Is the wheel to spring....that distance static? Under load/turning...distance doesn't change?

 

Correct

 

Do we really need wide front tires like 911 racing cars ? I see 11-12J rims in front of newer models or even @grandpa 911 gt1 from 1996 and they are even lighter than our cars and more DF too

I might be able to fit a 10.5-11J rim, might consider in this case to run

27/65-18F & 30/65-18R Michelins
or
305/660-18F & 325/660-18R Pirellis or at least 285/645-18F (they are close to 650 tall)

Will test 680 tall tires too, but afraid will not fit, or at least not at the optimal height, I see newer cars running 30/68-18F and 31/71-18R, not gonna happen here

Till the end of the week we are doing various tests using the tires we have now to see how wide can we go but also to determine the biggest outside diameter of the front tire.

My guess is a 26.0" wheel will be ok, but will need 26.3" to be safe even with the 305s in the front, car is like 4cm (1.5 inch) wider each side front and 7-8cm (3 inch) wider at the rear

Having a wider front bumper we should be able to push further more the side radiators and the front fender shape is more permissive to bigger tires, in the end will use the measurements to build some custom rims, guess will go quite low on ETs

 

tried hankook 280/660-18 - 306mm wide tire, seems a bit too much both diameter and too wide, guess with some more work can make it work

We used a rear oem rim )) 11J with 2 large spacers to avoid hitting the suspension arm, guess 11 Rim is overkill for my setup, 10" will give some error margin, 10.5 might work too

we tried the hankooks and LOL some MT DRs 305/35-18

265/35-19 on 8.5 front rim, Cup2 - they seem to work well and would be a perfect match for 305/30-19 rears even if converting back at some point to 4WD


Will have to decide if going 10" or 10.5" although we should be able to custom build even 10.25" rims if needed... Still dont know if should put some more effort and just use 10J and call it a day, the 27/65-18 Michelins would be nice, they recommend 11" rim for those and they run at 295mm wide... 10.5J would be almost optimal, 10" not so much..

Tomorrow will try few new tires to see how they fit in front...our goal is to test a tire like 295-305mm and like 26.0-26.3 (650-660) tall
295/30-18 on 11 oem rim, Cup2
305/30-19 on 12 oem rear rim, Cup2
275/35-18 on 8/11? ,R888



for the reears might give a shoot for

335/30-18 on 11rim, R888 - but spacing in the back is huge... I guess can run even 375s or more if available by some manufacturer

 

Really happy, managed to fit easily 265/35-R19 in front, they are going to make a perfect pair even AWD with 305/35-R19 rears, tires are MPSC2

The 660 tall slick tire works also, with a bit of effort perhaps being able to fit 670-680 tall tire, even might hit the fender at the top of the tire, still not sure about that.

So we should be able now to run (F&R)

27/65-R18 & 30/65-R18 Michelin Slicks
260/660-R18 and 300/660-R18 Hankook slicks
285/645-R18 or 305/660-R18 fronts and 325/660-R18 Pirelli - 285front is 25.79"

Having some 305/68-R18 Pirelli, will do some more tests with those too, unfortunately dont have like 4 tires, only 2 of them

Car expected to be out and running 1st of April on 275/335 R888, cant wait..

 

nice!

 

wider will help with front grip. But fitting 11inch plus will require some work. You can compromise by going shorter and wider in front to give you a little more playing room.

 

Drive with the OEM ABS and learn how to modulate. You will stunt your growth as a driver buying a ton of parts without learning the limits of the ones you already have. Factory ABS is not a hinderance in 99% of situatuions. There are only a few it doesn't like and these occur very seldomly. At some point you will have to develop the driver to match the capabilites of the car or you will still get passed by good drivers in GT3's. If you mod too fast and run too much hp you will stunt that growth.

 

I might end up with a car way over my driving skills, even tho hoping that better suspension, aero and brakes along with a lot lower weight to make my car easier to drive as was a handful anyway. I did drove last month a Mclaren gt3, full carbon, 12xx kg and like 650hp+ big aero etc, that was like driving a golf compared to the 996, really easy to drive, very forgiving car, loved it but not feared and intimidating racecar. The feeling is more intense in the 996tt for sure and that was a 500K+ car...

I am taking very seriously your advice anyway as this is my belief too, we have to grow together and feel the car with every modification, already feeling nervous as made so many upgrades over the winter, waiting for improved times on the local track and hope for like 2s/mile gain or so on the same tires. I remember you told me to keep expectations low when did just some minor upgrades like gt2 kit, rwd, slight increase in front wheel width.. and you were right, didnt gain too much with those, but now Im confident can shave few good seconds on the local track

In the meantime I have made final? estimations for the rims, they will be matte gold and polished lip
10.25J ET24
13J ET-5

 

The mods you are putting on certainly will make the car capable of faster laps. Extracting said abilities will be much tougher, and more risky. You will greatly reduce the effectiveness of the additions if you don't learn how to drive a car to utilize it's aero. You have to put more faith in the car. Most people (including myself) initially drive the car the same way negating the benefit of aero. You have to enter corners faster and apply throttle earlier than you think to utilize the aero grip. The faster you are going while cornering, the more DF you have. It takes some getting used to. You are almost certainly going to lose some top end as the aero and wide body will add drag and the wheels/tires will probably add some unsprung weight. The aero will negate the unsprung weight in the braking zones which may be where you feel the biggest difference initially. Braking distances will be dramatically reduced, which is why I say to learn with the OEM ABS. The OEM ABS is very capable. I brake at nearly the same place as 2010+ cup cars with a few hundred lbs more weight and more top end. And that's just stomping the floor and letting ABS sort it out. Also just with 4 piston stock big reds and PFC pads. I can stop shorter with modulation.

I suggest hiring a pro to help you set the car up and give you some in car data to compare to. A good coach is worth more than several thousands worth of mods when it comes to lap times. Learning how to study data will pay big time as well. Invest in an AIM SOLO/Smarty Cam setup. It's also worth it's cost in lap time. Harry's won't cut it for real data analysis.

 

Reminds me of a story I once read of a pro driver switching to the Porsche platform, one of those series with the huge aero. The driver was having issues in the corners and sweepers so he asked the crew chief for help. The answer? Go faster! The driver was hesitant but on his next lap instead of braking he held the gas for a sweeper and sure enough it planted! High pucker but the aero was able to work for him and he went faster..

 

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.

[url=https://flic.kr/p/SRRG7M]

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

 

John where does a guy go about getting these custom rings. They will probably be and interest of mine as my car continues to go through the never ending build process.

 

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]

 

Amazing stuff John, really pushing the limits of these cars by finding always new ways to improve...good tips ! Maybe if we get some interest of few guys here can do a group order to your fabricator, I would be interested even using the flares and wide front bumper I was able to push forward the front radiators by a LOT, also modified the their mounting brackets and now can easily run a 660mm (26.0") tall front tire, so the 0.9" difference wont be such a big problem as before. With some further modifications might also git a 680 tire in the front, but for sure can not run too lowered if so, still might hit the upper side of the fender, not sure can fit


As an update to my build, we picked the rims color (thanks Pete), should be gloss gun metallic even the producer says matte might be better, we have some glossy elements - carbon, black and guess glossy would be better..

Final specs are 10ET27 and 13ET05, we kept a very conservative setup as still lots of variables

Pics
- Hankook slick 280/660-18 (306mm wide) gets out of the flares but can see how it fits
- Rims model from a drift car, just to have an idea