Torsion bar spring rate / Slip Slidin' Away ?

[Jeff]

My car is in the process of transforming into a full on track car. At some point I plan on upgrading the torsion bars to a stiffer/ higher effective rate. From my reading I have found most go with the 23/ 31 effective rate.
Is this good for all weights of 911s? Or will I be Slip Slidin' Away on bumpy turns because my spring rates are too high?
I do understand the need for matching shocks to the torsion rate. Eventually I plan on adjustable sway bars. Will this allow me to rid my car of any unwanted skidishness (?)?

I am shooting for a 2200 lb car in the end (not sure if it is possible yet) and only want to buy this stuff once, so please feel free to give your opinion on Torsion/ Sway/ Shocks.

Thanks.

[IROC]

Well, everything is a compromise and 23/31 might be good on some cars at some tracks, but not all cars at all tracks. People with more experience than I will hopefully chime in, but on a 2200lb car, I would think that 23/31 torsion bars are going to be too stiff on anything but the smoothest tracks.

Matching the shocks to the springs is critical (as you note). I think once you've dialed in alot of roll stiffness with big torsion bars, you're not going to dial it back out with adjustable sway bars. At best, you're balancing F/R traction at that point.

FWIW, I have 22/29 torsion bars on a 2400lb car and have not found any situation (on the track) where I wish I had more stiffness. I am using red Konis and could probably stand some additional damping, but I'm happy with the torsion bars.

I'm interested to see some other responses.

Mike

[304065]

The reason the factory went to coilovers in the early 70's is because even the largest torsion bars didn't give enough spring rate.

Yes the car will skip, jump and slide sideways. The first few times out with the car at speed will require MAJOR adjustment by the driver, so be prepared to feel like the car is jumping sideways.

[Jack Olsen]

People think that because it isn't possible to put bigger bars into a 911 suspension that the thickest available sizes equal some kind of maximum useable spring rate, but this isn't the case. When the 911 was designed, tires were terrible and no one imagined that one day there'd be a need for much stiffer springs.

23/31 is the same as 250#/332# coil springs, which is pretty mild by contemporary standards. 22/29 isn't so different; it's the equivalent of 210#/254# springs.

I run 600# springs in the back of my 2500# car. There are 2400# Cup Cars out there running 2000# (and higher) coil springs. The bigger danger of very high spring rates isn't that your car will slide off the track -- it's that your chassis will start to pull itself apart.

23/31 is a great place to start, in my opinion. How extensively will your cage be tied into the suspension?

[Jeff]

Thanks for the responses guys.

Jack, As of right now I am just running a roll bar connected at the door sills, behind the seats, and the rear wheel arches. If I do run a full cage, I would tie it to the body as much as possible.

So, if I get to my desired 2200 lbs, it would still be hard to over spring the car, correct (using torsion bars that is)?
How about adjustable sway bars? Are the biggest possible the way to go and back them off for certain situations? Or use mid size sways so you can adjust up and down for various tracks?

John, When you say major adjustments, should I expect a full season to get full use of the new suspension or a few track days? I know it is kind of a loaded question due to the fact each driver is different, but let's use an average driver as the constant.

Jack, What were your spring rates before the 600lb coils? How long before you could maximize the new set-up? What was the biggest hurtle to over come with the new spring rates? What kind/ size of sway bars are you running with your set up?

[don911]

I also have a 87 and have removed just about everything possible and still keep it streetable. I'm hoping to get into the 2500-2600 range after fiberglass hood and bumpers. Are you planning on fiberglass fenders, doors, etc? If you get to 2200#, please post how you got there.

FWIW, My car is set up with 22/30 tbars, #27 SRP sway bars front and rear, RSR struts and shocks valved to match.

[Jeff]

Don, I only have a few other things to remove from the car, then I will weigh it. Then I will start replacing things with fiberglass. 2200# is the goal, but I won't give up safety or balance to get there. I will post how things progress.

Did your car come set up like that or did you upgrade it after you bought it? If so, how long did it take to get used to it?

[don911]

It's been a work in progress for the last 6 years. I initially put on 22/28 torsion bars when I first bought the car. The 22/28 combo is ok but 28s are a little small for the track..in my not so expert opinion. I ran 22/28s as a daily driver until last summer when I put on 22/30s. I also put in all elephant bushings with the new tbars.
anyway, the 22/28 is just stiffer than stock but I think has the same balance as stock. It still pushes like crazy with 22/28s. I never had the stock tbars on the track so it was easy to get used to for me. I haven't had the 22/30 combo on the track yet but it shouldn't take too much time to adjust. It should have better turn in and less push though.

[Jeff]

Thanks Don.

[jaydubya]

I used to have 22/29 in my SC. They worked very well but not the ultimate setup for a track only car.

I just changed to 23/33, with new shocks all around. I asked around a lot before going this route (versus 23/31). Those are the most common combos.

My car is currently 2500 lbs w/o fuel.

Steve Weiner talked me into the 33s for the back of the car versus 31s. You might want to send him an email or give him a call - extremely knowledgable and very helpful.

[Jeff]

jaydubya, Why the 33s over the 31s? What shocks are you using and are they custom valved for your set up?

[rdrr]

jaydubya - My car is 50/50 track/street. I've been recommended 23/33 but am worried that it is too stiff for the street. What is that combo like on the street?

[jaydubya]

Jeff (C U L8R) - I went back and forth, but there were a few things:

I never seem to be able to get enough rear swaybar. Bigger rear torsion bars means I can run less rear swaybar.

Steve Weiner's comment was something like, "You can't get enough spring rate on the rear of a torsion bar 911". I've heard this from others too.

I talked to a lot of people about this and got recommendations both ways, about 50/50. However, most of the race shop people generally considered "in the know" by our community who recommended 23/31 weren't aware that you could get 33 mm torsion bars for the rear. One of them said that now that he knows they are available he will be recommending them to his customers.

I'm getting JRZ double adjustable shocks for the rear and Bilstein custom valved inserts for the front (from Steve Weiner at Rennsport Systems). I'll upgrade the front struts to JRZ at some point in the future when I can afford it... But revalved Bilsteins should be fine all around if you decide to go with stiffer t-bars.

rdrr - I think that 23/33 is TOO MUCH for the street, or a 50/50 car. I'd suggest 22/29 or 22/30 for an SC/Carrera. The downside is when you decide to make your car a dedicated track car you'll wind up changing them again If it was an 80/20 car I'd say go for the 23/33.

Cheers,

Jeff

[Jeff]

I was on the Elephant Racing website yesterday and saw Chuck sells 24s for the front. Should I assume that bigger is better, even in the front? Also, I have always read the magic number (difference) between the front and rear should be 7. With the biggest torsion bars the difference is 9 how will that effect (if at all) the balance of the car?

[jaydubya]

I considered the 24 mm fronts but was told that they are for a car with a wider front wheelbase (widebody) since they have a lower effective wheel rate than a standard body for a given t-bar diameter.

As far as mm differences between front and rear, the relationship between bar effective diameter and torsional stiffness is highly nonlinear (4th power of radius) so I don't think you can just look for a 7 or 9 mm difference in dia. front-rear.

Bigger rear t-bars will reduce understeer, reduce front wheel lift, and let you use less sway bar in the rear.

Here are a couple of links listing effective spring rate and wheel rate for different torsion bar sizes. The take home point is that the wheel rates for even the biggest torsion bars are just not that high.

http://tech.rennlist.com/911/pdf/settings.pdf
http://www.instant-g.com/Data/911CoilConv.html
http://www.pelicanparts.com/techarticles/911_torsion_bars/911_torsion_bars.htm

Give Steve Weiner a call.

Cheers,

jeff

[Jeff]

Thanks jaydub, Will do.