Q about reverting back to torsion bars..
 

I own a 76 turbo carrera. Currently I have a powerful 3.3 motor in the car with 398 hp at .8 bar.
Just after I bought it I switched the suspension to coil overs on the recommendation of a friend.
The car was previously set up with upgraded sways and torsion bars 23/29 I think.
I drive this car almost daily
And sometimes at the track.
I have spoken to several old school 930 mechanics who say unless it’s race prepared these old cars handle better on Tbars etc..
That basically the cars don’t ‘set’ in the turns As well with more modern set ups and can handle squirrely.
Honestly I miss the squat my car once had
I have looked at old treads about this
But most of it has been about going from torsion to coils.. never back.
Has anyone experienced converting back to torsion bars from coil overs? Any regrets? It would be nice to hear from someone with track race experience on the subject :)
Thanks!

Subd

Interesting. Sub'd too

I read not to long ago that Jack Olsen was going back to TBs in the front. But that was to optimize geometry (scrub radius) as the coilover prevents higher offset wheels.

No real direct experience, but for the most part a spring is a spring. A coil spring is really just a torsion bar wrapped into a cylindrical shape. That said, both have their pros and cons.

With coils you can do more, like progessive winds and adding tender springs. Coils also move the force application from the pivot point out to the shock attachment point, so the A-arms / spring plates no longer have such a strong bending moment in them. Coils also give you a LOT more rate options for cheap, rather than the few pretty expensive options for torsion bar sizes.

T-Bars mount lower so lower CG, also free up real estate for tires up front. They're 100% sprung weight, where coils are at least partially unsprung weight.

I think either works about equivalent in the grand scheme outside of the differences noted above, but again no direct experience so ymmv.

Interesting question. But I think you're just making the same mistake you originally made. You changed the setup based on the recommendation of a friend without first living with things. I guess if you factored in the cost of a suspension refresh anyway it was an easier decision to pay for the coil over change in the first place.

The reason I say you're making the same mistake is that other than the "squat" you're not addressing a clear issue that you were trying to fix in the first place and you're not addressing a clear issue that you're trying to fix now.

Not saying that what you did is wrong, we all go about things in different ways. So think about what it is you're after. If it's just rear squat you should be able to fix that with softer springs in the rear... much cheaper than changing everything back to T bars.

The 'squat' could also be achieved with a damping adjustment.
Slightly softer compression/bound settings would net the same result.

This is backwards. A torsion bar's mass is supported entirely by the body of the car; when the suspension moves, it twists about its axis only. The mass of the bar essentially doesn't travel. A coil spring on the other hand is generally supported from the bottom and 50% or more of the spring mass must follow 100% of the suspension travel.

Dan

Are you sure? Unsprung mass is the wheels, brakes, hubs, ~50% of the suspension arms, etc. Unsprung mass is what you want to minimize for best suspension action, so this is a positive for torsion bars since it's part of the sprung mass.

Not a significant difference of course, so it probably doesn't matter.

I think another point for coil overs is that the springs on a coil over are lighter than a T-bar. can anyone confirm this?

You know what? I can't read. Sorry to correct your already correct post!

Dan

If I remember correctly, the factory race team went to coil overs when they needed more spring during testing at an event than could be accomplished with torsion bars.

A coiled spring takes up less space so it allowed them to go to heavier springs than otherwise could be accommodated in the space they had for T bars.

Some modern formula cars have T-bars and others have coil springs. Both provide different packaging options when designing a car, but both are just springs. How the suspension is configured is what makes a big part of the difference mores than the type of spring doesn't it?


I think that this post by McTag is the best post so far though

You know, without knowing the OP's current setup, spring rates, shocks, tires, it is hard to offer any advise.

Seems to me trying different springs may be the best option. Can't imagine Turbos handle better with torsion bars than coils....

Agree with this - we have had coilover for several years now on a race car and my son
really likes the set up - I haven't heard of anyone going back to TB . . .

But, the coil specs and damper specs need to match - Elephant did this for us.

IIWM I'd keep the springs and work on the overall suspension set up - and like others
have said maybe try different spring weights - we run 400/600 for 2500# car - we
tried some 700# in the rear and didn't help at all . . . but our TB were 24.5F 35R . . .
with adjustable sway bars . . . tires are Hoosier 245/40/17 315/35/17 . . .

Regards,

And with the shift in what part of the chassis bears suspension loads, torsion bars vs coil-overs, the rear crossmember and shock towers are often reinforced due to the change. If performed when your coil-overs were installed, no harm, no foul back-switching to torsion bars. However, if not reinforced, check/inspect the upper shock attachment structure.

Sherwood

Exactly! So many people convert to coilovers but neglect to reinforce the rear crossmember and shock towers and wonder why they ripped apart the welds.

To the OP's original question, I'd have to ask where he got that advice to switch back. In 35+ years of 911 ownership, and having converted 2 of my 911s to coilovers, I'd never go back unless for originality. On the other hand, unless someone is tracking their 911, I always question why someone would go through the trouble and expense to convert a street car to coilovers when TBs work just fine.

My suggestion. Talk to someone who KNOWS! Then be HONEST with them about its REAL use. I talked at length with Clint at Rebel Racing. I went coil overs on my 3.6 car. 250lb front and 350lb rear. Car squats nice, drives beautifully, and handles really well. Clint runs the same rates on his car. Ironically in an unrelated conversation with Steve Wong, he essentially agreed this was a great setup for my use, a lowered street car that may see a track once or twice a year.

My shocks are also matched to those rates and my ride height. My other car is torsion bar, and staying that way (its original and more rare). My suggestion, spring rate change may help you but again TALK TO SOMEONE WHO KNOWS THESE CARS AND SUSPENSIONS WELL, and BE HONEST WITH THEM.

Duc’s post is a good one


I’ve realized what this discussion is really about

the OP question should really be is which spring rate, not how to get it

If a person has torsion bars and can get the right spring rate in a bar, why not stay with t bars

On the other hand if you’ve outgrown the rage if T bar spring rates do to improved tire size/tire traction etc, and space doesnt let you go bigger, then you have to go coil over to get up to the next range of spring rates.

If you already are in that larger range of spring rates, but have gone too far, you can always drop down to a smaller coil spring without going back to a T bar

Wayner nailed it. Also coil springs are cheaper to buy a set, and swap them in your driveway to change the ride of the car, or ride height. Torsion bars are a nightmare relative to coil springs.

Also, if your coils are 650lb coils and the shocks are set up for them, dropping to my 250fr/350rr combo may not ride right, as the shocks would be really over damped for teh lower spring rate. My fronts are yellow Billi coil over struts. The rears are rebels steel bodied Billi’s that are valved right in the range for my springs out of the box. Many people have said I can go up/down in rate as much as 30% before my shocks are really out of whack in terms of damping. For a street car that is fine. If I was a very good driver, tracking the car a lot, then that range would lessen as I would be more sensitive to better damping. At the same time if I was that good, then I would be wanting a different shock and spring package per track, and even per different conditions, (summer vs winter, rain vs dry). I long ago in my youth realized I should set a car up for the street and enjoy the piss out of it. If it does some track days or autocross’, improving my driving would make a MUCH bigger improvement in my times than any suspension set would (except maybe super sticky track day tires).

Bottomline on the street my 250/350 combo is great. I would want stiffer if it was a track car, but then it would not be very tolerable on thestreet.

Again talking to someone who knows will really help.

I’ve got a 245/275 combo

Sport shocks up front and HD on the back ( maybe opposite I keep forgetting)

Rear T bar is 31

Fantastic for the street
Doesn’t beet me up

Pretty good on track but I have to dial in a bit more rear sway bar than I would like

I need just a tad more rear spring for the track

If I moved to more agressive R compounds I’ll bet I’d need even more spring and would be squarely in Coil over territory