The Camber Compensator

[redhot]

So, what will I gain by using a camber compensator without changing the torsion bars? Nothing as far as I can see? I`m not to sure of whether I should install one or not.

Found this post on thesamba. VERY good one.
http://www.thesamba.com/vw/forum/viewto ... light=zbar



The Z-bar and camber compensator should not be described as being 'the same'. This is really an over-simplification, although they have common effects.

One thing to remember is that there are two types of CC; one which simply cradles the axle tubes and one that is 'tied' to the axle tubes. In the simple cradled version, it limits the simultaneous downward movement of the axles in either straight ahead driving or cornering. In the case of 'straight' and at high speed, the car raises up naturally, which reduces traction at the rear and increases the feeling of instability (cross-winds etc). Add to that the sudden need to brake hard, and the rear raises up even further. The CC limits this upward movement. In cornering, it allows the car to role but still limits the axle movement and so resists wheel tuck. When you tie the ends of the CC, I think it adds stiffness at the back while still preventing the angles necessary for wheel tuck. However, it should also promote over-steer, which is not a good thing.

The Z-bar works entirely differently. First of all, the Z-bar is not actually the primary element here. The 'system' is based around the fact that these cars also have softer rear torsion bars. Softer rear suspension, increases rear roll, placing more of the roll forces on the front axle and in turn reduces over-steer (or increases under-steer). This has the inherent effect of avoiding the conditions for wheel tuck. What the Z-bar does is put back the suspension lost through using the softer main torsion bars, only when needed. So it is completely ineffective when simply cornering but under heavy loads, it will increase the spring rate progressively (the connecting bar running from left to right is a long thin torsion bar).

What the CC does not do, is reduce over-steer or provide progressive rear suspension. There is an argument, however, that suggests that the inside rear wheel exerts some upward force on the outside wheel through the CC which could result in more under-steer, but I am not convinced of this. What the Z-bar does not do, is limit the simultaneous downward movement of the axles tubes, but VW did alter the camber of the rear wheels to limit the negative effects of this. The Z-bar can be made to replicate the CC characteristics by removing the inherent play in the linkage. However, this may result in some interference, in the system, during cornering.

All in all the Z-bar system is a little more subtle about how it goes about its job, plus, it has more ground clearance and does not use the gearbox as a mounting point.

While the Z-bar cars provide what I would call a more "positive" neutral handling characteristic, IRS goes a step further and makes the vehicle actually under-steer. Manufacturers prefer under-steering cars as they consider them inherently more safe.

[FJCamper]

Hi Redhot,

You're on target with your understanding that a camber compensator with some type of axle connection (straps, end links, whatever) affects upwards axle movement as well as downwards axle movement.

And the plain CC only affects downward axle movement.

The reason you'd want one over the other is in application. The CC with an axle attachment (call this the Porsche model) is that it is better for road racing, whereas the simple unattached traverse spring type is better for very rough roads where you have to have full upward axle travel.

I used the simple type on our Mexico Ghia because we had to survive the car-killing topes (big speed bumps) in Mexico in villages.

FJC

[moTthediesel]

I'm setting up a 356C for this September's Targa Newfoundland. I've gone around and round as to what to do to help the cars handling. There's not much doubt about what can be done up front, maybe a couple of shims worth of negative camber and a Weltmiester 19mm sway bar and you're there. The back end though, is another story entirely.

Please correct me if I'm wrong, but it seems the idea with a swing axle rear is to be sure you're not resisting body roll, but are limiting tuck-under of underloaded wheels, no? This can be accomplished with a Z bar, transverse CC spring, or limit straps.

*What we don't want to see--*



For a variety of reasons (simplicity, durability, unrestricted up-travel for rough roads, etc.) I've decided to go with an unstrapped CC spring like this. (Also we can see from the above picture just how the original Porsche CC spring did NOT prevent tuck-under, as you can clearly see that this coupe has one!)



I've got to fab up a mount for my Porsche 741 transmission anyway, so I'm thinking about just how to make it work best. Which brings me to a question, should the spring be free to pivot under the tranny or not?

The bracket that comes with the spring clearly allows it to pivot. It seems to me though, that while this would not matter when both wheels are unloaded (i.e. under hard breaking, or <see above>landing from a jump), that this would limit the springs' ability to keep the inside wheel from jacking when the body rolls in cornering.

I guess the question is, what would be the down side of a solid mount? Would the ridged mounted spring be adding unwanted roll resistance to the rear of the car by supporting the underloaded inside wheel in a turn? I'd be interested to hear opinions from the people who have contributed to this thread.

moT

[FJCamper]

Hi moTthediesel,

I don't see a solid mount problem. And we ran the compensator you've pictured in the 2007 Carrera Panamericana with good effect.

We took third in class (under 2-liter) even with losing two days out of seven for suspension repairs.

FJC

[kdf]

Having a pivot or solid center mount makes the transverse spring a different device. Neither is wrong, but they work in a different way.

If it has a pivot point in the center the device is a camber compensator. As you explained, it would only be working in droop travel without affecting the roll stiffness.

Having a solid center mount the device would be a "droop limiting spring". When driving in a straight line it works like a camber compensator, but when cornering it adds roll stiffness by stiffening the inner wheels spring rate in droop.

Both droop limiting and camber compensators have been proven to work in a swing axle rear suspension. The swing axle rear suspension has already pretty much roll resistance because of the geometry, so my choice would be to go with the pivoted design.

[FJCamper]

Hi KDF,

Because the Carrera Panamericana is on smooth and rough roads, I wanted the "anti-droop spring" effect on the rear axles -- and I do realize the difference in between the true camber compensator and this Sway-A-Way traverse spring.

My theory was the axles could go up easy, but not down except against the resistance of the traverse spring. Sort of to help out against the jumps over the topes.

It worked for us. It might work as well for moTthediesel in the Targa Newfoundland.

If it were just a smooth race track, the true camber compensator would probably be the way to go.

FJC

[moTthediesel]

kdf & FJ,

Thanks for the thoughts, that pretty much matches what I've been thinking as well.

Maybe the best thing for me to do is to use part of the original bracket with the pivot. Then I could make blocks to fit under the spring and try it both ways.

moT

[63busguy]

There was a mention of limiting straps earlier in the thread. I have seen them used in off road applications to prevent shock damage but for a road racer trying to limit jacking are they that affective? I was thinking if the straps are too short limiting articulation would make for a "go cart" feeling suspension. If they are too long they wont do anything to limit jacking.

What is the correct way to measure for the correct length of strap? When the car is at ride height with the load on the suspension is 3 inches of strap slop enough or too much?

Has anyone ever used limiting straps with a sway a way style compensator or is it too much overkill?

[FJCamper]

Hi 63Busguy,

Limiting straps work, and you size them by measuing how much slack you need for the axle to hang level, or stop level, in a rebound.

My own experiences with limiting straps were not good. They stop the axle abruptly, and (wham/bang) sound like the rear end is coming apart ... but they work.

FJC

[63busguy]

Thanks FJ,

Besides the wham/bang what other bad things did you experience? Do they help in the corners at speed? I would think they would not allow ANY jacking during hard use.

I was planning to put them on the shock bolts, do you think they are stron enough?

[FJCamper]

Hi 63Busguy,

The limit straps stop the downward movement of the axle past whatever slack you give it. The axle goes up (no problem) and then down -- and hits the strap limit length like a dog hitting the end of his chain.

Limit straps are probably the least expensive way to stop "jacking" and like I said, they work.

The stock shock bolt is plenty strong for mounting purposes.

The only drawback is that big bang you feel with each axle rebound.

FJC

[63busguy]

Thanks again FJ,

Most straps Ive seen are made of a nylon strap like a seatbelt, does anyone make some out of the material like a tow strap that stretches or gives a little softening the shock?

[FJCamper]

Hi 63Busguy,

I have not seen anything except the heavy duty no-stretch straps.

Lots of people have experimented with this problem, big rubber bungees, springs, etc. The neatest I ever saw was a Speedster with coil springs hung off the body to the axle, and they acted as limiters.

FJC

[gimmesomeshelter]

Hello-

Has anyone tried to install the Skirmants Camber Regulator on a VW? I recently found a picture of one installed, and it looks like it will take some work, but is possible.

http://www.postimage.org/image.php?v=Pq2csJti

Unlike the typical VW CC, it doesn't reside beneath the axle. Instead, it's positioned in front of the axle, and connects to the forward most spring plate mounting bolt.

I believe I've come up with a solution, but not having one on hand, it's tough to tell.

First, I would swing the mounting plate 180 degrees so the spring would rest behind the axle. This would allow me to avoid the shock mount tower.

Second, I would use the lower of the two rear axle mounting bolts to mount the spring.

Third, since this bolt isn't symmetrical to the front mounting bolt, I would have to 'lower' and 'move forward' the spring to spring plate mounting position. I think I could do this by drilling a new hole in the mounding plate, and by using a generic sway bar bushings to take up the slack.

Comments anyone?

Thanks,

Paul

[FJCamper]

Hi Paul,

The best effect of a camber compensator is to do double duty. Originally, Porsche strapped the ends of the compensator to the axles. This allowed a preload (tighter strapping) that resisted up and down movement, so that the compensator was a spring that worked in both directions.

The Skirmants and 356 Enterprises compensators act this way, only better.

A leaf spring under the axles, well mounted, and connected to the axles with adjustable links, can be set to try and hold the axles level, taming the swinging axle beast.

FJC