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Discussion Starter · #1 ·
What is the largest size Hoosier R7 that fit a 987?

I am planning on getting OZ 8.5 x 18 and 10 x 18 wheels.
I have used 245/35/18 Front and 275/35 Rear Hooisers in the past on smaller stock wheels (8 x 18 Front and 9 x 18 Rear). They are -2.6% front and -2.9% rear smaller diameter than stock.

The 245/35/18 still looks like the right choice for Fronts. They are 815 revs/mile and -2.6% diameter from stock
Could try 255/35/18 in front, 806 revs/mile and -1.5% diameter from stock.

For rears, has anyone tried 285/30 (-6.1% stock diameter, 815 rev/mile) or 295/30 (-5.2% stock diameter, 808 rev/mile) wheels? Will they fit for R7 which sound like they are wider than same size R6? These smaller tires are getting close the the front size which I have heard can cause an ABS sensor problem.

Any experience here?
 

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18x10 +40 offset with a 15 mm spacer fit a 295 r7. No issues, no rubbing. Also buy 18x9's for the front. I ran them with bilstein coilovers, camber plates, and control arms.

Running a 245 with that 295 above will induce some ice pedal. You want to try to run as close to a square setup as possible as that really helps with ice pedal. The other thing that is helpful is a taller tire in the rear relative to the front. That said, I found staying closer to square as better option when compared to the tire height solution.

I wouldn't get real hung up about the size compared to stock, that doesn't matter for anything else other than your speedometer. Given you are talking r7's, no matter if that's not accurate as you're on the racetrack.

There's a thread somewhere on here where John Tecce from BGB Motorsports shared similar experiences with another member (I have a few posts there too if you want to search by my screen name.) Worth a read if you're worried about ice pedal....
 

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Discussion Starter · #3 ·
Thanks I followed your posts and found the old thread and the post from BGB Motorsports.

Seems clear that 245 front and 295 rear will fit with 9" rims front and 10' rims rear. Thanks for that info.
Tire Rack OZ wheels I was looking at also had +40 offset. Good to know I will need spacers, I have some 15mm ones.

On tire diameter, I was trying to keep the same ratio as stock for front to rear. On stock tires, the rears are about 3.5% bigger diameter than the fronts.
As BGM Motorsports points out a 245/35/18 front and 285 or 295/30/18 rear are very close to the same size. He says that confuses the ABS, which I have heard before.

He suggests the 295/40/18 size for the rear. That is a big tire, over 10% bigger than a 245/35/18 front. Is this what you have used?
 

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Thanks I followed your posts and found the old thread and the post from BGB Motorsports.

Seems clear that 245 front and 295 rear will fit with 9" rims front and 10' rims rear. Thanks for that info.
Tire Rack OZ wheels I was looking at also had +40 offset. Good to know I will need spacers, I have some 15mm ones.

On tire diameter, I was trying to keep the same ratio as stock for front to rear. On stock tires, the rears are about 3.5% bigger diameter than the fronts.
As BGM Motorsports points out a 245/35/18 front and 285 or 295/30/18 rear are very close to the same size. He says that confuses the ABS, which I have heard before.

He suggests the 295/40/18 size for the rear. That is a big tire, over 10% bigger than a 245/35/18 front. Is this what you have used?
So its a combo of both tire height and width. I ran 285/645's and 305/645's (pirelli's) last year with very very very mild issues with ice pedal (one turn, on one track and I was able to drive around it.) Those tires were the exact same height and they were waaaaay more predictable than the hoosiers 245/295 under braking. Since that thread you read, John and I traded data again when I happened to be in his neighborhood. He confirmed the same experience I had - where by they went with a 265/295 with identical (or close to it) heights on continentals with one of their cars and it ran great.

As for the R7's - I did not end up going to the 295/40s. I bought them, coupled with a 255/35 - but had a mechanical before qualifying 2 years ago and they weren't mounted and balanced yet so I just returned them. At that point I switched to the Pirelli's mentioned above.

For what its worth, I switched again this season to a 305/315 setup and the car loves it so far. While I am still getting data on different tracks - it is consistent with all practical experience I've gathered and furthers my belief that closer to square is better.

One other thing, there's someone on here who auto-x's that stuffed a really big hoosier R or A7 front tire under the stock coach work. Do a little research in this competition section....that should tell you what you can fit underneath the car. I'm guessing a 275/295 setup is doable, and probably great for the ABS. Also, don't get caught up on the people who say 245/275's are all you need. More tire is better on our cars from all the testing I've done (this includes back to back sessions on different tire configs across multiple tracks.)
 

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I ran 245/35 and 295/30 R7s - they are MUCH larger than most tires of these sizes (particularly the 245), but they did fit. I believe I needed to roll the inside of the fenders.

A quick tip on front wheel sizes: the stock 9" rear size and offset works well as a front. I have a couple of OZ sets (9"F and 10"R) that I bought this way.

Personal preference, but I never did like the R7 setup on my car. Lots of grip, but never felt that great to me, created a lot of ice pedal issues, and just never got my full confidence. YMMV - I know a lot of people who love the Hoosiers.

And as others have said, the ice pedal issue is more complicated than just F/R diameters....I've run times with identical F/R diameters and did not have the level of issue I had with the hoosiers.
 

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Discussion Starter · #6 ·
I ran 245/35 and 295/30 R7s - they are MUCH larger than most tires of these sizes (particularly the 245), but they did fit. I believe I needed to roll the inside of the fenders.

A quick tip on front wheel sizes: the stock 9" rear size and offset works well as a front. I have a couple of OZ sets (9"F and 10"R) that I bought this way.

Personal preference, but I never did like the R7 setup on my car. Lots of grip, but never felt that great to me, created a lot of ice pedal issues, and just never got my full confidence. YMMV - I know a lot of people who love the Hoosiers.

And as others have said, the ice pedal issue is more complicated than just F/R diameters....I've run times with identical F/R diameters and did not have the level of issue I had with the hoosiers.
I talked with Paul at Trackside Tire last night. He does trackside tire support for our events.
He said most Boxsters he supports are running 8.5J x 18 Front and 10J x 18 Rear rims, with 245/35 -18 Front, and 285/30-18 Rear R7 Hoosiers. So it would seem this is a pretty standard setup that would not require fender rolling. I don't want to get into body mods right now.

Thanks for the tip on the stock 9" rear fitment on the front. I will take my stock 9J x 18 with 265/35 rears (Michelin Super Sports) and put them on the front to see how it looks. I think a 9" front rim would better support whatever tire is up there.
 
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