Composite versus Good Steel Leaves

[Bad Bird]

Dear Pro-touring,

I'm from Australia, and my car is a 1975 XB Falcon hardtop. In suspension layout, it is very similar to a 71-73 Mustang. This car is a weekend warrior and will be used for Auto-X (ratio of street/track of 60/40).

Due to the Australian design rules, I must stay with leaf springs if I am to drive the car on the street. Sure there are other legal options like the RRS torque arm, but I'm not convinced that it will be advantageous to a set of well thought out leaves.

I could potentially run a composite leaf spring, as hardly anyone knows anything about leaf springs where I live. I'm just not really sure if they are better than good quality steel springs. I'm really keen to hear some feedback, especially from Chicane.

Something, to me at least, more important than that is what kind of bushings would best suit my needs. Some people suggest monoballs in the front and rear spring eyes, with Del-a-lum in the upper shackle-to-body pivot. Others suggest solid front bushes with softer rears. Others still suggest rubber fronts with poly rears. Something that may effect the choice is my inability to run a lateral locator. There is no way a panhard or Watt's link will fit between the diff and fuel tank.

Thanks in advance for the feedback,
-Matt

[GetMore]

Okay, here's my two cents:

First, some people have had problems with composite springs breaking. It actually seems to be an issue with the mounting of the axle; If the housing is allowed to move it can contact the spring (instead of being isolated by the spring pads) and this contact point can sometimes break. It is usually experienced by people with good traction and high power.
In my opinion this is just something that you need to make sure you have correct on installation, not a reason to say that composites are no good.
FWIW, I have run a set in the past, and will be running a set on my current car.
Also, they are not unheard of in OEM applications. Chevrolet used them on some Astro Vans, and Mecedes uses them on the Sprinter vans. In both of these applications the springs are mounted directly to the rear end, exactly are a steel leaf spring would be. The Sprinters also have a composite transverse leaf spring up front, though that spring is not subjected to the different kinds of loads that the rear leafs are.

On the subject of the monoballs: Since the balls are supposed to mount in the spring eyes they don't add deflection. You will not need to add a lateral location device. If you install solid (such as Del-A-Lum) bushings in the frame for the upper shackle bushings you will actually be locating the rear better than you would with the rubber bushings.
In my opinion, the monoballs in the spring eyes with the Del-A-Lum shackle bushings in the frame will allow the suspension to work the best. I am not sure of the down sides, but I assume it is the possibility of wear in the monoballs.

Even if you don't go nuts with the high tech components you can do quite well with plain steel leaf springs. There are a few factors in chosing the proper spring, and while I don't know them I do know that someone on this board does.
A leaf spring suspension, when properly set up, is one of the (if not THE) best all around suspensions. They all have tradeoffs, positives and negatives.

[Bad Bird]

I agree wholeheartedly about the greatness of well setup leaf springs. The vintage race guys down here are faster than many of the more modern classes and they still use leaves. There is no way I'll ever be able to push a car as hard as they do, nor will my lap times be close to theirs.

I'm sold on the virtues of good leaves, especially with a nice lightweight differential.

Maybe Chicane could build me a set in the future. It wouldn't be cheap though...