Quattro tyre question

I beg to differ. Differentials of all types jiggle the torque from the engine to the most appropriate wheel. When a car is going along on the flat the torque is split evenly between the wheels on each side, and some ratio front/rear in the case of 4 wheel drive. When the car is cornering this split varies as the differentials differentiate. If the car had different size (or type) tyres on each side and/or front/back then it /might/ be the case that the differentials would find it easier to send the torque to one or the other. Imagine on the front you had some track-day stickies on the front and rock-hard economy tyres on the rear. A conventional differential would send the torque to rear as it is 'easier' that end. In otherwords the same situation as when traction is lost.

This would have two main effects. Strange handling/tyre wear and possible premature diff wear.

However the situation is slightly less severe in a car with 'intelligent' 4wd as the diffs do not proportion the torque evenly.

It might be the case that the construction of, lets say, a dunlop and a pirelli means that the traction provided is similar at each end in which case there will be no problen; but this would have more to do with luck than engineering/design. If it was my car then i'd definately have the same tyres on all corners and swap them round occasionally to keep the wear even.

Obviously tyre wear is more even on 4wd cars, but tends to be less on the front as these steer/tilt the vehicle. Having Different brands shouldnt pose a problem at all. Less tread on the back is common on high powered vehicles, or drivers who like to floor it off the line, as most of the power is split to the back.

What tyres are you using for a start? Pirelli's for instance wear a lot quicker than say Nankangs....

Given how Audis are generally engineered to understeer, the conventional tyre wear pattern for a 4wd car, i.e. rears before fronts (in the case of A4's anyway since it is Torsen permanent 4wd as opposed to the predominantly FWD Haldex version) is almost thrown out of the window... I know for a fact that my fronts are worn more than the rears on tyres that were all fitted brand new with the wheels when they were new simply because, out-of-the-box an Audi will understeer an awful lot more than oversteer unless you physically force it to oversteer by flciking it all the time. In the case of a neutrally set up car with permanent 4wd the wear pattern would be far more 'conventional' so-to-speak since the majority of torque is split to the rear wheels properly, i.e. neither front nor rear, under or over steer biased. So the power is more naturally delivered to the correct set of wheels determined by the greater torque output via the differential.

In summary, the understeering properties of an Audi virtually cancel out the 'conventional' front/rear torque split/tyre wear issues... although quite how this would affect a car that has different sets of tyres both ends I can only guess at... (?)