OK,, here is an interesting one---I have oversized wheels and tires on my 04 350z went from 17' stock wheels to 18" 245/40/18 front and 265/40/18 rear. here is my question? obviously my speedometer and odometer are going to be off. it is had to tell if i am reading fast or slow in the car and all the information given on the tire web sites for how speed and distance readings are impacted by Plus size wheel/tire setups are for a particular single size wheel/tire i guess assuming that you are putting 4 of the same size on the car. nothing is given if you have multiple sizes on one car. so, I am trying to find out where the input comes from for the speedometer and how the speed is calculated. I have the online maintenance manual and it talks about each wheel sensor sending a signal to the ABS or TCS box and that box sending a 8 pulse signal to the speedometer. however, it does not say how the box is manipulating the input from each wheel. does it take revolution counts from each wheel, average them and send a signal to the speedometer--or does it just use the signal from one wheel--if one wheel, which one?