Yeah - thing is, I'm not exactly "stock" with the 26mm bars in back. Essentially, I guess I have a turbo's suspension on a '74 car.

Anyway, I just finished ripping a new one in the S curve along Cahuenga just below Sunset; I was trying to chase down a 996 4S. Everything seemed fine, balanced, etc. I think it's the tires that are really giving me the problems (soft sidewalls and all).

BTW: I caught the 996. No biggie. Overpriced VWs are always fun post-breakfast snacks. :D

My only thing is that gosh-darned squeak. I think I'll "rack it" and poke around with a grease gun. (Shrug)

23/31, 2100lbs, big-ass-wing, understeers like a Camaro, even with -2.25 negative camber in the front. Going to move up to 33 rears when I get the chance.

ARB didnt help?
What is your front toe set at? Too much toe in could be an issue too.

Many years ago after the input of altering just about every variable on his own G series (SC) our raceshop's senior partner settled on the formula of 23/30 hollow torsions, revalved Konis (to their proprietory formula), STOCK sways, 15x7+8's and 205 + 225 Rcompound tyres, turbos ties, strut brace and full cage. I think most cars (depending on the chassis' individual alignments) run more than -2.0 front camber if possible.

Every car he set up this way dropped 3-4 seconds on most of our tracks. In fact he was investigated for cheating as other members thought he'd made engine mods.

Please note that our club cars must have min. weights of 2552lbs as they are in "stock" class and our tracks are generally short and have relatively rough "roadlike" surfaces. In addition our competitiions incorportate as many autox events as track events. So our cars are set up really as tarmac rally cars.

My car was set up this way but with the addition of polybronze bearings and it retains road tyres on 16inch wheels and does not have a cage. It weighs a portly 2800lbs but handles brillantly yet rides quite well.

When I asked my mechanic why my car road so well yet didn't feel "squirelly" as he warned me it would without r compound tyres he attributed it to the modern road tyres (Michelin), polybronze and weight.

When I ordered all my parts off Chuck he questioned my choice of 23/30mm torsions and suggested either 22/29 for a more acceptable ride or 23/31mm if I was more track orientated. I debated this issue with my mechanic but settled on his recommendation as he was recommending a suspension "set up" rather than just "replacing" suspension parts.

There is no easy answer for this one because every factor from how much the car weighs to where it's being used to what rubber it's wearing to.......must be accounted for.

Simon

Hmmm,
I'm not certain this is true for the rear. Sure for the front this makes sense since the torsion bars are located along the axis of the car and the track width affects the length of the "lever" against the torsion bar.

But think about the rear: given the torsion bars are located perpendicular to the axis of the car, the "lever" against the torsion bar is determined by the length of the springplate assembly (and the weight of the wheel), but not by the track width. Theoretically, one could increase the track width and, all else being equal, the mechanical advantage would remain the same since the length of the lever has not changed. Any MEs please feel free to correct me on this :)

Edward

Edward, you certainly have a valid point. I guess I never thought of it that way. However, since body roll comes into play here, I think I'm still partially right AFA the rear goes. I don't understand the "weight of the wheel" aspect. What does the unsuspended weigh have to do with spring rate? Some sort of reciprocating mass theory? Maybe a real ME can sort this one.

well, when it hits a bump the wheel wt. will affect how quickly it moves and prob. the total displ. as well - as does spring rate

Well, I'm an ME, but I have already professed my ignorance in this thread. Every car needs a setup which is basically unique to the car, it's intended use, weight, etc. Off the top of my head the overall handling of the car is a function of at least 20 variables, of which torsion bars are one. Common sense and experience is worth as much as theory in this case. Look at Simoms post above; someone found a formula that worked, and applied it across the board. Was that formula optimized for each and every car? Probably not, but it was an improvement.

Well I'm an ME too, but my brain hurts from figuring gear ratios on another thread. My point was that if you're going to stiffer Tbars, you can use the front to rear ratio of your current bars to choose the ratio on the new bars, all else being the same. If all's good, keep close to the same ratio. If you're having handling problems, adjust accordingly.

It also seems when people go to stiffer bars they tend to go for a ratio that produces less understeer.

Thats pretty much what I did when I chose the bar sizes originally. I think adjustment is nesessary, in my case, on the anti-roll bars. The thing about torsion bars is that there is no optimum solution, as they come in only a finite number of sizes, and I suppose there is a variance in effective spring rates from manufacturer to manufacturer.

BTW, I'm going with smaller tires for track use. So, then I'll have to re-tweak the ride height to get the balance back in order. This introduces more variables into the equation. I'll bet we could write an optimization algorithm when our brains get refreshed! My brain hurts from studying control logic for four days.

Isnt the size of the t-bar less important than making sure its a good match for your shocks?

I have 22/28s w/Koni sport yellows on one car and Im going 23mm front t-bars with rear RSR coilovers on the other car.

True, if we go to stiffer T bars and try to duplicate the factory torsion bar spread then too we should also duplicate the shock control to the same percentage that we increase the spring rates.

If you play it safe and go stiffer T bars, still with the factory spread but don't address the shocks you haven't been true to the factory set up.:)

Although I am not interested in a factory "safe" set up. These in part (like all car manufactures) are designed in the case of the 911 to prolong the lives of unknowing new drivers that might get into trouble, for example lift and spin.:)

Here's a little something to think about.


When the Factory built the RS America, they increased the rear spring rate, but left the front alone. Then they increased the front swaybar diameter, but left the rear alone.


This method could be applied to our cars as well, and it works. The reason is this: You want the rear tires to stay in contact with the road as much as possible. So it's better to use spring rate to control roll in the rear. The other benefit is that it reduces squat. The stiffer front swaybar restores the handling balance.

I wound up with Noticable Oversteer. I haven't tweaked it yet but this thread taught me a lot. Old and same thoughts is to increase the ft swaybar to the Carrera 22mm and see what happens.

21/27
Bilstein HD x 4
stock sways
Welt bushings
car is overweight about 75#
6x16 on all four
stock alignment & euro height

what seems to be different than other guys here is that I increased oversteer.

Just to offer as a data point:

So my 82SC has 22/28 torsions (and Bil Sports f/r), and 7/8 Fuchs. So with this torsion bar selection, along with obviously increasing spring rate I have increased understeer, according to the ratios chart (thanks for the chart, BTW!). Compound this with the fact that the 8" rears increase the rear track width, along with the 245s adding rear grip, which together results in my having increased understeer yet again.

But thus far, having driven one AutoX course (in sopping rain) and ButtonWillow (full track, dry and hot), I find the car to handle pretty darned neutral, with both over or understeer easily inducible given driver input. Keep in mind that I am still "feeling out the car" on the track as it is still new to me so I am most certainly not driving with full afterburners ...perhaps this is one mitigating factor. Another may be the carrera swaybars (at 22mm/21mm), which obviously should reduce understeer. The question is, of course, to what degree does this swaybar selection act against the "added" understeer from the aforementioned conditions.

Anyway, I just thought that I'd mention (in no way as a definitive statement, mind you) that thus far I really like the way my car handles in its current state. And when I had sought advice as to torsionbar selection, I was advised 22/28 by three shops that I trust very well. Now you all have got me thinking I should have 29s or 30s at the rear, despite my enjoying the car is it is set now. But as a few have said in previous posts, "good handling" is a system that is more than the sum of its parts. I guess I could also try and figure in the effect of my modest weight reduction efforts and camber settings, but I'm already befuddled as is. Oh well, guess I'll just have to enjoy driving it :)

Edward

I ditched my Carrera rear swaybar for an adjustable 22mm, and tightened it up as far as it could go. Result: if there once was understeer, there's certainly not much now...

...but as I'm finding out through Tyson and Dr. Island, it's really all apples and oranges with these ideas. For instance, my car weighs less than 2300 pounds, so I'd caution you against using my car as an example toward a standardized suspension set up.

Edward, I've got an '84 that weighs about 2570 or so empty, has S-03 205/16's front 225/16's rear, polygraphite bushings, 22/28 mm torsion bars, stock sways, turbo tie rods, bump steer, and a Rennline strut brace.

The car handles great. I would have to say that it feels very neutral, with little understeer or oversteer, although I have yet to go for a big lift of the throttle while really pushing it. Small throttle adjustments mid corner allow me to easily change the car's line and balance. The car does exactly what I ask it to do. :D :cool:

Thats the same specifications I´m going to this winter, exept I will use Polybronze.

I already got the the 22 mm front swaybar, I thought that was standard with the rear swaybar.
With no rear sway (standard I think) they used a 16 mm front swaybar, is that what you have in front?

I just spent the weekend at Watkins Glen. The semi-final analysis on the suspension is this:
the car was pretty neutral, I didn't get a lot of oversteer backing out of the throttle (which I did hard a couple of times in traffic on the chute), and the car handled very well. I think I get away with the stock sway bars up at WG, but they may be more of a factor at a shorter, more technical track, or an autox. My slippery Yokahama tires need to be considered in the sway bar analysis.

Pat

Hear, hear.

People looking for recommended sizes should look for a car, car use and driving style that is similar to theirs. Valid comparisons between apples and oranges rarely works unless you're comparing apples and oranges straight up.

Sherwood