Sanjeevan

From the pages of High Performance Handling Handbook by Don Alexander (I highly recommend this book),..

"There are situations where increasing the stiffness of an antroll bar will have the opposite effect. Most stock vehicles have excessive understeer because it is easier to control and provides more stability for the average driver than a vehicle that oversteers. A big part of this comes from excessive body roll, which induces too much camber change, and a good portion of the front tire contact patches loses contact with the road.
In this instance, adding a stiffer front antroll bar, which would typically increase the extreme understeer, actually reduces the understeer by reducing the body roll-induced camber change. The front tires now stay in better contact with the road surface, creating more traction and reducing understeer."

How about that,...I am using p-zero corsas in my 996C4S, which can use more front negative camber and understeers, I don't want to use camber plates or chang my suspension, how about a stiffer fron antiroll bar, will this reduce understeer and minimize the need for more aggressive camber change.
Thanks
Jeeva

Steve Weiner-Rennsport Systems

Jeeva:

Increasing front swaybar size on your C4S will INCREASE, not decrease understeer,....

If you want to increase grip at the front end, stiffen the rear of the car by either increasing rear swaybar size, installing an adjustable one, or increasing rear spring rates.

You can look at http://www.rennsportsystems.com/1-e.html as that handling chart applies very nicely to your AWD car.

Sanjeevan

Steve, yeah, that's what I have known about swaybars, was curious to read otherwise in this book,...may be it applies only to family sedans with huge body roll.

So it sounds like short of messing with the springs sway bars will be the way to go, but stiffening the rear will help with the understeer, but how about the front tires wearing on the outside with a lack of camber. Could there be an adjustable sway bar for the front and rear, stiffen up the front a bit and stiffen the rear more..will this eliminate the understeer and the need for front -ve camber.
Thanks
Jeeva

Sanjeevan

O.K, the reason I am going through this exercise is similar to Paltings,....even my instructors have mentioned how well balanced my car is, Walter Rohrl said the same thing when he was testing the C4S. So, I really don't want to change the suspension. When using R-compounds the front outside heats up more, which tells me there is inadequate camber (with the corsas it's livable, but i'd like to change it, if one it's cheap and two does'nt affect any other part of the car's handling).

Camber plates are an option,..but it's more expensive, some say not an ideal way to approach camber change, and does nothing for the oversteer problem or body roll issues.

The alternate route which I am pondering at this stage is the roll bar. I NEED SOME HELP FROM YOU GUY'S ON THIS ISSUE.

Again from Don Alexanders book, " Camber gain is caused by suspension geometry changes caused by body roll,........most suspension gain positive camber during bump (compression) travel, and the outside tire goes into compression....stiffer front springs and antiroll bar reduce body roll, which reduce bump travel and camber gain. This reduces the amount of static negative camber needed.....

So, it appears to me by stiffening the front antiroll bar one can reduce the need for more negative camber in the front, but this will worsen the understeer (which is certainly livable at this point). I was hoping it would not worsen understeer, and thus the reason for my initial quote from the book, but it seems like it will worsen it for my C4S.

So, what are the options,...the springs will stiffen pitch and roll, and the car is quite stable in acceleration and braking, so it's the roll that's the issue and not pitch. So, could tuning front and rear antiroll bars solve both issues ( camber and understeer).

How about front and rear gt3 adjustable sway bars ,....stiffer bars stiffen all ends, so going to stiffer bars all around with the same ratio of stiffeness for each wheel will keep the weight distribution the same but will minimize body roll, which will cure the camber issue (not the understeer, as the weight distribution is still the same). After which I will adjust the rear for higher stiffness which will transfer more weight to the rear and cure the understeer problem. So, in theory this should solve bothe issues,...do I have this right, or am I wrong with my thought process.
Thanks
Jeeva

swftiii

Jeeva,

What is your current setup - that would help us to understand the situation more. Are you on stock suspension or a lowered and adjustable suspension? Stock sways or aftermarket ones?

I have PSS9s w/ RS Sway bars and Steve helped me with the setup to minimize the understeer and I have found the setup really nice. I have understeer in the slower corners, but it seems to be an even feel in the higher speed corners. I like it this way and the car handles really nicely. My settings are full stiff for the PSS9s and the sway bar in the rear and then middle stiffness for the sway bar up front and a setting of 2-3 for the front PSS9s (1 being full stiff).

-Skip

Sanjeevan

I have a stock setup,...turbo suspension with non-adjustable X73 sway bars. Camber is maximized at both ends, I am hoping to replace the stock X73 sways for gt3 adjustable sways, only if it can help me, primarily to be able to get away with the current front camber -0.3 (which Don Alexanders book says I should be able to), and secondarily tune the understeer out.
Thanks
Jeeva

JimB

Jeeva,
Adding adjustable sway bars at both ends will allow you to dial in understeer or oversteer but I don't think it will help your camber problem much. As you know, one of the big problems with the 996 is that at US ride height you can only get about -.5 degree of camber in front. That's just not enough. My car is 400 lbs lighter, has GT3 sways and much stiffer springs and I still need -3 degrees of camber to get even temps and even wear in my front tires.

I really doubt that you will be able to even out your tire wear at the track without adding camber. I could be wrong.
Jim

Sanjeevan

Jim, B....thanks for that info....400lbs lighter with the bars and -3 camber is way better than my current setup,....So, I think the only reason the corsas are O.K is it's the kindest of the R's for lack of camber and my speed . So, I am hoping whether the gt3 sways on their own will at least improve my situation a bit. I am not ready for a suspension change yet. (I've got a few questions for you on lightning your car and still be in stock class, and why you are selling the motons, I'll p.m you later)
Thanks
Jeeva

kary993

Yes, I agree with this, you need more camber if you want to have even wear across your tires. Sway bars will not change the camber issue, though they will help reduce some rolling over but you will not overcome the your lack of camber.

Be careful not to try and tune your car with sway bars as bars are only one part of the equation!

Sanjeevan

Well, I've heard of this need for more camber many times,...but WHY?...the tires will wear even and will have uniform temp. across if the contact patch is even,...obviously during cornering it's not even, with zero static negative camber, the weight on the outer tires will cause the camber to be more positive through a corner and thus wear the outsides more,...the question is, WHY is it doing this,...if the answer is ONLY because of body roll as Don Alexander says,..you can compenstae for this by either increasing the static negative camber or stiffen the car with springs and rollbar.

But, this is theory,...but with you guy's with real life experience it seems like there is a need for both an aggressive negative camber setup and stiffer sways. So, I really appreciate these inputs, keep it coming...
Thanks Jeeva

Edit: Kary, I hear you about over doing the sways, I certainly don't want to be lifting my inner wheels in the process.

kary993

One area that is not readily noticable nor even understandable until you see it in a picture is when the tire is actually sliding off the wheel rim under heavy cornering. I have 4 degrees of camber in front and 2.75 in the rear. I have adjustable sway bars, and a very stiff shock/spring cup car set up. I run Pirelli slicks which like this much camber and have very little body roll while cornering so body roll is not entering into this equation for me in any large way.

I have a few pictures from various tracks in hard cornering where the rear tire is actually adjusted inward on the wheel at the bottom of the wheel during the cornering. What does this do to your tire? Well, the camber compensates for the tire "bending" under the car making the contact patch flat in that situation. Great grip under heavy cornering because there is maximum contact for the tire to the ground!

In your case, under heavy cornering, your tire is "bending" under the wheel and with little or no negative camber the tire is merely rolling to the outside edge reducing your contact patch. Not an optimal situation to be in when you need the traction the most, under heavy cornering. Though what you were talking about was also body roll which effectively does the same thing, allow the tire to roll under the car because the entire car tilts creating more positive camber. This is why you need to look at the entire issue not just the roll bars, springs play into this as well as sway bars.

This is just one reason why you need more camber .... along with adjustable sway bars, and the correct shocks/springs to optimize handling performance for a car/tire setup. BTW, all tires are different in their set up for a given car so you need to pick a tire and then set up the car for that tire for it to be effective.

Sanjeevan

Kary993,

Thanks a lot for that explanation,..there is a good illustrated explanation of what you are saying in Fred Puhn's book, he talks about the tire rolling under the rim and the outward force acting on the wheels by the bent tire. I am going to read through that again,....but, now I see why roll bars alone cannot entirely solve the issue. It also makes sense why corsas are tolerant to minimal negative camber, they have very stiff sidewalls.
Thanks
Jeeva

RedlineMan

Hey Jeev;

If you went back to the old days, and took any garden variety flivver and put anti roll bars on it, you'd have a revelation. Man... what a difference. Cars have come a ways since then, and in truth, anti roll bars really are only a small part of the overall system when it comes to making a car handle. Putting bigger bars on a modern car is a very incremental change.

In reality, anti roll bars really are relgated to doing little more than offering you the chance to change the front/rear balance of the car. What really controls body roll when you get serious is anti-dive geometry in some cars (which I believe 996 kinematics do in the rear), and for most cars, spring rate. It's really the springs that do the work.

There are two ways you can keep the car from tipping up onto the outside edge of the tires; either more negative camber, or stiffer springs. Both are a compromise, but a combination of both can be found that improves track driving while not ruining street comfort.

Still, to be honest with you, I think guys like you should either buy somebody's track car, or stay on street tires in your new rocket. Street tires not only can take more abuse, but will teach you more about car control than all the fancy suspension stuff. Sparring with my buddy in his bone stock SC on streets this weekend at The Glen reminded me of that again quite clearly! He had more power, but was sufficiently brave in the sweeping turns. I had more grip and could smoke him in the more demanding corners. Back and forth all session long. THAT was driving!

The real problem with performance driving these days is everyone is component driven, but never thinks to maximize the most important component first. The driver.

Sanjeevan

John, But R-compounds are a whole lot of fun though...., it's great passing 996tt's, gt3's and ZO6's with my measly 320hp . Kidding aside, I agree with you when you say street tires are more communicative and more educational,..... I am trying my best to avoid the temptation of any further "component driving", and that's one of the reasons I am staying away from any suspension mods., but the curiosity of R's got the best of me. But, I have to say, I am trying my darn best to ward off these demons that's constantly conjuring up various projects in my mind. Anyone know of a cure for this.

JCP911S

Suspension is a complex system where all the pieces have to work together... springs, geometry, tire construction, weight... on and on... huge number of variable. Just changing one piece is likely to do as much harm as good.

Where the "rubber meets the road" so to speak is how the car handles at the limit. A change that makes the car feel responsive at street speeds can make it twitchy and dangerous at full race speeds... conversely a car that is sweet at the limit can be a PIA to drive on the street.

Define the performance window and put the entire package together that is optimum for that application.