Torsion bar diameter

[bose213]

Hi everyone,

My car is 79 911sc sportomatic. I’m still running the original factory torsion bars on my car. They’re pretty old now, and I think it might be time to replace them since metal wears out over the years.

Here’s the issue: when I fill up a full tank of gas, the front of the car drops noticeably lower. As the fuel level goes down, the front slowly rises back up.

So my questions are:

Is this happening because the torsion bars are simply worn out and no longer holding properly?

Or is it because they’re too small in diameter (currently 19 mm)?

For reference, I’ve already installed new Bilstein B6 Performance shocks. I’m actually satisfied with the overall stiffness of the ride right now — I don’t want the suspension to become uncomfortably harsh.

What torsion bar size would you guys recommend for mostly city driving, while keeping a balance between comfort and proper support?

Thanks in advance!

[David 23]

21/26 is a popular size for spirited driving without being overly harsh.
I run 22/28 on my hot rod '79 my wife likes 22/28 on her 72, as she likes the firm ride without the 911 wallowing.

[Mr. Merk]

They aren't too small. Porsche used 19mm torsion bars all the way through the 89 Turbo, even the infamous RUF Yellowbird

If you wanted an "upgrade" I'd recommend switching the rears out to 25mm as on the 86-89 Carrera.

Your front bars could be getting weak, I'd just get a replacement pair

https://www.pelicanparts.com/More_Info/SAW1819.htm?pn=SAW-1819&SVSVSI=566&DID=55636

[Bill Verburg]

Originally Posted by bose213

Hi everyone,

My car is 79 911sc sportomatic. I’m still running the original factory torsion bars on my car. They’re pretty old now, and I think it might be time to replace them since metal wears out over the years.

Here’s the issue: when I fill up a full tank of gas, the front of the car drops noticeably lower. As the fuel level goes down, the front slowly rises back up.

So my questions are:

Is this happening because the torsion bars are simply worn out and no longer holding properly?

Or is it because they’re too small in diameter (currently 19 mm)?

For reference, I’ve already installed new Bilstein B6 Performance shocks. I’m actually satisfied with the overall stiffness of the ride right now — I don’t want the suspension to become uncomfortably harsh.

What torsion bar size would you guys recommend for mostly city driving, while keeping a balance between comfort and proper support?

Thanks in advance!

a gallon of gas weighs ~6.1#, add 10g and you added ~61# to the front weight

stock 18.8mm t-bar wheel rate is ~152#/in w/ Bilstein's, 61# will then drop the font by ~.2"

It would be normal for the front end to rise ~..2" after using 10g of gas.

The 2 main reasons to use other than stock t-bars are
1) to get less roll in cornering
2) to change the base handling of the car i.e. more/less over/under steer.

if you are happy w/ the handling and nothing else is changed then keep the 19/23 or use 20/26, for more under use 21/26 for more over use 20/27

the bigger bars will reduce roll w/o degrading ride too badly, of course you can stray further from stock too at the cost of poorer ride and poorer mechanical grip.

[PeteKz]

Here we go again: Torsion bars, and steel springs in general, do NOT get "weak" or "tired" or "wear out." The spring constant (stiffness) stays the same unless they fail. In normal use, you will never wear out a Porsche torsion bar, or a quality aftermarket bar.

However, the rubber bushings do wear out. Inspect and replace the front and rear bushings, especially if they have never been replaced. Also the sway bar bushings. They almost certainly need it after 45 years. Do not replace the t-bars with stiffer ones before you renew the bushings.

T-bars or springs do not increase the felt stiffness or harshness of the suspension near as much as stiffer shocks. You already have those, so stepping up to 20/26 t-bars will not decrease the ride quality appreciably, but as Bill V noted above, it will reduce the tendency of the car to roll in hard turns, and it's front to rear understeer/oversteer.

Because you want to keep this a comfortable car on the street, I recommend that you first change the bushings, then go up to 20/26mm bars, and keep the B6 shocks you alraedy installed. That will give you a comfortable, but livelier road feel. Then drive it for a few thousand miles before you contemplate further changes.

[unclebilly]

I have 23/29s in my 911. My Turbo is stock.

The 911 is not nice to drive on the street.