Have know people with this issues on in warranty cars get rejected on repairs bc they were running 315's in the rear. I would stick with stock to be safe and reliable.


It was his Diff that blew out.

 

whoa
guys
dont let the infamous tire size questions kills brain cells like it did in the 996 forum.

you CAN run wider tires, as long as theyre within spec.
within spec on the 997 means that the rears are slightly taller than the fronts.
a 235/305 set up gives you a rear that is around 8/10ths of an inch taller than the fronts

a 245/325 (oem gt2/gt3) set up gives you a rear that is about 8/10ths of an inch taller than the fronts. so its absolutely fine.

you can NOT run a 245/325 set up on factory wheels. a 12" rear is required.


if doing 20s, you need to be running a 325 25 / 245 30. NO OTHER SIZES (not a 305/25, not a 315/25)

 

Not true. In my pics above, I am running 245/325's on factory 11.5 wheels. Installed and recommended for more grip at my local porsche dealer.

 

No kidding I've also requested nitto to manufacture a 305/30/19 not sure why they haven't as they have our OEM fronts. 10 heatcycles? Might as well go with Ho-ho's.

As far as alignment I would align my car with car setup for track meaning with the 18' wheels. Yes you can continue with the 19's on the street. I do the same thing except going from 19- 20" 245/315 is not the right config, you want a 245/305. As far as rim width front is okay, a 12" inch rear may make a 305 rear look stretched depending on the tire.

Offsets can be subjective and again dependent upon wheel and tire width. If you stick with an OEM tire set up and OEM wheel widths I consider a Front ET 46 and Rear ET33-36 to be perfect. (independent of wheel diameter)

 

white
997 turbo wheels are 11 not 11.5
11.5s will be ok on a 325

 

Whoops. I assumed all factory wide body rims where equal.

 

".....you CAN run wider tires, as long as theyre within spec.
within spec on the 997 means that the rears are slightly taller than the fronts.
a 235/305 set up gives you a rear that is around 8/10ths of an inch taller than the fronts"

Steve K,

Are you saying that the rears MUST be slightly taller than the fronts i.e., that a slightly taller front would likely not work or cause damage?

The Nitto 01 in 245/40/18 has a diameter of 25.55" & the 315/30/18 25.35" which is less than a 1% difference BUT it is the front, not the rear, that is larger. Thoughts, please?

 

yes the rears MUST be taller than the fronts. must must must.if its the other way around (fronts taller than rears) you WILL damage your awd system for certain. not to mention causing havok on your PSM/abs.

you would need to run a 305 35 in the rear.

 

Steve, thanks for the advice! They don't make a 315/35/18...sigh.....and the 305/35/18 has a 26.42" diameter per Nitto which is 3.41% greater than the front at 25.55". I thought front to back needed to be <3% delta or is that just street-lore?

 

thats the size that 997 guys run when when going down to 18s.
im currently at 26.5 rear and 25.7 front (more likely 25.6x because im slightly stretched on a 9" wheel.
no issues whatsoever.


gt2 spec (245/325) is on a lot of 997tts (it will be my setup for next summer). fronts are 25.8 rears 27.2.

 

gt2 spec (245/325) is on a lot of 997tts (it will be my setup for next summer). fronts are 25.8 rears 27.2.

Hmm, that's a 5.43% delta. Some guys say you can get away with 4%, others say keep it below 3%. The GT2 is rwd which means you can do just about anything that fits in the wheel wells but unless you ditch the front drive train and deal with the attendant problems that brings, that seems pretty radical for an awd setup. What's your thought process or are you just feeling lucky?

 

i dont know how these percentages are calculated.
but i can tell you that a gt2 set up has the same difference front to rear as a 997tt.
in fact, Champion Motors, GMG,and wheels boutique run their 997s on gt2 sized wheels.

a 235/305 set up and a 245/325 set up are both .8 inches taller in the rear than the fronts, respectively.(.8 and .9 to be exact).



steam, my bad. i meant to type 26.7 for a 325 30 19. not 27.2

 

Street-lore Dean. Ask anyone to show you documentation from Porsche showing this mythical creature called 3%. You're gonna be waiting a loooooong time... With that said, stick with the OEM difference of 0.8" or so and you'll be fine. Both Nittos and Kumhos are in that ball park, Hoosiers are not. You can also run Pzeros in 245/645-18 and 325/660-18 for mega grip. That's what I'm gonna run for time trials.. Running other than the factory split is a bit of an unknown. It may work just fine running around on the street with occasional full throttle blasts but it's a different ball game running ***** to the wall for 30 min at the track where your diff will be subjected to much higher stress. My $0.02. All of your best performing set ups wil be 18s anyway. That is all you'll find on cups and RSRs even through the 991s.

You won't find a better bang for your buck than the 245/305 NT01s. $1000 and I get 20 sessions on them. At HPR they are only a half second slower than Kumhos or Hoosiers. Kumhos are $1500 and I get 10 sessions. Hoosiers are $1800 and will last about 7 sessions. The math gets ugly in a hurry....

 

"...steam, my bad. i meant to type 26.7 for a 325 30 19. not 27.2"

Steve, that makes quite a bit of difference; the differential is then 3.48%. That seems to pass the reasonableness test (if there's actually any such thing).

John, the problem is there does not seem to be generally agreed upon parameters that confer "safeness" on this topic and as my wife likes to point out, I've already had my Porsche mulligan and can't afford another $20K+ debacle. Insofar as the "math getting ugly", well, that happened some time ago! What a hobby.......Hope to catch a break in the weather and get to the track in October.

Off Topic: Saw where Ryan ran a 2:00xx last Sunday. Was that on the new Super Sports? If so, Simply Amazing!! He's got talent!

 

That's exactly why I said to stick with OEM diameter ratios. Doesn't matter if it's an 18 or 19 wheel as long as the diameters are pretty much the same as OEM. The October DE will be a good turn out. Hopefully the wx will hold and you can make it.

Yep, Ryan ran on the Super Sports. Those are great tires. From what I have heard they are just below the performance of the Sport Cups but wear like iron. I've driven Ryan's car out there before he put the Super Sports on and it was solid. I'm sure it's even better now. Chris did a great job setting it up and it feels great. On top of that, Ryan is a quick learner and a great driver. I'm betting he'll get into the 59s next time out if it cools off a bit. The time trials on Sunday were fun. I was just very hard to get heat into the tires with only one warm up lap. Take a look at the picture below taken on my second hot lap. On my first hot lap I lost traction at 80mph out of turn 12 all the way to the cork screw. That cost a full second and was a bit hairy. 2nd lap was better as the tires heated up. Fun weekend overall...

[url=https://flic.kr/p/pnjKRX]