With stock suspension and as much negative camber as one can squeek out (-0.6 F and -1 R for me) if I were to get a GT3 sway bar do i just add a front or must one add a rear bar at the same time? Also what settings should one start out with?

Is this a reasonable mod at this time or should one be looking at springs/shocks or coilovers first?

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AFRIDI
Cayman S 2007

I would strongly recommend only doing the sway bars as a matched set. Any bar that works with the stock bar at the other end is basically the same as the stock bar, and thus a waste of money. Any bar that is worth installing is going to be far enough from stock that it will really mess up your handling if you don't put a matching bar at the other end.

Just my personal opinion, but if you're looking for a bang-for-the-buck suspension upgrade, and don't want to do something else at the same time (like lower the car), then sway bars are a very good place to start.

I have the TPC bars in my CS, and really like them. The only drawback to them is that you'll either have to replace the front sway bar links with TPC's link kit or shorten the stock links (like I did, I turned mine into turnbuckles). Another option that people have spoken highly about is a GT3 bar in the front with a Tarret Engineering bar in the back.

The conventional wisdom about front/rear swaybar balance makes no sense at all to me. I am not a skilled driver, and I may be so far out in left field here that I'm not even in the game. But I do know a bit about Mechanical Engineering and dynamics...

Compared to the stiffness of the suspension, the Cayman's unibody chassis is essentially rigid. Not perfectly rigid, but so much stiffer than the suspension that we can regard it as rigid for the purposes of this discussion. So, if the body is so much stiffer than the suspension that it is essentially rigid, then it shouldn't matter where the anti-roll stiffness is added - at the front or the rear. You should be able to add a given amount of anti-roll stiffness to either the front or the rear without it making any difference at all. It's simply not possible to have body roll at the rear only, or at the front only. Body roll is body roll - it's the same everwhere. So why would it matter where I grabbed the body and added anti-roll stiffness????

I'd love to see a carefully controlled experiment to test this idea.

It's not so much the amount of body roll, it's how that body roll gets transmitted to the tires.

Basically, the only thing that makes a car turn is the traction of the tires. The amount of traction a tire has is dependent on how much weight/load is on that tire. If you take a well-balanced car and increase the roll stiffness at each end by the same percentage, say 50%, you will have decreased body roll but kept the same percentage of dynamic corning load on the tires.

However, if you were to take that same car and increase the front roll stiffness by, say, 75% and the rear roll stiffness by 25%, then the body roll may be reduced by the same amount as above, but the front outside wheel will receive a significantly higher amount of dynamic weight transfer than the rear outside wheel, affecting the amount of traction at each end, and thus affecting the car's drivability.

So, if you take a well-balance car and change only one sway bar, you can really hurt the vehicle's drivability. That's why I recommended always changing the sway bars in matched sets. However, "matched" does not necessarily mean "same rate" -- the appropriate bar rates depend on many factors, such as suspension spring rates, tires, vehicle weight distribution, etc. Because of the complexity of all the factors involved, a vehicle engineer can calculate a rough idea of where to start testing, but testing is usually required to find the best sway bar rates. That's also why most aftermarket sway bars are adjustable -- the desired front-rear balance can change with track conditions, tires, weather, etc.

Sway bars (more technically, anti-sway bars), are essentially transverse springs. They act by transferring spring force from the inside side of the car to the outside side, thus effectively increasing the spring rate of the outside spring (while simultaneously decreasing the inside spring's rate). Basically, sway bars increase a car's roll stiffness without affecting its up-and-down stiffness -- an infinitely stiff sway bar will have the same effect as an infinitely stiff suspension spring, but only in the roll axis.

So GT3 front sway bars plus tarret rears would be a good combo. If one goes that rout does one start at the softest settings for both, middle settings or some other starting point?

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AFRIDI
Cayman S 2007

OK - I see now. It's about how the anti-roll forces get shared by the tires - it's all about the loads on the tires. Thanks!

I am still not clear how they work. The bar connects two suspension together, so when the car rolls, the bar should just roll with it with the same angle. So how does it counter the roll?

When you hit a bump straight on you compress then rebound left and right suspension at the same time.
Sway bar swings in it's bushings with no effect.

When the car rolls right (left turn) the right side compresses the left side droops.
Which twists the sway bar and increases spring rate on the right, decreases on the left.

I am not too familiar with what it means by spring rate being high or low. High meaning stiff? And stiff meaning less bounce? So the bar stops the left spring from drooping as much? And the left wheel stays on the ground more?

Yes,
yes (well stiff meaning harder to compress),
yes,
and yes.

Sway bars link the two sides of the car together, effectively increasing the spring rate in turns on the side that wants to compress. This keeps the car from 'rolling' toward the compressed side as much. The reason to do this is to make the suspension less affected by quick turns and therefore ready to take the next quick turn to the opposite side earlier- like in a slalom.

It DECREASES traction, though, as do stiff springs and stiff shocks. The sloppy feeling roll provides much better traction, so it is a tradeoff. Do you need traction or quick transitions? It's up to you and the type of course you race on. The better question is usually; do need more oversteer or understeer? Tweaking the sway bars is a primary way to adjust the handling balance (nothing to do with weight balance).

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996 GT3 lower control arms at all corners
997 GT3 front sway bar
Tarett rear toe links
Quaife TBD
DMC harness bar/G-force harness