Just wondering if the speedometer and Odometer tied to the front or rear wheel?

To make sure the tire height is correct for accurate reading.

 

its not a mechanical link, its all done with sensors (which the car has one at each wheel).

As for which set the ECU uses or how it calculates speed...I dont know. Since it is electronic it can do so many different things.

My guess would be its an average of the 2 rear sensors.

 

Theoretically it doesnt matter what size tire you are running because when you are using sensors to calculate the speed the speedometer is only going to read what the sensors are telling it to. When you are using a cable and gears like on older cars it is a whole different ball game because they worked off of the transmission.