18x12 et40 running -2.5 camber is ideal..

 

Fadi, if 19" you should do 305/30/19, the 325/30/19 looks too tight fit for track use.

12x19" ET51 is OK to begin with, but you have to mess with spacers like I've done. You have to install either 5mm spacers, or 14mm+ spacers depending on your overall suspension setup and other stuff. (I have 15mm and the tire is surprisingly not sticking out with -3.0 camber, but this depends on some other stuff as well)

I would not do spacers between 5mm-14mm as you cannot get the rim properly hub centric with those sizes... AFAIK.

Pwdrhound, my studying of 996RS MY2004 street car uprights show they have a better geometry than 996Cup uprights, while 996Cup uprights were directly from the 996GT3 street car. As Preuninger says, the RS uprights provide "improved dynamic camber control" because the 996 suspension configuration tends to exaggerate bump steer, the lower the ride height gets

And then in 997GT3 street car Porsche started to use 996RS type of uprights. So, I am not talking about race car parts, but the 996 GT3 RS street car parts.

 

I've found finally the ETs from OEM GT2RS wheels and tire specs

wheel size front 9J x 19 ET47
wheel size rear 12J x 19 ET48
tyres front 245/35 ZR 19
tyres rear 325/30 ZR 19

and also this
STOCK GT2/GT3RS RIMS
Fronts: 8.5 x 19 offset 53 with 235/35’s MPSC’s tires mounted
Rears: 12.0 x 19 offsets 51 with 305/30’s MPSC’s tires mounted

Gt2 runs 235/325

Guess will do 235/305 but might try as well the 245/325 the GT2RS runs especially if going RWD, guess the 245 tire can fit the 8.5J rim instead of 9J on the gt2rs.

Thanks guys, speaking now with AP Racing for my next rotors

 

You can use 245/35/19 on 8.5" rim yes. Bit tight fitment depending on your caster angle in front, but doable.

The 325/30/19 will be too big for rear I am afraid. For street driving it's ok but I guess for track driving would have a too big overall diameter. Remember these cars came stock with 295/30/18, the diameter difference becomes huge. I would love 325's for rear if they would fit properly though...

Hope you are also getting upgraded brake calipers!

 

For those who drive mostly street and some trackdays once or twice a year, a handsome brake upgrade could be the bigger 350s disc in front and rear with standard calipers. You just need adapter brackets.
For sure the 6piston calipers are better for the front in combination with the 350s, but i am too slow on the track.

 

Have seen pwdrhound running 315/35/18 thats a 26.7 tall tire, same as 325/30/19. Guess will need maybe new fender lines and maybe other modifications in order to work

Will run like 10-15 time attack/ track events per year, was thinking to use 997tt calipers or ask ap racing for new ones

 

I am wondering anyway if the 235(245) / 325 setup on 19" would be possible as I used to have problems with ABS and PSm ( in RWD) using

235/40/18 paired with 305/35/18 - Circumference diff 3.9%
solved by replacing fronts with 245/40/18 - diff 2.7% (under 3% that I know is safe limit)

Pwdrhound setup 245/40/18 and 315/35/18 - Circumference delta is 3.8%
Gt2rs setup 245/35/19 and 325/30/19- Circumference delta is 3.6%

So I wonder if can use 325 in the back and not trigger any ABS or PSM errors, still want to be able to use PSM when I want to, ABS can not see any reason to give up on it.
Dont know how 997tt/gt2 ABS&PSM units work and whats the maximum tolerance but seems like a problem for the 996tt platform, anybody used these on 996tt RWD ?
One solution might be to use 255fronts if they will fit.. that will give 2.6%

Otherwise I will surely use 245/35/19 paired with 305/30/19 with MPSC2 that guess and hope would be better than MPSC2 running oem 996tt sizes 225/40/18 and 295/30/18

Considering now to buy some Pirelli/Michelin slicks for serious track days and use OEM rims 245(235)/645/18 and 305/645/18 as they should fit, not sure how stretched the tire will be.

For next year I am considering more and more to use only 350/350 brakes as might use also 18" wheels, for calipers what is the minimum I should look for ? 997.2 gt3 or gt2 / 997.2 any carrera, etc ?

 

Guys, gone with 997 gt3rs wheels 8.5F et53 and 12R et51 and ordered 350/350 Girodiscs, going to keep the 996turbo calipers one more year if not finding some cheap 996gt2 calipers.

Was going to put MPSC 245/35/19 and 305/30/19 on the new wheels, but as I already have a lot of tires for my OEM wheels -
MPSC2(good shape) in 911turbo sizes and
usedR88+new PS2 in 996GT2 sizes

I am thinking to reconsider my options and just run all those next year for street and track and try to fit some slicks on my new rims, searched Michelin website and didnt find any options to fit, but Pirelli has some options that might fit if not too big
245/650-19
305/680-19 - this is like a 26.7 tire so almost like the 325/30/19 but not that wide as the 305 reflects the actual exterior size for Pirelli tires, not like the Michelins
19"

Pirelli 19
325/705-19
325/725-19
305/680-19
305/690-19
295/680-19
255/650-19
245/650-19
235/645-19

Pirelli 18
325/650-18
325/660-18
325/705-18
315/675-18
315/680-18
305/645-18
305/660-18
305/680-18
295/680-18
285/645-18
275/645-18
265/645-18
245/645-18
235/645-18

Michelin 19 - seems for fronts the fronts should be at least 10J gues the the 24/65-19 with real 249mm width might be overkill for a 8.5J front wheel, isnt it?

24/65 – 19 S8A P2E · P2G 647 230 249 1986 10
27/67 – 19 P2E 672 260 289 2063 10,5
28/69 – 19 P2E 686 275 306 2148 11
29/67 – 19 S8A S9A 670 322 322 2057 11,5
31/71 – 19 S8H S9A P2G 706 353 353 2192 12,5
31/71 – 19 GT S9L - - - - -

Should I try those or just put some MPSC2 245/305 on the 19" and buy some narrow slicks for OEM rims for next season ? Car will be back RWD

 

Fadi,
You will find a 26.7" tall tire very challenging to fit at a proper (read low) ride height especially when using modest spring rates. You will need 1400-1500# spring rates with Motorsport shocks to keep compression to a minimum while providing proper control. I am running a set up like this and clearance is still at a minimum especially under heavy compression. The fronts I run are 245/40/18 and are 25.7" tall. The rears are 315/35 and are 26.4" tall. I run 100/120 ride height. I don't really see how you could make it work with softer springs without running a higher ride height which would be counterproductive. It's a catch 22, the larger diameter tire you fit in the rear, you will need to lower the car by the corresponding amount to maintain a proper chassis ride height. As such, your tire to body clearance is drastically reduced (larger tires and lower ride height to compensate). Just something to keep in mind.

Finally, I would stick with 18" wheels for performance reasons. 19s will provide you zero performance benefit over 18s, none. A 245/645 is optimum on 9" wheels and a 315/680 on 12" wheels. 8.5" front wheels are really to narrow. You want a 9" or 9.5". The 680 will be an extremely tight fit and will require heavy fender rolling and a very careful offset selection to work. The 325/660 would be ideal as it's 26.3" tall but unfortunately it is not designed by Pirelli to be used as a rear tire and as such will not have the proper load rating. Probably not an issue on for short track stints but may be a problem during long sessions or high speed highly loaded tracks. The 325/660 is designed as a front tire for the ACR Viper. Hope this helps.

There really are no Michelin slicks in the proper size for our cars. Only Pirellis.

Finally, the ABS/PSM calibration will become more and more of an unknown with large 1"+ differences in diameter running tires with much greater grip levels over what the stock street ABS is calibrated for. You will be OK but will start to run into issues when really pushing the brakes 9 or 10/10s on less than perfectly smooth surfaces. You will need to back off in certain areas and learn to "drive around" these shortcomings. I battled this for a long time until I installed a proper Motorsport ABS which is programmed for slicks with a 1.2" diameter delta front to rear. All my brake problems went away at that point. I would keep an eye you for a 996GT3 Cup ABS system which pops up on the used market from time to time. PMNA no longer makes them and they are worth their weight in gold and sell literally overnight as guys are installing these in all sorts of car including 997Cups.

 

Thanks John, the plan was to be able to get wider MPSC2 tires as in 18" the widest rears are 295 only..., after your (great as usual) post, will consider only R compound tires for mixed driving on 19". these will be my street and occasionally track tires

Guess 245/35/19 and 305/30/19 will be ok with ABS (and PSM for street) as rears are only 1.7% bigger

My suspension is a simple kw v3 so not the best and not even a pure racing suspension, will add some uniball topmounts and check if custom springs are available

Might try first slicks on OEM tires and after to buy some dedicated 18" wheels (9.5 and 12.5 maybe) seems Allegerita OZs clear also 380mm brakes and they are light and cheap, but not the best looking imo.
Dont know if narrower slicks on 18" (like 225/295) will perform better than MPSC2 245/305, guess will have to see.. Trying to get some dimensions from hankook and other too during this winter

996/997 cup suspension components were hard to find here, guess will go with RSS instead, hope they will work good, what do you think ?

 

You won't have any issues with ABS on the street as you're not running at the threshold of the capability of the system. 245/35 and 305/30/19 will work fine. The 245/305 MPSC2 is a very good combo. You will like it at the track.

I would check with KW and see what the stock valving will handle as far as increasing spring rates. Keep the front to rear split to a minimum. After testing a bunch of set ups, I've found using slightly stiffer rear helpers works well. I run 1400 mains with 150 helpers in front, and 1500 mains with 250 helpers in rear. This is very close to 997 cup rates and works very well even on bumpy tracks when the compression is softened. I don't believe KWs will handle rates that high but I've run 1100/1200 before and that set up was very good at the track and not quite as hardcore on the street. Very good dual purpose actually.

I'm surprised you could not get the the Porsche Motorsport parts directly from Germany. All the stuff is made there. Did your shop contact PMNA there? I would call Manthey as they can get any PMNA parts you need. The RSS stuff is fine but just not as good as the PMNA part and you will run into some issues when trying to bolt on the Porsche brake ducting as it's designed to clip on to the PMNA parts. AS such, you will need to perform some mods to make it all work. Not a huge deal though.. Keep us posted on the progress..

Fadi, if you ever decide to upgrade your suspension give me a shout. I'm a dealer for one of the large European Motorsport shock manufacturers based in Europe and could have a system shipped directly to you from their factory in Europe. All custom built to spec with about a 2 week lead-time.

 

Pwdrhound, is 996CUP ABS plug and play install for these cars?

I will continue to use street legal semislicks like Trofeo R. Haven't had ice mode type of problems since PSM has been disabled.

Do you think I could feel the CUP ABS improvement already with Trofeo R type of tires instead of slicks or "Hoosier" type of almost slicks? I see from all of my friends with slick type of tire the CUP ABS is a must, but what about with my street friendly tires...?

I'm unwilling to go to full slicks because of few reasons (lack of trailering etc.), should I still do the CUP ABS?

Of course the answer seems to be yes from you but as you know, it's a big investment and wondering whether I could spend the money elsewhere for better gains. The stock ABS (while it isn't a proper modern ABS) is not undriveable at the limit with semi slicks, IMHO.

 

I'm Hi Kai. Ice mode has nothing to do with PSM, it is strictly a function of the programming in the street ABS unit. All of the street ABS units do it to varying degrees whether it's a 996GT2/3/TT or 997GT2/3/TT. When the ABS senses a sudden loss of all braking (car gets light or even slightly airborne after hitting a bump or bumps) it "thinks" it has hit ice and releases all brake force while retaining a hard pedal. You have to fully release the brake pedal and reapply to regain braking force. The Motorsport ABS units do not use this logic. With that said, I started having issues with it on R compounds when pushing the brakes at the threshold limit of the ABS on bumpy surfaces. In my case the issue may have been more apparent due to the fact that I've always run a Cup style larger rear tire (the Cup ABS is programmed for the larger rear tires) which was not optimal with the stock ABS. As you mention, the stock ABS is not undriveable. It is however very limiting and you have to learn to "drive" around it's shortcomings. You don't really realize how much better the Motorsport ABS is until you drive with it. I consider the Cup ABS one of the best performance mods I've done to the car. It's also a huge safety improvement because I can trust the brakes 100% as many people have put these cars in walls due to ice mode. The performance difference is quite noticeable on R compound tires and my data shows an extra 0.2Gs under braking compared to the street ABS. On R compounds I see 1.1-1.2Gs and on slicks it's closer to 1.6Gs. Get ready to eat through pads and rotors at a much higher rate!

The Cup ABS is physically a basic 4 channel 986 Boxster hydraulic unit with a Motorport brain. Physically it looks like any Boxster unit that sells for $150 on Ebay. It's the brain part that you are paying the $5K+ for. The ABS unit is a direct bolt on but you will need a new mounting bracket along with new brake lines that connect the abs to the distributor block. You will also need a Cup brake fluid reservoir. All the parts are about $150 and can be bought from the dealer. I looked up all the part numbers in the 2005 GT3Cup PET.

With that said, this is not an easy (or cheap) mod. While the physical install is simple, the wiring will require someone who has the Cup and TT wiring diagrams with a thorough knowledge and experience doing this type of work. My shop actually discovered some errors in the factory manual regarding the labeling of the respective wheel sensors. The stock ABS connector will need to be completely de-pinned (see 3rd pic below) and the correct wires re-pinned into the Cup connector which needs to be purchased separately but it's cheap (you can see all the unused left over shrink wrapped wires sticking out of it in the 4th picture). The Cup ABS communicates with the instrument cluster over K-line while the street ABS over CAN bus. As such, while the Cup ABS will be operational, your instrument cluster will not be able to get speed information from the ABS module which means that your speedometer and odometer will not be working. This is not a problem as long as you use a standalone dash display like the MoTec I'm using. MoTec displays countless selected parameters including speed and odometer information of course (plus you can't see the speedometer anyway with the standalone display ahead of it). We are also feeding the Cup ABS information directly into MoTeC which will display any fault codes if they were to pop up. Obviously with the Cup ABS you will loose PSM and the pump and yaw angle sensor and associated wiring can be removed as they serve no purpose. Hope this answers some of the questions Kai...

[url=https://flic.kr/p/y8FKhp]

[url=https://flic.kr/p/ynT9MG]

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

[url=https://flic.kr/p/ziy7vf]

 

GIVE THIS MAN A MEDAL!

John, once again appreciate a lot the info. I feel it's an old ABS (as it is) so thinking about the change... I could have one unit available for EUR2K or so...

P.S. Where is the story of your engine build? I remember you were making a 3.8L build for this season, would love to find out the thread with detailed facts, figures and your opinions after the build? Will be copying your ideas if possible...

 

Hey Kai,
If you can get the Cup unit for 2K Euro I would not hesitate. That's money in the bank. The last one I saw on Rennlist was listed for $8K but that included a 997Cup wiring harness to go along with it. Usually these units alone go for $5K. Remember, these units are no longer sold by PMNA so the prices on the used market just keep going up. Funny thing is, these were originally $2k from PMNA, then they gradually kept increasing the prices all the way to $8K before they discontinued them. If you find one, just make sure it is the latest version which was labeled as "Diagnosestand A02" on the white sticker under the wiring connector. When you scan the unit with PIWIS, version "A02" will come up.

[url=https://flic.kr/p/zZkB7H]

Oh, yeah, here are the part numbers for the ABS unit and lines:

PMNA 996Cup ABS module 996.355.049.92
Brake fluid reservoir 997.355.013.21
ABS module bracket 996.355.033.02
Brake lines:
996.355.311.43
996.355.313.02
996.355.315.03
996.355.316.05
996.355.326.05
996.355.327.04