Torsion Bar and Suspension question

[stcan]

Hi

I see a lot of recommendation torsion bar size of 21F/27R. Seem to be for heavier SC /3.2 car.

I wonder for the long hood 71 911, if the same recommendation apply.

The car will be mostly street driven, with couple track days couple times a season.

I have the Sander Hollow 20F/27R that I can install, what did you think of that combo. Or am I better to get new combo 20F/26R or 21F/27R

I am thinking of getting the Bilstien HD front and Bilstien Sport rear digressive re-valved to match the torsion bar. Is that worth it for street car? Who else does re-valved other than Elephant?

I also want to raise spindle 19mm. You would need the bump steer kit after that? Who else does that other than Elephant, just want to see other option.

Thanks

[Tyson Schmidt]

For a mag case engine and gearbox early car, I'd recommend 21f 26R. Especially if it is still narrow body and running a square tire setup.

Yes, you need a bump-steer kit with raised spindles. The drop-link style. The rack spacers won't get you enough with a 19mm raised spindle.

[Bill Verburg]

Originally Posted by stcan

Hi

I see a lot of recommendation torsion bar size of 21F/27R. Seem to be for heavier SC /3.2 car.

I wonder for the long hood 71 911, if the same recommendation apply.

The car will be mostly street driven, with couple track days couple times a season.

I have the Sander Hollow 20F/27R that I can install, what did you think of that combo. Or am I better to get new combo 20F/26R or 21F/27R

I am thinking of getting the Bilstien HD front and Bilstien Sport rear digressive re-valved to match the torsion bar. Is that worth it for street car? Who else does re-valved other than Elephant?

I also want to raise spindle 19mm. You would need the bump steer kit after that? Who else does that other than Elephant, just want to see other option.

Thanks

It will depend on how you want to alter the cars handling
20/27 t-bars decreases under steer/increases over steer by 59% compared to a stock early Carrera

20/26 does the same but only by 37%

21/27 by only 20%

don't forget to factor other changes such as wheels, tires, weigh distribution etc into the net result



A lighter car will have the effect as a heavier if the weight distribution and wheel/tire set ups are the same, but the lighter car will roll less and react quicker.

For a 2800# street car I'd go no bigger than 26 rear, for a 2200# street car 24 or 25, w/ a stretch to 26

if the spindle is raised then rack spacers will only be needed if the can is ultra low down ~160+/-

if at a more usual 140+/- even less need

Bilstein San Diego used too do revalves but the gut doing them retires and there was no replacement

yes, digressive is worth it for street and track, you can comfortably go a step stiffer on the bars w/ digressives

the revalve specs will be based on wheel rates and chassis weight

[stcan]

I don't want to alter the handling.

The tires will be 185-70/15 CN36 or Avon 6CRZZ all around on 7" Fuchs wheel. Stock flare

If I were to go 24 or 25 in the rear, what front would be good

If I go digressive than 26R is better than 24, 25R? What's for the front?

[Bill Verburg]

Originally Posted by stcan

I don't want to alter the handling.

The tires will be 185-70/15 CN36 or Avon 6CRZZ all around on 7" Fuchs wheel. Stock flare

If I were to go 24 or 25 in the rear, what front would be good

If I go digressive than 26R is better than 24, 25R? What's for the front?

I would go
20/25
or
21/26 for the least change in handling

185/70 on 7 all around already reduces understeer compared to a Carrera.

what sways are used?

[stcan]

stock front 15mm and stock 15mm rear.

Should those be change too?

[Bill Verburg]

Originally Posted by stcan

stock front 15mm and stock 15mm rear.

Should those be change too?

Those sway bars were also used on the early Carreras so don't change them unless you want to change over/under character

[stcan]

Is Sway-A-Way good torsion bar? Hollow or Solid?

How are they compared to the Elephant torsion bar.

[Kraftwerk]

I believe 'effective spring rate' changes according solid vs. hollow... someone please correct me on this.

[stcan]

Originally Posted by Kraftwerk

I believe 'effective spring rate' changes according solid vs. hollow... someone please correct me on this.

Yes I understand that, I would look at the effective rate if I were to get the hollow

[Bill Verburg]

Originally Posted by stcan

Is Sway-A-Way good torsion bar? Hollow or Solid?

How are they compared to the Elephant torsion bar.

I would only use the Sander's hollow, plated t-bars that Elephant sells. They are a very high-quality product that fits well and even provides a minor weight saving.

Elephants quoted size is the solid bar equivalent for comparison purposes.

[Tom F2]

Originally Posted by Bill Verburg

Those sway bars were also used on the early Carreras so don't change them unless you want to change over/under character

Wouldn't that be the very reason to have a the heavier rear sway bar? I have the 15 in my 73 and find understeer is reduced, plus the transition to oversteer is easier.

[Bill Verburg]

Originally Posted by Tom F2

Wouldn't that be the very reason to have a the heavier rear sway bar? I have the 15 in my 73 and find understeer is reduced, plus the transition to oversteer is easier.

of course

anything that stiffens the rear while the front stays the same will induce less under steer

but he said that he doesn't want to change the existing over-under character of the car

[PeteKz]

stcan: I have much the same car as you, a 1973T and it's a 99% street car with occasional track use. See my signature line for details. My experience parallels Bill V's recommendations.

I run 21F/26R torsion bars. I also have the Rebel Racing bushings front and rear, which reduces the spring rate somewhat, compared to the stock rubber bushings. My 21mm front bars are Swayaway. I don't doubt that the Sanders bars are very high quality items, but I can't knock the Swayaway bars either. They fit just as snugly in the splines as the OE 18.8mm bars, and have not settled measurably since I installed them over a year ago (about 7000 miles). The rear 26mm bars are OE out of a 930 turbo.

Important point: Shocks contribute more to the felt stiffness of the suspension than the springs because spring rate increases linearly with suspension compression, but shock forces increase roughly as a square of suspension movement velocity. The rougher the road, the more the shocks dominate the overall stiffness. That's why digressively valved shocks are great if you decide to go that way.

Personally, I use the Koni Sport adjustables at all 4 corners and I like them a lot. I run them at their softest settings on the street for best suspension compliance and comfort. Even so, the car feels very stable and planted, even on roads with big bumps and frost heaves. I think my setup is about as balanced as you can get for a light street car, driven on real-world (meaning crappy) roads.

[Michael.]

Interesting read. I have 22/29s on my 86 (bought the car with them installed) I was concerned it was going to ride horribly. But quite the contrary. It's very compliant while remaining taut. If I had to guess my car is in the 2500lbs range. (quite a bit of weight has been removed from stock)

[Bill Verburg]

Originally Posted by PeteKz

stcan: I have much the same car as you, a 1973T and it's a 99% street car with occasional track use. See my signature line for details. My experience parallels Bill V's recommendations.

I run 21F/26R torsion bars. I also have the Rebel Racing bushings front and rear, which reduces the spring rate somewhat, compared to the stock rubber bushings. My 21mm front bars are Swayaway. I don't doubt that the Sanders bars are very high quality items, but I can't knock the Swayaway bars either. They fit just as snugly in the splines as the OE 18.8mm bars, and have not settled measurably since I installed them over a year ago (about 7000 miles). The rear 26mm bars are OE out of a 930 turbo.

Important point: Shocks contribute more to the felt stiffness of the suspension than the springs because spring rate increases linearly with suspension compression, but shock forces increase roughly as a square of suspension movement velocity. The rougher the road, the more the shocks dominate the overall stiffness. That's why digressively valved shocks are great if you decide to go that way.

Personally, I use the Koni Sport adjustables at all 4 corners and I like them a lot. I run them at their softest settings on the street for best suspension compliance and comfort. Even so, the car feels very stable and planted, even on roads with big bumps and frost heaves. I think my setup is about as balanced as you can get for a light street car, driven on real-world (meaning crappy) roads.

It doesn't really change the wheel rate so much as adds a setpoint, a tiny one at that, similar to but much less noticeable than more modern suspensions w/ helper springs. Which I might add few will ever notice in practice.


For track use the solid bush options add precision to steering inputs and they are great for that,

On my 911 I have only used stock and sport rubber because it's a street car, My 993 has has stock, sport rubber and full mon-ball suspension, the sport rubber was best for dual purpose and the mono-ball for track use.

That said the solids can certainly be used for the street, they will just entail more maintenance.

[Bill Verburg]

Originally Posted by Michael.

Interesting read. I have 22/29s on my 86 (bought the car with them installed) I was concerned it was going to ride horribly. But quite the contrary. It's very compliant while remaining taut. If I had to guess my car is in the 2500lbs range. (quite a bit of weight has been removed from stock)

It depends on the road quality at the upper end of the options list

On smooth roads suspension stiffness it's an issue as it is on degraded roads,

and as Pete KZ says shocks have a big say too.

[Bill Verburg]

Originally Posted by PeteKz

stcan: I have much the same car as you, a 1973T and it's a 99% street car with occasional track use. See my signature line for details. My experience parallels Bill V's recommendations.

I run 21F/26R torsion bars. I also have the Rebel Racing bushings front and rear, which reduces the spring rate somewhat, compared to the stock rubber bushings. My 21mm front bars are Swayaway. I don't doubt that the Sanders bars are very high quality items, but I can't knock the Swayaway bars either. They fit just as snugly in the splines as the OE 18.8mm bars, and have not settled measurably since I installed them over a year ago (about 7000 miles). The rear 26mm bars are OE out of a 930 turbo.

Important point: Shocks contribute more to the felt stiffness of the suspension than the springs because spring rate increases linearly with suspension compression, but shock forces increase roughly as a square of suspension movement velocity. The rougher the road, the more the shocks dominate the overall stiffness. That's why digressively valved shocks are great if you decide to go that way.

Personally, I use the Koni Sport adjustables at all 4 corners and I like them a lot. I run them at their softest settings on the street for best suspension compliance and comfort. Even so, the car feels very stable and planted, even on roads with big bumps and frost heaves. I think my setup is about as balanced as you can get for a light street car, driven on real-world (meaning crappy) roads.

depends on the valving

here is a shock dyno comparison of Bilstein hd, Sport and custom digressive


While no perfectly linear hd & sport are good approximations of linear force increase proportional to velocity increase.

[PeteKz]

Bill, re the solid bushings (RSR in my case) versus the rubber bushings. After living with them for a thousand miles on the back and about 7000 miles on the front, if I had it to do over, I would replace the rubber bushings on my car with either OE hardness rubber bushings, or the harder "sport" rubber ones. As you recommend. You may have read my discussion of that on the thread about the RSR bushings. They do increase the noise and harshness on crappy roads somewhat. On smooth roads, I don't notice it. But crappy roads are more common than freshly-paved ones!

However, it was partly an experiment for me, and several others swore the RSR bushings were just as smooth as rubber, so I had to see for myself. For a street car, stick with rubber.