Fissionx

I just put on a gt3 suspension and aligned the car and it understeers a lot, much more than the ROW M030 I drove which was a perfect balance IMO. I can enter a turn off power and the car will still understeer. The second I get back on the gas i lose even more front end grip. I wanted to post my set-up and get some input as to what the problem might be...

GT3 suspension, stock (C2) bars with adjustable links
Stock GT3 ride height
Front:
-2.5degs camber
7.8degs caster
0.05degs toe in (i requested 0 but gave me a little in for even wear)

Rear:
-2.0degs camber
0.18degs toe in

Tires are 225/285 Pirelli PZero nero N4

This understeers worse than my us spec suspension, although I had 245/295 tires.

chsu74

What hole are you on the sways? That makes a difference. I went from a 245 fron to a 235 front and noticed understeer right away. You may have two factors that is contributing to your understeering problem. PM LVDell and he should be able to help you with the setup.

himself

The original post says "stock (C2) bars." Sounds like he is using stock sways, and not GT3 bars. I think if you upgraded the rear sway to a GT3 and ran it a bit stiffer, you could overcome the 225 front tires.

-td

Bob Rouleau

I assume the adjustable links mean you can alter the sway bar settings. What are they now? In any case to reduce understeer, soften the front bar, i.e. use a lower hole on the link (closer to the ground) and a higher hole on the rear bar. Ideally get yourself some GT3 sways and set the front in the middle and the rear one hole from full stiff.

A little more caster will also help reduce understeer, you want about 8 degrees, maybe a little more like 8.2. Use shims in the lower A arm to increase the caster and readjust the camber to neg 2.5

In the rear you can use 2.4 degrees negative camber for the ideal set up.

Best,

best,

AudiOn19s

Def. wierd. Wonder if it's more tires than anything. You still got the old set you could mount back up to compare?

Even with the stock bars you went from ~180F / 200 R springs to 228 F / 543 R springs which should have alone helped the car understeer less. Then add in the fact that you've got adequate camber at the front now and the car should be good to go.

Question....is this all on the street or also observed at the track?

Fissionx

I just aligned the car yesterday, haven't put it on track yet. On the stock suspension (and larger front tire) the balance was pretty good, but I wanted faster weight transfer, less body roll, lower CG / better aero, and higher limits which is why I went with the GT3.
I think the tires might have a fair amount to do with it, but wanted more input. GT3 sway bars will be my next upgrade, hopefully that will clear this up.
Should I toe the car out in the front? This worked well on the M3 to dial out understeer. I am thinking maybe drop the camber by 0.5degs front and rear and add a bit of toe out? I may just leave the car as is, until I get gt3 bars and see where it's at then.

My gt3 coilovers are using the 993.xxx front spring, which are said might be softer. Im wondering if the valving is too stiff for these softer springs. The understeer is more noticeable in slow corners, where there is faster weight transfer.

jyoteen

These are my settings as of 2 weeks ago. I have stock sways (well, widebody) but not as much understeer as there used to be. Although, I need more camber, but this is as good as it gets without going w/ other goodies.

AudiOn19s

Dan. You may want to try a little less camber for the street...and if you intend on tracking the car on street tires at first. Again our spring rates are different but I found -2.0 about right all around on street tires.

I get more understeer than I'd like on my street setup because I know I'm running too much camber all the time due to me leaving the car setup for r-compounds and track use. It's a tradeoff I'm willing to accept.

Fissionx

Cool, I guess i'll go get a new alignment.
-2.0front and -1.8rear camber
Any input on what toe values to run? I would like to run a hair out on the front

Andy, have you noticed bump steer issues with such a low ride height on stock wheel carriers? The front toe links had some angle to it, maybe 10-15 degs with the car on the ground. The toe link mounts higher on the C2 than the gt3, who all complain about bump steer.

Also, the car feels rather twitchy, not nearly as smooth in transitions as my M3. I'm wondering if this is just bump steer or something else. Do people upgrade suspension bushings on these cars? The rear trailing arm bushings and front control arm bushings are pretty common to stiffen up on the M3.

AudiOn19s

Yes. There's bumpsteer in my car...it's not horrible but it's there. I've got a set of bumpsteer adjustable toe arms for the rear that will go on this winter, still not sure if it's worth it to do the fronts yet or not.

I run 0 toe in the front for the street. I had .10 degrees per side of toe OUT for the track this season and drove the car with that toe and -3.1 degrees of camber on the street for a few weeks and the car tramline'd (sp?) like crazy. It would follow every little variation in the pavement but the steering input was crazy quick. Just not the way I like it for the street. I actually just had my car re-alligned today as I'm done with the track for the rear and I"m running -2.5 degrees at the front with 0 toe and even that small change made a world of difference in the way the car drives. It actually sticks better at the front with that setup on the street tires. At my current height and with the GT3 monoballs rotated in the position they're in -2.5 is the minimum value I can get for camber. I didn't bother rotating them again because I was too lazy to take everything apart when I'm just going to go back to where they are in the spring.

I run .25 degrees per side of toe in the rear. That combined with the stiff springs / bar keep the bump steer at the rear of the car to a minimum.

Andy

LVDell

Not sure why you haven't taken my advice on this yet as we have talked several times offline. To keep on guessing is just throwing money away and will NEVER get you what you are looking for. Why in the world do you have toe IN for the front? If anything it should be neutral. That right there will contribute to increased understeer. Think about what the direction of the wheel is at turn in??? And toe OUT is not the answer for street unless you want the car to be a handful of a nervous front end. Heck, I don't even run toe OUT up front on the track. It will do NOTHING for you other than INITIAL turn in which can easily be modulated through proper trailbraking.

You need to decide if you want a street or track alignment and then you need to get a PROFESSIONAL that knows what they are doing to set it up properly.

Are your springs matched to the shocks or did they just get "picked"?

Also, you need to get adjustable ARB's if you are going to "adjust" your suspension. Having adj drop links does nothing more than allow you to correct the length of the drop length based on preload.

What ride height did you settle on? If you went too low and didn't replace the toe arms with adj toe arms that allow for bump steer adjustment, you are not going to like the result (neither will your car for messing with the geometry).

If you want a good setup guy I have already given you a recco in G'boro. It obvious that the shop in Durham (not sure if you ended up using them) doesn't know what they are doing based on our last conversation.

Trust me, I have spent a TON of money on street and track setups and suspensions with years of experience to pass along. It's up to you if you want to take it or just keep guessing.

Fissionx

Dell, This is an OEM GT3 coilover setup with OEM springs and OEM dampers. I also went with factory ride height (118mm and 128mm front/rear) and factory gt3 alignment, save for maybe the camber. I requested 0 toe up front, but the shop owner suggest a bit in for tire wear Maybe it was wrong of me to agree to that. I was going for a street setup for a GT3 and will be running street tires on the track likely for the remainder of this year.

Brad at Digital Chassis came highly recommended from friends of mine with 996 C2s and GT3s. I am moving to Petaluma, CA in 8 days, and the TRG shop is on the same street as my new home. I assume this will be an adequate track shop.

Dell I do want your advice and value it highly. I don't recall (just looked through PMs) getting the name of your shop in Greensboro.
What are adjustable ARBs? Also, how do the toe arms 'adjust' bump steer? Are they not just longer links to reduce the connection angle? I think GT3 wheel carriers are a better buy at this point since the mounting points will be lower. IMO this is a more ideal solution.

Also, I just got back from driving my friend's GT3 with my car back to back. They behave very similarly, despite the obvious suspension (sways, geometry, etc) differences. It doesn't have as much understeer as my car, but the GT3 (on stock suspension) is definitely not as neutral as the ROW M030 I drove which had 225/265 PS2s.

LVDell

TRG will definitely be able to hook you up.

I don't understand why shops feel the need to do things to a car that you do NOT ask for. Toe in up front on the street is a recipe for disaster adn NOT something that is done primarily for tire wear. The best tire wear would be the result of all neutral settings. When you align a car you are trying to aid in direction change but also trying to have the car at neutral (or close to it) when under load. Toe in would actually accelerate tire wear.

ARB=Anti-Roll Bars (which most called wrongly "sways").

The only way to adjust "some" of the bump steer is with the eccentric location. However the only way (proper) to truly bump steer a car is the have (a) adjustable toe arms; and (b) a shop that knows how to bump steer a car. And no they are not longer lengths. The length adjusts the toe angle (in vs out). The vertical adjustment on the outboard side allows for adjustment and spacers to correct the issue.

Your understeer is more than likely attributable to the toe in up front and the inability to adjust ARB settings.

mglobe

Once the bars are taken care of (or for that matter even now), I wonder if 225's are appropriate for this kind of setup. Maybe a 245/285 stagger might help?

LVDell

He's just fine with the 225/285 setup but Mike, you are correct in that he can dial out some of that understeer with a wider front tire in front. However, the alignment isn't helping. To give a data point, I ran my fastest time at VIR on tires that were 230F 280R and with a proper alignment I had ZERO understeer issues so it's not always best to run a wider tire.