I was just curious what are your opinions on mixing sets of tires... I have a '03 a4 3.0Q and I bought a set of 19's and 2 have brand new tires, the others have cords showing. I was wondering what you guys think about buying just 2 tires (cant find any that match ones i have) I really dont think it would affect anything if they are close to the same tread patterns and size...

 

You might wanna check your local laws... Some places, as long as the tires on the same axle (F/R) match, you're OK. Other places require tires to match all the way around.

Now, with an AWD vehicle, you have mechanical differences to worry about, not legal ones. Generally, you want the tires to all have a pretty close match for rolling diameter. People who have gone to school for mechanic-ability can prolly give a more detailed explaination. But, if the delta between any given tire (or tire pair) and the other tires is too great you'll end up "winding-up" part(s) of your drive-train, leading to eventual catastrophic failure.