(Repost from the 996 GT3 section, had picked wrong forum ...)

My battle against understeer has taken a drastic turn, one that has me apply significant opposite lock in most turns, furthermore as I try to practice trailbreaking. From a stock set-up, I went through:
- corner balance + front sway 1 off from full hard: barely made a difference
- lower ride height by around 15mm, front camber 2.5, rear camber 2.0 with adapted toe: very noticeable difference ! So different I ended up sideways very frequently and spun twice during the day.

Video.

This particular track is more Elise than GT3 playground, but helped zoom in on handling traits.

Now I am going to lower the rear a hair and increase camber to 2.5 in order to regain a bit of turn in stability and track out traction. My next stop is another trip to the Ring, I don't want the car to be hairy in Schwedenkreuz, Kesselchen or Schwalbenschwanz.

I am also wondering whether the Corsa System are ageing well. This set has barely 3Kmi, but they don't seem to be holding up as well as my previous set.

 

Sounds like a rear toe problem you need 16 mind toe in per side in back. Would not increase neg camber in rear.

 

what Bob said, i just re-read your post on the 996 GT3 forum and yuo have waay to little rear toe for a stock set up.

I had that little toe and it was diabolical even with a full PMNA/Moton suspension.

 

So increase toe in from 15 to 20mm per side at the rear ?
What would be the downside of adding too much toe i.e. how do I tell that/if I've gone too far ?

 

...when you shred your rear tires in 100 miles.

Bob is talking 16 minutes of toe in per wheel, not 16mm. Not sure of the conversion rate. I stick with minutes.

Cheers,

 

Ze_Shark correct me in case I'm wrong but if I understand well your geometry settings is an arbitrary benchmark only to start with. Firstly I notice that none of your settings reflect either the driving on public highways or race circuit recommendations as seen on the GT3's manual. I was wondering whether you were aiming at any particular outcome with this mixed-up or is as I said is the starting point of your experimentation.

I can partially feel how your car handles now, basically due to the fact that I recently adjusted mine to Porsche's race circuit figures. Your extra effort to make it driveable in Circuit de Bresse is an additional reason. Do you by any chance have recorded your lap times of before/after these settings?

I attach a sheet showing the settings of each of the individual angles set up in my car. FYI, I am NOT prepared to keep up with these as I'm experiencing heavy oversteer along with accelerated tire wear. In just 5-6k kms after the new settings my rear tires were completely worn-out. (Ask for pixz if you wish to enjoy this horrible view).

 

Not sure I understand the question so apologies if answer is beside the point you're trying to make.
My goal is to have a track day car with a set-up that is safe (Nordschleife, going out is a big no-no) but still sharper than stock, especially in the slower corners.

I intentionnally started with a stock set-up, corner balanced to make sure that I have a clean base. Result was that I still hated the turn in/turn out understeer, but part of this has to with my driving skills too.

I therefore went back to my shop (they are specialized in 7'3s and run a bunch of cup cars for customers) and asked them to get me more bite in the front, within the set-up envelope that they have honed for GT3 and GT3 RS's. Result is a noticeable increase of turn in and turn out oversteer.

I don't have before/after lap times at Bresse, don't like the track so I don't go there often, so my comments are purely qualitative.

Purpose of this thread is to get different viewpoints on the next step so that I can ask the right questions to my shop.

 

Agreed! In terms of security, however, I do believe your current settings are far from being the optimal around, at least for that specific circuit. See the GT3 RS in front of you...

What's more I'm sure you were driving your car with PASM Sport Mode on...terrible combination. All in all this is a marketing button, not an advanced suspension setting. Imagine (and knock on wood) losing your rear-end in any of the dangerous NoS corners, just because the PASM Sport is on and because your shop has copied the Cup Cars' settings to your GT3.

Allow me to speak particularly for myself but as many others here I always repeat the same mistake in believing that my GT3 is next-to-kin to the Cup Cars just because of bearing some visual resemblance. I doubt! The knowledge accumulated from Cup Car races is extremely difficult to have it transferred in our routine track-attacks via some generic set-ups. Those machines are being tweaked in as many parameters as possible not only to meet each pilot's requirements but to also reflect each specific circuit constraints, be it in weight distribution, struts, or spring rates, tire pressure, high speed compression, rebound, to mention only a few of them.

I don't take pride in being the best suspension/geometry advisor, what I would suggest anyone newbie in this field is going back to their OEM settings before starting all over again with it. Provided your driving skills have gone to a certain extreme, see if you can afford or being interested in a set of adjustable suspension, such as Intrax, Bilstein or KW. Sooner or later you'll have mastered the essential combinations affecting the driving performance of your car and most important how to affect this in just a few clicks.

My $0.02 anyway. Wish we could live closer as to be able to carry such interesting experiments together. When do you plan on visiting NoS?

 

Thanks for sharing the opinion.
As a clarification, the shop I work with runs a bunch of Cup cars and also a bunch of GT3s and RSs for the same pool of customers. I did not say they apply Cup settings to GT3s. They seem experienced and competent. I however like to gather different opinions and experiences, I find that really valuable.
I don't think it's gone all wrong and I need to go back to OEM settings and drive height (I bought my car in the US), I wanted a sharper front and they gave it to me, now I need to settle the rear in.

To your question: yes, I am running with PASM sport and DSC off. I am getting a bit too much diagonal body movements in PASM normal. You may be right that the OEM dampers have their limits, but I don't think I am anywhere close to running out of improvement, neither in the set-up of the car, furtherless in honing my skills.
My next day at the Nordschleife is Mon 22nd with Manthey.

Any reason you run more camber on the front right ?

 

What is your rear sway bar setting? If you have not tried full soft, I would suggest that you give it a try.

Also, I agree very strongly with the rear toe. Close to 30 total toe is preferable. If you can imagine what the car does when the rear takes a set, anything less than the 30 total toe will give you some rear geometry movement that is not ideal for anything less than drifting.

What tires are you running? With the typical DOT R tire, anything more than 38lbs in the rear hot will likely make your rear slide more than necessary.

As for preferences, have you tried closer to -3.0 camber in the front and about -2.3 to -2.4 in the rear?

Lastly, you may want to try more rear wing as well.

 

You might also want to swap the rear bar for the GT2 part and set it 1 or 2
off of "full" stiff.

I am really having a hard time balancing your remarks about the competence
of the place you had the alignment done and the resulting drivability of their
work on your car ...

good luck ... Nordschleife is not a track you want to do alignment testing
on!

 

Sorry for the typo in my earlier post. Rear toe should be 16 minutes per side, total 32 minutes. I have tried reducing rear toe-in and my car was unstable under hard braking.

Normally the 997 GT3 understeers and we all work to dial it out. I also wonder about your tires. If they are the OEM Pirelli or 19 inch Sport Cups, hot pressures should be around 34lbs Front, 36-38 lbs rear.

On the tracks I have used, Sport PASM is superior to the normal mode as long as the track is dry and smooth. Bumpy tracks or rain call for the softer setting.

Regards,

 

Again, thanks for all for your comments.
Checked again the rear sway bar, it's on full soft, the 3rd hole, nearest to the bar pivots.
How does the GT2 sway bar differ ?

@Larry: maybe I did not explain myself clearly. They gave me what I asked for, just slightly too much of it. Check the vid, it will give you an idea. I am not running the full track set-up they recommend. I asked specifically to start from a clean sheet and go through progressive changes. Maybe I am dead wrong, but not knowing what to expect, I did not want to find myself with a car I would not recognize anymore. The irony is that the balance has changed a lot more than I was expecting.

@Bob: OEM Pirelli Corsa System. I have been trying to keep hot pressures around 35 at the rear.

@sasportas: running Corsa Systems, have to have rain-capable tires for the Ring. Have not fiddled with the wing, does that have any noticeable effect other than paddock smirks ?

 

You have a lot of rear toe. the conversion is a little over 2:1 deg:mm, you need 4 mm or 8 ish deg per side. explains your tire wear.

Your front caster is amazingly high you must have incredible straight line stability but the turning radius of a battle ship. I had that on my car and coudn't turn around without lighting up the rear tires.

I must qualify my posts, I'm not an expert as bob on the 997's as they have a different front geometry, but the physics is the same on all cars.

 

the cup I raced had 4 deg of camber and 1mm tow out in front and 1mm per side toe in in the rear. I had to dial out the oversteer with the sways. but they have blade style sways unlike ours and a brake bias controler so you can vary the braking stability unlike us.