"4-Way suspension" work alike?

[KentT]

That makes sense, if you think about it. Stiffer springs would tend to snap back and perhaps resonate. Weaker springs would give more back and forth movement before finally settling down.

I typically ran my fronts preloaded a bit up, though, not down and not enough to lift the nose -- I liked that to control weight transfer forward for braking and also understeer. I ran the rears at their neutral, at rest position. I think I was running E78x14 tires on the front on 14x6 wheels and F70x14s on 14x7s on the rear -- Jackman-type 5-spoke wheels. That's been a long time ago -- but I think it was the tire combination. Don't remember the offset, but the fenders were full... of bias ply. You didn't have the wide array of radial sizes and profiles available then like you have today - much less the tread choices -- and if you went with metric sizing then, you were almost limited to 80 or 85 profile. I had adjusted my swingarms down one spline to overcome "old-age sag" and regain a bit of clearance. It had a bit of nose-down attitude, but not much (almost level) and certainly wasn't a slammed Cal looker since the front wasn't lowered. That stance is what made a camber compensator or these 4-ways essential. I was more concerned with traction and handling than looks, though I did decrome it ...

Fun times... we'd often just set up cones in a parking lot and play!

[PhillipM]

That's when i remembered to pull the rear down some against the torsion springs.
(This is what you cannot do with only dual compression springs on coil overs)

You either wind the torsion bar off a little, or bin it and wind the lockring up on the coilovers. Same effect, you're only moving the crossover further into the compression travel.

[Roflhat]

So are you saying these work or not...?

Surely having suspension that "returns to centre" is a good thing as far as handling is involved?
I don't really know about damping or that stuff, but if you can explain (in easy words!) then please do

[Piledriver]

So are you saying these work or not...?

Surely having suspension that "returns to centre" is a good thing as far as handling is involved?
I don't really know about damping or that stuff, but if you can explain (in easy words!) then please do

There really isn't much question that it works, the question has been related to exactly how/WHY they work, how to tune them etc.

The dual spring coil over model proposed works, but still doesn't address the reduction in rate when the secondary spring on the 4 way pulls, as std dual spring coil overs cannot PULL to counter the torsion bar, not can they be preloaded AFAICT unless installed in an already sprung system. (AKA dual coil spring conversion with no torsion bar)

These SIMULATE a highly progressive single spring whose rate goes up fast when compressed from rest, and down very quickly on extension from the rest position.

Springs in compression only cannot pull as these do, so the conventional dual spring coil over model is a close but not quite model IMHO, although it's a damn sight closer than previous guesses, I am still dubious such a single spring could be made at a sane cost, (it would need to vary significantly in wire diameter and pitch at least) and ~certain it cannot be done with a torsion bar, or remotely as cheaply and effectively.

AFAIK there is no such thing as a progressive torsion bar, unless you connect to it via an eccentric linkage of some sort.

[PhillipM]

They don't need to pull, forget pulling, nothing is pulling on the wheel, the wheel is always being pushed down, the springs that are pulling are just reducing the rate at which the wheel is being pushed.

Lets say your base wheel rate is 100lb/inch with the torsion bars.
And lets say the spring on the 4 ways is 50lb/inch of wheel rate.

When the 4-ways are pulling, the spring rate AT THE WHEEL, is 50lb/inch. Nothing is pulling, still pushing down.
When the 4 ways get compressed enough that they switch to pushing, you're now at 150lb/inch wheel rate, still pushing down.
The chassis and tyre doesn't care about what the spring on the 4 way is doing, as far as it's concerned, the wheel is always sprung one way. Just at two different rates.

Now, lets say you stick single spring on the damper, just like a normal, easy to find coilover setup, and you get an off-the-shelf, cheap 50lb/inch spring.
Now, you put your 100lb/inch torsion bar in the car, and you put the grub screw in so that it doesn't work in droop, only comes in at ride heigh and into the compression travel.
Your first rate is now 50lb/inch. Your secondary rate is 150lb/inch.

Okay, got something similar to my rail with twin front torsion leaves and adjusters?
Take some leaves from the bottom stack, there's your 50lb/inch spring.
Put the top stack in, and set the adjuster so they only start to work from ride height and into the compression. 50lb/inch base rate. 150lb/inch secondary rate.
If you have a look at the rear pictures of the rail, you'll see there, in the back, a pair of standard VW torsion bars from a scrapyard, connected with some arms and droplinks (~£30-40 of material parts at most?). You can set that to come in where you like, and give you a step change in wheel rate. You can even vary the length of the arm by moving the droplink and alter the amount it changes the spring rate by.

Now, all this assumes a perfect world, the reality there's always a non-linear zone in the initial take up, and probably more so in the 4-way system because it has both the machining slack in the adjuster>spring and a non-linear area both ways on the spring as it transistions* - this is the bit that causes the weird handling Piledriver describes as going away when biasing it an inch one way (gets it out of the ride height area so it's not affecting the initial transistions/turn in of the vehicle), that's easily done on any of the above methods simply by biasing the second spring one way or the other for the same effect, and although they shouldn't suffer quite as much, the step change in rates still affects the response and predictibility of the car because it alters the feedback to the driver, so it's a good idea to keep it biased one way or the other as Piledriver has.

*This is the bit that allows a single progressively wound spring to do the same job, the transistion is never instant, there's always a ramp up, which immediately allows a progressive spring to emulate it, don't know what it's like over there, but around here I can get a full car set of custom wound progressives for £100 - that's a very cheap way of doing it if you have the mounting hardware, but less adjustable.

To address something else, Roflhat, all suspension will return to centre, that's how the spring works. If it was a good idea to keep the suspension always centred, you'd weld it solid to stop it moving, no?
I will say a lot of race and rally cars - those with seperate heave springs/dampers mainly - actually go the other way and have the spring rates soften on the corner springs in compression as it gives more grip, compliance and a lower roll centre.
You'll often see race bikes which have progressive suspension linkages as standard stick it in the bin and go to a linear setup for better rider feedback and control, the only reason the progressive linkage is there is to cope with lots of rider weights and terrain without putting in 2ft of suspension travel.
That's the same reason I use it and many offroaders do - it's not that we want to, it's just that we don't have the suspension travel available to both have a soft rate for maximum grip and still absorb jumps/landings, etc, without making the suspension stiffen up when it hits the big stuff. If I'd got 40 inches of travel I wouldn't bother, but I don't

[Roflhat]

Right, I think I understand what you're saying now. Any pictures of your setup?

[Piledriver]

Again i wish to point out your "simple/cheap " progressive spring equivalents... while I admit are probably possible,
require a full coil over conversion, so there is neither simple nor cheap in what you propose.

By "pulling" what I'm trying to say is the combination is not like taking the std bar then just adding to it.
With the combination the rate at full extension is reasonably close to zero, and could be easily made so it actively limits travel.(Limit straps would probably be a better plan.)

If you only add std coil overs of any description to the stock setup, it cannot pull on extension and reduce the rate of the stock bars on extension.
These do.

What I have is ~300-350 lb/in coils on the std suspension (F&R) . the shocks mount at ~50% distance on the arms.
I do not know what the stock setup we add on to works out to.

It's the only way I can think of to make a torsion bar based suspension progressive, or even to be able to soften/stiffen the rate w/o replacing parts. (other than the equivalent version: split swaybar locked in the middle)

The setup does work quite well esp considering its simplicity, except for the spring mounts which are not off the shelf items, but they can be made several ways.

You can't buy std coil springs off the shelf for too much less than $70/ea around here, and that's mail order only from the likes of Coleman racing, and you would have to have coil over$$$ anyway to use them.

I have not investigated the cost of custom wound , esp not variable wire size coils, and quite frankly my wallet puckers at the thought. (plus a set of coil overs to put them on and all else that entails)

I would like to see some pics of the other setups, esp the Atom setup with the adjustable rate bit.

[PhillipM]

Again i wish to point out your "simple/cheap " progressive spring equivalents... while I admit are probably possible,
require a full coil over conversion, so there is neither simple nor cheap in what you propose.

By "pulling" what I'm trying to say is the combination is not like taking the std bar then just adding to it.
With the combination the rate at full extension is reasonably close to zero, and could be easily made so it actively limits travel.(Limit straps would probably be a better plan.

I'm struggling to see why that's an issue? You've made coilovers here, you've got a top and bottom mount and a spring, that's a coilover, no? I don't know about over there but you can buy the hardware over here to convert even a damper with no mounts to a coilover with threaded adjustment for £30 for a pair of dampers - and stuff is usually waaayyy cheaper over there (the stuff I'd buy if I could fill and container over there an bring it back without the extortionate shipping and taxes )

If you're rate is zero, you've stopped the suspension moving, so as you say, you may as well put a couple of 5 dollar straps on it. That's a zero-droop type setup and whilst it can be a fast band aid for some bad suspension traits, you're usually better off fixing the issues to start with and keeping your suspension travel.

edit: If you have a look on the intrax racing site you'll see the unit that's fitted to most Atom racers and the V8 production model. Basically the ends are similar but cut all the way through:



So you can actually change the spring rate by winding it up the spring. (Shorter spring/less coils = stiffer rates)

[Piledriver]

Good point, that's an improvement on the 4-way design, it lacks the range of adjustability that provides.

I'm considering having some more made up, may move to 2.5" springs as well, although the 2" ID setup fit this car, I want to add these to the F/R struts on my Mk1 (Cabriolet) and perhaps on my sons super and my 914. (inside the stock springs, or working with the front torsions on the 914 suspension)

I can't find springs that cheap, but the ebay coil over kits would make for a good start for the strut based cars.