i know on rear wheel drives, i always replaced the rear at least once before replacing the fronts but have been told on AWD its not a good idea to have the front and rears with different treads.

is this just a sale gimmick or will new rears and used fronts or the other way around hurt my car?

 

I'd like to know also - my Pilot Sports are worn in the rear but look brand new in front. I can either just get new rears, or for less $$$ change all 4 with Sumitomos.

 

I think if the tires are similar in category and grip you should be fine. You could probably get away with Pilots in the ft and Sumis in the back as (from what I've read) they are similar in the way of grip and functionality.

I probably wouldn't go with snow tires in ft and an "R" comp in the rear though. Might get just a little understeer =). Unless you're in the snow, then you'd probably blow the ft diff as it would be doing all the work.

You get the point.

 

Why waste the front tires? Most Porsches use 2 sets of rears for one set of fronts. The problem with having different manufacturers tires on the front than the back is the differing slip angles that they make. This can make for loss of traction at one end before the other. I advise you against it.

 

always replace the pair on the same axle, i.e., if the right rear is bad, but right rear is good... you should really (recommended) replace both rear wheels. If front good, rear bad, just replace the rear (the pair). I have not heard anything about replacing full set on an AWD.

 

it depends on the awd system. our 997tt has had the rears replaced without replacing the front tires fwiw.
i know on my last car (evo) you must change them all. even says so in the manual.

 

It actually depends on the wheels/tires. Your last Evo, like my A4, has the same wheel/tire size all around from factory. For those cars, manufacturers recommend tire rotation front to back per side (driver and pass) to ensure all four tires wear evenly over time. Assume you follow the rotation (frequency) as recommended, tire replacement should happen all at once, all around.

The TT runs staggered wheels/tires. Without the ability to rotate front/back to give even wear all around, your rears will need to be replaceed sooner (also the fact the rear engine also accelerate rear tire wear). HTH.