Originally Posted by
pizzaguy
Ok, but when I put the bigger tires on the back, my speedometer went from being 1mph off the GPS to agreeing with the GPS. BUT, at 80mph, I lost some ~350 RPM.
This implied to me that the sensors in the front wheels drive the speedometer, and others here agreed.
Oh, and my car is a six speed.
And if the sensors on the front wheels do drive the Speedo, your experience would still verify that the electronic sensors in the Tranny are "doing their thing" when a bigger geometry is installed at the rear. If the rear wheels are turning a slightly lower RPM to maintain same ground speed, the front wheels would be turning the same RPM as before. Speedo would give the same readout. If the electronics did not compensate for the increased geometry at the rear, then the fronts would be turning at a higher RPM too resulting in the Speedo being off (slightly higher).