So I'm getting new tires... fronts are going to be stock height at 255/40/18..... but I am considering 295/35/18 in the back, which is slightly shorter than stock height and thus will throw my speedo off a smidgin. My question is, since my front rubber is stock height (speedo correct) and my back rubber is a little off, will it affect my speedo? In other words, if MPH is measured at the front tires I will be fine, but if its measured at the rear tires (which I am guessing since its RWD) then my speedo will indeed be off.

Sorry if I confused you. I think I just confused myself.[:@]

 

Lots of modern cars are measured at the transmission, thus the back wheels on the Mustang. With speed being calibrated through the ECM, I would bet this is the case, however I don't know this for a fact on our cars.

 

Yep, your speedo will be off.. We have an electronic pickup that sends the speed of the tail shaft to the ecu. So changing rear tire height or gears throws off the speedo

 

My *** [8D]