kouzman

My 09 carrera has the factory Michelin ps2 235/40-18 in the front and 265/40-18 in the back.

I am thinking of getting wider tires in the back, probably 295/35-18, again ps2s... The rim is 10.5 inch wide so i think it should be fine.

Has anyone tried this size change? My only worry is that grip will improve in the back and grip will remain in the same in the front so I might have more understeer...

Any ideas anyone?

okbarnett

you should go a little lower and wider. maybe 35s all around or 35 front and 30 rear.

ADias

You may be able to mount slightly wider tires, but check with Porsche if you care for proper car balance and performance. Do not guide yourself by looks, if safety is a concern.

mdrums

Make sure the over all diameter of the rear is larger than the front or you'll have issues with the sensors for the ABS and so forth.

I track with 18's and here are the 2 comobo's that work. You need 9x18 and 12x18 for these sizes to work.

245/40/18
305/35/18

or

255/35/18
315/30/18

These sizesek ep the over all front to rear diameter ratio in check. The 245/305 combo is actually the same size diameters as stock 19" for 997 based cars.

brad@tirerack.com

On factory 8.5 and 10's?

225/40 and 235/40 up front work fine.

265/35 and 285/30 out back. Some 295's that run skinny (Sumitomo, Hankook) fit fine as well.

kouzman

The rears are 10.5

I would want to stay with the PS2s that's why I mentioned these sizes...

I ll also check the tip about the rear diameter has to be larger than the fronts. Is there anything that I can read about it?

cello

I just ran a three day with RTR at NJMP Lightning in Black with the new tires: Nitto NT01s 18" 245/40 and 315/30. Mike, I think in a prior tread you asked for my experience with same (once I used them) so it follows:

Lightning is essentially a constant turn with two straights, including a three turn 'complex', and a turn cresting a small hill, and a sharp ~90 degree lefty; very quick, and very rhythmic. The front straight starts in a large banked semi-constant radius turn and if done correctly the terminal speeds at the end can be higher than at T'bolt. So there are both areas of braking modulation/trail braking and threshold braking. Weather conditions included dampness to high heat. Track conditions included rain-washed and wind-blown sand/debris. Pretty good conditions for testing ABS intervention/application. I encountered absolutely no problems with ABS during my sessions. I ran at good pace (haven't config'd the vids yet). I did data and coaching with Bob Turgeon and Larry Herman (TracksideData) all three days and we saw nothing in the data either.

So long as the rolling diameter is kept in % in either direction there is no ABS problem. Opens up other choices a bit. Quite happy with the Nittos (old tire was the Toyo RA1, these are track tires of course) BTW ...

mdrums

Cello thanks so much for the feedback. This is interesting news since I have been told different that your test and experience.

cello

Mike - I know, I was originally told the same. Found out it was OK by running the sizing by a very trusted source. Last weekend proved him right.

BTW here are the rolling diameters in inches for the fronts and rears: 245/315 NT01: fronts 245/40r18 (25.55") & rear 315/30r18 (25.35"). The rolling diameter has to be kept within 4% (in either direction) for the ABS to work properly.

Nice to have some additional options (for the track)!