more t/bar stuff - anyone got experience/comments on 21/31 combo?

[dickster]

this seems to be quite subjective with the different opinions etc. and people (including racers) do like their cars set up completely different as well to suit their own driving style.

in think theres some truth in what jack said in that any of these combos will probably improve the handling over stock - and its probably only at the limits that the differences will show up. ie snap oversteer.

thats all i can conclude at the mo.

[Wil Ferch]

When looking over all these posts....some things now become more clear that we didn't stress before...

How hard will you drive the car ( how close to .."at the limits"...)?

So...maybe try the 21/31 combo Dickster...and provide feedback. The one thing I've learned is never to lose an "open mind" attitiude about anything.

The only caution to Dickster or Dutchie or anyone else contremplating this:
- be honest about your own capabilities and whether or not you're truly going to get near the car's limits ( one way to find out is to do several DE's with a nearly stock car...you'd be amazed how much "more" the car has than you thought).
- if you're driving "hard" and find out you're only at 7/10's....maybe go for it. The discussion so far is valid if you're near "at the limit" handling.
- be careful in the rain , though
I personally think an agressive street up of 22/29...or even 22/30 would be just fine, and you'll notice a difference.
---Wil Ferch

[Randy W]

Lothar's point about shocks being dampers of the springs is a good one and goes to what I was trying to say: a 31mm rear torsion bar on a 911 that is insufficiently damped (read anything less than custom valved shocks- Bilstein, Penske, JRZ, Moton) is going to behave unhappily. At the limit on an uneven or slippery surface, this means rear wheel hop and (with a 21mm front) snap oversteer. The problem with saying that this is not a problem if you drive 7/10ths is that you do not always get to pick the time you will be driving over this threshold - what about a blind decreasing radius corner on a downhill section you started taking at 7/10ths. Not a time you want to be lifting or braking to get back under your limit, if you have time to do that...

[ted]

Originally posted by Wil Ferch
JacK:
True enough, but....
What he would end up with using 21/31 is the "most extreme" of all examples. I normally wouldn't recommend "end-of-envelope" type settings to anyone except perhaps seasoned veterans.
---Wil Ferch

Wil this is only the end of the envelope for torsion bar cars. When the 31 bar is not stiff enough 911 owners go to much stiffer coil over springs. A 31 bar is not that stiff in the racing world.

You can theory to death the effects but real in the seat feedback can't be discounted.

My theory is that from the factory these cars have some under steer engineered into them. Combined with rear weight bias and tendency to snap spin if you lift in a corner would lead the factory to create a more forgiving set up. So trying to maintain the factory balance is not the hot set up for track racing.

Where you race should be a consideration too. What type tires, street or R rated DOT?
Softer set up for parking lot events with street radials.
Firmer for high speed events and R rated DOT tires.

Adjustable sway bars can help improve confidence in your car too. With the 31/21 torsion bars adjust the front sway bar for full stiffness and race it. Soften the front sway bar for more steering as you become confident with the new set up.

That said I went from a 21/26 to a 21/30 set up on my 2200lb 911. The firmer rear bar suits me perfect. Next I would like to have my Bilsten shocks re-valved to handle the increased rebound from the stiffer torsion bars.

I did drive it 350 miles the other weekend while sitting in a Sparco race seat, the seat was not so plush but the car's suspension seemed acceptable on the street to me.

My car weighs 2200lb so a 31 rear bar in a heavier car appears acceptable to me.

[Wil Ferch]

Ted:
Points all well taken....
but Dickster ( it appears)...is not a racer and the car is not set up for coil-overs...I do understand you can go even further. I felt that was way "OT" for this type of discussion.
Nonetheless...what kind of "general" messge can we give Dickster?
First I say that this set up is extreme..then I recant and say fine, as long as you don't get near max limits...then someone says you can't "choose" when 7/10's occurs ( true enough)...yet others go on to say you can stay with 21/31 as long as you use adjustable anti-roll bars.

If I were Dickster...I'd probably say right now...WTF do I do now ???

I'll maintain that if he hasn't experienced any of these combo's yet...he wouldn't be disappointed with something just under the 21/31 extreme...wouldn't you agree?
--Wil Ferch

[curtisaa]

My 88' Carrerra is set up with 31/22 hollow torsions, with monoballs and sway aways in the rear. Tyres are the Victor racer series...and although I haven't taken to the streets of Willow nor Button, I seem to hang very close to Dave Buhaines white RS look, race car while heading through Angeles Crest Hwy. My car probably weighs a bit more than Mikes rocket or that matter Daves 3.6, but handling wise it seems to do just fine when it's time to perform.

I'm sure if Randy Wells were to drive it, he could determine more accurately his very experinced opinion. It appears that suspension symetry on these cars can be tweeked in many ways, but it does not compensate for poor-average driving abilities VS seasoned vets ala: Jack or Randy W...

These are guys have done their do-deligence and have invested alot of time "on the track" and, IMHO, can offer very good advice on this thread...

[ted]

Originally posted by Wil Ferch
Ted:
I'll maintain that if he hasn't experienced any of these combo's yet...he wouldn't be disappointed with something just under the 21/31 extreme...wouldn't you agree?
--Wil Ferch

True, and I assume his desire for a stiffer set up is based from experience with his current set up.

So yes your set up would provide an improvement.
In fact I think your setup would be preferred if racing on radials in a parking lot AX/DE/TT. His tire choice and racing location are still not clear to me??

Hopefully it would not leave him searching for a stiffer set up.
My .02 is I have what he is speaking of and it works for me.
It might be a bit stiff for the parking lot tracks but much more comfortable at the high speed events with race tires.

I would prefer to error on the chance that a car is a bit stiff. A soft car at high speed is less desirable to me. This just gets into personal preference.
Personal preference becomes the issue when spitting hairs between a 29 and a 31 rear bar.

Most of us want to avoid spending money for incremental changes that we redo more aggressively every year. Perhaps this is part of the reason this person wants to take such a big step.

Either way it's expensive if you go to shop and have this done correctly. Buy and install new bars and set ride height, four wheel alignment and corner balance could set you back a grand easy.

I am very interested in Jack’s set up experiences and I’d die for a chance to take Randy’s car for a couple hot laps. These guys are fast.

Good talking with you Wil.

Curtis how come Dave B has not got you out to the track yet?
You like to drive fast, your cars are very well prepared.
I think you would have a BLAST!
Your 3.6 monster would eat'm up on the Fontana straight too.
Give it a try once.

[Wil Ferch]

Curtissaa:

So...your advice is for Dickster to do what?......

Only Dickster can gauge his capabilities to detemine whether he goes for an aggressive or conservative set up....no? The info on this thread...from me or anyone else...is to get him to make a more "informed" decision..
--Wil Ferch

[dickster]

loads of great info/advice here.

If I were Dickster...I'd probably say right now...WTF do I do now ???

LOL - actually things are getting clearer!

Adjustable sway bars can help improve confidence in your car too. With the 31/21 torsion bars adjust the front sway bar for full stiffness and race it. Soften the front sway bar for more steering as you become confident with the new set up.

i'm realising from you guys and some reading that i'm gonna have to do these at some point.

True, and I assume his desire for a stiffer set up is based from experience with his current set up.

very true, i was at the cars limit at the track because of the understeer.

Most of us want to avoid spending money for incremental changes that we redo more aggressively every year. Perhaps this is part of the reason this person wants to take such a big step.

spot on

my driving is mostly street, but i want to go to the track and not wish i had a hotter setup. track is where i would push the car, on the street, well, its usually not possible.

it is more obvious now that experienced guys have different opinions based on their preferred setup. i can always increase the fronts pretty easily (the rear is more of a pita), and i'll get the sway bars.

its interesting that 21/31 should be less harsh on the street than 22/28 because of the fronts.

i feel happier with the decision now, thanks for all the advice.

[curtisaa]

Originally posted by curtisaa


These are guys have done their do-deligence and have invested alot of time "on the track" and, IMHO, can offer very good advice on this thread...

BTW...dickster...put some miles on your car "as-is". Learn the handling symetry, then "baby steps" so your car will be comfortable when driving on the streets...

[Wil Ferch]

Looks like everyone is happy...I'm glad...
--Wil Ferch

[Lothar]

To all,

This was a really cool thread. There was a great exchange of ideas and opinions. I am pleased to have been a part of it.

There is a lot of expertise and knowledge here. It's great when it bubbles to the surface in such a constructive way.

[Mike Feinstein]

FWIW...I opted for 22/29's with an adjustable rear sway bar (stock up front) and Koni adjustable sport shocks all around (set at mid point). Sway bar is set fairly neutral. Ride is firm with little or no body roll...gets a bit choppy if the pavement is rough, but that's rare in this part of the country. I enjoy the 'go-cart' feel.

On the track, with R-compound tires the balance is about right (for me). I can use controlled oversteer to get through turn 10a at Road Atlanta while not feeling the threat of unexpected rotation going through 12 or 1. Overall, it's a great track/street set-up....highly recommended Dickster.

[emcon5]

Wil,

Where did you get those numbers for the effective spring rates of the T-Bars?

Those numbers are different than the ones shown by Steve Timmons here:
http://instant-g.com/Data/911CoilConv.html

Thanks,

Tom

[lateapex911]

Hmmmmm!
Interesting! A couple thoughts to add. I heartily endorse adjustibility! By all means, go the adjustable sway bar route.

Secondly, check out some of the books like Fred Puhns "Make your Car Handle" (I think thats the title!) and read about the theory of frequency. That is, each spring will create a natuaral frequency, and the weight and distribution of that weight have a lot to do with it. After you feel good with your frequency balance, then make sure your shocks are capable of handling it.

If at all possible, adding adjustable dampers (2 way if possible) will really help fine tune the car. Often shocks can cause problems which are attributed to spings or sway bars.

By creating an adjustable set up, you can go stiff (which will help avoid the "I want more" scenario later) and then start at a safe middle point, and dial in gradually to the perfect set up for you.

Last, don't forget to corner weght it after all the changes!

All, of course, IMHO!

Adjustability is the ultimate hedged bet!

[TimT]

Ill help confuse things even further

I have 350/550 lb coil overs in my 1900 lb 911

[wevoid]

We run our weekend track / AutoX car on 21/26 torsion bars with 22mm ARB's front and rear.
Although this is a lighter early 70's car, we are pretty speedy with a 2.4 911E motor.
I subscribe to the process by Wil Ferch. With your heavier car, and modest power and rubber, go with 22/28. If you get to the track need more roll stiffness, do the anti roll bar upgrade next. If you are running street rubber, you probably wont find the grip to explore the extra stiffness from more torsion bar.
The 22/28 combo will allow you to run low enough to take advantage of the lower CofG too, without always being on the bump stops.

Regards

Hayden

[CamB]

So where does one LSD (or lack of) fit in this discussion

[Wil Ferch]

Emcon5:
I calculated the TB equivalent spring rates myself..and am quite sure of the results. It's in the Rennlist Tech area that I can't seem to cut 'n paste. Go to Rennlist.org, then click Tech forum / 911-964 / suspension...and then click "torsion bars".
I did note that the "relative" spring rates ( compared to one another as a percentage)...compares well to Timmin's notes..but all I can say is that I know what dimensions I took to come up with my numbers...I don't know Timmin's basis.
---Wil Ferch

[wevoid]

Wil,

Doing the calcs, did you take into account that the longitudinal tube, forming the inboard edge of the Front Winshbone, is also a torsion spring?
Being in series with the torsion bar, it has a significant impact on the torsion bar installed rates.

Regards

Hayden