In vehicles with All-Wheel Drive (AWD) systems, the differential (gears that transfer engine power to a vehicle’s axles) and the car’s internal computer work together to send power out to each wheel. The amount of power-per-wheel can vary, depending on each wheel’s individual work load. For example, in a straight line each wheel carries a reasonably similar load. In a cornering situation the stress on each wheel is very different.
So the amount of power the internal computer sends to each wheel – based on what your AWD vehicle needs to go down the road – helps to manage how hard the transmission and differential are working.
With inconsistent tire sizes or tread patterns an AWD computer’s readings will fluctuate. Various wheels will receive inefficient or incorrect power loads. As a result the drive train (computer, transmission and differential) must constantly readjust, do more work than necessary and eventually, may break down.
Bottom line: For AWD vehicles Manny Moe and Jack strongly recommend replacing all four tires at once.
You do not have to be concerned about your drive train if your vehicle suffers a flat and you have to run with the spare for a while. But remember a spare is only designed to function for a brief emergency. Also, rotating your tires on a regular basis will help provide consistent tread wear. And as you now understand, consistent tread wear can make the job of your vehicle’s traction computer much easier.