Tires: AWD tire diameters, AWD Tire Circumference

Question
I have worked in the Automotive industry for many years. I am a factory Rep for Alignment systems, Blancers etc. The question keeps coming up What is the allowable diameter variation,s for AWD's. I have called the dealers their answer is they no its important but mostly they have no guideline to quote. Subaru 2/32, Ford not sure maybe 3 to 4/32 and on and on. Can you shed any light on this subject

Answer
Dave,

This is a difficult question to answer - as you have already pointed out - because the answer has to come from the vehicle manufacturer - and obviously each vehicle manufacturer is going to have a different answer and probably a different way of expressing it.

First, I think you ought to think in terms of tire circumference - it's the most meaningful measurement that can be made using simple tools - and not tread depth.  Tread depth only works if the tires are otherwise identical - so even age can be a problem since tires grow - particularly when they are new.

Calling a vehicle dealer isn't going to work - they are only interested in selling and fixing - not advising and preventing.  Call the vehicle manufacturer directly.  BTW, don't expect them to be very cooperative.  I suspect they don't see the need to be customer friendly.