upgrade torsion bar size

For road racing, autocrossing, or just taking that curve in style. Oh yea, and stopping!
Post Reply
User avatar
markvwguy
Posts: 35
Joined: Wed Sep 09, 2009 10:36 pm
Location: Kenmore,WA

upgrade torsion bar size

Post by markvwguy » Wed Apr 26, 2017 7:44 pm

So, what I have is a lowered 69 vert. sits on 215/45/17 in the rear with dual spring plates stock, Rear discs CB performance.
I'm now installing a'76+ "ZIG ZAG" RIB SINGLE SIDECOVER TRANS with 100mm CVs and axles.

The rear has very little preload because of the lowered stance. I want to increase the torsion bar size to stiffen it up. Now, with the rear end off the ground I can pull the spring plate off the stop fairly easily. If I go over a speed bump the rear bounces and bottoms out the drain cover plate hard!!, it has a Berg sump 2 1/2". I also want better handling. Anyone have some input as to a good size to go with? The rear shocks are unknown?? Nothing special made in USA standard non gas or coil overs; just hydros. I reminder seeing in a thread percent increase in stiffness as the diameter went up in size can't find it anymore. If I have 22mm stock going to 24mm would that be a good increase and replace shocks with something better

Thanks,
Mark
Last edited by markvwguy on Tue May 16, 2017 8:53 pm, edited 4 times in total.

User avatar
Marc
Moderator
Posts: 23722
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: upgrade torsion bar size

Post by Marc » Thu Apr 27, 2017 9:16 pm

The rate of a torsion bar of a given free length varies by the diameter raised to the 4th power - just going up from the stock 22mm to a 23.5mm IRS Squareback bar results in a 30% increase. You might want to locate and try a set of those before you "spring" for bigger aftermarket bars.

http://oacdp.org/wog72/120_h.png



Assuming similar material, a 24mm bar would be ~41% stiffer than a 22mm.

Also there are other options besides $300+ for Sway-A-Way bars.
924/944 Porsche come in 22mm (same as what you have now) as well as 23.5, 24, 24.5, and 25.5mm diameters. Because the spring rate is proportional to the 4th power of the diameter, a small change makes a big difference. 23.5=> 30% stiffer, 24=> 41%, 24.5=> 54%, and 25.5=> 80% ....most `80-up 924 and non-turbo 944 are the same 23.5mm as the `69-`73 Squareback, I don't know which specific models have the larger ones but that information's probably available at a Porschephile board.

User avatar
markvwguy
Posts: 35
Joined: Wed Sep 09, 2009 10:36 pm
Location: Kenmore,WA

Re: upgrade torsion bar size

Post by markvwguy » Thu Apr 27, 2017 10:00 pm

Thanks Marc,

Yes, that is the proportion % I remember. I actually finally found it again a few posts down. The diameter to stiffness % I am familiar with; I have a 78 Westy 20+ years . I wanted to have a better sway bar set up. I went with the EMPI 7/8" bar, I hated it!! Far too stiff!! I went back to the OE sway bar and still have it installed over the EMPI 7/8" bar. I always wanted a few MM larger than stock up front and the NLA (no longer available) sway- away setup in the rear.
Now, I'm waffling between 23.5 and 24mm Porsche 944 bars. OE German metal metallurgy has proven time and time again superior to aftermarket. I think I will source both, and see what happens without replacing the shocks first. My focus is to reduce wheel hop on launch and cornering characteristics . The 215's rear and the 205's up front stick nicely. Also have to address some negative camber.... bushings maybe??
Anyone want to buy front and rear Type2 EMPI swaybars? hahaha!!
Most appreciated for the input.

Thanks,
Mark

User avatar
Marc
Moderator
Posts: 23722
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: upgrade torsion bar size

Post by Marc » Thu Apr 27, 2017 10:47 pm

You'll get a little negative camber from lowering the rear, but odds are some of it is coming from worn torsion bar bushings. Replacement choices are stock, red urethane and black urethane. The urethane (esp the red) are prone to squeaking which can be annoying when tooling through a parking lot but probably won't bother you much elsewhere. Personally I've been satisfied with new stock ones on street machines, but they may not last as long.

User avatar
markvwguy
Posts: 35
Joined: Wed Sep 09, 2009 10:36 pm
Location: Kenmore,WA

Re: upgrade torsion bar size

Post by markvwguy » Tue May 16, 2017 8:44 pm

I have an update for this thread. Currently I'm going through the rear suspension pulled the rear trailing arms and found the outer side of pivot bushing looking like the photo after 48 years. Included is an index reference for the rear torsions. Follow the link, the index calculator is live so you can adjust the numbers as needed + or - ride height.
Also attached is a link to get black urethane bushings and anti squeak greese.

http://vw.zenseeker.net/Wheels-TorsionBars.htm
http://www.energysuspensionparts.com/?g ... oCAnDw_wcB
You do not have the required permissions to view the files attached to this post.

Bruce2
Posts: 6771
Joined: Sat Oct 13, 2001 3:01 am

Re: upgrade torsion bar size

Post by Bruce2 » Tue May 16, 2017 10:51 pm

markvwguy wrote:
Wed Apr 26, 2017 7:44 pm
The rear shocks are unknown?? Nothing special made in USA standard non gas or coil overs; just hydros.
Start with shocks, not the bars.
Get some Bilsteins or some Koni yellows

Ol'fogasaurus
Posts: 13099
Joined: Tue Nov 14, 2006 1:17 am
Location: Just north of Seattle

Re: upgrade torsion bar size

Post by Ol'fogasaurus » Wed May 17, 2017 9:04 am

One must be cautious of what one marks the torsion bar with and where. A scratch awl puts stress marks in it and some chemicals can be not a good idea either.

As Bruce said: shocks/dampeners first then, unless your torsion bars are really that bad and/or the rear of your car is sagging, replace or update the torsion bars. I did a lot of adjusting of the torsion bars before I got some good shocks and what a difference they made. OEM/cheap shocks to fit standard use don't meet the requirements most of us want up to and including stock everyday driving. Shocks/dampeners are there to support your springs and make them act like adults not kids with no idea of what their job is. :roll: :wink:

As the shocks/dampeners age they can either get stiff (like the ones in my almost a truck are doing) or sloppy giving poor handling on the street or highway. Decent shocks should last in the range of 30K but if the car sits a lot that can be reduced quickly. Some of the cheaper shocks are PP roght out of the box.

Good post Bruce!

helowrench
Posts: 1923
Joined: Wed Aug 11, 2004 8:20 am
Location: East of Dallas TX

Re: upgrade torsion bar size

Post by helowrench » Wed May 17, 2017 1:36 pm

I have 944 25.5 bars on the back of my 70 vert bug, coupled with the 14mm rear sway bar from the 944 as well.
19mm front sway bar seems to be a nice balance, stock Sachs oil filled shocks all around.
Also, Ghia front disks, and larger rear wheel cylinders for brake balance.

The rears are set soft, to maintain a level-ish ride height, at roughly stock.
205 fairly sticky tires all round.

In cornering, I never was able to get either end to step out of line, but more power would change that. (stock 1600sp)

The ride improvement was quite stunning though, as it now feels very similar to newer cars.
Small bumps are absorbed and damped without any drama.

rob

H2OSB
Posts: 454
Joined: Mon Aug 21, 2000 2:01 am

Re: upgrade torsion bar size

Post by H2OSB » Wed May 17, 2017 2:55 pm

replaced with post that includes appropriate quote below
Last edited by H2OSB on Wed May 17, 2017 2:58 pm, edited 1 time in total.

H2OSB
Posts: 454
Joined: Mon Aug 21, 2000 2:01 am

Re: upgrade torsion bar size

Post by H2OSB » Wed May 17, 2017 2:57 pm

helowrench wrote:
Wed May 17, 2017 1:36 pm
I have 944 25.5 bars on the back of my 70 vert bug, coupled with the 14mm rear sway bar from the 944 as well.
I wish I could have found 25.5s. 23.5s are far more common and thus bought a pair for both my car and my son's (both 1303s, '74 and '73 respectively). Can you provide any details of the rear sway bar install? I have a 15mm 944 rear swaybar which I plan to run with a 7/8th front bar (approximately 22mm). I created torsion housing brackets to support the middle of the bar as well as end links, but I have yet to create the brackets for the trailing arms and would like to see what others have done.

Thanks in advance
H2OSB

helowrench
Posts: 1923
Joined: Wed Aug 11, 2004 8:20 am
Location: East of Dallas TX

Re: upgrade torsion bar size

Post by helowrench » Wed May 17, 2017 4:00 pm

I did a possibly bad ju-ju thing by literally drilling a hole through the spring plate, and used a Honda CRV swaybar drop link.
Holes were (1)deburred properly, (2) these are double spring plates, and (3) will never see off road harder than my front lawn.

Rob

User avatar
markvwguy
Posts: 35
Joined: Wed Sep 09, 2009 10:36 pm
Location: Kenmore,WA

Re: upgrade torsion bar size

Post by markvwguy » Wed May 17, 2017 7:25 pm

I have 24mm Porsche 944 bars going in. The black urethane pivot, and torsion bushings are also going in, stainless braided brake flex lines going in also.
I don't think shocks alone will control wheel hop on launch, rear end squat on launch , and cornering stiffness as a one item suspension part replacement. Yes, I love Bilstein, Koni and KYB; all quality accessories for a well put together suspension.

The front end of this car far out performs the rear, where all the weight gets thrown around. I will up date as things progress.

Thanks for the input.

Post Reply