torsion suspension setup

[vwrail10]

hi everyone new to the site and would really appreciate some help with my suspension. I have a vw sand rail irs setup with torsion in rear and standard king pin with torsion in the front. I am doing a frame up over haul and recently ordered some new shocks which are empi coil overs. they do have adjustments but at the softest point they are still very stiff. Question I have is , is removing some of the torsions the best thing I can do? sorry if I have confused anyone. thanks I advanced

[BL3Manx]

On fiberglass buggies, because the stock suspension is designed for a car which is hundreds of pounds heavier, many owners use well broken in hydraulic shocks in front. They don't use nitrogen charged and definitely not the helper spring type. If you do the front suspension is pretty much rigid.

To make the front suspension even more capable of absorbing bumps, they cut some of the torsion leaves. There are threads on the fiberglass buggy forum which show how its done.

[vwrail10]

thank you and also can you do the same to the rear?

[BL3Manx]

On the rear they have torsion bars, to make them softer you need to replace the bars with smaller diameter or longer bars. Using longer bars requires using springplates with deeper splines

[Dale M.]

[dustymojave]

Part of your problem is that those EMPI coilovers aren't worth the cardboard boxes they come in. And the springs on them are probably NOT needed, especially if you're talking about removing torsion leaves. That's like pulling teeth out so there is room for dentures. You would be better served to install KYB Gas-A-Just shocks on the front and sell those EMPIs.

In pushing down vertically, the front suspension will seem stiffer than it will ride. Especially if the front is rotated so the arms are at a steeper angle when the car is sitting. In offroading, if you drive it like a granny in a golf cart, it will seem stiff. Then if you drive the same car fast over big bumps, it will suck them up and seem smoother.

But the correct setup for your suspension depends entirely on where and how you will use the car.
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[flashho]

Sounds like this is a new ride for you? I would not do anything until I drove it a few hundred miles , then if you still feel it is too stiff, put some used kyb shocks on the front, toss the empi s. Then install suspension seats, which will make a huge difference.
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[TDCTDI]

I'm not trying to step on any toes here but reclocking the rear torsion bars is not going to change the spring rate of a torsion bar, only the height of the vehicle due to the different angle of the spring plate. The only ways to soften it is to change the bar length/diameter, add weight or lengthen the trailing arm.

[TDCTDI]

You can soften the spring rate in the front by removing some of the leaves from the spring pack.

[dustymojave]

[BL3Manx]

[PhillipM]

A torsion bar is not rising rate unless the pivots are offset to each other.

From a purely vertical displacement point of view, you could argue that the VW system is actually falling rate, due to the suspension arc from the arms rotating, even though it'd linear radially.
In reality that actually tends to keep the reaction fairly similar through the travel, as of course the vertical displacement speeds are lower when the ride height is high - as the arm can move backwards when it hits a bump more easily.

[race-desert]

I see this torsion bar spring rate thing both ways! but for the sake of just asking! when a rear torsion bar gets wound up, doesn't it get harder to wind up? which in turn would make it "raising rate" spring!?!? or is it the same rate as it twists, and wound so far that it breaks?

[Axitech]

Save yourself some money, take the EMPI shock/springs and cut the springs off of them. They have perfectly good hydraulic shocks on them, but the coilover springs are unnecessary. Cut 'em off. Or, as Dave told me, give them the 'lake test'. Toss 'em in the lake and get good ones!
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[PhillipM]

[BL3Manx]

Here is a chart that shows torsion rates(resistance to twist). You can see in the second section down that for each degree of rotation of a torsion bar with a given length and diameter, that there is just one torque value in in. lbs.

So to twist a bar 1 degree it requires X in. lb. of torque, two degrees = 2X in. lb., three degrees = 3X in. lb.. To twist it 10 degrees requires 10 times the torque required to twist it 1 degree, however the additional torque per additional degree of rotation remains constant whether its 1 degree or 10. That's a linear rate.

If it was a rising rate it would require X amount of torque to twist it one degree, then it would require more than 2X in. lbs. of torque to twist it a second degree. That would be a rising rate spring.

[DHale_510]

The rest of the arithmetic...... the conclusions are simpler than the math.

To find the wheel travel from the torsion twist you need a little trigonometry;
height = 2 arm lengths times sin of half the twist angle.
Arm lengths are about 16 1/2" stock, about 20" for a 3x3.
So for a stock IRS you get about [33"][.00873]=.288"/'twist.
For 3x3 IRS you get about [40][.00873]=.349"/'twist.

To find the wheel rate per inch of travel from the torsion rate;
rate/inch = rate per degree / inches per degree.
For stock IRS [swing is very similar], 22mm and 21 3/4" torsion,
558"# / 16 1/2" = 35.6 #/' and 35.6 #/' / .288 = 124#/" at the hub center.
For a 3x3 with 28mm x 26 9/16" bars,
1217"# / 20" = 60.8#/' and 60.8 / .349 = 156#/".
Notice that this is the same as paired 250#/" and 400#/" coilovers-
[250][400]/[250+400]=153#/"

You multiply your rate by your travel to see if you have enough travel and spring rate to support your car and loading. More spring or more travel is needed for more weight. Remember this is "up" travel, some of your total travel needs to be "down" travel in the real world.

I hope this helps.....
Dennis

As you increase the wheel offset the spring rate will decrease linearly. If you put wheel twice as deep as the stock axle length you would decrease the spring rate at the wheel by half, maybe with some weird duallies?[b]

[Aerindel]

My sand rail is a stock front suspension (except for hook and rod over travel stops) with some old hydraulic shocks on it.

Its maxed out at the top of its travel as a default since the front end only weighs about 150lbs and will happily balance on three wheels. It feels very stiff, essentially not moving at all when you push on it.

But driving on mountain roads the suspension uses ALL the travel it can get and doesn't feel stiff at all.

[DHale_510]

So I stopped a bit short last week on this topic. It seemed I said enough.
There was a debate about whether the suspension is a rising rate design. Both sides are kinda right.
The torsion springs themselves are constant rate.
The suspension design is rising rate after horizontal.
The wheel rate calculation around the angle of deflection shows that as the angle goes up the sine number tells the height, and this is effectively a rising rate since the sine value decreases the travel.
If the arms were straight up [that's an impossible if!] there would be no further travel to be had for an extreme example.
Dennis

[PhillipM]

But of course, the inverse is also true, in that it's falling rate on the way up to horizontal

So overall, most lifted rails, etc, are actually going to have a net falling rate on torsion bars, as they have more down than up unless they're running very tall tyres.
Saying that, I used to stagger the front torsion leaves to get a progressive rate anyway.