Well, I recently bought a set of 19" Champion RG5 from my bosses best friend for my 01 911TT. He had Pirelli PZero's on them in with 245/35/19 fronts on 8.5 wide rims and 295/30/19 on 11" wide rears. The rears were completely bald, so I ordered a set of Michelin PS2's from Tirerack in the 315/25/19 sizes. Whew they are pricey. Anyway, the front tires are still the PZero's which are still about 90% treadlife, but the car just does not feel right with the mismatched tires.
My question is what is the ideal front tire size when going with 315 rears. I would like to order them today from Tirerack. Tireracks website defaults to a 225 front when you put in optional 19 wheel size. My car is not lowered as of yet, and I do notice that the 245's ever so lightly touch the plastic inside the wheel well under full lock turns. Thanks everyone in advance.

 

235/35/19 is the most common front size with the 315 rears.

 

That's what I use. With that said, if you are running 315 rears, you really do need to go with a 235/35 front so that you can keep your tire rotation ratios in check. You do not want to fry your driveline with off-set rotational speeds.

 

Actually Ruiner, I didn't even take that into consideration, thank you for that info. I do seem to notice the car feels different when going about 25mph down the last big hill in my neighborhood in third gear. I usually drive about 1.5 miles at around 25mph til I pull into my garage. I live in a golf course community. The car seems to kinda push-pull going down that last big hill. Well, 235 up front it is....thanks again.

 

Once again thanks to Damon at Tirerack, the 235 PS2's fronts are on there way to me by Friday.

One of the weird things I noticed with this mismatched setup is that on sweeping on/off ramps the front left wheel triggers the PSM, and I get light to moderate braking. The first 3 times kinda scared me going 55-60 on an off ramp, I thought I hit a small oil spot, but was brought to my attention that the rolling diameters are out of the 4% of Porsche's tolerance. Thanks everyone.

 

Interesting that the 295/30's were completely bald. I am on my second set of 315/25's, and all of the wear is on the inside edges because of the negative camber. The only way I could imagine getting them completely bald would be to use them exclusively for tracking (or street driving a lot more aggressively than the local gendarmes would be likely to allow). Driving around town, I am essentially driving on the inside couple of inches of each tire. I have been thinking of going to the 295/30's at the next change just to get a little more sidewall to try to get use out of a little more of the tire.

 

Hey JayM, my bosses friend that I bought the rims from did track his car quite a bit. He is a regular at Summit Point, and from what I understand he is in the advanced group. He only had a tad over 5k miles on the rims and tires when I bought them from him. Funny thing is that the fronts are still like brand new, but with my odd handling characteristics, I have to get rid of them.

Another question I have is... I had an alignment done at the dealer about 2k miles ago, since I have a new setup with 19's, should I get another alignment to further straighten things out?

 

On the 'tracking the car quite a bit, and in the advanced group, regular at Summit......that info possibly suspect.
I don't think I've ever seen an experienced Turbo driver at the track with 19s (or even with street tires for that matter).

On your alignment & wear........do you have the print-out from 2K ago? (always ask for 'before-after' print-out....file it).
Rear 'spec' camber range is -1.2 to -1.7 ...........if you do not track the car, you can tend to the low end of that for better wear......but for street use a 315 with 38-42 lbs should still give you decent wear at -1.5 or above (if you do not track 1.5 should be more that fine....IMHO).

 

If you talk to Champion, I think they would recommend a 295 on the 11" rear. For my GT2 they recommended a 11.5" rear for the
315. The 315 sidewall might be rounded/bulging because of being slightly oversized, which might be causing the problems you are experiencing. They are helpful..give them a call.

Best of Luck

 

My opin but PS2s are fine on an 11J rim (look good, work well) but I believe Mich says use bet 11-&-12...... so whatever.

PCJR, you apparently have 19s on your GT2?.........the OE 18s have the 12J rim of course and 315X30 rubber.
Keep in mind, especially up in these tire sizes, from brand to brand the tires measure out diferent & sit on the rim diferent(though they have the same 'size').

 

You should run 315/25/19 and 225/35/19

 

Alan, when researching tire sizes on Tirerack, the 225 MPS2 were exactly the same rolling diameter as the 315 rears, and Damon at TR told me that, but also stated that there would be more understeer with a slightly narrower front. That is why I went with the 235 fronts. I do not track the car as of yet, and if I do, I would use the factory 18's, but I do enjoy driving my car to the limit to me.....even though I am probably only using 60% of the cars real potential. Thanks for the info also.