I've had a number of cars with either slip-and-grip AWD like the All4 (my current R32), or with fulltime Torsen AWD that is engaged all the time (an Audi quattro and a VW Passat W8).

Unfortunately, I seem to be a magnet for tire problems. When I've had problems, depending upon the mileage on the tires, I found myself buying multiple tires (sometimes 2, once I replaced all 4), because that was required to avoid transmission problems. Couldn't have tires with different diameters.

Will the CM All4 be the same? Will the use of runflats make any different? I wouldn't think so - diameter difference is diameter difference - but am curious as to what folks think.

Thanks in advance!

 

Coming from a WRX, tire replacement was one of my first questions. I too have been bit by the 'damage one buy four' bug! The ALL4 is front drive until slip is detected then the rear diff is engaged which means there is enough slip to allow different tire sizes without stressing the transmission or diffs. The caution is that tires on each axle should be the same diameter but the car will accommodate slightly different sizes on the front and rear axles. I confirmed this with the service department when we ordered our ALL4.

 

as an Audi quattro owner you may find even there it wasn't necessary. I think Audi's spec permits up to either a 2 or 3% difference. If you look at running circumference differences, that is often a full size step up--several tenths of an inch in diameter change. As the prior poster said, that's on a full time system rather than a reactive one like the Mini or most car based systems