I've had this issue with the truck since I bought it.
Was running 315/75-16 tires and the speedo was about 9.5% fast
Changed to 285/70-17 size and it is now running almost 10% fast.
By all rules since both tire sizes are taller than stock the speedo should run slower than with the stock size tire. I know there are a couple of tuners that do calibration and calibration only boxes. My biggest question is: do you enter your factory size tire then the size tire you have installed then it does all the math for you or do you say the new tires are XX size bigger/smaller than factory?
I'd be nice if it could all be done with just something as simple as a rheostat or potentiometer inline from the ecu to the speedo.
Was running 315/75-16 tires and the speedo was about 9.5% fast
Changed to 285/70-17 size and it is now running almost 10% fast.
By all rules since both tire sizes are taller than stock the speedo should run slower than with the stock size tire. I know there are a couple of tuners that do calibration and calibration only boxes. My biggest question is: do you enter your factory size tire then the size tire you have installed then it does all the math for you or do you say the new tires are XX size bigger/smaller than factory?
I'd be nice if it could all be done with just something as simple as a rheostat or potentiometer inline from the ecu to the speedo.