I'm looking for advice based on experience for fitting a non-stock sized 18" wheel/tire combination for FRONT and REAR of a 996TT.

This is what I know (correct me if I am wrong).

Stock TT:
FRONT: Wheel is 18"x8" , +50mm offset. Tire is 225/40ZR18
REAR : Wheel is 18"x11",+45mm offset. Tire is 295/30ZR18

Stock GT2:
FRONT: Wheel is 18"x8.5",+40mm offset. Tire is 235/40ZR18
REAR : Wheel is 18"x12", +45mm offset. Tire is 315/30ZR18

Stock TT: Calculated Rolling Circumference is roughly
FRONT: 343.8
REAR : 342.9

Front and Rear have really close rolling circumference (less than 1 cm delta). The car and it's traction control systems are happy. The fenders/wheel well are happy (no rubbing) etc.

Stock GT2: Calculated Rolling Circumference is roughly
FRONT: 346.3
REAR : 346.6

Front and Rear have really close rolling circumference (0.3 cm delta). The car and it's traction control systems are happy. The fenders/wheel well are happy (no rubbing) etc.

NOW.... I am looking to getting aftermarket wheels, which means I have the chance to go wider wheels (and wider tires).

I want to stay with 18" wheels. I just want lighter unsprung mass and tires will be less hurtful on the pocket book.

I could play it safe and just go with the GT2 width/offset wheels and tires. Can people confirm this will fit in a 996TT without need for rolling the fenders or anything else?

What have other people tried in terms of 18" wheels, with different offsets (front and back) and different tire widths/profiles (front and back)?

Also please mention any suspension changes (lowered height, etc.) that you had made that may affect fitment/geometry.

(btw. What kind of tires are you running and what's your feedback on them?)

Your experience and feedback would be greatly appreciated.

Thanks in advance,

Andy

 

i run 9x12x18 w 40 offset and and have been very happy with it. car is lowered 1-1.5 inch on h&r sport springs and rear fenders rolled ( not a big deal to do ) there is no rubbing but there is about 1/16th of an inch clearance inside rear at the intercoolers on a good day lol.

very hard compression gives a momentary rub. i use michelin ps2's exclusively in gt2 sizes and feel i get what i pay for in terms of stability and tread wear. i average two sets of rears to one set of fronts and go thru a set of rears about every six - nine months on average, with hard canyon driving with occasional trips to the market.

take your own advice and "play it safe" would be my advice to you. also, take a look at the new oz wheels they make in the gt2 sizes.. can't think of the name? but they look pretty good. i'm on forgestar f14's which are great for the money and custom ordered for fitment.

 

Thanks for the quick reply.

So, I'm guessing 9x12x18 is short hand for 9"x18" front, and 12"x18" back. and you have +40mm offset for both front AND back? Thanks for the info on the suspension. What size tires are you running front and back (got it on the Michelin PS2's)?

Also, based on that frequency of change, how much mileage are you actually putting on it? (obviously, hard canyon miles isn't the same as rolling traffic :-)).

1/16" clearance? nice :-)

On hard compression, 'where' (front ? back ? One corner?) are you getting momentary rubbing?

I am definitely looking to avoid spacers so want to get the sizing and offset right. That being said, I know that sometimes tires aren't the same as other tires, and there are 'tolerances/variances' in each car. :-P

 

yes, you've got it. gt2 stock sizes 235/40 X 315/30 in ps2's.
any rub is only the slightest of momentary rubs under hard compression which seems to be limited to the right rear fender liner and rubs on hard righthanders ONLY IF i am taking a corner a bit too hot and only downhill. normal conditions will produce NO rub if you duplicated that setup. bear in mind, my car is a bit ( 1/4 in? ) below normal oem gt2 height.

it would be fair to say i'm getting 5+k miles per set of rears but i change them at any sign of the wear marker being flush. they would last longer but i do not mess around at all when it comes to my tire tread depth(s).

they are often the only thing btw me and a 1000 ft drop below into a steep ravine. hope any of this helps, and you're very welcome.

 

Thanks, sounds like your conditions have to be 'just right' for the rub ;-) But, fun conditions ! :-)

One last question, and thanks so much again, what made you change the rear offset from stock?
Rear GT2 is 12"x18" +45mm, but you went with 12"x18" +40mm. So essentially, you 'pulled' the wheel further 'out' of the car by about 5mm, compared to a stock GT2 rear wheel set-up.
If you had not pulled it out, could you have avoided rolling the rear fender to avoid rub?

 

i too was coming from 18's with 7mm X 15mm spacers and like you, wanted to keep a low wide stance. it seems to the best of my recollection that the added few mm's rear helped even further my goal of achieving the widest/flattest stance i could while still maintaining "streetability". which i have. as to whether or not the added 4mm's contribute to the propensity toward the minor/occasional liner rub? i cannot say with any certainty, but it is certainly possible. but as it happens so infrequently, it remains an anamolous non issue in my book. great question to ask though!


add: no, i don't think so. rolling the fenders with a 12 on the rear is just accepted wisdom. far as i know. i have no idea what kind of clearance you might have if you don't roll them. i do know with certainty that the 12 rear is optimal. follow the gt2 guidelines and they knew/know best what works best.. and it does. fender rolling is a lot scarier sounding, than it actually is. fear not lol