ruler or use a computer map that measures distance.
Actually 8% is well outside the range of accuracy for a car's odometer. For a speedometer in a BMW (the least accurate of all brands according to several tests by car magazines) then 8% at 75 MPH is possible, but legally, odometers have to be accurate to within 2% or so. The exact legal requirements in the US permit up to something like 4% error, but as
this lawsuit shows even being off by 2.5% can result in an expensive and embarrassing lawsuit. Most odometers are in the 1-1.5% accuracy range on the stock tires at 50% tread depth.