回复：为什么我车的车速仪和GPS显示的时速不一致？- Error within Specs

First, since cars' meters estimate the speed based on the rpm of your tires to calculate the speed and distance traveled, a lot of factors affect the speed reading on the meter: tire wear, tire pressure, meter calibration, car-to-car variation, etc.;

Second,I heard manufactors design the meter with some tolerable variation, let say 5%.  Any meter is OK if it's within 5% difference from the average.  Also, car makers tend to be on conservative side to over estimate rather under estimate speed;

Third, I heard Honda is famous for over estimating speed/distance. It can be in 5-10%.  You can search the net to find user comments.  A friend of mine drives a Camry with old tires and a brand new Pilot on the same road by commuting to work found the difference is 10% with Honda overestimating the distance traveled.  Needless to say Camry may already over estimated the distance.

I would trust GPS.  Car's speed is a pretty rough estimate.  I also experience about 2-3 mph difference between car's speed meter and GPS.  I am driving Toyotas.