Rear torsion bar questions...

[thumper911]

I have finally managed to rip apart the rear suspension and pull the torsion bars out. My understanding of the stock setup is a 22mm bar, correct? And this is merely found by simply measuring the outside diameter of the bar, right? If so, 22mm seems to be the number I got. Now my question is, how stiff would 28mm (or 27mm for that matter) bars be compared to a stock setup? I plan on dropping the rear a couple "clicks" and I also want a "corner carver" when I'm done. The front end has already been built with lowered springs and fat sway bar. (and yes, it's a Fat Chick...72 Super). She handles great up front in the corners but the rear is mush right now. Would it make a major difference with the 28mm bars lowered, with a moderate sway bar or would I be better off to stick with the stock bars, lower it and add a fat 3/4 - 1"+ sway bar instead? I don't mind a stiff ride as this is obviously just the summer fun car. But would I see any benefit buying the stiffer bars that basically just keep the body suspended or should I spend the money on shocks/sway bars instead? Any input would be appreciated. It's going to be up on jacks for a while but it would be nice to know (and understand) which route may be the best to follow. Thanks in advance.

[Bruce]

You can calculate the difference in spring rate of a torsion bar compared to stock by taking the ratio of the diameters raised to the 4th power (or square it twice)  So your 28mm bars are (28/22)^4 = 2.6 times stiffer.  This is a HUGE step, so I don't recommend it unless you also increase the front spring rate by a similar amount.  Since front springs are very limited, I think you should stay conservative on the rear bars.

Stock bars exist in 23 (or 23.5?) from a Type 3 (Hans?).  Early Porsche 944s and 924s have 24 or 25mm bars (and more)  I think Geoff knows what's available from 944s.  There are a lot of different sizes in Porsches.  They had options of sport suspension, turbo, S, etc.

You can also look at Porsches for perspective.  Full race for a late 911 is a 28mm bar.  They have a LOT more weight to control, and a lot more hp.

I would go with the Type 3 bars or a 24 bar at the most.  Then upgrade your shocks.  Bilstein or Koni are adjustable, so you can play with their settings to find what you like.  Konis are $$$.

By far, the biggest contributor to great cornering is wheels and tires.  The more the better.

I believe the front bar is 19mm stock.  You can get a 7/8", and maybe more. 

SAW rear bars are 3/4".  If you decide you don't need such a big rear bar, you can bolt on the stock bar from a 924 or early 944.  I think they are 12 or 15mm, but don't quote me on that.

[thumper911]

Thanks Bruce...that's the kind of info I was looking for to get me started in picking out the right bars for the right direction I want to head. Gets the gears turning good...

[Hansk]

Sorry I'm so not a numbers guy . If I knew yesterday ,   it's gone today  But I do know that some type 3 squarebacks did have bigger bars.  Bruce , are you saying that 944 torsion bars will fit our cars?   I've always thought vw's were too soft in the back in general but especially for handling , even more so at high speed. I'm not saying you should try this but I personally would be temped to try a 28mm bar in my swing axle car.   2.6 times stiffer seams just about right to me.  When I watch a vw traveling down the road I see the front follow any bumps fairly closely but the rear always generates far more suspension movement and I can really feel this in the car . Just seams a little out of balance to me ,but thats just me.

I should add that vw probably did this to control over steer and that stiffer rear bars will probably increase over steer.

[Bruce]

When a swing axle car is going straight down the road, you can do anything you want to the spring rates.  However, if you want to toss that swing car into some twisties, having such an imbalance (stock front, 28mm rear) would be disasterous. 

I agree that a VW can stand to use a stiffer rear bar.  That's where all the weight is.

The rule of thumb is, the smoother the track, the stiffer the bar you can use.  A rough track needs a soft bar so the tire remains in contact with the road as the surface bumps along.  If you had a stiff bar, the tire would skip.  When that happens, you spin out.  The problem you will have is deciding how rough the "street" is.

[thumper911]

I'm thinking now with reading some more info online, that I might split the difference now. A 26mm bar setup is looking quite inviting...not too stiff but yet should be a noticeable improvement over stock. Using your ratio you mentioned earlier Bruce, I believe the difference should be nicely around 2x stiffer than stock. I plan on lowering the rear as well, and with a 3/4 sway bar and new shocks, that should be nicely matched up with my already lowered, taper spring 7/8 sway bar setup up front. If there is any more ideas that someone wants to throw my way, please, be my guest! 

[Geoff]

Mine are the 25mm 944 turbo bars if I remember correctly. You must use the long irs spring plates with these. Works perfect in my Oval...That being said a 944 has less weight in the back than a beetle. It works perfect for nice clean launches in my oval, slight squat and big wheelies.

[Bruce]

How did you use IRS spring plates with a swing axle gearbox?