I'm looking at buying a set of wheels and tires for my 996tt and the seller has 295/30/18's on the rear (std size) but has 235/40/18's on the front. Is this close enough to not cause any issues for the AWD system? I thought the std size for the fronts was 225/40/18. They are Michelin Pilots in those sizes. Thanks

youll be fine... 235 isnt that much wider than the 225 and won't really notice the difference.

its fine, better to go with 245 front 315 rear which fit fine on stock wheels.

I am buying a used set of 18" BBS RS-GT wheels w/Michelins Pilot sports and the Pilot's are almost new, but the fronts are 235 instead of 225 which is the stock size. I am more concerned about circumference and center diff damage due the slightly different rotational speeds, especially if I do a long trip etc. Thanks guys.

245 what aspect? 30?

It's fine IMO. Just ordered the same setup for my stock wheels based on talks with more than one specialty shop. I'm told it makes a noticeable difference in reduced understeer. Combine with a rear bar for max effect.

These cars aren't real AWD cars. You will never transfer enough torque to actually spin the front tires in the dry. No center diff. There is a viscous coupling which can overheat and fry, but it's NOT (CORRECTED)very common to fry these unless you run on a RWD dyno.

The fronts are 235/40/18 and the rears are 295/30/18. Thanks

That is less than 2% difference in rolling rate. It should be fine.

245/40