> In fact, most cars lie to you about the speed - reporting a speed slightly faster than reality. It's a cover-your-ass measure for the car manufacturers because it's illegal to sell a car (in the US, at least) where the speedometer is inaccurate in the other direction, that is, reading slower than actual speed.

Haven't seen that in a long time. Everything I've driven in recent years has a speedometer speed that matches roadside speed sign speed within 1 MPH.