The stock 996 Turbo rear tire is 295/30 18 which is 25.0" in diameter. I am not trying to scare anybody. Differential damage will in fact occur. There is no sensor in the front diff and the only way to learn of the damage is by diff failure.
There are no 295/25 19 tires. They have been discontinued.
I have fit a large number of cars with 235/35 19 front and 315/25 19 rear Michelin PS2 tires with no rubbing issues.

 

http://www.wheelenhancement.com/whee..._170_Black.jpg

http://www.wheelenhancement.com/whee...c%20Silver.jpg

 

However if differential damage were to occur why does the 997 C4/Turbo have this set up (virtually the same AWD system)? Here are the revised numbers:

997 AWD Tires
235/35-19 3.2in 12.7in 25.5in 80.0in 792 0.0%
305/30-19 3.6in 13.1in 26.2in 82.3in 770 2.9%

How does Porsche overcome the difference to reduce damage?

996 AWD Tires
225/40-18 3.5in 12.5in 25.1in 78.8in 804 0.0%
295/30-18 3.5in 12.5in 25.0in 78.4in 808 -0.5%

997 RWD Tires might be the best set up...

235/35-19 3.2in 12.7in 25.5in 80.0in 792 0.0%
295/30-19 3.5in 13.0in 26.0in 81.6in 777 1.9%

 

Probably a different gear in the center diff. I don't know for sure. I do know for sure that several 996 turbos have cooked their front diff when using the incorrect setup. The 997 awd cars also have a sensor to detect overheating in the front diff.

 

What thickness spacers front and rear do you recommend for use with the tire sizes you recommended (235/35 and 315/25) on a 996tt lowered with PSS9s? Thanks.

 

With which wheels John? If you are talking about 997 Turbo wheels in 8.5x19 front and 11x19 rear I would use 5mm front and 7mm rear. You can use up to 15mm on the rear.

 

Yes, I was referring to 997tt wheels. So I can go as aggessive as 15mm in the rear without rubbing even on a lowered car? thanks.

 

It is an application we have installed many times. There are some applications that are more aggressive.

 

Never liked them full stop

 

I am in the minority here...I really like the twists better. Funny, I like the time attacks (boss351's avatar perhaps) and the bbs wheels I have seen...but the 997TT stockers just don't do it for me for some reason. I want to like them...but cannot. Oddly, the leaked 998 wheels look much better on the stock and S coupe variants....just me. Heck, I actually like the Victor Eq Lemans better than the 997TT wheel....

 

Looks great. But Alan is right, I was doing some research and the oem 997T rims and tires will cook the front diff on the 996T

 

997tt wheels won't hurt your 996tt diff with the right tires.

I'm running 245/30/20 and 315/25/20 which are very similar to the stock 997tt overall diameters. 235/35/19 up front is about 25.5 and the 245/35/19 are about 25.8 which should be safe.

I might suggest 245/35/19 up front to be on the safe side but who knows maybe you can get away with the smaller 235/35/19 without screwing the diff up.

 

I have 997TT wheels on my 996TT. I have 7mm spacers all around. You MUST usr the correct tire size not to cause dammage.

Personally I'm not a big fan of aftermarket wheel period. I think they cheapen the car even if they cost a lot $$$. That said, I find the 997 TT wheels are, for me, the best looking Porsche wheel ever made, just my personal taste. After I put 997tt wheels on my car, I got a ton of compliments, more than before.

 

i have the 997 turbo wheels on my 996 turbo with the stock tires they came with.no spacers,no rubbimg issues. 5000 miles, no front diff. problems.. 3 of my friends have the same setup, they have not had any problems either.. i have to see it to believe it.

 

I have 997tt wheels on my 996tt too. I love em and think they look better than the turbo twists IMHO. I have 7 mm spacers on my rear tires. I noticed some very light rubbing on the rear. I'm running 305s in the rear. Although I'm going to get 315s in the near future as I've been told they're slightly narrower.

BTW, I don't have any differential problems.