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

[Wil Ferch]

Wevoid:
If I take your question to read did I understand that the TB is "co-axial" with a portion of the A-arm, instead of "in series"....
then yes...I did take that into account.
If, you're saying the A-arm itself is a spring, independent of the TB...then I would say "no".
Look up the thread.
---Wil Ferch

[MMARSH]

Originally posted by 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.

Curt

One thing. Driving on the street is not the same as driving on the track. I will never lose anyone on the street, cause I'm not gonna go that fast. But, ask Dave Buhaine what happened to him this weekend at Buttonwillow when he mistakenly went out on the track with the race group and tried to follow me through the Star Mazda. When I did a quick check of the times later, I was running about 8 seconds faster then Dave.

[wevoid]

Wil,

By packaging, the torsion bar is co-axial with the tube of the wishbone. For a force path calculation the spring elements are in series.
1/K_total = 1/K1 + 1/K2 applies.
The tube has spring rate of about 1360 lb/in using your load case.
The impact on installed rates varies by which torsion bar is in series, but for 25mm torsion bar, the installed rate is reduced from 350 lb/in to 278 lb/in.
No doubt there are more springs in series, but the tube of the wishbone is the most significant and a calculable constant.

Regards

Hayden

[Wil Ferch]

Hayden/Wevo:
I'm intrigued...but need to fully understand the inter-relationship of the A-arm tube as being a contributor to the overall spring rate. If you would please, contact me directly via Email so as not to clog this thread. Contact me through a PM on this board or by WFerch911@aol.com.
--Wil Ferch

[emcon5]

Originally posted by Wil Ferch
Emcon5:
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.

Wil, here is the link to your article. I actually came across it Saturday while searching for other references to compare. Paul's (pbs911) comments in this thread got me wondering about the torsion bar size in relation to vehicle weight, and I wanted to do some Jethro Bodine cipherin' to see if there was much diference. What I came up with (using my extremely limited math skill) is 300lb in weight reduction is roughly equivalent to a increase in Torsion bar size by 1mm (from stock), as a ratio of spring tension to corner weight. The numbers came out nearly the same using both your and Dr. Steve's spring rates.

This discounts the other benefits of light weight, but it is kind of interesting.

Tom

[jluetjen]

Hi guys -- I just popped in on this thread and I'm getting confused by the recommendations. I understand that the Dickster's considering stiffening up the car to cure some low speed understeer -- and then everyone's whipping out their favorite springs and swaybars. I could easily come up 4 or 5 ways to cure understeer without even touching the springs and sway bars. If it was my car, before I started throwing parts at it, I guess I'd want to understand what exactly is happening when the car is understeering. Is it geometry related? How about cornerweight related? Tire related? Driver related? Once I've eliminated those would I consider where to start spending money? While you may feel that you have reached the limit of the car's potential because it is understeering, in fact tires and driving style often have as much if not more to do with ultimate speed then springs, shocks and swaybars. Just as Jack! Nigal Mansell was renowned for his ability to drive around a problem while racing with Prost and Senna.

Dickster - what sort of "slow" corners was the car understeering on?
Right turns or left or both?
Was it understeering on the entry? Mid-corner? Exit?
Were you on the brakes or the gas?
Have you tried chaulking the sides of the tires to see how far you are rolling over on the shoulders?
Do you know anyone from whom you could borrow a pyrometer? If not, try putting your hand on inside/middle/outside of the tread. Where did it feel hotter?

In my opinion there are still a lot of things to sort before you start throwing parts at the car!

[dickster]

john,

thanks for your thoughts.

its been a problem since i've owned the car (2 yrs). left handers are like its on rails and very neutral, right handers it understeers (under all conditions) like a pig.

i've looked at everything you mentioned. including alignment. it hasn't been corner balanced. thats mainly because all the bushes are shot, the front t/bars are new unknown quality, the rears probably tired oe. i just don't know why its much different one way than the other - rear bars perhaps?

so since i've got to rebush etc anyway, i thought i should swap out the bars for know quality items, and then have the full alignment/balance. then its got to perform - right? i only want to do it once.

[ted]

Originally posted by dickster
john,

i've looked at everything you mentioned. including alignment. it hasn't been corner balanced. thats mainly because all the bushes are shot, the front t/bars are new unknown quality, the rears probably tired oe. i just don't know why its much different one way than the other - rear bars perhaps?

At the AX have an instructor ride with you to help evaluate your car's condition before you spend any money on it.

If everything were correct then a tweeked or poorly corner balanced car would still not handle consistantly from right to left turns. I'd corner balance it.

[dickster]

If everything were correct then a tweeked or poorly corner balanced car would still not handle consistantly from right to left turns. I'd corner balance it.

we're talking chalk and cheese here. completely different characteristics left and right. i have tried messing with the balancing just to see if it made any difference - nada. i posted other threads about it, came up with nothing.

i thought it was toe on the left front, but i had it checked.

at the end of the day the whole lot needs rebuilding anyhow.

[jluetjen]

Ditto Ted. I'd do the following -- but once you've done the first you might as well do the second and third since you'll have it all apart anyhow.

1) Make sure that you have good bushings at all 4 corners as well as the sway bars.

2) Get the car corner balanced.

3) Get the car aligned to spec.

You'll be amazed at the difference!

[dickster]

and you're suggesting i do all that and leave the (unknown) bars?

like i said i only want to do it once.

[jpachard]

Dickster, You will be amazed at the difference after you replace the bushings and cornerbalance. These cars are very particular when it comes to corner balancing and the symptoms you describe are spot on. Remember that you want a car to understeer slightly in slow speed corners, that way your high speed sweepers won't be a rather exceiting balancing act.

Cheers, James

[Wil Ferch]

James:
your last statement was the crux of all my previous messages...you can't dial out understeer for *all* speed conditions..
Yes...other factors like corner balancing and alignment make a noticable difference. To cite just one example....you can set up for ( say) neg 1 degree front camber...and neg 1.5 degrees rear camber. If front/rear camber are close to equal , the car may be more neutral...if you dial-in 1/2 degree more rear neg camber compared to front...you dial in a bit of stabilizing understeer. A lot can be done with corner balance/ alignment / tire pressures, etc...before you mess with changing suspension hardware.
---Wil Ferch

[ted]

Originally posted by dickster
and you're suggesting i do all that and leave the (unknown) bars?

like i said i only want to do it once.

In the beginning here I thought your car was dialed in with stock components. With the bad bushings and a mystery front torsion bar it appears you have not had the chance to fairy evaluate how your car is meant to handle.

For the life of your car you can expect to have to align and corner balance it occasionally. This is something you will have to do more than once. Maybe you go off track (Cayenneing), nerf a curb, pot hole, change tires sizes or if you are lucky it's just been two years and you want to confirm your settings or try a more aggressive setting for R rated tires.

If it were me I'd plan on replacing the bushings first. This might mean all suspension bushings. Once you get into it you will find some other worn out stock component that you will need to replace. When this is being done you can measure the torsion bar. If stock then leave it. If you find you do have a larger front bar then you can decide if it is acceptable as is or either change the front or rear to keep the balance. It would be odd to put a larger front bar on an otherwise stock car. My guess is your front bar is OK the way it is.

If you have some money left over add adjustable front and rear sway bars so you can change your over steer and under steer with adjustments you can make at the track.

It's difficult to start with something that is not right and know what you want next. If you plan to race on radials and you put in T bars that are too stiff your car will not grip well either. My 30/21 set up has 245/40 and 275/40/17 R rated tires with a light car and a big motor.

You need to make your car right as is. Race it and become confident with it. Learn to throttle steer your 911 to overcome any low speed push. It may be too soon for you to make aggressive suspension upgrades.

It is very hard to do it only once when your basis is not in perfect condition.

[dickster]

ted,

It is very hard to do it only once when your basis is not in perfect condition.

sorry, i don't get it. i want to replace most parts with new. and like you said if i find anything else.......

thanks for your comments - the way i see it is that this is a known good upgrade.

the front bars are std size and of unknown origin, they are not the original bars - that much i know for sure.

the rears i haven't seen yet. if they were as easy to swap as the front i would have had them out for inspection by now.

i've already spent lots of time on trying to sort the handling. i had the alignment checked.

all i'm doing is dumping unknown/wornout junk and replacing with quality items. the method in my madness is that it should damn well handle great when its done.

i know how the car can handle in left handers so i know the potential. but believe me the right handers are another story. slow, mid, and fast sweepers they're all the same - loads of understeer/pushing.

[curtisaa]

Mike-

I would be the first one to say that "desire and ability" will usually outrun HP and technology. I suppose the boilerplate on this is the IROC series, where ALL cars are equal and it's the drivers ability along with a bit of luck (not crashing) which will prevail.

That was my point to dickster, it's sort of incumbent that he "do his time" behind the wheel to get the feel of how a stock Porsche handles. It would then be prudent for him to take the small, but incremental steps, that would lead to his level of performance.

Guys with your and Jack O's experience and track time is irrefutably the greatest asset when driving "at speed" on a track scenario.

BTW..good job on handing Dave a lesson on driving

[ChrisBennet]

Originally posted by dickster
we're talking chalk and cheese here. completely different characteristics left and right. i have tried messing with the balancing just to see if it made any difference - nada. i posted other threads about it, came up with nothing.

i thought it was toe on the left front, but i had it checked.

at the end of the day the whole lot needs rebuilding anyhow.

Left to right differences can be related to:
- alignment (which you already checked/fixed)
- corner balance related (does "messing with" mean you already tried corner balancing it?)
- spring or shocks

If you intend to do some upgrades anyway and want to put off fixing the problem until then, that makes some sense. If you want to upgrade in order to fix the problem, well that doesn't make sense to me.

If it was me, I would find a garage with scales and have them just weigh the corners - not even adjust them. That would tell you if they were out of wack and it wouldn't cost much.
-Chris

[ted]

Originally posted by dickster
ted,



sorry, i don't get it. i want to replace most parts with new. and like you said if i find anything else.......

Yeah I know I kind of went conservative on you when you brought up the right turn push.

thanks for your comments, but the way i see it is that this is a known good upgrade.

True for wider R rated Kuhmo Victor racers of Ecsta tires, radials do better with a little softer set up. If you plan to go to softer tires then firmer torsion bars are more important.

the front bars are std size and of unknown origin, they are not the original bars - that much i know for sure.

That's fine, wonder why they had to be replaced? Hopefully no accident repair?

the rears i haven't seen yet. if they were as easy to swap as the front i would have had them out for inspection by now.

Most likely stock too.

i've already spent lots of time on trying to sort the handling. i had the alignment checked.

Do you remember what the camber was front and rear?

all i'm doing is dumping unknown/wornout junk and replacing with quality items. the method in my madness is that it should damn well handle great when its done.

Yes it should be fine, as long as the tub is without a doubt undamaged before you start spending money on it...

i know how the car can handle in left handers so i know the potential. but believe me the right handers are another story. slow, mid, and fast sweepers they're all the same - loads of understeer/pushing.

Since it has been aligned the corner balance should make your car turn equally well right and left. Just an unlikely longshot..... In the worst case the car can not be corrected with a corner balance or won't hold adjustments due to a damaged tub. Don't really want to go there, hope it's not the case. But it would be nice to eliminate that possibility before you spend the money on your new set up. At this point we are just hopeing your right turn push is the result of something you plan to replace.

What if you could just drive it onto some scales just to check it and not to adjust it. Maybe the tech can tell you it may be off, that the direction it is off would create the right turn push and that you have ample adjustment remainng to corner balance the car. Might be worth the $50 to identify why it's pushing in right turns before investing a lot into it. If it's the same garage that will do future work on your car they might be willing to help you.
When that car handles the same in right or left handers it's all going to worth it!

[ted]

Originally posted by curtisaa
Mike-

BTW..good job on handing Dave a lesson on driving

Hey I'm not all that, but thanks for the kind words. I don't have Dave's number by any means.

At the bottom of the hill I turned my video camera on and then picked up the pursuit. A slower car bunched us up and then we had some nice two lane side by side action. Those hairpins got some heat into my R rated Ecstas and gave me the confidence in my car that I feel on the track.

Soon after on the shady side of the hill by the ICY sign with snow on the side made me question road conditions. You got Dave to that point. I just nudged him another couple of hairpins. The whole experience has me looking for a 3.6. You would of reeled me in on the flats had you not had to pull over. Your car with sticky tires at Fontana would be awesome...

Agree if we were younger and had several years of racing ahead then incremental changes would make us better drivers and suspension tuners. I'm 45 and still ramping up. Though I am trying to expedite the process before age does catch up.

Glad you enjoyed that last couple miles up the hill, I did too.
It can be like that for 20 minute sessions at the Fontana track May31/June1 .
http://www.touringcarclub.com/events/events_schedule.htm

[jluetjen]

Dickster;
In general I'm not aware of T-Bars going "bad" (unless it breaks outright). They may take a set, but that gets dialed out during the corner weight process. So yes, I'd put the same bars right back and and put the money you save into more track time.

See how the car feels during the coming season and work on consistancy. Once your laps are consistant to the same second (in gross terms), you'll be in the position to identify handling improvements. Once you've identified a persistant issue, try to adjust it out with first with tire pressures, then with toe, then with camber. At the end of the season, evaluate any persistant handling issues that remained and then consider the appropriate t-bar/sway-bar/shock update.