18.8/26 torsion bars on 79 SC?

[Brian Cameron]

Overhauling wife’s 79 SC including suspension. Front t-bars are rusted/worn at 145K miles, so need to replace them. I suggested we replace the rears too, which she ok’d, as she likes the idea of replacing old parts as a set. Also replacing all rubber bushings and ball joints. The Koni sport adjustables are ok with only about 10k miles on them.

It currently has stock 18.8F / 24R. Need to keep the ride comfortable for her so staying with stock replacements up front. But would like go slightly larger on the rear, as the other stakeholder is my youngest son who is helping with this project, will likely inherit the car one day, and is an autox enthusiast. I want to stay with the stock roll bars for cost reasons.

Ideally we would go with a conservative 25mm on the rear but looks like that size isn’t available as aftermarket eg sway away, and oem is NLA on one side. So the next size up is 26mm from sway a way. From research on the forum that means about a 35% increase in stiffness.

Is that a bad idea? What would the 18.8/26 combo mean for handling and ride quality? Is that a good or bad combo for a mild improvement to handling with little impact on comfort? Is this combo ok with stock roll bars?

Hope the pelican brain trust can guide me, thanks in advance!

Per Randy W on another forum thread:

Originally Posted by Randy W

Here's a chart I put together from various resources:

Torsion Bars for Porsche 911:

Front: size mm/lbs per inch/% of 19mm

18 Stock (64-68)
19 110 100% Stock (69-89) - includes 67-68 911R, 68-69 T/R, 70-72 ST, 73-74 RS, 73 RSR, 75-89 930, Ruf CTR
21 173 156% (Optional 70-72 ST)
22 210 188% (Optional 73 RSR)
23 250 224%
24 290 264%

Rear: size mm/lbs per inch/% of 24mm

23 Stock (64-78/80) - including 67-68 911R, 68-69 T/R, 70-72 ST, Std. 73 RS
24 122 100% Stock (78/80-85, 73 Safari RS)
25 140 115% Stock (86-89)
26 165 135% Stock (74 RS, 75-89 930, Ruf CTR) (73 RSR *plus coil helpers)
27 191 157%
28 221 182%
29 254 208%
30 294 241%
31 332 272%
33 427 350%

[IROC]

Ride comfort is a very subjective thing and depends on many variables like the quality of the roads where you typically drive, etc., so there is no one right answer. Having said that, it has been my experience that - to a very great extent - shocks make a larger impact on ride quality than torsion bar size.

Since you are already considering going larger in the rear, I think it makes sense to go a little larger in the front. There are lots of variables, but based on the numbers above a 21/27 combo adds almost the same mount of stiffness front/rear as what came from the factory. I don't think you're going to find that combo too stiff, but more opinions, etc. would be good. This combo would be good for handling and would be fine with stock sway bars. In fact, on the subject of sway bars, "while you're in there" the factory Carrera sway bars are an excellent improvement in handling while still staying with the "under-the-body" configuration.

The 22/29s on my car (a 2350 lbs, ex-track rat car) are great until I get on bad roads and then it is annoying.

[David 23]

I think you would find 21/27 a postive improvement over stock. Certainly handling will be improved, and honestly the more controlled ride will likely provide more confidence without sacrificing comfort.
I have 22/28 on 2200lb car and while it is certainly firmer, particularly over rough roads, the trade off to vastly superior handling is more than worth it.

[HaroldMHedge]

I upgraded an 82 SC coupe with Elephant Racing rubber bushings, sport were available, all around and 21/27 torsion bars. I really liked this setup even on rough roads.

[Bill Verburg]

Originally Posted by Brian Cameron

Overhauling wife’s 79 SC including suspension. Front t-bars are rusted/worn at 145K miles, so need to replace them. I suggested we replace the rears too, which she ok’d, as she likes the idea of replacing old parts as a set. Also replacing all rubber bushings and ball joints. The Koni sport adjustables are ok with only about 10k miles on them.

It currently has stock 18.8F / 24R. Need to keep the ride comfortable for her so staying with stock replacements up front. But would like go slightly larger on the rear, as the other stakeholder is my youngest son who is helping with this project, will likely inherit the car one day, and is an autox enthusiast. I want to stay with the stock roll bars for cost reasons.

Ideally we would go with a conservative 25mm on the rear but looks like that size isn’t available as aftermarket eg sway away, and oem is NLA on one side. So the next size up is 26mm from sway a way. From research on the forum that means about a 35% increase in stiffness.

Is that a bad idea? What would the 18.8/26 combo mean for handling and ride quality? Is that a good or bad combo for a mild improvement to handling with little impact on comfort? Is this combo ok with stock roll bars?

Hope the pelican brain trust can guide me, thanks in advance!

Per Randy W on another forum thread:

If you want to reduce understeer/increase oversteer 18.8/26 changes the base state to more over/less under by ~35%
Car setup is an interdependent system so other changes like wheels, tires, setup add their own flavor to the net result

Ride quality is not bad IMO but again it depends on the wheels and tires and local conditions as well as the owners taste.

[uwanna]

Originally Posted by HaroldMHedge

I upgraded an 82 SC coupe with Elephant Racing rubber bushings, sport were available, all around and 21/27 torsion bars. I really liked this setup even on rough roads.

I did the same thing to my '80SC, couldn't be happier! One of the best upgrades I've ever done, not "rough" at all. One thing others have done when using larger torsion bars with great results is to have Bilstein shocks revalved to work in digressive mode (Bilstein and several other folks do this mod).
A fellow Pelican friend (Tirwin) did this to his '83SC and the change is remarkable,
roughness is greatly reduced!

[Bill Verburg]

Agreed, a digressive revalve takes a lot of the sting of a stiff suspension away

[Brian Cameron]

Ok, here’s the plan: replace the stock 18.8/24.1 with 20/26.

Can’t replace all 4 with stock even if i was ready to pay the Porsche OE tax, as the 24s appear to be NLA. So it looks like some kind of aftermarket upgrade is the only way to put new TBs in all 4 corners, ie no mixing old & new.

Sounds like there should be little impact to ride quality, and hopefully no need for new shocks and/or ARBs so keeps cost down.

Fronts will be 128% of stock, rear will be 135%, ie a net 7% change from the front/rear ratio, so not dramatically different from the original. But should slightly reduce understeer which should make our son happy if he gets to autocross it someday.

Good point from Bill about tire sidewalls, will have to give that a think when the next tire purchase comes up.

I really do want to keep the wife happy, and that includes both ride quality (so she will actually drive the car) and keeping cost under control (so she doesn’t feed me cat food when we retire).

This resto is waaaay over budget already, with new fuel and injector lines, vacuum hoses, engine drop for new seals, sensors etc, DIY engine wiring harness, frunk fusebox replacement, SSI exhaust and dansk 2-1 sport muffler, an unexpected tranny rebuild, might as well get a new clutch too etc etc. Then i found rust under the battery and so now I’m replacing the suspension pan... and since the suspension is out anyway, now this, along with bushings, spring plates and a few other incidentals.

So I am lucky to still be married. She bought this car to keep me happy and busy with a new project since i finished my 993 overhaul a couple of years ago - “mechanical therapy” she calls it. She’s a keeper for sure.

Anyway, thanks all for the input and helping me overcome the mental block i had about going higher than 19 on the front. Since Porsche stuck with 19’s on the front for 20 years from 69 to 89 i guess i had it in my head that was the magic formula for comfort and the only option. But keeping the front/rear ratios in line makes sense to me and this conservative upgrade will hopefully tick all the boxes for this project.

[Driven97]

IMO, going up on rate in the front has more impact on ride quality than going up in the rear. I've had stock, 21 & 23. In the rear, I've had stock, 30, 33, and 36mm. Absolutely, positively stick with rubber bushings.

I was putting my car back to OE bars, and had only the fronts returned to stock, 33s in the rear. A late season local AX was scheduled, so I decided to take the car out as is, and I'd park it if it was undrivable. Car was so much fun to AX on 18.8/33 that I've left it that way. I do have a bigger front bar though, so YMMV.