Torsion Bars and sand rails

[Therealkoop]

Hey everyone, I've had a bent trailing arm on my 2 seat rail for a bit and wanted to "upgrade" to a 3x3 setup for no real reason (95% street driven). Looking through threads until my eyes hurt and I see that most people going to a 3x3 are also upgrading to 28mm torsion arms, but the relevant threads I am finding are also in a "baja bug" context.

As of right now the suspension actually seems kinda stiff, Im guessing due to weight. When using a 3x3 setup on a rail specifically, does anyone have a preference for torsion arms? It looks like 28mm with 3x3 will give a slightly stiffer rate vs stock, but as I said, the stock seems somewhat stiff as is.

Thanks for any thoughts. Ive got a laundry list of things im slowly figuring out.

[Vanillagurilla]

I'd put them on and see how it works with the stock bars first. Rber with 3x3s you will need longer axles.

[cbeck]

Is the rear suspension preloaded until it is always on the droop stop? I went with 27mm bars and still seems a little soft.
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My cut in half and rebuild thread
www.thesamba.com/vw/forum/viewtopic.php?t=647779

[Vanillagurilla]

[Therealkoop]

Yes I the suspension was preloaded. You can jump on it and it moves, but if you hit a good bump the rear end absorbs what seems like nothing and it just bucks the rear end up.

I suppose just going for it and buying new bars later is the ticket. Just wanted to see if there was a "rule of thumb" type setup.

[jsturtlebuggy]

Have you weigh the buggy?
Things you really need to know before changing suspension are total weight, weight front of front and rear, and corner weight.

On my 2500lb Manxter I was using 26mm 26 9/16" length torsion bars in the rear before I went to coil overs.
This is with 3x3 rear arms and 12in of wheel travel.
It rides very nice on the street and worked well off road and is fun to drive over the woops.
I have a bad back and like a soft ride.
Yes you need good shocks to control the suspension.

There is nothing wrong with using stock dimension rear trailing arms. Going with wider rear trailing arms, your are going to want to also widen the front beam to match for it to handle properly. If you look up track width specs on vehicles the front always matches rear width or is a little wider. Makes for a better handling vehicle.
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Joseph
Fair Oaks/Orangevale, CA
Elrod Motorsports
Motion Tire Motorsports
Having fun with Dune Buggies since 1970
Into Volkswagens since 1960

[Therealkoop]

Thanks for the thoughts guys. Im not positive on the weight, but through different methods I estimate less than 1200lbs. I wanted to get a 6" wider front too, again for no reason, mostly aesthetics if anything. I plan on upgrading 1 thing every winter. The first I went through and fixed anything that was shoddy with the frame, then wiring and getting it running, now im doing suspension. Maybe next winter will be an engine upgrade.

Slightly off topic, is there a good source for tie rods to match up with a stock steering box and a 6" wider front? That is one thing I havn't sourced yet. I could make them if need be.

Thanks again

[cbeck]

With any steering you should check tie rod to bottom frame rail at full droop, wouldn't be a bad idea to check at full compression also. The long side might hit first.
_________________
My cut in half and rebuild thread
www.thesamba.com/vw/forum/viewtopic.php?t=647779

[Therealkoop]

So I got the 6" wider front, rack and pinion, and 3x3 rear installed and have been driving it for a few months. Works great.

Currently the rear is set to 30% compression at ride height with the stock rear torsions (26" style). This works great for general driving and smashing potholes ect.

However, any hard driving and the thing wants to bottom out and hit the upper stops. I usually dont drive very hard, but of course im a bit more spirited with the new suspension and want to try it out. If the wheels leave the ground at all, i get hit with a hard bottoming out.

I considered putting pre-load on the stock rear torsions, but I think over the winter im going to try and get some bigger bars. Not sure what size or if this is the correct path vs more shock, but I think it will help.

[DHale_510]

Leverage.
A 3" wider trailing arm reduces the effective spring rate of your torsion bar about 30%. [The rate is reduced by the cubed value of leverage change, pretty geeky math here. 19" vs 16" is more than you would think.]
A 3" wider offset wheel [most common 8" rear wheels are 3" or 4" offset] also reduces the spring rate about 30% for the same reason.
So you have maybe half the stock 75#/" spring rate with a buggy that weighs maybe half a street car but that you kind of drive places you never would that car. And it bottoms out the rear suspension.
Maybe better than math on the 'puter, you want to measure some stuff. Measure twice, buy once...
A yardstick and some weight will give you your true spring rate, it's just pounds per inch of travel. Remember that you are working both sides at once. Stock stuff is very close to 75#/", and your extended arms and wheels will be less than 50#/".
Your car with passengers is maybe 1500# and your available suspension travel is maybe 8" up travel, so you will want about 100#/" per side to keep the suspension doing it's work. That's 25mm, 26mm torsion bar territory.
28mm torsions are about 3X as stiff as 22mm ones, 25mm ones are in the middle.
Your numbers will vary.
There are specific current threads more specific if you care to do more homework/math. Buddy Dale has posted very complete charts.
Dennis.

[Therealkoop]

Thanks DH that is great information, I appreciate it.