SWB front / Rear Sway Bar Sizing

[1968DT]

I am currently installing front and rear sway bars. I have a 15mm for the rear and 13mm for the front with 21/26 TB. Is it necessary to have matching sizes for SB's? I am also of thinking about a single shock tower brace for maybe a DE run a few times a year.

[Jerry L]

They don't match, front is larger than rear. Listing the T Bars as you did is a help, someone will join in to help more than I. as "somewhat" of a reference I am running 19 F 15 rear, using a strut brace, externally adjustable Koni"s running on 205 - 55 16's on my 66 912 Coupe, cant remember t bar size now but you have more weight and a lot more in the rear.

Regards

[chris_seven]

Typical tarmac set up used to be 15mm front with a 16mm rear but this was for standard torsion bar sizes.

By uprating the torsion bars you have significantly increased the wheel rates by 25% at the front and by 70% at the rear.

This will change not only the roll stiffness but affect the ratio between the front and rear roll stiffness and hence the balance of the chassis.

It may help to drive the car and learn about its basic tendency to either understeer/oversteer and decide what sway bars you need to fine tune the handling in the direction you prefer.

[Chris Pomares]

My car is a 67. I went up 1 mm in torsion bars size from 18/23 to 19/24 and have 15 mm front and 16 mm rear sway bars. The car has a little less roll in the corners, can be driven fairly hard, and is still comfortable on long drives.
Chris Pomares

[1968DT]

Thanks for the responses. I am going to stick with the 13 mm for now. New Pirelli 165/15, turbo tie rods, and bump steer. New ER rubber bush all around. I want to get the car much lower than its original profile, any recommendations without being too excessive for a "sports purpose" SWB. We are going to dial it all in on a Hunter alignment system but any advice for a plan of atack is welcome.

[chris_seven]

My car is a 67. I went up 1 mm in torsion bars size from 18/23 to 19/24 and have 15 mm front and 16 mm rear sway bars. The car has a little less roll in the corners, can be driven fairly hard, and is still comfortable on long drives.
Chris Pomares

I thought that 18mm bars were from a 914 and their use requires a 914 control arm as the spline pattern in the 914 is different to the 911

[Chris Pomares]

I hope Randy is OK with me posting this.

Here what the factory used on 911s:
Torsion Bars:
Front: size mm / lbs per inch / % of stock / application
18 Stock ('64-68)
19 110 100% Stock ('69-89) - including '67-68 911R, '68-69 T/R, '70-72 ST, '73-74 RS, '73 RSR, '75-89 930 (also Ruf CTR)
21 173 156% Optional '70-72 ST
22 210 188% Optional '73 RSR (also used by many privateers early on)
23 250 224%
24 290 264%
Rear: size mm / lbs per inch / % of stock / application
23 Stock ('64-78 or 80) - including 67-68 911R, 68-69 T/R, 70-72 ST, Std. 73 RS
24 122 100% Stock ('79-85, '73 Safari RS)
25 140 115% Stock ('86-89)
26 165 135% '74 RS, '75-89 930, '73 RSR also had rear coil helpers (Ruf CTR)
27 191 157% (I think Alan Johnson and Richie Ginther may have been the first to make these and 28mm rears in '69)
28 221 182%
29 254 208%
30 294 241%
31 332 272%
33 427 350%
Randy Wells
1972 S - Early S Registry #187
1972 T/ST - R Gruppe #51
http://randywells.com/blog http://images-of-america.com


http://www.pelicanparts.com/techarti...rsion_bars.htm

My torsion bars are basically 78 SC to 85 Carrera.

[edmayo]

Just one itty bitty little nit Chris, please check, but pretty sure 68 one year only used 22 rear bars.

[Chris Pomares]

Ed,
You are correct.
Chris

[chris_seven]

If you check the Parts list for the 911 then you will find that the 'Stock' Front Torsion bars have the following Part Numbers:

Left: 901.343.101.12
Right: 901.343.102.12

These numbers were used from 1965 until 1989.

The 'earliest' Parts List I have is dated December `1964 and contains the above numbers.

I believe the bar is an 18.8mm diameter and we commonly refer to this as 19mm.

This accounts for the small error in the '% of Stock' figures when compared to a 19mm bar.

I also believe that the 911R was fitted with a 17.1mm diameter front torsion bar Part Number 901.343.101.13 and 901.343.102.13 for left and right respectively.

The Parts Lists for the 2.8 and 3.0RSR only show 19mm Torsion bars with the standard Part Number. The other sizes shown on this list are the sway bars.

None of the Homologation Forms for the 911 list alternative Front Torsion bars but as Group 4 allowed these parts to be changed this isn't particularly surprising.

I can understand that other bars may have been used but they are not shown on the basic Parts Lists.

The wheel rate calculations are useful for comparison but will vary slightly depending on the 'assumed' effective length of the torsion bar and the ride height.

I would agree that errors would be small

We have specialised in SWB cars for a few years now and the only 18mm bar I have seen was on a crash damaged car that had been fitted with a 914 control arm on one side.

It's interesting that there are two different part Numbers for the 17.9 bars fitted to the 914.

Both bars are shown as 17.9mm but the 914 has a different Part Number to the 914-6.