Originally Posted by Mr.Manchester
I thought adding bigger than standard wheels actually appeared that you were going faster than you are according to your speedo?
ie, when i was doing 80mph in my escort with 17's on my GPS calibrated i was actually doing 76mph, worth a thought
nope, opposite.. the speedo measures the driveshaft speed effectively, fitting larger diameter wheels will mean you are travelling further and hence faster for every wheel revolution.