Torsion Bars - Tubular vs. Solid - Targa Stiffness

[DANNOV]

I am in the process of upgrading the torsion bar setup on my 1985 911 Targa. I am considering going to 22/28. I use this car a lot for DE and X-cross, but I also use it sometimes on the street. It is really a third car that doesn't get a lot of street time except in emergencies. If I sell this car - not likely, but who knows - I don't want it setup so stiffly that it is a ass-buster to drive and perhaps hard to sell. I have two questions:
1.) It appears - per Weltmeister advertising - that a 22 mm tubluar bar has an effective rate versus the solid of 22.5 mm, and the 28 mm has an effective rate of 29.4 mm. Is the tubular bar really noticeably stiffer than the solid? In other words if I go tublular should I go just a bit smaller than a solid torsion bar, or are we talking about differences that are too small to matter?
2.) The second question concerns the Targa configuration. I have gotten many warnings about going too stiff in a Targa; but, no one seems to be able to tell me what is too stiff. Has anyone out there gone over the edge in a Targa and set it up so stiffly that you have a real problem with frame deformation and chassis alignment?
I don't think going to 22/28 should be a problem but what if I go to stiffer sway bars and sport shocks. At some point do I go over the edge and and hurt the car?

[Jack Olsen]

I don't think the problem is of hurting the car so much as it is reaching a point of diminishing returns with a very stiff suspension on a (relatively) flexible chassis. 21/27 bars might be a worthwhile compromise for your application -- stiffer than a Turbo, but not too tooth-rattlingly 'race car.'

Then again, you could go with the 22/28 and hold onto those old bars to throw in as a bonus to a prospective buyer.

[Tyson Schmidt]

Well, first off, you have it backwards on the tubular/solid torsion bar stiffnesses. The tubular bar has to be larger in diameter to have the same stiffness as a solid bar. IE; a 29.4mm tubular bar has the same effective rate as a 28mm solid bar. Drilling a hole down the middle takes away some stiffness, so they must be larger diameter to compensate.

The advantages to a tubular bar are: lower weight for a given stiffness, and supposedly, quicker reaction.

As for chassis stiffness, Jack is right on the money in regard to diminished returns. You reach a point where you flex the chassis more than the suspension. At that point, the ride is degraded ten-fold what the handling improvement is.

As far as where that point is? That is a good question. Unfortunately every car is different. I've lifted cars on the hoist that barely changed at the door gaps, and I've raised some whose doors could not be opened on the lift. (Targas,Cabs) You know best as to how solid your car is. Does it creak and twist now? Can you jack up one corner and still open and close the door?

My personal recommendation would be 21/27. Hope this helps.

[Clark Griswald]

I think you may have missread the Weltmiester lit. Tubular bars are softer than equivelant diameter solid bars.

As a general rule of thumb, a tubular bars stiffness is about equal to a solid bar that is 1 mm smaller. Refer to the manufacturer for specs.

As for the chassis question, I have 21/27 in my '86 cab. I don't notice any problems with excessive chassis flex. I also don't feel any desire to put bigger tbars on the car. I track regularly and the car corners very flat.

[DANNOV]

You are correct. I read it wrong. Weltmeister literature says: "22mm Effective Rate (22.5 mm)". That means the bar is 22.5 mm. It is all logical, just a mental goof on my part. But, I get the general idea, going too stiff just causes me to hit the law of diminishing returns because at some point the chassis flex offsets the any advantage of the stiffer torsion bar. Seems to be a good reason to go 21/27 and not push it any stiffer.

[mm86911]

Just ordered 22/29 for my '86 Targa - solid bars - hope thy'r enot too stiff. . .

[StuttgartDavid]

I have 22/28 solids on my 1982 SC, which I use the same way you describe your car, and I love it. The combo is not too stiff on the street, but close, especially at the front. I kept the rubber bushings for street ride quality, which helps on the street, but not the track. This combo handles perfectly on the autocross course. It does very nicely on a big track once the car has taken a set in the corner, but there is still a little more wiggle during transitions than I would prefer due to the rubber bushings - a good incentive to be smooth! The 22/28 is a proven combination, however the current trend is toward stiffer bars on the rear like 22/29 or 22/30. I also think the 22 front may be too stiff for this street application. I would consider a 21/28 combo.

I think the bars have less impact on ride harshness than shock choice. I have Bilstein sports all around. They feel great on the track, but hate rough roads and expansion strips! People say the Sports are too stiff to use on the front for the street. My buddy has a similar car with Sports on the rear and the softer Bilstein HDs upfront, and it feels really nice.

If I had it to do over again, for a street driven track car I would go 21/28 with Bilstein HD front and sport rear.

I kept the stock swaybars due to budget, but am quite happy with the combination as is. The Tbars and shocks are a much more significant upgrade than sway bars alone, and almost render the sways irrelevant- they control pitch as well as roll, which is even more useful for managing weight transfer. My car used to take forever to settle down from the transition to braking or changes in throttle, now I can be much more aggressive and timely with control inputs without upsetting the balance of the car.

Also, don't forget your bushings. Worn ones allow too much slop, especially the banana arm bushings, which many people ignore. Additionally, a good front strut bar really does help. I believe the Weltmeister Cambermeister is by far the best because it also limits movement in the rubber shock bushing, which you need to keep for street use. And even more important than the hardware is a good alignment and corner balance - don't skimp here!

Good luck, and remember that you matter much more than your hardware, and how it is set up matters as much as the pieces themselves!

[curtisaa]

did that say 911 T "Cab" ????

Just curious...........

[Tyson Schmidt]

Yup Curtis. The 72 is a Cabriolet conversion.

[Jdub]

I found Braniac!

I have seen Tyson's car(s) and he is a gamer. They are in production (aren't all of ours?) but the possibilities are endless...

Jw

[SRT356/911]

One of the most important and significant things that is missed when changing torsion bar sizes is the revalving of the shocks to match the bar.

When using Bilsteins you are at an advantage, because there are sources that can do the revalving for you. One bump or one track drive and you will notice it right away.

Racecars used to have a trailer full of shocks to match the bars/springs. For those of us that have only one, it works great. The results are amazing.

Craig Watkins at Smart Racing sent my shocks to Bilstein and had them done for me at a great price. Craig knows his stuff and can match you easily. Send him an old worn out Bilstein and you will get a rebuilt revalved shock back. And less than a new one. Front or rear.

Steve

[89911]

I have 22/28's on my 911 coupe. I took the advice of my mechanic who warned me about potholes, curbs, and the harsh ride I would get. Bad advice. I am now selling these, and going to 23/30mm bars and getting the shocks revalved. I don't give a crap about street driving and I WANT PERFORMANCE . My car is a track car even though I didn't initially see it that way. Steve was correct about getting your shocks revalved. Any significant increase in torsion bar sizes should be with shocks revalved to that stiffness. Most shocks, even the sports, are valved with the original torsion bars in mind. It is hard to forsee what your future is with your 911. I guess that is why Panorama has a large classified section. As for your Targa, you do have inherent body flexing that counters your suspension. The other suggestions are correct. 21/27 or 22/28 tops would be my choice.