Originally Posted by pwdrhound

Here it is Fadi. This is what we are using. These are the front tension bolts with the custom ABS pick up rings. By varying the amount of teeth (48 is OEM) on the ring we can run what ever front/rear tire diameters and fool the ABS into thinking that the diameters are exactly what the ABS is programmed for. In the case of the TT the ABS is expecting the fronts to be basically the same diameter as rears. When I ran the stock ABS with a 0.9" larger rears, I think I was on the ragged edge of what the ABS would put up with. There is naturally certain range of tolerance in the ABS to account for tire wear but it has limits. For optimum performance staying close to the stock ratio is always best.

For example, on a 996GT3 where the factory tires are basically the same front to rear, we found the ABS would tolerate up to 0.9" larger rears. With 25.5/26.4" tall tires the ABS still worked pretty well. When the split however was increased by running 996Cup sizes (25.5/26.9) the ABS would go into ice mode at speed under hard braking. By decreasing the amount of teeth on the front ABS pick up ring to 46, we can get the ratio back to what the ABS is happy with and run Cup tires on a regular 6GT3. On my car, on the other hand, a 49 tooth ring is appropriate because the ABS is programmed for a 0.9-1.5" larger rear but I'm now running a 0.6" larger rear (used to run a 1" larger rear). The extra tooth thus brings the ratios into the range the ABS is programmed for.

The outer ABS pick up ring is bolted to the OEM GT2 tension bolt (which has the OEM toothed ring machined off) and can be swapped with everything on the car.

Originally Posted by Jferrante

it never ends with you lol - very interesting and informative!. I am running 245-645 and 325-660 Pirelli's so I am right at the .75" difference which should be good with stock ABS. I am worried about the rains (although they are supposed to be the same size they look different). I also got the GT2/3 uprights so will be upgrading coils as well at some point. Enjoying this thread keep it going.

Originally Posted by pwdrhound

You should be fine. You'll know when it's not happy. I'll have a set of JRZ remote canister Pros up for sale in about a month.

Originally Posted by jferrante

great let me know!

Originally Posted by pwdrhound

This is what we are using. These are the front tension bolts with the custom ABS pick up rings.

Originally Posted by pwdrhound

See if the wheel manufacturer can knurl the wheel bead on the wheels they are building for you. It'll keep the tire from slipping on the rim. If it was me Fadi, I would try to fit a 680 rear as it is designed as a proper rear tire application on Cup cars vs the 660 which is a front, albeit used on the rear by many. If I recall, the 996Cup originally has 660 rears but pca mandated the taller 680 as they had a number of failures of the 660s, probably when running on an oval. Since you're doing all the custom work anyway, might be worth it.

Originally Posted by pwdrhound

Hey Freddy,
This is stuff is made for me by my machine guy. Same guy that did my 300M hubs. He's pretty amazing but stays real busy so I have to plan ahead. In case the moderators are lurking, I AM NOT SELLING ANYTHING!!!.

The rings require a pair of new GT2 tension bolts to be machined down in order for the custom rings to be fitted. You have to be using 996GT2/3/Cup uprights in order to use these so these would not work with the AWD uprights which I believe you are using (unless I'm mistaken). There is a guy on Rennlist that makes custom TT front stub axles. You might contact him to see if he could make some with a different amount of teeth. It's a simple calculation to figure out the optimum number based on tire size. Again, it's generally not an issue unless you stray a good bit from the OEM tire diameter F/R ratio, generally 0.75" or greater based on what we've seen. 95% of TT guys do not fall into this category as most run similar tire diameters. Fadi with his build might be an exception if he tries to run 680 rears...

This is something that might interest you if you end up going to 275 fronts with stock fenders. When you fit 10" wheel with wide tires, at large steering angles (near steering lock) the tires will make contact with the inner fender area where the coolant pipes run and also in the rear inner fender area on the tub. This is due to the fact that the entire wheel assembly is "pushed" further into the wheel well. Do this enough and you will tear stuff up. Lot of GT3 guys run into this problem when they flip their front upper mounts to a motorsport high camber configuration and then realize their front tires tear up the upper air ducts attached to the coolant pipes. This happens even with 245s in some cases. To prevent this, you need to reduce the amount of max steering angle slightly. These are steering angle limiters which will fit on your steering rack shaft on each side and reduce maximum steering rack deflexion thus reducing steering angle by about 1.5" at the tires. These are made out of aluminum with a set screw. Interestingly Porsche used to make steering angle limiters for some of their 964 applications but nothing for the later cars.

[url=https://flic.kr/p/SERpN6]

Originally Posted by pete95zhn

I bought an used steering rack from a 996 RSR few years ago. It arrived with similar spacers which looked like OEM. No 996 or 997 GT3 Cup/R/RSR PET has part number for those, so they might have been from 964/993. Tension bolts with changeable ABS rings is a good idea! Fortunately I have a fabricator nearby who can make a set for me if necessary. Thanks John for tooth number calculations!

Originally Posted by Fadi

Asked the manufacturer and their answer was

" We can't make it on the inner/outer lips on stock. We made all our racing wheels without knurling because It's not necessary with the modular 3 pieces aluminum wheels."

Dont know exactly what is better with the 3pcs wheels so they say no need to knurl