emmo.84

hi to everybody and thanks for the unestimable infos I got in your forum!
I am racing in the swiss porsche cup with a 997 GT2 well set up for track use.
as many 997rs have switched to slicks, Michelin as the cup is sponsored, I wanted to do the same on the GT2. I got some BBS in 9x18 and 12x18, and I am now looking for the correct tires.
First step will be to try the 18 PspCup tires, better than the 19 PspCup, but I have difficulties in finding a 345/30x18 for the rear.
Next I want to try some 18 slicks, in 24/65 (or24/64) + 30/65 (or 30/68). The wheel diameter doubt is for wheel clearance with my low set up car.
The swiss guys who tried on the rs and gt3 say the 18 PspCup is 2 seconds faster than the 19... seems to be a lot.
The slicks SHOULD give another 2-3 seconds advantage, but I want to see the lap times before any announce.
I am aware of spring rates problems and all the rest. I don't want to turn a GT2 in a Cup car because there are 400 Kilos in the middle, but would like to get fun using the almost 600 HP it has and stay on the track for more than 5 laps.

emmo.84

the issue about 18 PSpCup tires would be a compromise... but I am a bit scared of the fact that my car would join the Police car fleet if they get me on an open road... Of course I am referring to the free practice, as for the race my Team can carry the wheels, (or the car), to the races.
Basically up to now I drove my car to the races, saving some good money for car transport. I know it's not so clever, but it was ok up to now.

NJ-GT

the 997 Cup slicks are very sticky for sprint races, you may get better lap times out of the Cup spec slicks (pilot SX) 24/65 and 27/68, they are fine for 9"/12" wheels. You can also run non-Cup slicks 24/65 and 30/68 (avoid 650mm in the back), but even in the softer compound I don't think they can keep up with the slicks from the Cup car. The new 997Cup green tires are testing faster than the blue label cup tires.

I ran the Blue cups slicks against Michelin Pilot Sport Cups (street dot-r) and saw a difference of 2.8 secs per minute of track time. My Sport Cups were 19" (265/345) not the OEM MPSC that have been reported to have less grip.

You can run 265/335 MPSC in 18" with those wheels.

I doubt the fast MPSC are 2 secs faster than the OEM MPSC, 1 second at most.

emmo.84

Thank you very much NJ-GT!!!!! YOur help is really precious as I am getting mad with this tire issue! What I have discovered or been suggested was to mount the following slicks: 24/64 x 18 front and 30/65 x 18 rears... as the 30/68 is too big and touches on the car frame, + it gives slightly longer ratios, (19 MPSC rear is 678 mm.)
Why not the 30/65 rear? I guess it is a LMP front tire... will it stand 600 HP?
Same problem with the rear 27/68, cup car has 430 HP and weighs 1200 Kilos mine has 600 HP and weighs 1400 Kilos.
A guy in the swiss cup runs 24/64 front and 27/65 rears and goes fast... but still that's a 415 HP car...

emmo.84

I have checked your 19 265/345 specs and the car would be too tall for me + too long gear ratios. You quote porsche cup tires as 24/65 and 27/68 but at least here and in swiss they show on catalogs the 24/64 for the front cup tire. Compounds are S8B and S8C...
I had also chosen the 24/65 for front but then they told me it's the REnault CUP rear tire on a rear engine car...
Problem is if I put on the rear the 30/68 I don't think I can get back the weight balance I have now, because the 325/30x19 OEM is already touching up when I hit kerbs. .
Would really like to understand if the 30/65

emmo.84

sorry, did not finish the message... I would really like to understand if the 30/65 could explode or such things if I put it on the GT2.
For sure LMP lap 30 seconds faster than me, but it's true they are very light.
Thank you again for your suggestions. Should you come to Italy I'm in debt of some good Italian food!

NJ-GT

Avoid 650mm tires in the rear. There are a few threads in the Racing forum about low profile tires in the rear of a 911, they get trashed very quickly, and in some cases the overload could result on a blow-out.

I ran a 285/30R18 Kumho V710 in the rear of the 996 GT3, and the tire was shot after 16 laps (2 autocrosses). Grip was gone.

The stock 997 GT2 rear tires already have a 680mm diameter, although lower profile as they are 19". I ran different sway bars with the 997 GT3 RS and the Cup slicks. The stock suspension reaches the bump stops on slicks per my initial measurements, so I decided to run a stiffer rear bar, and I did not lower the car as usual, to have an extra 0.5" of suspension travel.

Yes, and 30/65 LMP front tire fits in the rear, but that tire is not designed as a rear tire for a rear engine car, especially one with 600Hp and massive torque.

Stick to the 24/64-18 and 27/68-18. Perform a test using a data acquisition system, and test them again DOT-R MPSC or any other tire, you will see a decent drop on lap times. However, I would change springs and sway bars before running racing slicks.

gweedo911

[QUOTE=NJ-GT;7032403]You can run 265/335 MPSC in 18" with those wheels. QUOTE]

Does Michelin make PSC in 335/18?

I've been looking to switch to 18" but I drive to the track and the current rubber selection in 18 is not too great........

emmo.84

Thanks again NJ-GT! Had the luck to find Michelin racing depnt this morning and he said the same: no 650 in the rear, 24/64 in front and 30/68 rear or 27/68. He said it's smaller but surely better than a 30/65.
If I have enough room he said I can use the 30/68 also on 12 rim. I decided to order the CUP tires and make with them the first test. I will also try to understand the blu and green label issue, it there are both overhere.
The michelin man agreed that the 19 slicks are still on the development way, so 18 is the choice now.
Plus he adviced NEVER to run a fresh new tire in Monza, but one that has been warmed up before and got back cold. (chemical reasons he said).
About 18 PSC there is no 335, there was a 345/30 for corvette but has been dismissed. There is somewhere a 315/30x18, a few sets have been sold, but it's not easy to find; so for sure it's not so popular.
I'll try to fit the 68 in the rear, more than the clearance I'm sorry for the gearing... I hoped to shorten it a bit with slicks, but no way.
Thanks NJ-GT for the bar issue, I'll sure make some tests, but before that I want to mess a little with my MOTONS, on the very soft side (hydraulic), at the moment.
LOOK FORWARD TO FINALLY USING ALL THE POWER OF THIS CAR!!!!

emmo.84

hi everybody, I finally made the test with the Michelin Slick on the 997 GT2. I got 24/64x18 in 282G compound, (Porsche Cup tire) and a 30/68 S8A in the rear.
Now the front was a huge step forward in braking and grip from the MPSC, but the era was not good on this car.
In my opinion, the 30/68 is an almost unused tire by racers or track day people, and it may lack development.
My only other choice at this point would be the rear Porsche Cup tire, 27/68 x18 in 331C compound.
Which was the worls Supercup Porsche tire and and is now also given to national carrera cup racer.
That is: the best tire Michelin has made for Porsche up to now.
The Michelin people I spoke to say it's not a matter of compound 7 - 8 or 9, it's just that this 331C tire has been developed for Porsche.
How this will go on a 997 GT2 with 250 Kilos and 150 HP more it's another story...
Anyway I'll wait for the France Michelin guy that is now in Brasil and almost surely I will then order the rear 27/68 in Porsche Cup compound.

Kaizu

Good stuff, if you know the Michelin racing dept say them PLEASE to bring wide 18" Pilot Sport Cups to the market again! This is a big problem for the Michelin brand. Now as the 315/30/18 MPSC has been discounted many cars with 11.5"-12.5" wide rear tires (there are plenty of those cars) are in huge problems because you cannot run the best "street legal" and "street driveable" tire anymore.

The fastest street legal cars in time attacks etc. have run wide MPSC 18" tires...but now they cannot...This is a problem...(as MPSC seem to be fastest tire of street legal tires you can also drive to and from track.)

NJ-GT

Definitely the MPSC is the fastest track tire that can be driven to and from the track. Keep in mind that they still make 265/345 with the full race compound, and they fit the wide body 997 with minor fender work.

Kumho V710, Hoosier R6/A6 and BFG R1 are DOT legal slicks, that should not be driven on public streets, although some people do.

The Toyo R888 cannot produce the same g forces I have produced with the MPSC.

emmo, you should not mix Cup slicks with non-Cup slicks. There is plenty of information about this in the GT3 Cup forum. I ran 265/345 MPSC and 240/270 GT3 Cup (blue) slicks on the 997 RS, same track same day, there was almost 5 seconds difference per lap.

I just tested fairly fresh (40 laps old) Hoosier A6 this past weekend at the same track, and fairly fresh Toyo R888. The R888 proved lower g forces than the MPSC, while the A6 gave me the best g-forces of all the tires I have tested, except the Michelin Blue Cup slicks.

The Michelin Cup Blue slicks offer a much greater level of grip, improve acceleration out of turns, turn speed and braking by a huge margin.

stevecolletti

NJ-GT,

I've been running R-compound tires on the street, on multiple cars for 20+ years. Other than the tread (or lack of it), is the V710 that different from the VictoRacer V700?

I've tried the VictoRacer, V700 Ecstas, R1s, PSC, P-zero Corsas, and Yoko A-008 series before them. I have to admit, I never had the nerve to try a Hoosier though, since it doesn't seem like it would survive running over a soda can, or contact with the first pot hole

Thanks

NJ-GT

The V710 is vastly different to the V700 Ecsta and Victoracer. It is a slick tire with a very soft compound. It is the closest competitor to the A6 for autocross, and it is also a very fast track tire.

I would prefer not to drive on the streets on V710, A6, R6 or R1, due to their soft compound, and lack of tread.

stevecolletti

Thanks, you saved me some future trouble.

My R1 experiences are with older versions (late 90's/early 2000).