GPS mph accuracy

[Giller]

Interesting. My Boxster always shows faster, which is apparently quite common. I set my cruise at 105 km/h which actually means I am going about 98 km/h. I don't think 16 vs 17 tires would make any difference. Something isn't calibrated right. Get a buddy to ride behind you and track his speed....see if it's your car or your gps.

[Giller]

And Fyi - German cars are never designed to show a lower speed than what you are going. Due to European law, their speedos are always to show a slightly faster speed than what you are doing. Google it up, lots of info on it.

[Chuck W.]

Originally Posted by Giller

Interesting. My Boxster always shows faster, which is apparently quite common.

Agreed. All of the Boxsters seem to read 3 to 4 MPH higher. I have never heard of on reading higher.