The average car speedometer may be off by a few mph There are several GPS and 3rd party apps that show your actual speed The speedometer, of course, tells you how fast or slow your car is moving when ...

If you drive your hot rod, even once in a while, then you depend on all of your gauges to be reliable and accurate. Just a small percentage of miscalibration can result in engine damage or failure, ...

Yes, it does! Though not as much as speedometer fudging by your car manufacturer. Your car can only measure rotations of the axle, with expectations of tyre circumference based on its standard tyres.