Back to torsion bars?

[Redgard]

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..
Honestly I miss the squat my car once had.
I have looked at old treads about this..
Has anyone experienced converted back to torsion bars from coil overs? Any regrets?
Thanks!

[infraredcalvin]

I’ve only heard of people going back t bars stock to sell... especially on a 76. Most discussions about suspension here tries to eliminate the squat.

Although if you decide to ultimately sell your t bars listed above, I’m interested...

[Redgard]

I have heard some pretty convincing arguments about how the action of ‘squating’ reduces pontential wheel spin with hard excelleration.
I have also heard these cars handle better with the higher side walls of the original 15” wheels
I have tried to look and see if Ruf’s BTR had coil overs but I haven’t found info about this either.

[dannobee]

The "squatting" is actually a function of the rear suspension geometry. If you want the car to "hook" harder, you'd INCREASE the rear anti-squat, like porsche did on the race cars. Look at pictures of drag cars with the front wheels off the ground and you'll see the rear suspension is actually lifting the rear of the car, too, not squatting.

There is a limit though. Rear anti-squat calculations of independent rear suspension have a force vector through the center of the axle, not at the contact patch of the tire with the ground, like live axle cars. And a ton of anti-squat helps on acceleration, but when you let off the gas, those same forces want to tuck the rear wheel back into the body. This tends to make the rear end "loose" and snap around when getting off the gas. Just like 930's do.

[gumba]

What are your spring rates?

[jadewombat]

Keep in mind as danno was saying the point is to keep the inner front wheel planted on the ground accelerating hard out of a turn. Increasing the rear spring rate is to counter the twist of the car wanting lift the front inner wheel.

Steering out of a corner on one wheel is no fun.

[tailwind22]

I have owned 4 different 930s and all had coilovers plus HP mods. I didn't track them but liked cutting edge performance. Top Porsche shop Rothsport convinced me on my last build to take it back to T bars. Great recommendation and never looked back on the decision on that car. Great ride and stance and plenty of support in the corners for my requirements.

[quattrorunner]

Interesting to me as I've sold my coilover setup and bought larger tbars in the rear. 31mm! I hope 31mm is't too large

[Mocker]

Originally Posted by jadewombat

Steering out of a corner on one wheel is no fun.

I dunno, it looks like fun!

[Redgard]

Thanks for all the interesting technical points.
I guess I have been trying to quantify the sensation change that I experienced with the coilover set up.
There was something about that almost imperceptible rocking on braking before a corner and accelerating out of it that gave a real feeling of ‘getting it right’ when you took a turn well.

From my perception,
The flatness of coilovers sometime makes it feel like your floating and thier is a distinct sensation that the rotation point of the car is significantly further forward.

[Redgard]

Originally Posted by tailwind22

I have owned 4 different 930s and all had coilovers plus HP mods. I didn't track them but liked cutting edge performance. Top Porsche shop Rothsport convinced me on my last build to take it back to T bars. Great recommendation and never looked back on the decision on that car. Great ride and stance and plenty of support in the corners for my requirements.

What was thier rational for the choice of Tbars?

[Redgard]

Originally Posted by infraredcalvin

I’ve only heard of people going back t bars stock to sell... especially on a 76. Most discussions about suspension here tries to eliminate the squat.

Although if you decide to ultimately sell your t bars listed above, I’m interested...

One got cut on the removal unfortunately..

[Redgard]

Originally Posted by dannobee

The "squatting" is actually a function of the rear suspension geometry. If you want the car to "hook" harder, you'd INCREASE the rear anti-squat, like porsche did on the race cars. Look at pictures of drag cars with the front wheels off the ground and you'll see the rear suspension is actually lifting the rear of the car, too, not squatting.

There is a limit though. Rear anti-squat calculations of independent rear suspension have a force vector through the center of the axle, not at the contact patch of the tire with the ground, like live axle cars. And a ton of anti-squat helps on acceleration, but when you let off the gas, those same forces want to tuck the rear wheel back into the body. This tends to make the rear end "loose" and snap around when getting off the gas. Just like 930's do.

By ‘ drag cars’ do you mean race cars? Is the lifting of the inside front wheel a positive thing? Seems like it would increase potential for understeer do torsion bar cars have less of a tendency to do this?

[Redgard]

Originally Posted by jadewombat

Keep in mind as danno was saying the point is to keep the inner front wheel planted on the ground accelerating hard out of a turn. Increasing the rear spring rate is to counter the twist of the car wanting lift the front inner wheel.

Steering out of a corner on one wheel is no fun.

A picture is worth a thousand words.. the car in the photo is running on Tbars you think?

[slow&rusty]

I spent a ton of time developing the suspension on my car from varying Torsion bar set-ups then finally coilovers. After dialing in the coilovers I will never go back to T-bars, the coilovers transform how the car handles and drives, it actually makes the car feel modern and much more progressive and predictable.

[911tracker85]

I am having this dilemma also, but leaning toward Tbars.

one issue I keep encountering is these 930s were not designed for coil overs. if you want to do that you need to consider a wide range of chassis reinforcement.

for my 930 conversion build got a set of RS raised spindle front struts and revalved Bilstien f/r shocks that have coil over perches.

well... one consideration is to use Tbars with low rate coil overs. but have read how hard it can then be to get the suspension set up.

but one issue about coil overs is you can use progressive rate springs, where Tbars are pretty linear.

have a while before having to make that decision, car is now an empty tub getting ready to put on rotisserie to blast the whole tub.

good luck on whatever you decide to do.

[jpnovak]

Originally Posted by Redgard

T
From my perception,
The flatness of coilovers sometime makes it feel like your floating and thier is a distinct sensation that the rotation point of the car is significantly further forward.

This description would point me in the direction of incorrect rebound damping.

If the rear damping is too fast then the car will not set over bumps causing a rear lift and float sensation over bumps as the spring recoil pushes the weight transfer forward. This would also give you the same sensation as a forward bias for the center of rotation when turning.

Its like built in off-throttle rotation due to damping.

LIkewise the lack of set in a corner or squat on acceleration is too much compression damping.

Are your coil overs adjustable? Sounds like they are not matched to the spring rate. Your spring rates are too high for the current damping. In genearal, you need to soften compression (jounce) damping and increase rebound damping when you go up in spring rate.

[dannobee]

A three wheeled car will never beat a properly prepared car that uses all four tires. If you notice the picture above, the left rear tire is barely contacting the ground. This is not the fast way around the track.
I’ve been forced (by rules in various classes) to use several types of springs/torsion bar suspensions. Wheel rates and front roll couple help you go faster than what spring is supporting the car. But there are FAR more choices in spring rates with coil springs than torsion bars. And they’re a LOT easier to change, too.

[flightlead404]

Originally Posted by dannobee

A three wheeled car will never beat a properly prepared car that uses all four tires. If you notice the picture above, the left rear tire is barely contacting the ground. This is not the fast way around the track.
I’ve been forced (by rules in various classes) to use several types of springs/torsion bar suspensions. Wheel rates and front roll couple help you go faster than what spring is supporting the car. But there are FAR more choices in spring rates with coil springs than torsion bars. And they’re a LOT easier to change, too.

or

[dannobee]

https://www.youtube.com/watch?v=QQh56geU0X8