Factory Suspension. How to correct slight understeer?

Well I have had my 2000 996 for a few weeks now. The only things I have changed are the tires. R-Compund and some clear corners. Well I love the way this car handles, much better than my old G35 sport coupe. Anyway like a lot of cars when pushed to the limit there is some understeer. I am wondering what is the simplest easiest way to remedy this condition? I think maybe a beefier rear adj sway bar would do the trick. What is your experience and what do you recommend? Where can I get a rear sway bar anyway? If there was one item less than 500 that would make you faster on the track what would it be?

Suspension Tuning Cheers,

I was wondering if simply increasing the amount of negative camber in the front (make it equal to the rear) would clear it up well enough for street driving...

I'd recommend either the rear, or front and rear, swaybars from the M030 sport suspension package. I did the rear bar first while I was waiting to have my ROW kit installed, and the difference in handling was really significant. It made the car much more balanced. Installing the front bar will bring back a touch more understeer, but it's "balanced" the way the factory wants it.

Every car has its suspension design flaws from the factory to err on the side of safe understeer. The rear is too soft on this car. My '01 996 Cab and current '02 Coupe have the same nasty habit of getting all bobbly when a high speed bump is contacted while turning. It is actually kind of scary and my ex-'01 996 TT did not have this issue, nor the factory standard suspension. My solution was pretty simple and cost effective. The culprit is the standard rear shocks which are 26 and 36% softer in rebound than US M030 and RoW M030, respectively. Albeit, both springs are also 28% stiffer than stock; so technically the shocks are supposed to be well matched to too soft rear springs. M030 rear springs ($90), Bilstein Sports which are the same as X74 specs in rebound and compression (approx. $400), M030 rear bump stops which add progression into the rear linear spring rate at full compression (approx. $80), and lastly the M030 rear anti sway bar only which is 24% stiffer than stock. By leaving the front bar stock, it gives another 10% in stiffness biased to make the car oversteer to neutral. With stock 18"s, I lost under 10mm in rear ride height which means no need for engine safety pan while biasing the ride height towards a little more oversteer if you drop the front below stock. I threw on M030 fronts on the stock shocks to drop the front down almost an inch. The car is now perfect for my road only 996. With the rear weight bias of the vehicle's design, it begs for more dampening and increased spring stiffness in the rear. The bars should be used for fine tuning only, IMHO. I also left my stock alignment alone to add a hair more neg camber. Not bad for under $1K to fix the factory design with mostly factory upgrade parts. Hope this helps.

Is this going to be a track car? How much are you planning on tracking it vs. street driving?

Instruction?

Oversteer you need a front sway bar, understeer you need a rear sway bar. Your goal is to help change these. For a street car this will do fine. For a full race car you want it to be dialed with corner balancing using adj control arms for camber and toe as well as front camber plates. I would go with our Sway links front and rear and then H&R sway bars like I run.... I can give you the best advice via phone as I daily drive and track mine...

Well it's my daily driver, but I'd like to go to some DE events. Just trying to get an idea of what is the best and most economical way to get the car to handle even better. I am on a budget unlike most porsche guys so keep that in mind. So PSS9s are out of the question.

I am thinking of lowering my car but purely for cosmetic reasons, so I wan to do so at relatively low cost. I may track it twice a year (haven't yet) so not looking for more control/stability (yet). Do you have any pics of your car you could post so I could see the height difference? Before and after would be even better. Thanks

Fred C4S's "suspension tuning" implies that worn down front tires reduce understeer and worn rears increase understeer...now that sounds counter-intuitive, unless they are talking about R-cmpnds. shaven vs. unshaven. CAN SOMEONE PLEASE EXPLAIN THIS, it's really bugging me.

Jeeva, Why not call Steve Weiner at Rennsports, the site I listed, and ask him. He is always helpful when I have called. Or you could find one of his many posts on RL and PM him. Cheers,

I'm going to guess that by worn down he means about 50% worn, not "worn out". I'm also going to guess that most tires give maximum grip as the tread blocks wear down, owing to the fact that the tread blocks at their lower height flex less and that results in less tire squirm. This doesn't take into account the effect heat cycling has on street tires, though. This is why shaved street tires will perform better than new off-the-shelf street tires of the same brand and model. My experience in World Challenge Touring, where we were racing on Toyo T1-S shaved street tires, was that the car was fastest on the first 2 or 3 runs, and pretty much heat cycled out before the tire was even close to being worn out. But street tires usually are not subjected to the stringent requirements of racing. As far as the original poster is concerned, I'd echo the sentiment that track time and instruction are the cheapest way to go faster. But that won't reduce understeer, so for that go with GT3 adjustable sway bars, front AND rear, and then adjust them and tire pressures to dial out understeer. Worked great on my car!

I have a before and when i can get my digital camera back from a friend I will post an after.

SRL, thanks for that explanation...I was thinking in similar lines as well....Hey! but interested in your comments about the Toyo street tires heat cycling it self to waste before the tread wears down. Now, does it become rock solid then, and how do you tell, is there a tremendous loss in grip or by feel ???, and I would guess the initial heat cycling and rest cure for 24-48 hrs. on R-compounds would eliminate it. Sorry for hijacking this thread...but, fo9r the initial question, to reduce understeer I am planning to install wider and taller tires in the front, and narrower and shorter tire in the back.

There was a loss of grip in general. It wasn't tremendous. But remember, we were measuring the tire's performance in terms of tenths of seconds. An initial heat cycle will help longevity, but not eliminate a tire's tendency to lose grip with additional heat cycles. We didn't initially heat cycle the Toyos because we didn't want that additional heat cycle in them. Qualifying was their initial "heat cycle". Tire strategy was: brand new shaved set for qualifying, then put aside for the race (rules required same tires used for qualifying be used for the race). 2nd heat cycle was the race, then last 1 or 2 heat cycles was the practice sessions for the next race weekend, then the tires were thrown out, even though they looked fine. Typically from last practice to new tires for qualifying, you could pick up 1-2 seconds just from the new tires.

To give advice on how to get rid of understeer, don't you really have to know under what conditions it's happening? i.e. into a corner under braking, after the apex under acceleration, on a sweeper at neutral throttle. The answer to correcting the problem is very different in each case.

Jim,B, Oh, I hate to do this....but I think it will help Bowman too.. How about for after apex and under acceleration (I know it's mostly inevitable, But...), I'll be curious to know the answer for a sweeper at neutral throttle, mine does'nt do it, but I could'nt dive in like a car with JRZ suspension, he was diving in in the middle of tracking out to pass a car, and I have barely enogh track to track out.

That's why I asked way earlier in the thread if it was for a track car or a street car. You're right when it comes to fine tuning, but for overall "balance" and eliminating the "type" of understeer these cars get from the factory, I don't think you have to analyze it that heavily. The GT3 bars on my car GREATLY reduced the natural tendncy for my car to understeer, in pretty much all of those scenarios you mentioned. Optimizing the suspension for max. performance in EACH of them would be a whole different thing altogether, requiring much more adjustability than he sounds willing to pay for.

So what settings did you put the GT3 Sway bars on? Are they adjustable. I was thinking Stiff in the back and Med in the front so that I have barely any understeer. I mean I don't want to exit any track back end first. December 1st there is a track day at Laguna Seca. Long way off but I want to get a couple track days in before. I'll probably get the H&R rear sway.

SLR, I agree with you. I just think that these threads lack a good dialog on what's happening that causes a car to understeer or oversteer. If you don't understand that, which I know you do, how can you understand and make good choices on how to fix the problem. It just doesn't seem to be enough to say "slap on a xxx" and everything will be fine. Does that make any sense? Jeeva, The short answer is that while accelerating after the apex your understeer is likely caused by weight shifting back. Sway bars don't help as much here. You need to reduce the shift. You can do that by reducing lift in the front or reducing squat in the rear. If you have adjustable dampers, you can tighten up rebound in the front or compression in the back, or both. Any sport suspension helps just by reducing the movement of weight around the car. With stock suspension you just need to be aware of what the car is doing and adjust your right foot accordingly. Just my 2 cents worth. Jim

Yah know, I was looking for a fairly inexpensive way to improve the cars hanling characteristics on an otherwise stock car. Just forget it Jeez. And if you don't like my "Dialogue" then don't read it. I certainly don't need you making me feel stupid.

bowmanm98, I don't think anyone was trying to insult you. It's just that it helps to understand where in the corner you are experiencing understeer in order to provide a solution. If you read Jim's answer to Jeeva you can see how increased data helps. It'd be a shame to pass up on some of the knowledge that's available here from people that really know these cars. -KJ

Man, Calm down, they are spending their valuable time trying to help you.....what's so bad about a dialogue ?, do you just want to go blindly without knowing the reasons, no one is making you feel stupid here,...they are just trying to help you. I did'nt see KJ's answer, well said.

Sorry about getting a little defensive. I do appreciate the help. Well like most cars that I have experienced with front engine and rear drive you can usually mash the throttle and the back end will come around. But this car is totally different to me. When I mash the throttle it seems to almost pick the front end up and understeer. I also know that if I am carrying too much speed into a turn and I am on the brakes it's on rails. I basically understand the dynamics of what's going on. I know I need more experience but that is the whole point of this forum for me. It's to ask the people who have already gone through this learning curve what they would do first. I mean there are thousands of 2000-2001 996s out there so I basically asking where to start on a stock 996. How about I simplify the question? I am asking for your opinion, obviously there are a million variables. You have a stock 2000 996 and someone gave you $1000 to improve the suspension, what would you select and why?

Jim, you and I are 100% on the same page. Bowman, you're taking some of the comments the wrong way. Jim's questions were totally applicable. Remember that you're asking questions here that for the most part are answered with opinions. Opinions tempered by personal experience. So if you're looking for the "be all and end all of all answers", this is not a great place to find it, especially with regard to questions that have much to do with driving style and balance preferences. In other words, you may take a setup I and Jim are perfectly comfortable with on track and hate it! So in that case no answer we could give would be applicable to you. As far as your question goes, the GT3 bars have (if my muddled brain remembers correctly) 5 adjustment holes in the front and 3 in the rear per side (I may have that backwards). Anyway, mine is set up midway front and rear and understeers ever so slightly close to the limit. I do have H&R coilovers, though, so your mileage may vary.

Great comment. Bars are not going to help if that's where your problem is. The only cure is to stiffen the rear (springs/shocks) to eliminate the weight transfer rearward under acceleration (just like Jim said above) to keep more grip on the front tires. Unfortunately, if someone DID give you $1,000 to improve the suspension, they'd have to give you about another $1,500 more to cure that problem. Sway bars won't do it.

Jeeva, you're not going to significantly change the height of the front tires in relation to the rears, are you? If so, you're going to have to be sure you're not causing headaches for teh AWD system. Typically they are very sensitive to differences in front-to-rear rollout.

My feeling is that messing with tire sizes to control overall handling balance is an excersise in futility. I mean, what if you're not happy? Keep buying new tires until you are? What about the effects tire wear has on the balance? Go through 3 sets of tires and you could have had a coilover/bar setup with some good adjustability. Adjustability is King.

Yea, all those things the other guys said. Bow, I certainly didn't intent to come off as an ***. That's not what this board is about. My comments were more on the general topic than on your question. Understeer is a big topic on the 996 board. I think we could all benefit from a discussion on 996 suspension dynamics and I'm just enough of a geek that I find this stuff to be very interesting. Anyway, welcome to the board. I assume you'll find us all facinating and become a member very soon. BTW, I have 1300 lb springs over Motons on back and if I mash the throttle my car will push like a pig. I think changing that includes buying a vette. Jim

i had a '00 c2 996. out-of-the-box, the US, non-m030 spec car understeers in just about all conditions. you can try to drive around the problem--play with tire pressures, aligment, etc--but you're leaving a lot of potential on the table. an easy fix is to step up to the row m030. andial has them for under $1,200, it's factory, can be installed by anyone, and makes the car more driveable. imo, unless you really know what you're doing and willing to spend lots of time under the car, then adjustable bars, shocks, springs, etc, are not necessary. a step up from the row m030 is the x74 for about $2k from carnewal. re excessive understeer, the factory alignment spec coupled with the US spec suspension is to blame.

Here's my plan FWIW: I haven't decided between ROW M030 and X74, but the front and rear sway bars are the same (I think). Those seem to be available for about $200 plus shipping. I'm going to install the sways, see how the car acts, and then I still have the option to choose either factory suspension route.

the shocks and springs separately cost way more than the whole kit. like double. beware...

Save yourself another hundred bucks. Install only the rear bar first. If it is too drastic, then buy the front bar to counterbalance it by about 10% more than the stock front bar. Rear bar # 996.333.701.13

-- as noted earlier in the thread, I drove my car with only the rear sport bar (otherwise stock non-sport suspension) for several hundred miles and it worked great. It fit my needs well enough that I contemplated never installing the rest of the ROW M030 kit...

stiles & SRL, Thanks to the extensive rennlist archive I am aware of AWD?PSM problems associated with changing tire dimensions. I should'nt say I am tweeking car dynamics by changing tires, as SRL explained it would certainly be futile. I know my tires need replacement, and I know my car understeers a bit, so when I purschase my next tires, and if i decide them to be Toyo RA-1's, I'll go with the 275's instead of the stock 295 which toyo does'nt make. I've already spoken to a guy who uses them on 996 C4S, and he is very happy with them. But, now it looks like the p-zero corsa "system" is not that much more expensive than the Toyo's, and I just may go with those and stay with the stock sizes. As Jim.B said, a plan to fix understeering on acceleration should include purchasing a vette Edit: So, my plans for fixing the understeer on acceleration for now and keeping the car stock, (thanks to Jim,B) is trying to rotate the car before hitting the apex.

Now you're talking Jeeva. Forget this slow in, fast out crap. Turn in early, trailbraking on the edge of disaster, this will get your back end moving. When you're pointed in the right direction, hard on the throttle. Your back end will settle and you're off to the races. Fast in, fast out and it works just fine with a little bit of understeer. Jim Disclaimer: the above should only be done by experienced drivers and only on a closed circuit race track. I accept no responsibility for the massive carnage that will result from minor miscalculations.

A cool link for a generalized overview of suspension tuning. Kraus Corrections Overview

when i first got my 996, it really did not hold it's intended line very well--especially on fast sweepers when the suspension was loaded. the front end would bounce and send the car off line if there were any mionr undulations or bumps. it caused one to back out of the gas to avoid bigger problems . i remember thinking "this can't be right! this car handles like ****" i found the stock shocks to be under damped and the springs too soft. changing bars helps the balance but you'll still get ocillation problems at speed. i'd do everything at once, you'll end up doing it anyhow.

Rob, My C4S comes with the "sport" turbo suspension and is lower, from what I hear it's heck of a lot better than the standard C2 in understeer, and the traction transfer to the front with AWD minimizes the acceleration understeer, so that's why I can just change the driving style a bit. The C2 guy's may certainly need hardware changes. Jeeva