I'm just gonna put on one tire for now because I plan on getting all new wheels by the summer anyway.

 

When I first got the S4 I remember reading (I think in the manual) that it's okay to run tires of the same type with different treadwear. I don't think tread wear is going to mess with the Quattro system enough to cause it to send improper power balance to the wheels.

When I got a Geared LSD for my truck it said to use tires of the same treadwear and to rotate them on the same axle to keep it from enganging at improper times.

 

Just updated my sig, I didn't have the "include sig" button selected lol... I have a few cars but my DD is the A4 1.8TQ.