Quote:
Originally Posted by RichardP
All speedos, except those that have been specifically calibrated for police use for example, will over read. It's illegal to have an under reading speedometer, they must be within the range 100% to 110% so most are in the region of 105% which is not far from where yours is. As the tyres wear the reading will decrease as the rolling radius of the tyre reduces, so they have to be set to over read on new tyres.
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My other vehicles are near exact, my GM vehicles can be easily calibrated based on tire sizes changes. I'd prefer it to be no more than 2-3% over on new tires. That would still be over slightly on wore tires. There's no need to be off by more than that.