Havic, where are they rubbing in the rear, inside or outside. FYI I have 7mm with the 315's no rubbing at all.

 

Check my pictures
I think the wheels look great,so far very happy
i have 5mm spacers all around 19" and Toyo and no rubbing!
By the way pss9's

 

I thought I read in another thread that the reason that the 997 can run diff tires sizes than the 996 b/c it does not utilize a viscous coupling diff. that the 996 has.(?)

 

They are lightly, rubbing on the inside. Good to know that the 315s take care of that.

 

Rolling the rear fenders opens at least 10mm in the rear for even more spacer.

I run 15mm rears with my champion 11.5" wheels

 

Okay, I am little confused (not a new situation). Reading this, and a few other threads, the information is not really "conclusive" to me so I thought that I might bring this this thread back and find out if there is any further insight into this.

I have a set of 19" HRE wheels that I have put on my 996TT.
The fronts are 235/35/19 and the rears are 305/30/19. This is stock 997TT sizes, but will they cause grief on a 996TT with AWD?

BTW, Last year I was running 265/35/18 fronts and 305/30/18 rears and this also seems a little off.

Thanks for the help.

 

I have no issues with rubbing in mine with PSS9s set to GT2 height. I don't run spacers.

If you have 235/35/19 fronts, then to match them you need 315/25/19 rears. There have been a few long threads about this discussion regarding tire diameter and revs per mile. You want the revs per mile to be as close as possible between front and back, and the overall diameter to not be more than I think 26.5"? Otherwise you will rub. I forget exactly the diameter number but you can search it on the threads.

 

To the poster that mentioned that the mismatch will work fine on a 996 because it does on a 997, this is not entirely true. The 997 has a completely different electronic differential that is designed to use different front/rear ratios than the 996.
Sure, you can run incorrect ratios and may get away with it for a long time without a front diff failure but that doesn't mean it is the right thing to do.

Here's a link explaining how the 996 AWD system works. This is an excerpt about tire sizes specifically from the link:



"There is no evidence to suggest however, that PAG attempted to use different wheel and tyre assembly rolling diameters. As with the 993 series there are no special tyre requirements for the Carrera 4 models as compared to the rear wheel drive only Carrera models. There are no warnings about tyre sizes in the owner's manual regarding maintaining front-drive through the correct selection of tyre combination.

NOTE-
No data is provided anywhere regarding the impact of rolling diameter variations and front-drive percentages. There is nothing in any factory Porsche AG or ZF company documentation either. Anything on the Internet, in books, or in magazines about rolling diameter differentials and which tyres to use is just speculation because it's not supported by any technical documentation. Always stick to the tyre size recommendations in the owner's manuals because the ABS/ABD/TC/ASR/PSM systems all rely on specific wheel speed inputs and wheel speed differentials. Exceed the tolerances and the systems fail."

 

x2

235/35/19 front
315/25/19 rear - Goodluck finding new 315/25/19 anymore in a brand name tire

OR your other option is

225/40/19 front
305/30/19 rear

 

wow that looks good.

 

I have the wheels on 305/30 19s in the rear, now the big problem is getting ahold of some 315/25-19s. Supply Issue? I would rather not go bigger on the fronts as I have a bit of rubbing already (they are not 997TT wheels).

 

i've had 997tt wheels on my 996tt for over a year with front 235/35/19 & 7mm spacers and rear 315/25/19 & 14mm (or 15mm?) spacers and no diff problems. i now need new tires and 315/25/19 are impossible to find or crazy expensive.

does anyone have any experience with 295/30/19 rear and 225/40/19 front? that'd basically be the same as OEM except on 19's instead of 18's. this would only be 1/2" taller (from the hub), the same width, and matched revs/mile so i'm thinking it should work. alternatively, 245/35 up front seems like it would work too? plz tell me if i'm wrong...and help me get out of 315/25's!!!

fyi, the car is otherwise stock and my daily driver with 2-4 track days/year.

 

I'm on 997 turbo wheels lowered on h&r coilovers on my 996. Running 7mm and 15mm spacer on rear. Tires are 235 /35 front and 315/25 on rear no rubbing handles great

 

those 997 oem wheels are monoblok forged? I thought only the 997.2 oem's where stock...

 

i discovered another viable option...i just put these on my 996TT and they're perfect:

225/40/19 (773 revs/mile)
295/30/19 (777 revs/mile)...only 0.5% difference

you may recognize this as the OEM size but on 19's instead of 18's so obviously this is safe on the differential, plus it maintains the contact patch that porsche designed the car to have from the factory (whatever that's worth).

i debated whether the extra inch of height would be problematic, but i bit the bullet and installed some pilot super sports on my 996TT which has 997TT wheels and 7mm front/15mm rear spacers and they don't rub at all. in fact, i even just did a track event at Putnam Park (outside of Indy) this weekend, and they did awesome. no rubbing on the suspension, fender, fender liner, nothing.

so add this to the list of readily available, reasonably priced tire options for 19" tires on 996TT instead of the ridiculously priced and impossible to find 315/25/19!!!! btw, the nice thing about the 225/40/19 fronts is that you could also use 305/30/19 rears (770 revs/mile...or 0.5% difference) and also be safe on the diff, and lots of guys have run the 305/30/19 without rubbing issues.