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

Re: I'm NOT a racer...
 

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.:D When I did a quick check of the times later, I was running about 8 seconds faster then Dave.

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

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

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

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!

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.

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.

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.

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!

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

like i said i only want to do it once.;)

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

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

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 :confused: as is. Race it and become confident with it. Learn to throttle steer:eek: 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.

ted,

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.

Havin fun..
 

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;)

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

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!:D

Re: Havin fun..
 

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:D .
http://www.touringcarclub.com/events/events_schedule.htm

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.

ted,

thats a damn fine idea:)

it never occured to me that the tub might be twisted/damaged:eek:

i'll see if i can get it on some scales.

thanks for all your input guys.

i know i'm jumping the gun going for these mods that are way beyond my ability....... ;)

well, i went with 22/31's in the end and very pleased that i did.

however, having chnaged the rear bushes for neatrix at the same time, the left/right handling problem remains:(

although i have now spotted that the left side tie rod bush is very worn, i am hoping turbo ones will fix it........................

good call on the 22/31. It was the right decision...as you found out.

Chew the fat with some of the p-car shops that PCA race at the front and they'll lead you in the direction of a good bilstein valving spec for those bars.

911's are difficult to get the roll stiffness correct in the rear. That's why the trend has been towards bigger t-bars. More t-bar, less sway bar.

Also as tire technology advances then spring rate goes up. The first big jump was when the Hoosiers came out and the second was recently when the Michelins started becoming popular. They respond well to this higher spring rate.

Keep evaluating your stuff on the track and not the street.

I am joining this one a little late but here goes. I currently have 21/27 t-bars and 22/21 sways and Koni sports all around. I wanted a little more rear t-bar and thought about 28 or 29. Now I think I should look at 30 or 31?!?! I am "pretty competent" behind the wheel and the car is more for autox than track, but it will see the track 5 or 6 times this year.

Should I go with 29 or 30 and see what happens? I don't mind spending the cash to do it twice more to get it right. Some one will buy the bars that I do not end up using .... right .......guys...... someone will won't they......
oh ya, Wil, I like your idea of 7's all the way around.
Chuck, You are suspiciously missing from this thread, I value your advice!

Thanks, Jeff

Hmmm...I'm going to deviate from the idea of increasing torsion bar sizes by asking how many out there now know how to drive their car at consistent speed with the torsions they currently have on their cars?

It would seem that the best way to find out if one needs larger torsions is to effectively use up all the "spring" their current torsions offer - and at speed.

My idea is to take what you have for your suspension, corner balance and align it, then drive the daylights out of it until you are certain you've surpassed its ability. Only then will larger torsions, tires and such truly matter.

With that said, Dickster, I believe did the right thing: he figured out he wanted more oversteer, and installed appropriately-weighted bars to insure that oversteer.

In my opinion, even if you're not a racer, you will learn a huge amount about your car if you take it to a track and drive it hard in its current condition. As my car did with me, I found it surpasses my driving ability, showing me that the mostly stock setup I have on it now is more then adequate until I "earn" the necessity to change torsion bars or anything else.

Until then, there is an infinite amount of things one can do to their car - as I've found out. Tire pressure increase or decrease, ride height adjustment via the springplates or torsion bar indexing, toe in/toe out adjustments, and camber/caster changes - to name a few - can make a big difference. If at all, heck, you'll spend less than what it costs to r/r torsion bars you may not need.

I agree with dd74.
Dickster...you and I have had lengthy discussions on this topic (others...see archives)...and if you look at the equivalent spring rates I published for the various bars...I *still* think you went a bit overboard on the rear bar size. The fact you say that it's fine might be good as to how it feels on the street, but I will guess that as you near the absolute cornering power of the car ( like on the track...or an aggressive street avoidance maneuver)....you will find the car hard to balance on this new edge.
Summary of my previous points.....upgrades are typically quoted at 21/27 and 22/28. This maintains the fr/rr spring rate balance of the stock car with smaller bars. Typically too much low speed understeer as Porsche intended for "legal" purposes. The suggestion then is to go 21/28 ( or even 29)....or 22/29 ( even 30)....but IMHO....31 is pushing too far toward high speed oversteer...noting that at low speed it may indeed feel neutral and better. Let's remember that the spring rate goes up to the FOURTH power of diameter...a big stiffness increase for a small diameter increase.

Then again..if it works for you.....OK ... just make sure it's still OK at some extreme driving conditions.

---Wil Ferch

I run 22/30 t/bars, 27mm f&r sway bars & re-valved shocks on our 2525 lb. '73 targa track car w/3.2. A race engineer friend of mine implied the 30mm rears were too stiff. The problem being the front tires floated over road irregularities causing less grip. He suggested I try 28mm w/245 rears or 29mm w/275 rears. I guess it depends on how you like the car to feel.

Hi all together,

this is my first post in this forum.
I read all your opinions about the torsion bar diameters front and rear an how to adjust them, but nobody was talking about a correlation of the weight of the front end and the rear end and the diameter of the torsion bars.
The stock 911 ever had a 19 mm (o.k.it is 18,8) front torsion bar- even the last 89 turbo. But the rear diameter was increasing over the years from 23mm(?) to 27mm at the 1989 5 speed turbo (I dont know if this car was sold in USA ).
The most increase of weight over all the years was in the rear(for example 915 gear to G50, turbo (where the engine is more than 1 inch further in the rear of the car) , etc.).
When we look at the Carrera with 915 gear box (car weight 1160kg), we have 24,1 mm torsion bars. With the havier G50 (car weight 1210 kg) we have 25mm.
The turbo with 4 speed gear box (weight?) had 26mm, the 5 speed (car weight 1350 kg and more) 27mm.
The sway bars were always adjusted to the torsion bar changes. But the cars ever had a built in understeer character- a forgiving set up.
When they changed the rear tb from 24,1 to 25mm, they increased the front sb from 20 to 22 and the rear from 18 to 21mm- and the car is 50 kg heavier with the most weight increase in the rear.
We know that the Carreras have 40% of weight in the front and 60% in the rear ( my example, a 1987 Carrera G50: 519 kg front (full gas tank)and 734kg rear, which is 1,41).
When I look at Wils List I see: Front Spring rate for 19 mm=110, and rear spring rate for 25 mm=140. 140/110=1,27 The car does understeer.
But there was a sport suspension from the special wishes programm of the factory in the 80s with 26mm turbo torsion bars in the rear (and Bilstein shocks and adjusted sway bars).
26 mm =165. 165/110 = 1,5! The car is more neutral.
We know that the turbos have a front/rear weight relation which is more like 35% to 65%. For example 530 kg front and 820 kg rear- this is 820/530=1,5. With the built in understeer we have 165 (for26mm)/110=1,5 or 191 (27mm) /110= 1,72. But with the 27mm tb the sway bar was reduced from 20mm to 18mm.
What I want to show is, that, in my opinion, the torsion bar diameter depends more on the front/rear weight distribution then on the equal spring rate. For a street car I think much more than the stock 19 mm is to much- especially on german autobahn with 150 mph. Last summer I was at RUF factory and talked about tbs and sbs. They recommended (or example for the Yellow Bird) tbs: 20/29 , sb 23/20. The RUF cars are street cars- no race cars. But with reinforced chassis.
Since two weeks I have tbs 19/27 on my 3,2 Carrera.
Why? I didnt like that the car squatted in corners in the rear (and lifted the front wheel oposite a little bit).
Now this seems to be o.k, but I feel that I have to change the sbs (perhaps less diameter in the rear or more in front-or both), because it has more oversteer. But I will test this in the next months.
I hope this was not to boring.

Thorsten

Thorsten:
Your reasoning is sound.
Turbos usually are 37-38% front....62-63% rear.
If you adjust *only* for the weight difference...and keep everything else the same...then you didn't change the low speed understeering characterisitc that Porsche built in originally. For a given wieght, you'll see that the "common" 21/27 and 22/28 combinations fairly well match the fr/rr balance that Porsche had originally. For each of these, many have gone stronger in the rear TB size to dial out a bit of understeer .
Another thing to consider is that the stiffness of the TB should not be compared simply to the fr/rr weight distribution. The "leverage" affect of the suspension arm that acts on the spring... must be taken into consideration. For example, a 50/50 weight distribution car might come with equal spring rates front and rear only if the "A" arm length that acts on the spring is the same front and rear. If the "lever arm" is longer on one end..it will make that end softer...and higher rate springs will be needed ....quite independent of the fr/rr weight distribution.
One other thing....for our 911's....whatever you end up with will have different low speed vs high speed characterisitics. A low speed car that understeers terribly might be nice and neutral at high speed...because at high speed you use less steering angle and have more optimum tire contact patch to the ground. At low speed there is a great deal of steering angle for the same cornering load...and generally more understeer.
Thanks for sharing and commenting...welcome aboard.
----Wil Ferch
Ich spreche Deutsch...aber bloss ein bischen !

Hi Wil,

ich schreibe trotzdem hier in Englisch weiter ;-).
Yes, I agree with you and the TB rate does NOT ONLY depend on the weight- but it is ONE reason (some engineers from the factory told me). And for race cars from the factory they had combinations like 22/28, when only torsion bars were allowed by the rules. O.K.
In this thread was a question about a street car. As I wrote in my last post, Porsche had a sport suspension from the special wishes programm for 3,2 Carrera with 19 mm and 26 mm for cars until 1986.
When I look at the 968, there was a M030 sport suspension (968 CS), too, where they added coil springs in the rear to the stock tbs.
And for the 964 there was a M030 too, where only the rear coil springs where 40 % stiffer than stock (and a sway bar in front, which was 1mm bigger than stock + shocks- I think this was the suspension of the RS America).
Here in Germany I know nobody, who is driving bigger tbs in front on the street. I think its because they do not response very well on bumps and waves at high speed.
So you are right: It makes sense, to change the original balance with stiffer rear bars, to dial out a bit of understeer.

Viele Grüße

Thorsten

Thorsten,

Thanks for the post.

So from what you are saying, your setup 19/27 tb at 1.73 is actually more agressive (towards oversteer) than my 22/31 1.58 (near neutral?) setup?

This ignores the fact that the stiffness in mine is probably better suited to track than street. But then that is always going to be a compromise. i wanted to be able to have a blast on the track, so then running stiffer makes sense?

Granted my original plan to go with 21/31 at 1.91 would have been more oversteer orientated than you have found yours to be.

Dickster:
If the spring rate equivalents you're using are correct ( I don't have my list in front of me now)...then what you're saying is true...the 19/27 combo has dialed out more understeer than your 22/31 combo.

What isn't addressed is:
- Thorsten's point that there is a supplemental component ( sway bar sizes)...that also come into play. He admits he may be too aggressive and will find out later...to be fixed, presumably by different sway-bar sizes.
- the overall effect of running "stiff" ( overall) vs "soft" ( overall)....regardless of balance. There is a view largely held in Germany that some suspension compliance is necesary. In the States, we seem to feel that going stiff all around is an OK compromise... a lot depends upon the roads you drive on...and how dry weather / wet weather friendly , etc, etc...the set up is. I presume the stiff set up if over-done can cause wheels not to follow road irregularities well.In addition, overly stiff will also result in rather "quick" transitions at the limit...like "snap" oversteer instead of a more gentle oversteer with softer springs.

There is a lot to this...no simple answers... the suspension guru's kept by race teams surely earn their keep !!

---Wil Ferch

Hi !
I have an -86 Carrera. I`m rolling on 17" RUF`s 8+9 with 205/255.
I have dialed out some of the understeer caused by my wheel set-up by adjusting my Koni-Sports.
Now I wonder if going to 26 mm rear without any other changes will make it handle well on the road and at DE`s as well.
I don`t want it to oversteer, but as it is now with stock 25mm it handles like a fat pig with absolutely no turn in at highway speeds if my shocks aren`t adjusted minimum half stiff at rear and full soft front.
I somehow imagine that this setup must be great for a car with this wheels (to broad at the rear) that is mostly used on twisty highways and some DE`s.

Thanks Wil for the quick answer to dicksters questions. You have been faster than I, but you wrote all things that I would have written.
Another short story I heard last summer, which was told to me by a former Porsche factory driver: In the early 70s they tested the 2,4S and the 2,7 RS on some bumpy streets in the black forest (not on the plain race track). They beted which car was faster. The stiffer RS or the softer 2,4S- and the 2,4S was faster!
Magnus: Do you surely have the 25mm rear torsion bar (as you wrote) and the 22mm/20mm Sway bars? This change was made in 1986- thats why I ask.
Perpaps you know this link: http://www.9mracing.co.uk/html/modules.php?op=modload&name=NinemeisterContent&fil e=index&req=viewarticle&articleid=19&topic=7&artic lename=Tuning%20Guide:%20911%20Carrera%2083-89


Thorsten

Thorsten

Yes, i can understand that. On bumpy roads a stiff setup will struggle - that makes sense. But if you use a car on both street and track you cannot get the ideal setup for both. i just thought it would be more sensible to do insane speeds on the track rather than the street;)

Dickster is absolutely right to keep highly lethal speeds on the track :)
Magnus...I don't think you'll help under/oversteer simply by shock settings, although it might feel you're doing something along these lines. Shocks should simply damp the springs. You're running unusually ( vs stock) front/ rear aspect ratios ( 205/255 ....vs 205/225 stock ) and that combo will tend to give you a lot of understeer. Try running 225's in the front if you can...or something like a 225 or 245 in the back. You can try 26 mm torsion bars in the back ( up from stock 1986 25's)...but 27 might suit you better with that wheel/tire combo. Either one won't get you into trouble...in my opinion.
---Wil Ferch

well, thorsten's other thread and a road trip prompted me to resurect (sp?) this one.

currently i have the 22/31 bars fitted, with neatrix bushings, and bilstein sport shocks - all other parts are oe and mostly very worn. i have set ride height and front toe only, still to set rear camber (currently around 4 degrees!) and toe.

with the car in this state i went on a 350 mile non-stop, round trip today, mostly motorway (freeway?) miles. i got back dissappointed that the trip had ended! the car is a joy on those types of roads, very solid, confidence inspiring handling, and not too harsh. i have to admit that the setup is a bit harsh on small bumpy back roads, but if you do alot of m/way miles its perfect - imho.

the steering feels "darty" at the moment, but i have gone to 25" in the front and need to fit the turbo tie rods that i have and a bump steer kit that i'll get soon.

got to sort the rear camber quickly as the tyres were warm on the inside and pretty cool on the outside - this will no doubt result in rapid wear that is not too good for my wallet!