You can say the same for the airbox - why spend more money on diff airbox when you already have an airbox. Have you asked the previous owner if there were any problems with the current wheel/tire setup? By the lack of answers you can conclude 1) nobody knows or 2) no problems. Good luck.

 

ASK YOUR TUNER! Since they have the car and the tires you are Questioning let them tell you if there are any problems with it.

You go round and round on something you don't have yet. If TIM is your tuner I am sure he knows what it needs and let him decide what is RIGHT for your car.

Do the math on the NORMAL SETUP which is 245/30/20 and 325/25/20 from YOUR SETUP of 245/30/20 and 315/25/20...What is your difference?

GT RUS - First your car is a 1/4 mile car, then a show car and now a touring car. Which is it?

 

If u read my topic about the boc carefully I state there...with our special set up we think it might be beneficial at higher speed = make more POWER with more AIR !!!

Previous owner doesnt know or want to know anything...I think nobody 100% sure cause not one runned that set up yet...unfortunately...

 

Why is it now touring ???

My car is everything to ME...my tuner has other prolems then thinking about my tyres...we decided to get 315/25 tyres but I am worried if I will be OK or not with diff clutch...I dont want to ahve any probs...

 

Different clutch will NOT solve the issue of running with 315/25 tires. It's the AWD/Traction/PSM system that will cause problems.

 

This threaqd is about 19 315/25 mine is 20 315/25 which is bigger diameter then 19s so I wont if tuner say 325/25 is good with 245/30 on 20s...can 315/25 be OK as well ???

 

Here are the PS2 diameters from Michelin:

Stock TT front 235/35-19 25.5 inches
Stock TT rear 305/30-19 26.3 inches
Ratio front to rear = 96.96%

Your setup:

GTRUS front 245/30-20 25.8 inches
GTRUS rear 315/25-20 26.3 inches Is this a PSC since I don't see a PS2 in that size?
Ratio front to rear = 98.10%

You've been focusing on the rear tire and say you can't go bigger because of the wheel width. Why not consider changing your front tire to 235/30-20 with a diameter of 25.6 inches then your front to rear ratios are pretty close to stock - it would give a front to rear ratio of 97.33%.

I'm no expert but I don't think your current set up will cause problems - the front to rear ratios are within 1.2%. To get more comfort change the front to 235/30-20 and you get very close to the OEM setup. The problem Fred had was going to the 315/25-19 with a diameter of 25.2 inches - with a 235/35-19 front his front to rear ratio became 101.12% - more than 4% different than OEM.

 

Thanks u my freind...so u think 245/30 and 315/25 shouldnt cost any probs cause they are within a limits

 

I don't think there will be any problems...but then I'm not an expert...and it's not my car.

 

There is if the wheel won't fit the correct tire size...

 

What size tires will be okay for these wheels 20x9 and 20x13 ?
The car is 997 TT 1 cabrio,tiptronic .

 

A couple points: 996tt is less sensitive to circumferential differences than 997tt because 996tt has hydraulic diff---997tt is electronic, and so lighter, faster to react, and more "accurate" in its operation. Second, props to Deitz, Tech1mike, et al for noting ABS doesn't like to be confused, either. bottom line.....3%-4% seems to be the allowable range.

 

go to 1010tire.com they have a tire size calculator where it will calculate for you when you put in the tire size. Stay under 3% difference and you should be fine.