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Is it possible to fit 265/645/18” Pirelli race slicks mounted on factory offset 9” wide CCW alloy wheels without any major modifications?
I cannot source any more of the 245/645/18” Pirelli slicks in North America. This is the front tire size that I am currently using combined with 305/645/18” rears.
I believe that the 996.2 GT3 cannot use the taller tires that newer GT3’s use due to the ABS specifications.
Not 100% sure in the 265. I have seen nt-01 265 run but the fan/rad bracket and liner had to be altered.
i run the 305/680s with no abs issue. Our cars use individual sensors on all 4 wheels and with no psm they r fine. On a psm car it needs to be unpluged at the abs pump.
It'll work with the right alignment setup with the understanding you won't get full lock to lock steering without it rubbing on the liners...but the rubbing won't be at steering angles you'll be using on the track anyhow.
When I say the "right" alignment settings, I was in the process of changing my car to fit the 265 Pirelli but moved into pretty seriously racing karts and lost interest and never completed it. I was always in the camp of wider track wherever possible which meant that I never rotated the front strut hats for more camber and went with large spacers on the lower control arms only to get maximum width at the front on a 245 tire. The 265 will sit basically right on the fender if you don't have the top hats rotated and will cause issues there. So you need to go to rotated hats up top and adjust the lower shims accordingly to make the 265 work, but when that is complete it should work. Again won't likely get full lock but you'll get enough lock you won't have to worry about anything on the track. Of course when you get everything dialed you'll then need to pay particularly close attention to where the caster is at to control front to back clearance / rubbing as you're going to get some rubbing at full lock but it can be minimized with attention to detail.
Ride height is going to be a tertiary consideration but unless you're down really low you should be fine.
This was my test fit of the Pirelli 265 on a CCW 9" wheel without the top hats rotated, camber is at 3.8 here all on lower shims.
The other good news about the Pirelli 265 is it's a relatively small tire for a 265 which will also help. You can see how with the top moved in from top hat rotation there's going to be more than enough clearance.
Is it possible to fit 265/645/18” Pirelli race slicks mounted on factory offset 9” wide CCW alloy wheels without any major modifications?
I cannot source any more of the 245/645/18” Pirelli slicks in North America. This is the front tire size that I am currently using combined with 305/645/18” rears.
I believe that the 996.2 GT3 cannot use the taller tires that newer GT3’s use due to the ABS specifications.
265/645 its easy to fit on a 9 or 9.5" wheel. I run the Pirelli 275/645-18 on an 18x10. Front ride height is 98mm. Tops need to be rotated and pushed all the way inboard in the slots with the rest of camber set with shims. You want Cup steering angle limiters to prevent rubbing on the inside ducting at full lock. Basically reduces the steering angle by about 1" on the inside. Otherwise just keep in mind not to go full lock to keep from rubbing.
Btw, the 305/645 is not a rear tire so be cautious. It's designed as a front tire and does not have the loading for the rear. Porsche originally used a 660 rear on the Cup and went to 680 due to tire failures. The 680 has totally different construction and is a proper rear tire. It provides a much larger contact patch than the 645 but on a 6GT3 it will not work with the stock ABS. While it will work Ok with moderate braking, with aggressive brake application the stock GT3 ABS will freak out and go into ice mode due to the disparity in front and rear tire diameters as the 645 is 25.5" and the 680 is 27.0". We tested this years ago on a friends 2005 GT3. Trust me, it does NOT work.
I run the Pirelli 315/680 on an 18x12.5 but use a 996Cup ABS which is programmed for those diameters. The 305/680 can be run on narrow body car with a 11-12 wheel. There is a workaround to the above mentioned diameter issue as you can install a custom front toothed ring on the tension bolt with 47 teeth (instead of 48) which will fool the ABS into thinking your front wheel diameter is the same as the rear. That is what I would do if I wanted to run the 645/680 with a stock GT3 ABS. It's worth doing as the 680 is a vastly superior tire to the 645.
Cheers...
275/645-18 on 18x10
Custom tension bolt
27" 680 v. 25.5" 645
Last edited by powdrhound; 10-06-2022 at 08:27 PM.
In addition to powdrhounds info above, I would like to add that with -3.2 camber on mine (strut tops rotated), I still rub on the inner brake ducting when at full lock. This is with the stock wheel and tyre size. Only an issue at low speed maneuvers but the noise is like nails on a chalk board to me so I stop turning the wheel at about 3/4 lock to avoid it.
I hope the 245/645 and 305/680 dont ice mode my car? With no psm my abs seems fairly nonexistant on the track. Altgough im a little worried now because powderhound knows his $hit
Just had a friend run these sizes in a standard c2 and his car did fine once he unpluged his psm from the abs modual.
I hope the 245/645 and 305/680 dont ice mode my car? With no psm my abs seems fairly nonexistant on the track. Altgough im a little worried now because powderhound knows his $hit
Just had a friend run these sizes in a standard c2 and his car did fine once he unpluged his psm from the abs modual.
What car are you running the 305/680's on? If the track is smooth that minimizes issues the issues. If the braking zone is bumpy and you come on the brakes hard, watch out! My buddy on his GT3 ran a few laps with them and had a huge off when the brakes went into ice mode. This was confirmed on another 6GT3 that tried the same set up. Just be careful.
[QUOTE=powdrhound;18399553]What car are you running the 305/680's on?]
My gt3ish. The car has full 2004 gt3 abs, brakes and uprights so it will behave just like a real gt3. The tracks at njmp r smooth but thx for the heads. I dont usually drive at the edge of the brakes so maybe ill be ok? If not ill know whats going on.
If it does turn out to be an issue ill have a few sets of scrubs to sell and ill have to look for hoosiers, i guess.
My gt3ish. The car has full 2004 gt3 abs, brakes and uprights so it will behave just like a real gt3. The tracks at njmp r smooth but thx for the heads. I dont usually drive at the edge of the brakes so maybe ill be ok? If not ill know whats going on.
If it does turn out to be an issue ill have a few sets of scrubs to sell and ill have to look for hoosiers, i guess.
If you drive the car at 7/10s or so the brakes will be fine. It's when you are aggressive and at high rates of deceleration that issues crop up. I would get a 47 tooth tension bolt and run the 680s. Hoosiers are lousy tires. There is simply no comparisson between slicks and Hoosiers.
I guess the next question would be.... Does running a 47 tooth stub cause issues with street tires or nt-01s that r the correct size.
Also where would one find a custom 47 tooth stub?
To your first question, yes, when you change the number of teeth, you are changing the ratio. By going to 47 teeth in the front you are basically setting the ABS up to run a stagger with a taller rear like on a 997GT3. With NT01s you would want to run a 245/40/18 (25.5") and a 305/35/18 (26.4"). Street tires would need to be 997GT3 sizes
Your second question, you would need to have a custom stub made. I had a few made a few years back. Have one pair left but with 49 teeth. The outer ring is bolted on and replaceable (see pics in post above) so you would need to have an outer ring machined with 46 or 47 teeth.
10-05-2022, 08:57 AM
Front tire fitment
