Todd Serota [TracQuest]

Michelin Pilot Sport Cups are no worse than other R compound tires as far as breaking away suddenly. If you have good SOP feel and car control skills, you can drive MPSC's at the limit and work them as well as other R compound tires. I think NJ-GT was comparing them to street tires, which as I said in my previous post give more warning, both in terms of feel and especially noise.

If you've driven comfortably on other R compound tires, there's no reason to avoid MPSC's.

Bob Rouleau

Watt - Yes a set of P 0 Corsa or Michelin Cups will change the car's handling dramatically. Soon after you'll want a more track oriented alignment.

Metal Solid If you are wearing out the inside edges of the rear tires I suspect that your alignment is not at the stock setting. My experience with dealers aligning a GT2 or 3 has been very poor. They don't even know about the additional adjustments - for example there are two sets of camber adjustments in the rear and two in the front (one is the shims). A regular 996 has only one front and back.

NJ-GT (and others I bet) putting a st of R compound tires on the car will give you better grip. If you read the info from the manufacturer you'll note that they are designed to work best with camber in the neg 2.5 to 3 range. To get the best performance out of them you need a track alignment. Running them at neg 1 will be better than a street tire but the car will really carve to corners with the correct amount of negative camber.

As a general rule, 996's I have driven which feel unstable in corners have turned out to have insufficient toe in at the rear or not enough in front. The GT2/3 is very sensitive to toe adjustment.

The Porsche rear suspension tends to toe out the wheel under load. If you don't have enough toe-in the car is quite a handful. Like negative camber this is a compromise since more toe-in will wear the rear tires more quickly.

Lastly (Todd) I recant my neg 2 compromise although it worked for me on various 911's. I should have emphasized that I wear tires out on the race track, not on the street so preserving tread life on the street is not a big factor for me. With the P0 Corsa, I end up heat cycling them to death and scrap them even though there is still plenty of tread. The Michelin Cup tire is stickier but less durable. Hoosiers are a disaster on my GT2. I got exactly ten heat cycles out of them before they went off. Note that a 20 minute DE session is a heat cycle!

Best,

macfly

If you don't have enough toe-in the car is quite a handful
Bob, what would the car feel like without enough toe in at the rear?
My issue is with speed of 80+, under there the thing feels really fast, stable and strong.
Over 80 it becomes progressively unsure and loose feeling, not at all confidence inspiring.
When you get it up to around 100 entering turn 8 at Willow it feels like its about to go away from you, but I used to go into turn 8 at 115-120 in the M3, and it felt fine.
(nb, all this is under heavy cornering loads, not straight line, that feels fine.)

Also in this thread not much mention has been made of the Bridgestone SO3's which I used on the BMW. They were very good tires on that platform, they felt much better than the OEM MPS that came with the car. Do they not work so great on the GT3?

Finally, are these the tires that I should order for when my OEM's are shot, as it may take a while to get them.

Jack

Andrew: While I'm not Bob, those are the tires -- Michelin Pilot Sport Cups. Rumor has it that the correct front size of 235 will be available later on this month or in early March. Some posters have reported using the smaller 225 size in the interim with no excessive understeer issues.

macfly

correct front size of 235 will be available later on this month
they had some in stock already, I just ordered them, the big surprise is the cost differential between the tires?

2 235/40YR-18 Michelin Pilot Sport Cup In Stock $159.00 $318.00

2 295/30YR-18 Michelin Pilot Sport Cup In Stock $314.00 $628.00

Bob Rouleau

Macfly -

Easy one first - those are indeed the tires - Pilot Sport Cup. Also worth noting that I have run them on my GT2 and GT3. Both cars call for the 235 fronts whereas Michelin had only the 225's. I observed no ill effects whatsoever with the 225's. I suspect that the width of the real tire patch is less than the nominal 10 mm differential. The slightly narrower tire ends up with a straighter sidewall (same rim as for the 235) . As a reference I was using the P 0 Corsa which is available in 235 front. This experience was repeated on my GT2 which uses the same 235 fronts and a 315 rear. No change in the handling characteristics except the car on Michelins had more grip in the dry. If the 235 is unavailable I would not hesitate to use the 225 fronts.

Rear Toe-in has two effects, one it makes the car more stable in a straight line at speed - in the old days we'd use tons of rear toe for qualifying and reduce it for the race because with a lot of rear toe, tires wear out very fast.

If your car feels unstable at high speed on the straight I would be suspicious of incorrect rear toe. With the factory spec for toe the GT3 is very stable at speed. The front spoiler and rear wing do a good job of cancelling lift.

Entering a corner, the Porsche rear suspension transitions from the nominal toe-in setting tending to a toe-out position under load. this is a deliberate form of rear wheel steering. Think of a hook and ladder truck with the rear wheels being steered. The front wheels on the truck are turning right (for sake of example) and the guy on the back is countersteering, his wheel is turning left. On your car this effect is much more subtle but it does have an effect on how the car reacts in a turn with a decent load on the outside wheels. What you want is to have the rear loaded wheel transition from toe-in to less toe in or at most zero toe while loaded. Inadequate initial (static) toe-in will result in the back of the car steering itself - oversteering for no apparent reason and that makes the driver nervous (me at least).

I'd also be wary of front toe settings. I drove a GT3 (was asked to try it because the car felt "darty" and the car was a beast. Someone had set the front toe incorrectly and the car was unstable at speed in a straight line and tended to change its line while in a corner. I can't say how much toe-in or even toe-out it had but a quick trip to the pits ensued. We turned the toe adjuster exactly two flats on each side and the car went from beauty to beast in 15 minutes.

I believe Todd S suggested a good alignment shop. If it's in your area it would be a very good thing to get the car set up correctly. My car was misaligned by my dealer on delivery. They "checked the alignment" as part of the standard PDI and found it to be "wrong". Perhaps so, but after they tweaked it it was very wrong. A race shop took car of it in 2 hours.

Best,

macfly

Inadequate initial (static) toe-in will result in the back of the car steering itself - oversteering for no apparent reason and that makes the driver nervous
Bob, that is exactly what I'm feeling, thanks so much for the clarification.
Do you have any updated figures showing what I should set it to, or should I go with the previously posted French settings?

Todd Serota [TracQuest]

Hi Andrew:

I've always run 3/32" of toe-in in the rear of my 911's and that has worked great. I'm not familiar with the French settings that were posted, but 1/16" to 3/32" is the generally accepted toe-in figure for the rear.

Front toe, btw, will vary depending on the desires of the driver. Most people run at least a bit of toe-in on the street - around 1/16" to a/32". Autocrossers and totally dedicated track cars often run a bit of toe out because the car turns in like there's no tomorrow. Since I drive my car on the street and the track I compromise and run 0 toe. Some people say the car wanders too much with 0 toe but it's never been a problem with my other cars and it's fine on the GT2.

Bob Rouleau

Mac - As usual I agree with Todd. I run 3/32nd total rear toe. It works on both my cars. In front I have a bit of toe-in, I have to rummage in files to find the print-out. I tried zero toe and I found the car a bit unstable on the street - roads here are much worse than in CA and bumps caused the car to change course more than I'd like. If you want, pmail me with an email address and I will send you the suspension set up for a GT2. It was sent to me by Roland Kussmaul (yeah, him!) when I asked Alwyun Springer for help setting up the GT2 for track. It is a full on track setup mind you but there are elements you might want to incorporate for your car. The GT2 and GT3 have the same suspension although the spring rates and shock calibrations are no doubt tweaked for the heavier car.

With 3/32nd toe both cars go down the straight like they were on a mission from God. With the speed potential of the GT2 that's as Martha would say, "a good thing".

Regards,

rockitman

Special Thanks to Jack for turning me on to Wheel Enhancement. I purchased a set of Kinesis K58's, standard shot peened anodized, polished lips. John was very helpful and knowlegeable. He steered me away from the dark anodized and the black anodized. He has a seal TT and indicated the standard anodized matches the car in most light and offer's a nice contrast under different lighting. He idicated that the black can develop a purple hue over time and the dark developes a green hue, fyi.
For those interested in weights:
stock GT3 wheels front: 25lbs 2oz. Kinesis K58 front: 21lbs. 3oz.
rear stock: 27lbs 11oz Kinesis rear: 22lbs 5oz.
That's an overall weight savings of: 19lbs. not bad...That makes up a significant amount of the weight diff between steel and pccb rotors for unsprung weight.
They have fitted other GT3's and there is no spoke clearence problems with the 6 piston front calipers.

Sadly, Anne does'nt come with the wheels...

Sun Ra

chris,

is that anne coulter?

pls post a pic of your kinesis; they seem as light as the fikses

rockitman

Why yes, it is Anne Coulter!!! We had a great night slamming libs!!!

My wheels are on order and here is a pic. Anne photoshop job courtesy of Noel..

PS: PM me if your interested in the price I paid

Sun Ra

thanks,

i find Anne a little too moderate, but she'll do.

i PM'd you

Sloth

Congrats on the wheels. I look foreward to seeing some pix. I am still surprised that the OEM wheels are as heavy.

You got PM!

Todd Serota [TracQuest]

That's nothing, Sloth. Have you ever checked out the weight of GT2 wheels? Boat anchors.