67 bug feels unsafe

[Slow 1200]

Spring rate and suspension travel have to work together. To me it seems like a bad idea to have suspension travel below the rest state of the wheel (i-e- no preload), the only way it would make sense to run such hard springs is to limit downward travel so you do have some preload, of course this could open another can of worms.

[GARRICK.CLARK1]

Yep. I ca see how wrong it is now. At some point, the vehicles back wheels will be in the no pre load zone. This will be quite often with roads that dip and rise. Those 28's are getting removed.
I've also got new spring plate rubbers on it, inner and outer, I doubt it's the springs toeing in n out and rear steering it.

[Ol'fogasaurus]

Spring rate and suspension travel have to work together. To me it seems like a bad idea to have suspension travel below the rest state of the wheel (i-e- no preload), the only way it would make sense to run such hard springs is to limit downward travel so you do have some preload, of course this could open another can of worms.

Without getting into a long detailed discussion on this but for example, those of us who off-road Bug vehicles or vehicles made from Bug components changing spring rates (a torsion bar is a type of spring) front and rear plus doing a lot of other necessary mods is pretty normal. The suspension needs to stay in contact with the ground (unless you are jumping but then you have to deal with the compression when landing) which requires changes to the stock (Autobahn designed for) road that the Bug was more or less designed for.

"Sand Cars" (as I remember) refer to specialty vehicles where the suspension travel distances start at something like 26". The "can of worms" is what we are here for and so are all the questions and answers.

When not in a vehicle a torsion bar (spring), coil spring or leaf spring is at rest but when a load is put on it things change. A coil spring is a torsional spring so when compressed or stretched the round stock twists just like a torsion bar does. In the front of a Bug the leaves in the beam also twist to handle loading and unloading. The front beam also can be modified for different reasons/applications. Leaf springs also change shape by the arc changing which also stretches or compresses the material like the material in a torsional (coil or torsion bar) setup does.

I never have understood the slipping in of the torsion bar and no application so that when the vehicle's weight is added that it sits on the stop with no hang (down) motion. Unless I am missing something some preload has to be there even in stock setups or you have no real/limited suspension travel.

Lee

[Slow 1200]

Hi Lee I completely agree with your message, I'm not an engineer or a racer, but I believe I have a decent understanding of how suspensions (kind of) work

I agree that running so much preload that the car sits on the bottom stops at rest doesn't seem to make much sense, I was referring a different situation (another of the many wrong ways to set up torsion bars ): This is when the spring rate is way higher than stock and spring plates are set at the angle needed to set ride height, which turns out to be way above where the bottom stop usually is (think track car with thick torsion bars for example) . As I see it, if you don't add a positive stop to limit rebound travel, the wheel can potentially flop around the "rest" position in certain situations, specially on a swing axle car that is already trying to jack at every corner.
Of course running wrong shock valving, big tires, heavy wheels, worn bushings, bad alignment, would all exacerbate this situation

[Ol'fogasaurus]

Hi Lee I completely agree with your message, I'm not an engineer or a racer, but I believe I have a decent understanding of how suspensions (kind of) work

I agree that running so much preload that the car sits on the bottom stops at rest doesn't seem to make much sense, I was referring a different situation (another of the many wrong ways to set up torsion bars ): This is when the spring rate is way higher than stock and spring plates are set at the angle needed to set ride height, which turns out to be way above where the bottom stop usually is (think track car with thick torsion bars for example) . As I see it, if you don't add a positive stop to limit rebound travel, the wheel can potentially flop around the "rest" position in certain situations, specially on a swing axle car that is already trying to jack at every corner.
Of course running wrong shock valving, big tires, heavy wheels, worn bushings, bad alignment, would all exacerbate this situation

vw swing axle.jpg

vw-swing-axle-irs[1].jpg

Adding preload to the torsion bar (usually the stock one) raises the pan/suspension up usually for either looks or travel/clearance so playing with preloading a "Swing Axle" vehicle that can be good or bad mainly because of the single pivot point on the axle. Like everything else there are limits to most everything. Remember that with a swing axle setup there are also 2 arc's involved also; one with the suspension travel we are talking about and one dealing with the axle's arc (and some other things). IRS has basically three arcs if done wrong (torsion, trailing arm and axle things).

There are several ways to control this angle change on a swing axle vehicle with the "Z-bar" being just one of them. They used to use straps but that was a long time ago.

With adding preload you basically move the pan higher off the ground because the adding more preload to the torsion bar makes it stiffer. The suspension travel stop on the bottom of the torsion tube which the spring plates don't normally sit on once the vehicle is back on the ground (vehicle weight) unless you add too much preload. In the stop is there for when you jack the car up and the weight is not on the suspension any more it stops the un-loading of the torsion bar preload from returning to 0-degrees. By notching the spring plate the notch in the spring plate allows the suspension angle change allowing for more drop angle/more suspension travel. Very common in off-road toys.

When lowering a VW (the lessoning of the preload angle) lessoning the torsion preload angle in the torsion bar allowing the vehicle to sit lower plus it gives a softer ride.

Your last sentence I totally agree with.

Lee

[Ol'fogasaurus]

"Preload angle setting"

setting the angle of preload 02.jpg

The torsion bar is inserted in the torsion housing with no load set then the spring plate is inserted and by rotating the inner and outer splines of the torsion bar and inserting the spring plate to the preload (angle) is set in this pix at 26°.

Unloading the torsion bar.jpg

Once the preload angle you want the torsion bar is rotated up and worked onto the stop then the rest of the suspension is connected (make sure the tool is clamped so it won't slide on the spring plate). You need to be very careful here and not get any part of you under the spring plate 'cause it can unload so fast that you would not have a chance to even see or react to it before it has gone through all it's unloading gyrations. Hands, arms and other body parts including one's brain can be damaged quite badly... again before one can react!

Once both sides are done and you put the vehicle down on the tires the spring plate will lift off the torsion housing's stop and you should be where you want to be. Quite often it will take several preloads to get what one really wants.

I hope this is what the conversation is after.

Lee

[GARRICK.CLARK1]

Chaps. Not done any thing to the rear been busy with life. Just been out in it. Did a boost rolling burn out, its wet out so it does it for fun. Anyway the suspension didn't dip down but the tyres wobbled side to side for a good few seconds. Who else's bug does this. I'm sure the big 70 side wall is too soft. There pumped up too

[Ol'fogasaurus]

Are the tires radial or Bias-ply?

Bias-ply are more apt to do this especially if the tire pressure is low. Do a search on the differences between the two styles of tires as there is a lot of info out there.

Like anything else, trading things for one thing causes other things to act up . I'm not into the current tall and wide rims using "rubber band" tire craze but I guess they do have their place also.

Lee

[GARRICK.CLARK1]

There Nexan CP661.

[Ian Godfrey]

I know a lot of drag racers have problems with tyre shake, here's an interesting article about causes, not so good on the solutions.
http://mooregoodink.com/garlits-talks-tire-shake/

[Ol'fogasaurus]

What kind of tyres (radial or bias-ply) and what kind of pressure are you running in them? Also, are you mixing the type of tyre in front vs. the type of tyre in the rear.

Lee

[GARRICK.CLARK1]

I'm sure there a radial. I've been reading up on bias ply. Fronts are 145 michelins
28psi on back

[Ol'fogasaurus]

The article was pretty good on the subject but old too.

One thing is you don't mix radials with bias-ply tires. 28#s in the rear at launch isn't low as I remember.

I ran "wrinkle wall" tires in the rear with low pressure (I don't remember just how low as that was back in the early 90's) and didn't have much, if any flexing of the tires on launch. One thing though check your suspension for alignment and the torsion bar setting (preload and/or strength of the torsion bar itself (dia. and strength as the metal can age and get weak). Here is another article on the traction subject: https://www.hotrod.com/articles/drag-slick-tire-tech/

Lee

[GARRICK.CLARK1]

Update.
Cars sold, less the engine. That's going in an irs'd buggy. Just need to find a good 1