stin

I just realized that my car was going slower than what my speedometer was saying when i was driving from LA to Vegas today... i told my parents (who were driving their car) to set the cruise control at 80 and i tried to drive at the same speed on the next lane....i had to do almost 90 (not quite) to keep up with them.... y is this so?????????? with the technology and everything i assume it had to be done on purpose by the factory.... for safety issues maybe???