roll resistance - swaybar vs torsionbar

[safe]

I have a 77 targa that I track and auto-x with. It has 21/27 torsion bars, carrera 3.2 front swaybar and an adjustable rear weltmeister swaybar.

Last year I had problems in auto-x with oversteer, it just let go all the time, fun and educational, but not fast.
This year I loosened the rear swaybar a little and the it made a huge difference, much more balanced now.

But I need more roll resistance, it is too soft. I remembered that I had a set of 29mm rear torsion bars on a shelf in the garage and I'm thinking of installing them.

If I do that will the car behave like when I had the rear swaybar too hard or will the result be different?

[Flieger]

The sway bar has more mechanical advantage than the rear torsion bars. It will go in the direction of the stiff sway bar but not as bad.

[Walt Fricke]

I think 29 is a bit much with 21 in front.

But now's your chance to install a big front sway bar. Say the old standby 22mm Weltmeister.

With this setup, I'd set the rear sway full loose (out at its far end), and the front full tight. I'd set the new adjustable front sway full loose, and go try. I'd expect the car to be loose. So tighten up the front sway bar. With luck, at some point before you get it full tight you will find the car pretty neutral. If you still have adjustment left on the front sway, move the rear in some, and maybe the front full tight. If the car has a push, you can keep nudging the rear sway attachment toward the T bar until it is balanced.

Remember that the sway bar arm does not act like a simple lever. An inch of collar movement out toward the end equates to a fraction of an inch in by the attachment to the cross bar. 3d power? Anyway, not linear.

[winders]

21mm front and 29mm rear torsion bars is just fine.

[Flieger]

FWIW,

21/29 would be 43.4% front elastic roll stiffness on my car (no sway bars at all). Not bad but probably could be better.

I run 22/31 which is 41.6% front. I the weight distribution is about 37.5% front. So I am in the ballpark 5% more roll stiffness recommended by some texts as a starting point.

But I think I could still go stiffer in back- I'd really like to try 22/32. I can still feel a bit of push as it is, but it is very close to neutral. But my alignment settings may have something to do with it. I run -2.5 degrees camber front, -2 degrees rear, so the extra front camber will give more bite and combat the extra weight transfer percentage at the front.

I can say, having gone from 22/27 to 22/29 to 22/31, each step stiffer in back has improved both the longitudinal ride (pitch) quality as well as handling. But the corner balance and alignment probably did the most for stability. The bars helped the steady-state balance.

The downside of being so neutral with torsion bars is that you must have sway bars front and rear or else none at all, since even a small sway bar greatly increases the roll stiffness due to its mechanical advantage. I had intended to run only a front bar to gain rear ground clearance and not have to worry about the rear mounts breaking, but some things came up along the way and I really like it with no bars.

I'd like it stiffer all around, though. My wheel rates are on the order of 200 lb/in front, 300 lb/in rear. I'd like something 1.5 or 2 times that.

[Walt Fricke]

With the coilovers on my 1960 lb track only car (without me in it - add 200 lbs for that), I am at 400/500 for spring rate. I was at 400/600 (kind of matching weight distribution) but suspected that might be making the car a hair loose on a long uphill sweeper where I learned I could keep the right foot down. Since I had the springs, I dropped the rear down. Wheel rates (and I have never translated my coilover rates into wheel rates) in that range seem to be close.

The Cup cars, with their much more modern suspensions - at least in the rear - and shocks have springs over 1,000 lbs/inch. Of course, they are heavier, too.

Some guys are now running bars which are larger than the splines, and are as large as will fit through the limiting openings. These are custom jobs, but may show up on the market. That would let you get closer to optimum wheel rates for track use, which seem to be much like the 400/600 you are looking for. Actually, I think you can't get to optimum (don't ask me all that goes into that, or how to calculate it) with torsion bars installed in the usual way.

But closer is better. Assuming you will accept harsher and harsher street ride.