Hi,
I'm brand new here and just bought and drove about 400 miles back home in my new (to me, now with 7k) 2011 X5 today. I have a trusty GPS that I've used in our cars for a couple years now with a slight amount of error, maybe 81 on the speedo is really 80. So I'm driving home today and notice that I have to do "84" BMW Mph to get 80 GPS mph. It looks like 5% at every speed

I've got the fat 214 20" rims and big tires and wonder, just tonight driving home, if some setting needs to be changed for the diameter of the wheel and rubber. Is this option out there at all? Still a blast to drive but I need to know how fast I am going. 120 wasn't really 120 today...
Cheers!