Torsion bars - Are fronts and rears matched?

[autobonrun]

My 79SC suddenly started squeaking like a 5 year old Ferrari. Also a clicking sound came from the front. Diagnosis is worn torsion bar bushings. While replacing the front bushings, I'll upgrade the torsion bars. My question is whether the front/rear ratios are matched? If I increase the diameter of my fronts, must I replace/increase the rears also?

[Bill Verburg]

Absolutly!

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Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page

[orbmedia]

Certainly from the factory Porsche tuned the suspension spring rates front and rear to deliver a good compromise of street/hi-perf driving. If you are happy with that balance you should retain the stock bar setup.

However it is very common for people to change the torsion bars to tailor the handling to some different criteria, like aggressive street, autocross, track, etc. In that case there are various combination that you can go with. General the rates are increases front and rear together.

The short answer to your question is that you should not consider changing the front without considering the overall balance of the car and the effects on the handling.

[Superman]

Agreed. Don't change one without changing the other. I believe that stiffer torsion bars would be one of the best upgrades for my needs. As firm as these cars are compared to others, mine could certainly be stiffer within my tolerance for ride discomfort. I believe my car has 19 and 25 or 26mm bars. I suspect 21 and 28mm hollow bars would be better for me. I have driven an SC with 28mm rear bars and I definitely did not find the ride offensively stiff.

I would expect stiffer (sport) shocks or stiffer anti-sway bars to be more offensive than stiffer torsion bars. In fact, if torsion bars were stiff enough, I'd connsider going without anti-sway bars entirely. In short, I think stiffer torsion bars is an excellent upgrade choice, depending upon your preferences.

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'83 SC

[emcon5]

There is a great chart in the Automotion / Performance Products catalog that lists pretty much every suspension change, and it's effect on the overall handling of the car.

According to the chart, increasing front spring rate will lead to more understeer.

Disclaimer: I only use the PP catalog to find things to order from Wayne. Besides, I don't have a PC in the room where most of my catalog reading happens

Tom

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82 911SC Coupe

[autobonrun]

Thanks for the feedback. I was afraid I would have to match the front and rear. So now I must decide whether to go back with stock and keep the rear the same, or pay for the additional parts required for the rear if I upgrade the front's size. After looking at the options, I'd probably change from the current 19/24 to 22/26 Weltmeister if I decide to do it. If my math is right, there is an extra $500 for parts plus the additional labor for the rear over and above the cost for the fronts. I guess you have to pay to play.

Maybe it wouldn't be too dangerous if I upgraded the fronts now and the rear a few months later. I probably won't drive it much during the winter anyway and definitely not too hard.

[Hellgate]

My suggestion would be to us the Neatrix bushings vs. the ploy-graphite bushings. The Neatrix is closer to stock, transmit much less road noise than ploy and are more comfortable. All while improving the handleing of your car.

The hollow t-bars are nice too. They seem to have a greater spring progression to them and the solid ones. ie: Softer on the first part of the travel and firmer on the top.

I have this set up on my '87 and I very happy. DE instructors are always surprised on the qucikness of "turn in" of my car.

Pete

[ChrisBennet]

If your front torsion bars are squeaking, replacing your bushing will probabably not stop the squeaking. BTDT. The torsion bar cap/adjuster wears a groove into the crossmember allowing the torsion bar to ride lower/off center in the A-arm. The side of the t-bar then rubs inside the A-arm. The solution is to build up the bottom of the cap with a little weld and file it smooth so the t-bar is centered in the A-arm again. While you're in there, remove the torsion bar, clean and regrease it. You'll probably find that is is rusty where it has been rubbing.
If Neatrix makes a front bushings now, that would be a good one to go with. I was only aware that they made rear ones.
-Chris

[This message has been edited by ChrisBennet (edited 10-04-2001).]