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Join Date: Nov 2008
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Changing Rear Torsion bars in 968

I am about to upgrade my standard 25.5mm dia torsion bars to new solid 26mm dia units by Sway-Away. I propose do this without reomoving the torsion tube from the car, that is, drop one side at a time as per Elephant Racing's website recommended procedure for '944 Spring Plate bearing Installation'.
Before I start I have a number of questions for which I would appreciate answers from anyone having done a similar operations or has a good understanding of torsion bar suspensions:
a) what is the effective life of a torsion bar?
b) what is difference in the angles for pre-load setting between the 25.5mm and 26.0mm dia bars?
c) Any major pitfalls I should be aware off in attempting this process.
Old 11-27-2008, 02:05 PM
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Would not bother. I've done several upgrades to 28mm for racing. It's difficult, & you will probably have to do a few times to get height correct, and I don't see any benifit; unless you are lowering car.
http://www.clarks-garage.com/
search susp-06 for indexing forumulas. Not easy to follow thoe...

Good Luck
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1987 924S with 968 Drive front to back, Bilstein Insert on mod/stock Struts, 450# Hypercoils, 28mm Torsion Bars, Weltmeister Adjustable Sway Bars, Lindsey 968 Light flywheel, Spec Stage II Clutch, ToYO RA1's, Auto Power Cage & 6 pt Harness, KLA Strut Brace, Greasy hands, heavy foot, and lots of smiles
Old 11-27-2008, 03:12 PM
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i'm willing to bet the "26 mm" solids are in fact the standard 25.5mm solids that are stock in the 968

torsion bars last as long as any other spring, for the same reasons

the job is indeed a bear, and may well take 3 times to get it right - it is a huge pain in the butt - so much so that i deleted them on my 968 altogether and went with coilovers
Old 11-27-2008, 07:02 PM
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Agreed - that's utterly worthless, given the time it takes... few would feel the difference anyway!

Maybe you could sell them to someone with 23.5's - a 944 or 924 guy - and get some big ones for your car - yeah, like 28's or 30's (the latter if you're really hitting the track).

Not sure what use you have in mind for the car, but hopefully there's a front spring and all-around shock/strut upgrade planned too?
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Old 11-28-2008, 05:21 AM
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i don't think there is any difference - i think it is misrepresented, and actually IS 25.5mm, and they just rounded up - if it is indeed a 26, it is only a bump from the stock wheel rate of 175 to 189 - not worth doing in my book either

assuming they are solid:

the 28s (254lb wheel rate) are decent for a plus 1 upgrade, but you will need a 250 lb spring up front

the 30s (335lb wheel rate) will need a 350lb spring up front, and are a bit much for most people on the street

in either of the above cases, shocks and struts need to be changed to accommodate the new rates, as the oem stuff can't handle it properly
Old 11-28-2008, 07:39 AM
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They are 26 9/16" long bars; I am not sure of the 'effective' length but if you are calculating spring rates based off of a length, diameter, elasticity modulus, and the trailing arm length then you would need the length of the exposed, non-constrained bar (i.e. bar length minus spline length).

I did a lot of calculations a while back for torsion bars and compared them with the values you see on a lot of websites to re-confirm this. All the values I calculated were within 5-10% of the given values on websites, and I did some small rounding and estimating that would account for that small of a difference.

I believe Volkswagen 26 9/16" 1200 series torsion bars (used in some buggys) are a direct swap and can be found for cheaper; I am not sure of this however.
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Old 11-28-2008, 09:53 PM
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For a comparative percentage difference (as you probably know) you only really need the ratio of the diameters to the ^4th power (info placed here more for the quiet observers)... so, for example, my situation, car came with 19mm t-bars (!) IIRC and we went up to 34mm (equiv - they're actually hollow)... (34/19)^4 = 1025%

IOW, the car's about 10x stiffer than stock. (note - this is a pure race car, no street use whatsoever).

Or, for comparison with my teammate who's running the 30's, I'm still 64% stiffer than his setup. I did run 30's for a while, then wanted MOAR!!!
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Old 11-29-2008, 04:18 AM
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Follow this link to charts and other spring rate informaton:

http://www.tech-session.com/kb/index.php?article=39
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Old 12-01-2008, 04:09 AM
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