Yargk

It seems to me the GT3 RS just doesn't have enough rubber on the front end, nor the wheel width to support that rubber. The RSR has 11 and 13 inch wide wheels. If you look at 930 track cars you'll see 9.5 and 11 inch wide wheels. The point is, if there are 12s in the rear of an RS, there should be 10s in the front. Then use suspension settings to balance it. Now I realize 10s won't fit. However, the standard GT3 has the same wheels and the RS simply widened the rear body. 9s will fit on the front, I say widen the front fenders to get 10s to fit, and it should still be balanced because you won't have to widen the front more than the 44mm the rear was widened over the standard GT3 (front track will still be more narrow than the rear in the way it is on the standard GT3). Cargraphic widened their 996 GT3 RS and put big wheels on for the best results at the track. Going with 18 inch tires for your new wheels, I'd suggest 265 front 315 rear MPSCs or 275 front 335 rear Toyo R1As. Then hold on...

PogueMoHone

I don't think understeer is the common gripe "right out of the box" with the RS. If anything, they are set up (Rear full stiff and front almost full soft) to oversteer from the factory.

Chris R.

Actually for many guys on the board, it is. See Bob Rouleau, Alexlate and racerron....

mooty

the car with factory recommended "track set up" does understeer a lot on the track.
i am still playing around with it. now waiting for new tires.

Yargk

There are two ways to look at this. If you assume that a mid position for each sway bar is neutral then yes, it's meant to oversteer. However, if you consider that the car probably has a natural tendency to understeer due to a comparatively huge track and wing on the rear, then the factory sway bar settings are simply a move to undo understeer not necessarily implying that the understeer was fully solved with that setup. BTW I'm not against the effective wing and huge rear end grip. You could make the car more balanced by losing some rear end grip, but that wouldn't make you faster. I'm just saying: great the car has amazing rear grip, let's get some front grip too. Again see the cargraphic 996 GT3 with 9.5s and 12s.

NJ-GT

Tire sizes and wheel widths are not the problem. A GT3 weighs twice as much at the rear axle as it does at the front axle, so it requires bigger tires at the back compared to the front.

Front my brief experience, I noticed a softer sprung rear end compared to the 996 GT3. If the new rear springs are softer than the ones on the 996 GT3, that will explain the understeer. Given the extra weight on the new car, the front end will get lighter on mid-corner and corner-exit while the rear end will get heavier, so less grip at the front axle more grip at the rear axle.

If you want to keep it stock, play with the sway bars, toe-out at the front, more negative camber at the front.

If it was my car, it would get the exact treatment my 996 GT3 got.

930man

im with nj gt

Yargk

I knew the 996 GT3RS was widened by cargraphic front and rear, but I didn't see what they did to the 997. There still doesn't seem to be a complete description of their 997 GT3RS that won this year, but it appears like they left the rear width alone and widened the front. I can't read German but I think that's what this webpage shows.

http://www.cargraphic.com/index.php?...,3166/&start=9

As a physicist, I'm with you N-GT, I have seen curves of maximum cornering grip per area of contact patch vs. contact tire pressure (take weight on tire and divide by the area of the contact patch). This is not a simple linear relation as the basic physics equation simplifies it to. A larger contact patch does yield more cornering force for a given weight. However because of the weight distribution in a 911, to be on the same point on the graph you should need only a contact patch area which is proportional to the weight distribution. So with 12 inch wheels on the rear you'd only need 8s in the front. It just seems that there maybe is more to it (slip angles, differences in how the front/rear grip is used in a turn I don't know) since race cars like the RSR don't follow the weight proportionally and for cargraphic to win the tuner GP they thought it was good to move up the sizes in the front. I mean they widened both front and rear in the 996 because they wanted more grip overall, but it seems like a calculated move for lower lap times to just increase the front in the 997 RS and leave the rear only because only the front needed it.

khaug

"I don't think understeer is the common gripe "right out of the box" with the RS. If anything, they are set up (Rear full stiff and front almost full soft) to oversteer from the factory."

I don't agree! My 997 GT3 plows something awful as delivered. Drop-throttle rotation isn't possible. I've reset the front sway bar to the softest setting, but I don't expect much from this minimalist solution. Also. see Bob Rouleauxs' complaints!

My GT3 was delivered with the front sway bar set 1 hole short of softest, and the rear sway bar set full hard! This is a setup which would normally produce oversteer, with minimal adjustability! And it still understeers! It appears likely that this is a result of the lawyers getting their filthy hooks into the equation!: Nice, safe understeer uber alles!

Suffice to say that the OE suspension settings won't give you either fastest lap times or best tire wear! and, schizophrenia: Lawyers' suspension settings + sub-optimal lap times and sub-optimal tire wear!


Fix # 2: Owner's Manual "Track" Settings": fix # 3: "996 Roland Kusmaul" suspension settings (see 996 GT3 forum).

Good luck!

Nordschleife

Where is that rule written?

As far as understeer goes, there is more than one way of dealing with it. One option is to increase the weight on the front axle (traction being a function of weight and contact patch area), so 'brake' on the front axle only, i.e. cause the front tyres to 'bite', momentarily tranferring weight forward and increasing the capacity to function as required. Once you are able to do this, you will find that oversteer is less of a problem.

Alternately, when presented with understeer you can unwind the steering wheel to increase the amount of turning effort, this may or may not be accompanied by increased power at the rear wheels, but take care that unweights the front wheels.

What I am saying is, don't get fixated by understeer, its there to look after people. Learn to drive through it.

FYI, most race drivers prefer understeer to oversteer. Most F1 cars actually understeer.

R+C

NJ-GT

The GT3 RSR and GT3 Cup have very different weight distribution compared to the street cars, so they get away with closer spring rates front/rear, and closer tire/wheel widths.

Let's take the 997 GT3 Cup as an example. It loses about 30 lbs at the front end by running a carbon hood, and no trunk panels/carpets, but the car is 700 lbs lighter that the street 997 GT3, most of those 670 lbs come from the center and rear. It loses a lot at the back, lighter exhaust, no A/C, a lightweight trunk lid with a very light wing, a plastic rear window, the rear carpets (they sit on top of the rear axle), and the power steering pump that by the way gets moved to the front trunk adding weight there. When I look at corner weight numbers from the 997 GT3 Cup, I see 43/57 rather than the 37/63 on my car. On the Cup car they run closer spring rates and 9"/11" wheels and skinny 240/270 tires.

Yargk

All of this makes complete sense and I agree. I suppose my question boils down to: "why did cargraphic do it if it's not the way to go?" Their car is just a highly modified GT3 RS, it should have a similar weight distribution to the street car that it started out as. Also their goal seems to only be lower lap times in the Tuner GP.

Nordschleife

Cargraphic and the Tuners' Grand Prix

In Germany the Tuners' Grand Prix is enormously important in terms of prestige and the attention the top performer re4ceives, it certainly got your attention.

Surprisingly, many of the 'top' tuners took a very long time to get hold of the best tyres and drivers.... this is now understood.

As the Tuners' Grand Prix takes place on a race track, and the prize goes to the car with the fastest lap, it pays to study what race teams do, and to apply the lessons learned to the cars entered in the Tuners' Grand Prix.

You will be aware that race teams i9n the GT1/Gt2/GT3 categories have found that the benefits achievable from building cars with the widest allowed tracks front and rear, and the greatest amount of rubber on the track are faster than cars which are narrower and with less rubber and less air resistance.

Now, this is a very particular situation - race cars on race tracks with race tyres, driven by professional drivers for whom dealing with understeers/oversteer are part of the job.

Very little of this has much relevance for cars that are driven on streets with moderately 'normal' suspension set-ups and tyres.

For street cars, more rubber on the front wheels might really pay off for hard driven AWD cars, such as the Turbo.

R+C

Terry L

I have now run 2 events with the GT3, both with the OEM Pirellis and street alignment. On a very slow speed technical track, Jefferson Circuit, run clockwise for those who know it, the understeer was so bad that the front end actually hopped as it scrubbed the front tires, and I couldn't get the rear out no matter what I tried. I tried changing the traction control setting and shock stiffness but couldn't fix it. The only solution in those corners was to round them off as much as possible and be patient. OTOH, at a higher speed track (Summit Point) I found no problem at all - the car was spectacular even in the relatively slower corners. At Pocono North, there was a lot of understeer in turn 3 but no scrubbing, and the rest of the course was benign. I plan to realign to the track specs and switch to the Sport Cups when the Pirellis die. Any additional suggestions?

NJ-GT

My 996 GT3 with full monoball and metal bushings in the suspension, Moton, 450/650 spring rates, rear bar at full stiff, front bar at one from stiff, 285 on 10" front tires and 335 on 12" rear tires, Manthey camber plates, all these and the car understeers if I use the front toe alignment settings from Porsche (0.10 degrees toe-in per side).

Even at zero toe at the front it still understeers a little bit, I currently run it at 0.15 degrees toe-out per side. Jon Groom was running toe-out on the 997 GT3 Cups. He won the 2006 Speed World Challenge GT class. Those cars ran on 245/305 Toyo RA1 (spec tire).

A wider wheel/tire will help the 997 GT3 to stop in shorter distances at full braking, but it won't help the understeer problem, because it happens at mid-corner and corner-exit where the front end is very light, more rubber with no extra weight won't help.

Apply more caster, more negative camber and toe-out and the car will be neutral.

I suggest you try the following specs (Alignment is a cheap modification):

Front:

Camber: -3.0 degrees (use 7mm of shims on the control arms)
Caster: non adjustable, it should be around 9 degrees
Toe: 0.15 degrees Toe-Out per side

Rear:

Camber: -2.5 degrees
Toe: 0.25 degrees Toe-In per side

After these alignment settings, the car should be neutral with a small tendency to oversteer, just move the front sway bar to a stiffer setting 1 or 2 holes until you like it.