Patangatan

I'm a black group driver running a 2012 997.2 GTS. The car was very balanced with some understeer at 1.0f/0.8r camber, until I recently put on 996 GT3 LCAc. Now the car oversteers heavily and I literally have no rear grip, particularly mid-apex. The rest of the suspension is stock SPASM with Porsche lowering springs; also have LSD.

Specs:

2.5f/2.0r camber
0.05f toe out/0.2r toe in
MPSC 245f/325r, 32f/33r hot (even looser when at 34-36 rear).

Tire temperatures front are even across, in rear the outside is a bit hotter; the car seems to roll over and ride on the outside of one wheel in heavy cornering?

Thinking about going GMG Turbo sway bars.

Thoughts?
Thanks,
-P

Spokane5150

Here is a good article to read:

http://rennsportsystems.com/letstalk...nsion/#Springs

aaks38

Adding more neg camber and more toe out would be the easiest guarantee. Some would say to reduce rear tire pressure or soften the rear suspension to increase grip but they dont necessarily work as well as alignment settings

MagnusB

So how did you change the alignment when adding the LCAs?
What are your current numbers?

Patangatan

I used to have 1.0f/0.8r camber and 0.05 toe out f/0.2 toe in r. So basically the only thing that changes was camber. Front grip is obviously better, but in sections were I would go faster with the rear stable; I now loose grip in the rear? More camber in the back has actually given me less grip!

MagnusB

It just sounds weird. I run 275 front 315 rear and have plenty of rear grip.
With Sway bars you would have to go soft in the back and stiff up front to counter your symptom.
That is kind of counter what you want to do with the weight in the back.
I would go with aaks38's advice, more rear camber and/or less front camber.

MagnusB

It's a balance.
Now you obviously have more grip up front so the camber change works better for you there.
Use a pyrometer to see if you are using tires evenly.
It's not that common to have more camber up front since the weight is in the back.

alexb76

Lower the front negative camber a bit, that's the first that comes to mind. I am actually in the same boat, got the 997 GT3 LCAs and am planning to put them on later, but don't wanna make the car over-steer.

cello

How to fix oversteer? Throttle.....

Seriously, tho, be sure first that it is OS as a result of the car and not the driver.

With your new specs your turn in is crisper. You might now be dailing in too much steering before apex, for example. Opening the wheel a bit might cure/manage it. You also might be carrying in more speed from turn in to mid apex and having to lift off throttle or delay throttle, allowing to car to rotate. Staying very lightly on the throttle or being ready to apply the throttle during roation might cure/manage it.

The ONLY way to truly know what is happening is via data. If you have a data system, post the velocity distance and Lat Gs for a turn where you experience the OS...

Remember, however, "loose" (OS) is 'fast' .. LOL. You can manage it by good throttle technique (and ***** ). Unless you have a lot of seat time in already after the new specs, I would be slow to change the car again and would first let a driver you know/respect take it out and give you a second opinion. You might just need to get to know the set up a bit better; ie more seat time with it...

My car is set to OS and I do roll the sides of the tires (NT01s) a bit ... That is all stock except LCAs and alignment (no aftermarket roll bars).

If you are sure its the car and not 'the nut behind the wheel', or you just want a good data point on settings, PM Mike (mdrums) for advise as he has a .2 GTS and it is pretty sussed out suspension wise... He would know re the sways/settings/sweet spot

utkinpol

your setup is OK from a high level. 0.5 deg split between front and rear is usually normal. it will feel very different from what you had with -1/-0.8 deg camber. you do have now much more front grip, as of rear oversteer it is difficult for me to say, what it is do you feel exactly - is it a normal rotation when you keep feeding in power mid corner or does car now slips out where before you had it under control? with new camber your mid corner speeds had to increase a lot so now you must be working with new dynamics of 9/10th driving compared to what it was with old camber and it is something to get used to.

i would say that oversteer is good, understeer mid corner is much more dangerous. ideally you need to get car to slide in a controlled manner on all 4 contaqct patches when you get close to the limit, as you got gt3 LCAs you do need put on gt3 adjustable sway bars, set them both first to middle holes and try to work on car`s setup. i suspect with much higher cornering force stock small rear sway bar you have does not do any work anymore, you need to beef it up.

mid corner stability requires stiffer sway bars. it is exact opposite compared of corner entry grip where you want to soften a sway bar at that axle to enhance grip at that axle, front or rear.
at mid corner sway bars should be tuned to limit amount of tilt so car`s angle will be optimal for your springs and camber and tires to maintain the maximum possible area for contact patch. then you tune sways a bit to adjust your balance between grip on front/rear axles by using pyrometer and locating where contact patch was on each tire afte ryou do several corners on a hot lap, before tires cooled down on a straight.
corner entry tuning is good for beginners, advanced drivers tune for max mid-corner grip and corner exit stability - means car should be driven flat out after apex and should not to try to fly off track. with such tune it will not turn-in as you used to it anymore, you need to learn to trailbrake to preload front axle, sometimes you will start steering input like you go early apex while car still does not turn yet and you have to be extremely careful with brake to throttle transitions. so, it takes time. it is also, well, may be not as safe as it was with stock setup.

i run -2.8/-2.4 deg camber now, 0.10 toe out front, 0.10 toe rear. i keep rear and front tire pressures equal now, at 34-36psi hot, old tires were 275/335. next season i will try to run on 245/315 nt01 tires, i want to have less grip in rear as i scrub edges of front tires badly on old setup, 335 in rear is a lot and even wide 275 tire in front hardly helps.

to understand what happens with your car now you need to get a pyrometer and after several hot laps go to pit lane, jump out of your car there and quickly check where tire gets hot most. if you do not have a pyrometer you can use a palm of your hand - it is sensitive enough to feel where tire is hotter, to some level, you need to see where contact patch is - that will tell if your setup is right. but your camber as it is should be ok for sport cups. i think you`re just trying to get used to new setup.

again, if you are in black you should know/feel the difference between uncontrollable oversteer slip of rear axle at mid corner and a throttle steering rotation. when you start going close to traction limit at 9/10th you have a very slim margin where it all starts to get very close. again, ideally car should be tuned to slide on both axles at mid corner, that is how i like it. some prefer for rear end to start sliding while front is still solid.

if you still not sure - best is to sign for nearest autocross event, go there and push car very hard until you brake it off into spin, then after you get adjustable gt3 sway bars try to adjust balance by having front bar at mid hole and rear bar at full stiff, try same AX course until you spin out, if you have data logger (there is an app for iPhone also that logs it) you would see actual G forces at moment when car goes into spin and that will help to see how grip changes. good luck. it takes time to get any setup to work and get used to it.

ps. to exclude one more thing - at same AX run or on a skidpad try to run with PASM on and PASM off, check if understeer/oversteer balance changes in any significant way or not - to rule out if your shocks are shot or valving is bad. but one thing for sure - if you got gt3 lcas you need to stiffen up car to reduce amount of tilt in the mid corner. that will also save your tires.

as of GMG bars - may be a good idea, if you still use soft springs. usual rule of thumb is to use stiffer bars with soft springs and to use softer bars with stiffer springs. imho a usual set of stock GT3 bars suncoast sells would work same great for your car and save some $ but GMG bars are good too. I think they have stiffer front bar so if you do oversteer already it may not help much but you can try. i would buy stock gt3 bars, set them to mid holes both, then tried them full stiff both, then tried front mid stiff and rear full stiff and checked with chulk how you change your outer tire edge level of contact as you drive with same/similar pace on your home track. it should tell you a lot of how your car behaves, and use pyrometer too.

if you run with clubs where some folks in cup cars have on-track support or you know such folks who provide on track support - buy them some beer/lunch, get friends and speak to them on how to check on all this.

also, what lowering springs did you put in? eibach, i hope? if you had h&r they are known to sag with time, and if you compress them completely in a corner it may be a different issue.

utkinpol

what tires you run? i mean, what brand?
i had front 275 nt01 and 335 ra1 rear, front 275 tires got really eaten on edges, i was thinking as they were on 9" wide CCW rime those sidewalls were way to overstaggered and tire was moving around way too much so even -2.8 camber was not enough, i was thinking to go with 245/315 setup next season, how did you like 275/315? how is your front tire wear?

MagnusB

CCW 9 and 12. NT01 with 275/30 and 315/35. I really like them and it seems you have to drive them hard.
The only problem I have is the fronts hit the perch a bit when loading hard, after hard breaking and loading up.
I have GT3 sways but not LCAs yet so only 1.1 front camber with this car, by far not enough. LCAs coming.

They do get eaten around the edges. 1st from left is rear, 2nd is front.
Do you mean you can feel the tire move sideways?

utkinpol

i have same problem with edges eaten up, with -2.8 deg camber in front. i suspect it is due to non-optimal width on a 9" wide rim, it should not be that bad, my tires are much more beaten then yours but overall wear on edges is exactly same. i think 275 does not work on a 9" rim, it probably needs at least 10" wide rim after all.

i can tell for sure comapred to A6 hoosiers or 245 RA1 tire those 275 nt01 on front do have more of a 'wobbly' feel, not such a crisp response that i used to, but they do have a ton of grip mid-corner. problem i had was that i could not get car to turn and it did result in eaten up edges, so i suspected sidewalls were moving around too much so tire was not working. my rain set is 235/275 z1 star specs on 8"/10" rims and even those tires feel much more precise at turn in, so, i want to try something different. ideal sizing for 9/12 would probably be 255/315 but i hope may be 245 tire will work better than 275, not sure. 18" tires do not really have many options...

Patangatan

Throttle does help. I don't mind skidding and sliding for fun, but I also want to improve track times... I have two instructors drive the car after the change and they too were very surprised about the lack of grip. With much smoother throttle and smoother wheel motion, it's still looser than before.

I think the recommendations thus far make sense; slightly more camber in the back and stiffer bars with front set a bit stiff to reduce OS.

Thanks!

Patangatan

Thanks for all the great tips; I think a pyrometer will be necessary to 'fix' this setup...