Quote Originally Posted by shibby75 View Post
No amount of tire size would give out a discrepancy of 31kph.
Yup.

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It should be noted that almost all stock speedometers run a little bit fast. In the past several years that I've been calibrating speedometers against the VBox, the only one that has matched the VBox to 100 km/h is mine. And my car wears tires that are 5% larger than stock.

Most cars have speedometers that read 5% fast, some 10% and a rare few more than that. None have speedometers that read lower than actual speed. That's a lawsuit waiting to happen.

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Chances are, if their cruise control is set to 100, they're doing about 95 km/h. (and no, Google maps is not carthographically exact when it comes to roads)