Advice on best tyre size - please

[Jason Taylor]

I have a set of 20" Carrera S 111 wheels fitted to my 997.1 TT with 15mm spacers at the rear and 12mm on the front.
I really love the look on my car but on lock they rub on the wheel arch liners, my Indy has said there's nothing to worry about but I feel if I can resolve the issue by changing the tyres then it's worth doing. I've been on various websites trying to figure out what tyres would give the clearance I need but in all honesty I don't have the confidence in the little education I have on the subject to push the button.
I currently have pirrelli p zeros fitted so would ideally like to stick with those.

Front tyre sizes are 245/35/20.

Original tyre size are 235/35/19

I'm wondering if I need to reduce the sidewall size to maybe 30 or is it the tyre width which is the issue, if so can I safely fit a 235 tyre on that wheel?

This is outside my field of knowledge and would appreciate some guidance.

Cheers

 

[IMI A]

I think you should maybe think about down sizing to 19 inch with an ET 50 offset front and rear. You can go to ET 45 front and rear on the alloys if you want that GT3 RS look. On the front you can then go 245 35 19 and rears 325/30/19.

You want your aftermarket 19 inch alloys to be 8.75 to 9 inches at the front and 12 inches at the rear. If you want more front end grip on 19s you can even go 255 35 19 with no rubbing but the car will tramline a little more and 255 fronts really better as a track set up on cup 2s.

I know its a pain as your turbo looks fantastic on 20s but you can easily get the GT look on 19s too. Looks better with the thicker side wall on 19s too imo and better over our bad roads in UK.

Tyre / wheel are your only contact with the road. I'd always go 19s on a 997 tbh.

You can even run this larger tyre on your stock 19 wheels for road but I wouldn't use it on track only because its harder to keep the temps at optimum level on the larger tyre size especially on Cup 2 with OEM 8.5 and 11 inch alloys from experience over 100,000 miles on this platform. Next time I go on track I'm gong to try a Cup 2 (R if available) up front and P4S on rear

 

[MaxA]

https://www.wheel-size.com/calc/?wh...35-20X9ET50&fcl=50mm&wcl=30mm&scl=50mm&sr=0mm

Have a play with this tool from the US, according to which your 20s are only what they call "+1" sizing, but if you adjust the clearances in the 4 boxes on the left you can see what'll fit.

You may just need wider spacers up front, but I'd agree that you're better off on 19s.

 

[Alex]

With your car being AWD and having the old style viscous coupling, you need to make sure your circumferences are within spec of each other or you can end up screwing your coupling up.

 

[IMI A]

^^^ 997 turbo doesn't have VC system. It has PTM.

Those sizes i've mentioned on 19 optimum as well as OEM of course fine too. 996 turbo runs VC system as well as 997.1 C4S. 997 turbo and 997.2 C4S got whole new systems completely different actually.

 

[Alex]

My bad, I always thought the PTM only came out on the Gen 2 turbo.

Everyday's a school day :thumbs:

 

[PhenomStaR]

You just need to bring the profile down from 35 to 30 and that should solve the problem.

I am sure the rear wheel should be 12J on your car however and running spacers on a sports performance car is a big no, no... without the spacers the car would drive so much smoother and even more refined that is one thing I can guarantee you.

I would never run spacers on any of my cars I have learnt this the hard way as I used to take my cars track days and really push them. Had a very bad incident on one of my old e92's the bolts started breaking off under the pressure of the strain of the hard driving.

Anyway wish you all the best and hope you get your issue sorted.

 

[1marc]

I'm with IMI A on going back to 19's. The 20's encourage a worse ride and IMO don't look as good.

I'm on 19's, with Cup 2's with 5mm spacers (Porsche OEM). 8.5 F 235/35/19 and 12 R 305/30/19. Could go up a size to 245 F / 325 R.

 

[Indischrot]

@1marc are those BBS CH-R's? They look great on the 997 but every time I see them for sale online they have a 'motorsport" engraving.

 

[1marc]

They are mate. Mine had the motorsport script too, but it's only lazer printed, so is removed if you have them refurbed (which I had to do, as I wanted Weiss gold wheels).

 

[1marc]

I am sure the rear wheel should be 12J on your car however and running spacers on a sports performance car is a big no, no... without the spacers the car would drive so much smoother and even more refined that is one thing I can guarantee you.

12J only on 997 GT models (GT2, GT2RS (gen 2), GT3, GT3RS), all others are 11J, although there is one OE narrow body wheel design in 11.5J and the smaller C2 wheels in 10J. Strangely enough it's the fronts that are slightly wider on the turbo at 8.5J, vs. 8J on all the rest (non GT cars).

Largest OE rear tyre is 305 even on the 12J, with the exception of the GT2 and GT2RS which are 325's.

 

[Indischrot]

They are mate. Mine had the motorsport script too, but it's only lazer printed, so is removed if you have them refurbed (which I had to do, as I wanted Weiss gold wheels).

Ah good to know, cheers. They look so good in Weiss gold too.

 

[1marc]

They are mate. Mine had the motorsport script too, but it's only lazer printed, so is removed if you have them refurbed (which I had to do, as I wanted Weiss gold wheels).

Ah good to know, cheers. They look so good in Weiss gold too.

Cheers mate. The decals are being replaced as they are not a close enough match to Weiss gold IMO. The new ones are matched perfectly to the OE GT3RS colour so will also match my wheels. Hopefully should be complete in a few weeks.