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    Sep 9, 2002 12:39:20 AM

    cjv
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    Wider Tires

    I have been interested in installing wider rubber for awhile now on my 2001 996tt. Availability of larger tires that are compatible is not good. I found the other day what I believe to be a good match but would require some slight fender work (widening the fenders just a little which I would do all in metal, undetectable to the naked eye). Michelin in the Pilot Series makes a 335/30ZR18 and a 255/40ZR18. The 335's have an outside diameter of 26.1" and the 255's have an outside diameter of 25.9". Changing the outside rims on my present three piece Fikse FM/10's would be fairly easy. I already have a spread inside due to the GT3R brakes. The JRZ triple adjustable race suspension would be easy to adjust. I have already modified the gears, so my current top end @ 7000 rpm's is 185 mph. These tires would raise the top end to about 193 mph and the new motor we are building with a 8000 rpm red line will raise the top end to about 210 with these tires.

    Any input as to how this should affect handling?

    Sep 9, 2002 1:24:05 AM

    Roland Roth
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    Reply to: cjv

    Re: Wider Tires

    One small caution! My experience with 993TT car at very high speed is this: above 330 kph the ABS does not function! The warning light will flash.Actually my whole panel lights up when we exceed that speed. Ruf says the ABS function will return when the speed drops below 330 kph. We have done very hard braking from 330 kph without incident however the panel lighting up is a major distraction.
    Hey bring that bad boy to the Silver State. You got a roll cage yet?

    Sep 9, 2002 2:25:23 AM

    cjv
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    Reply to: Roland Roth

    Re: Wider Tires

    Roland, thanks for the heads up on the ABS system. To date the car just won't go that fast. I am not sure even when I'm done if it will see 210 mph or 330 kph. It will be close. The trip to 330 kph will be like catapulting off an aircraft carrier. Time to 185 mph is right at 18 seconds currently. Hopefully by Christmas time we will be done with everything. I have had the car for fourteen months, eleven of those months have been with three different tuners. It has been at S Car Go Racing for the last two weeks. Not scheduled to see it for another two weeks. I don't have a roll cage, but do have a pretty stout roll bar. I really don't want the cage part unless the cage part can be made removable.

    Sep 17, 2002 8:48:28 PM

    Grant
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    Reply to: cjv

    About handling...

    Just remember that you're adding alot of unsprung weight by doing that, so car's handling will suffer a little (but ultimate grip may increase). Also, I have 255s on the front of a 944TS track car and it does tramline pretty badly on the street (follows the grooves in the road).

    Sep 18, 2002 1:47:50 AM

    cjv
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    Reply to: Grant

    Re: About handling...

    Grant, good question. Which set up would handle better?

    Sep 18, 2002 12:42:05 PM

    Grant
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    Reply to: cjv

    Well, with the bigger wheels/tires,the car wouldn't be as

    nimble (able change directions as quickly) or ride as well (the weight of the wheel going up and down would overwhelm the shocks and springs more),but you could probably go around a corner a bit faster. So, I think for the track (or very smooth road), the bigger setup might be better,otherwise, you might prefer the smaller ones.

    Sep 19, 2002 12:10:32 AM

    cjv
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    Re: Well, with the bigger wheels/tires,the car wouldn't be as

    Grant, the car is presently set up wit JRZ triple adjustable race suspension, monoballs and GT3R sway bars front and rear. Also GT3R brakes 380mm front/350mm rear. Would this set up change your above opinion?

    Sep 19, 2002 12:17:48 AM

    RCA
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    Reply to: Roland Roth

    Re: Wider Tires

    There is no problem with the ABS on the 996 Turbo, even at speeds over 330 kph. We know a guy (he's tuning 993/996 Turbo engines) who drove slightly over 360 kph (speedo reading) in a 996 Turbo and no problems occured. However he said that it was pretty scary (20 kph more seem to mean worlds at that speed) and he didn't trust the tires (which were actually approved up to a top speed of around 350 kph (incl. the "upper margin").

    I don't know, I think cjv is doing the right thing. Building a real power giant and keeping a more "real life" top speed to avoid tire problems.

    Sep 19, 2002 1:15:22 PM

    Grant
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    Reply to: cjv

    CJV- Well you certainly have the suspension to cope w/ it

    Even though you have an awesome suspension, it will still react quicker with less unsprung weight. But it you're looking for maximum grip, you definitely have a suspension that can handle the extra weight if you choose!

    Is there a way you can try some bigger wheel/tires before buying? That would be the way to go - short test-drive...

    Good luck with your sweet ride,

    Grant

    02 C2 coupe
    88 944TS track car
    73 911S
    03 GT3 on order

    Sep 19, 2002 3:33:11 PM

    FixedWing
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    Reply to: Grant

    Grant is right

    CJV, it all gets very complicated. If the road is glass smooth and the suspension extra hard then unsprung weight won't be important. But if the road starts getting bumpy then it becomes very important.

    In my own case, there is one corner at Nürburgring which is bumpy at the final braking point and at the apex (Kallenhard). Everyone tends to brake off-line and go around the outside of this corner. Before adding the PCCB's I would do likewise. But now, with the lower unsprung weight of the PCCB's, I am able to brake and corner through the bumps of this corner. Unsprung weight does make a very big difference.

    Wider tyres increase unsprung weight. But they also increase the amount of contact with the road. And wider tyres can also mean a slower turn-in based upon the geometry of the contact patch (which is what Grant is talking about). Going wider has deminishing returns and could have costs in terms of the flexability of the car.

    And let's also remember that the size of the tyres is one of the biggest factors in the aerodynamic area of the car. So increased drag with wider tyres (the C4 vs. C4S shows this well).

    The only way to answer your question on how wide to go if you want to go that route is to experiement.

    But if I were you CJ, given the number of miles you are travelling each year, I would be looking not for wider tyres but for stickier tyres. I would look to using Pirelli Corsa, Michelin Cup or similar. Sure they won't last as long but do you care? If you have to contend with rain then I'd look for some sticky wet weather "R" tyres on a second set or rims. Or alternatively you could use standard tyres for the rain (and believe me, width is not an advantage in the rain) and some really nice "R" compound tyres for those beautifully sunny days.

    Barely street legal "R" compound tyres are just going to blow your mind so far as braking, turn-in, cornering, etc. are concerned. There's no comparison to regular street tyres no matter how wide they are.

    S.

    Sep 19, 2002 5:57:35 PM

    Grant
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    Reply to: FixedWing

    Fixed Wing -Please tell me more about the PCCB's

    I have ordered a new GT3 and will have to decide whether to buy these or the more conventional brakes. Some people have said that they didn't care for them, but I've also heard that they have improved them since their introduction.

    I'd love to hear a review from you!

    -Grant

    Sep 19, 2002 6:19:37 PM

    FixedWing
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    Grant: check email.

    Sep 20, 2002 5:07:17 AM

    cjv
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    Re: Grant is right

    FixedWing, Pirelli makes two sizes in the P Zero Corsa that would be compatible. For the fronts the 235/18's and the rear 295/18's and 315/18's. I am currently running the Fikse FM/10's. They are 8.5" wide in the front and 11.5" wide in the rear. Which rear tire do you believe would be best.

    Sep 20, 2002 5:51:09 AM

    FixedWing
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    Reply to: cjv

    AWD

    If the AWD is still hooked up then I personally would go with the 295/18 Corsa at the rear. My reasoning would be that I prefer a more neutral handling car and I think a sticky 295 is more than enough. If you go with the 315's with the 235's at the front then I suspect that you will maintain, or maybe even make worse, the understeer on the Turbo.

    If you prefer an understeering car then you might want to go for 315's. Also, this could be a good choice if you've disconnected the AWD (a la GT2).

    With Sticky Corsas and AWD you will have absolutely no trouble getting the power down. If anything, you might have to be a little more careful about breaking things as these tyres just aren't going to slip the way a street tyre would if you do a high RPM standing start.

    Just lately, people prefer the Michelin Cup tyres to the Pirelli Corsas but I think you will have trouble getting the sizes that you need. That might change 1Q2003. But either of these is going to give you a much more solid car in the dry. Not only will it handle a lot better but that handling will be a lot more dependable (by this I mean that when the car takes set in a corner it will just stick -- you won't find yourself constantly having to catch the back and make little adjustments mid-corner). For this reason, I think a car with a little less understeer would be acceptable -- and for me, even preferable.

    Does this help?

    S.

    Sep 21, 2002 5:35:08 AM

    brookstt996
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    Reply to: RCA

    Re: tt996 at 360!?

    This may seem silly/trivial, but how much tuning is required to get the car up to that level of performance?... Is this a Gemballa job? I am looking for tuners in the USA (New York city area)... and was interested (not that I intend to take the car up to that high a speed around here).
     
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