would also need a larger diameter rear wheel i believe...think the gt2 rear is a 12

 

Is there something about the 20s performance wise which is less than the 19s? C'mon bonehead don't do it...your avatar pic inspired me to get the tint and I was working up to 20s.

 

Haha. Well, tint is not optional 'round these parts. My left arm is 6 shades darker than my right
The 19 vs 20" debate is likely irrelevant to me since I don't push this car nearly to its limits, but I would like to think that if I were to ever go 9-10/10ths, that I would have the equipment to back it up. Otherwise, no question that 20's look better

 

I have thinking about this thread and, in my mind, I keep coming back to the fact that I am just not exactly sure what you are trying to accomplish. PS2's in the stock 19" tire sizes can easily take you past 9/10's driving. I just don't think the tire width is the issue holding the 997TT back.

If the extra width is an aesthetic issue, then why not just stick with the 20's and a wider tire? If max performance is the issue then consider R-compounds and maybe even 18" wheels. The 19's with a good street tire are a bit of middle ground that, in my opinion, offers the best compromise.

There are lots of good reasons for choosing any of the above, but I think you are getting muddled answers partly because some of us are not sure what you are trying to accomlish: max performance, max looks, or a compromise between the two. It's a good discussion - I just want to make sure you are getting good feedback. The 325/245 combo in your first post should work.

And I always wonder where "the oven" is located? PM me if you don't want to post.

 

You're spot on in your assessment, spark. Looking for a mix of 'bling' from a wide footprint, and the performance benefit of 19's. If I did go back to 19's, I'd want more reasons to do so, otherwise, I'd just use the stockers again.

And although it's not too difficult to figure out, PM sent

 

You know, I think I would just stick with the wheels/tires you already have. They look great!

 

so what is the performance benefit of the 19s? I like the bling of the wider footprint myself. thought about the 345 Nitto Invars on 13 inch wide HRE 890s but I was told it might rub a little. Will likely go 12 or 12.5 inches wide if I do decide to upgrade.

 

Does anyone have experience with this and can confirm it works? My understanding is messing with the stock tire sizes is very risky re: burning up the differential.

 

I do not remember anyone running wider 19's (except for the people who tried 315's in the rear and had problems). I re-ran the numbers:
FRONT:REAR:stock rear/front: 1.0286
325 rear/245 front: 1.0762
325 rear/255 front: 1.0250

I just re-entered everything in my spreadsheet and I misspoke earlier. The 325/30-19 and 255/35-19 combo is the one that looks good on paper because the front/rear ratio is very close to stock. The 245's in the front will almost definitely cause problems. The 255's in the front will probably be OK. Personally, if somebody is looking to do this for aesthetic reasons, you are just a well off going with 20's in the proven sizes.

 

Sparky
Can you run the numbers on one last combo before I put this to rest (at least for me)?

235/35/19 fronts
325/30/19 rears

On their own, these sizes are well within tolerances of stock rolling diamters. However, how do they fare in relation to front/rear ratio compared to the stockers?

 

I seem to remember a discussion a couple of years ago about a change to bigger tires and the problem it created with the AWD. Wish I'd saved the link - I think it was one of Alex's (Sharkwerks) customers - maybe Kermit?? And it may have been 325/25-19 in the rear that caused the problems.

 

Thx. It was Fred's car but the problem was with 315 rears.

 

Hi Ed, are you trying to increase the rear width and keep front width the same?
I don't have any comment regarding the 4wd system, but with respect to handling, this may affect handling adversely, at least for high speed cornering.

Increase rear tire width reduces oversteer/ increases understeer, something that you may not want in our 4WD Turbo. If anything tuners tend to increase the front width and keep rear the same (Techart IIRC). I recall reading that Porsche cup/race cars all tend to have relatively bigger front width too.

 

Good point, Can. Reason I ask is there is a set of OEM GT3RS wheels I'm looking at with tires in those sizes. Understeer point well taken, but aside from that, does anyone know if the front/rear size ratio would bugger up the differential?

 

Okay...I skipped about the last five responses...biggest factor will be your rim offsets and ride height of your car. I saw 335's on a narrow body GT3 this past weekend with custom rims. I have a set of CMS RS171's that are 11.5 inches wide with offsets of 44, running stock 305's. They completely fill the wheel wells. I'd be a bit nervous trying to run 315's but would like to try them. I have set of stock GT2/GT3RS wheels that are 12 inch but only have a offset of 51. I could easily run 325's on those...NO WAY COULD I SQUEEZE 325's on my 171's or 335's on the GT2 wheels with my ride height.

The fronts you can safely run 245's...no wider.

Let us know what you decide to do and what works, but remember your rim offsets will make the ultimate decision for you.

PS: it was a Sharkwerks GT3 I saw with 335 Hoosiers....Alex was installing them at SP.