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I ran 235/35x 295/30 A6 and R6 on stock 19" wheels for a few years after getting my RS. But switched to 255/35/18 x 315/30/18 in 2009.
Putting the Ho Hos on the stock 19 wheels was a total biatch though. Took a lot of pressure to seat the bead. So much so that one tire guy refused to do them anymore. I do my own now and tried to do a set of 19s for wifey and could not get them to seat. Over pressured, plenty of slime, sat overnight. Still no pop.
A good setup is the 255/30-18 and 335-30/18 sizing that is available for the R7.
The 255 front will fit on a 9" or 9.5" wide wheel, and will require some camber (which you need for R comps anyways).
The 245/40-18 R7 is an option as well
Originally Posted by P.J.S.
Safe fitment
245/35/18
315/30/18
also works
255/35/18
335/35/18
Originally Posted by TAI2
I run 245/35/18 and 315/30/18
I believe what others are saying worked for them, but my experience is very different - while I would like to use a wider tire up front, I cannot fit those larger R7 sizes.
Car: 997.2 GT3
Front Alignment: -2.5 degrees camber (stock top plate orientation), 2' total toe-out, max caster. Stock ride height.
In R6's I used 245/35-18 and 315/30/18 and all was fine, but inner sidewall very close to the front main springs. Many of the R7 measurements are very different from the R6's, and a different corner edge profile (more square than the R6).
The R7 225/40-18 has the closest measured dimensions to the R6 245/35-18. Exact same diameter and maybe 2mm narrower. Used successfully.
I tried using 245/40-18, but it rubbed badly on my fenders. The combination of larger diameter, slightly wider and raised edge profile made for noisy carving of the outer edges under braking.
I did not try the 245/35-18 because it measures smaller diameter than the R6 and 9/16" wider, and I know that I only have a few mm space between the front main spring.
Okay, so I've tried to put this discussion in a numbers perspective to make sense of how some are running the 245/315 combo, and others the 255/335 combo...including contrasting against what I'm running now (NT01) and specs from the OEM tire (Gen1 MSC). Excel screenshot below. Couple things I notice...
First, either way you go, the Hoosiers are a shorter tire - specifically in the rear. I'm assuming there's a slight bit of low-end acceleration gained from the smaller diameter tire.
Second, the 245/315 combo is pretty close to the 5% mark on diameter difference. If folks are running it successfully though, I guess it's not tripping the tire speed sensors and causing unwanted on-track excitement.
And third, the 255/335 combo is actually much closer to stock diameter difference (3%), but you've gotta make room for the extra 1" in width.
So, final question for the gallery...my two sets of track wheels are 8.5" F / 12.0" R, I really don't want to have to get new 9" fronts if I don't have to. I'm also running Cup LCA's, so I have a wider front track. With that in mind, would I still be able to put the 255 on the 8.5" wheel? (Assume the requisite camber all around)
Okay, so I've tried to put this discussion in a numbers perspective to make sense of how some are running the 245/315 combo, and others the 255/335 combo...including contrasting against what I'm running now (NT01) and specs from the OEM tire (Gen1 MSC). Excel screenshot below...
...I'm also running Cup LCA's, so I have a wider front track.
This is a logical approach. BUT...you cannot go by the published numbers only, because they are not always correct. Do do an accurate analysis and comparison you need to mount the tire's an take measurementsside by side, and I have done that.
Again, not denying that some have been able to fit the larger width tires, but I cannot and neither can another buddy with a GT3. It seems that the key variable is narrowing the track by rotating the top mounts then removing some control arm shims to maintain the same camber, which neither of us have done.
Our very experienced tire resource lobbied for my buddy to try fitting the R7 245/35-18 on his car last week and I anticipated that when mounted the wheel wouldn't even turn due to tire contact with the spring (he only had 2mm clearance with the R6), and even so the tire would be proud of the fender. Well, his tire did turn - but only because the curb guard on the sidewall was aligned between coils of the main spring. It was protruding several mm inside the outer diameter of the spring, and was indeed proud of the fender. If he used enough spacer for safe clearance of the spring, the tire was well beyond the fender. I believe that there are many cases where people have this issue of the curb guard protruding between spring coils and don't know it. The springs do seem to stay fairly well in place and not rotate, but they do compress and if they were to ever rotate it would be a big problem.
Bottom line, we both concluded that for our setup, the 245's do not fit and we are using the 225's that match the R6 245/35 almost exactly. While a 335 may fit on the rear (have not tried), I am reluctant to use a wider rear tire without the ability to run a wider front.
In short, I decided to trust the herd and go with the 245/35 up front and the 315/30 in the rear. I haven't mounted them yet to see if the fronts are gonna be a problem, but I did a walk around the paddock two weekends ago at the Chin VIR event and saw a couple GT3's running the same sizes. I'm hoping with my front suspension setup I'll be able to avoid any rubbing issues. It's clear the tires are much wider than the 245/40 Nittos I've been running, but we'll see if they're "too" wide. I think the 1" drop in diameter will help when it comes to proximity to the fender liner.
If weather and timing permit, I'll mount a set this weekend at VIR and see how they do!
The 225 is definitely my fall-back if the 245's don't work. Are you and your friend running stock springs, or coilovers?
Originally Posted by RedRSA
This is a logical approach. BUT...you cannot go by the published numbers only, because they are not always correct. Do do an accurate analysis and comparison you need to mount the tire's an take measurementsside by side, and I have done that.
Again, not denying that some have been able to fit the larger width tires, but I cannot and neither can another buddy with a GT3. It seems that the key variable is narrowing the track by rotating the top mounts then removing some control arm shims to maintain the same camber, which neither of us have done.
Our very experienced tire resource lobbied for my buddy to try fitting the R7 245/35-18 on his car last week and I anticipated that when mounted the wheel wouldn't even turn due to tire contact with the spring (he only had 2mm clearance with the R6), and even so the tire would be proud of the fender. Well, his tire did turn - but only because the curb guard on the sidewall was aligned between coils of the main spring. It was protruding several mm inside the outer diameter of the spring, and was indeed proud of the fender. If he used enough spacer for safe clearance of the spring, the tire was well beyond the fender. I believe that there are many cases where people have this issue of the curb guard protruding between spring coils and don't know it. The springs do seem to stay fairly well in place and not rotate, but they do compress and if they were to ever rotate it would be a big problem.
Bottom line, we both concluded that for our setup, the 245's do not fit and we are using the 225's that match the R6 245/35 almost exactly. While a 335 may fit on the rear (have not tried), I am reluctant to use a wider rear tire without the ability to run a wider front.
In short, I decided to trust the herd and go with the 245/35 up front and the 315/30 in the rear. I haven't mounted them yet to see if the fronts are gonna be a problem, but I did a walk around the paddock two weekends ago at the Chin VIR event and saw a couple GT3's running the same sizes. I'm hoping with my front suspension setup I'll be able to avoid any rubbing issues. It's clear the tires are much wider than the 245/40 Nittos I've been running, but we'll see if they're "too" wide. I think the 1" drop in diameter will help when it comes to proximity to the fender liner.
If weather and timing permit, I'll mount a set this weekend at VIR and see how they do!
I am switching to 275/335s and thus clearing out my existing NT01/Kumho/P-Zero tire stash. I have one last set of Kumho V710 track tires for sale. These are the correct 997GT3 sizes with the same diameters as OEM which ensures there will be no issues with ABS or PSM. Fronts are 245/40/18 (25.7") and rears are 315/35/18 (26.4"). They are pictured below mounted on 18x9x12. They run wide. As far as grip, for me these were a shade quicker than Hoosier R6s. They are a slick with two thin grooves to make them DOT legal. They are brand new unopened set in the wrappers from the last Kumho batch. $1300 plus $80 for shipping.
NC....how did it go with the r7...what size recommendation for a 997.1 did you land on with r7?
Unfortunately in the 18's the 245 fronts just didn't work for me. Any undulations in the brake zone would cause my ABS to go into ice mode. So first I dropped down to the 225s for a few races (which is much closer to OEM diameter spread), then ultimately bit the bullet and had some 19" Forgelines made. So now I'm running the 19" setup - which works great.
02-15-2016, 09:29 PM
