I saw this on a Corvette Forum, thought I would share.

************************************************** *


Corvette and leaf springs. Many people are surprised to hear that the C6 Corvette uses leaf springs. This seams to conger up images of ox carts and old Ford pickups. I thought I would post my understanding of the technology with the hopes that other will post their insight.


Since 1984 the Corvette has used a transverse fiberglass composite leaf spring as part of the suspension. The C5 and C6 both have very similar double A-arm suspensions that wouldn't look out of place on any high end sports car. The only significant difference being instead of a coil over spring the Vette is using a single leaf spring. The suspension geometry and motion would be exactly the same if GM chose to use coil springs rather than the leaf. For those who might think the Corvette’s leaf spring is “outdated” technology, keep in mind that the composite leaf spring was introduced as an option in 1981 and in it’s current layout (acting as a partial anti-role bar) in 1984. It’s safe to say the coil spring is much older.


This is a picture of the C5's rear suspension.

http://www.corvettecavalry.com/exhaust/no-mufflers.jpg

The leaf is the black thing that runs from one side to the other just under the lower A arms.



A Brief History of Leaf Spring Suspension.

Excluding the Corvette I'm aware of 4 general types of leaf spring suspensions.

1. Model T style transverse leaf.

http://www.trainweb.org/toenailridge/vanradiator.jpg

This model shows the transverse leaf used on a Ford Model-T. The suspension has two lateral arms that keep the front axle perpendicular with the chassis. Lateral axle movement is controlled by the spring. This system suffers from poor control of the axle’s movements among other flaws. I’m not aware of any production car that uses this suspension type.



2. Conventional truck type, longitudinal leaf springs:

http://www.chris-longhurst.com/carbi...ion_bible.html (scan down)

This is the one we all love to hate. It’s also about the only type of leaf spring suspension still in use. It’s cheep, durable and handles badly. It suffers from friction between the leaves and from poor control of the axle’s location.



3. Golf cart style transverse leaf spring:

I couldn’t find any pictures of this but it basically looks like a double A-arm where the leaf spring is one of the A-arms. The geometry is probably OK under vertical loads but lateral loads would defect the spring and cause camber changes. Not an issue for golf carts but bad for sports cars.



4. Leaf with links. There are lots of variations on this suspension

Miller Indy Roadster

http://www.scaleautoworks.com/millerphoto.jpg

http://www.scaleautoworks.com/metalMillerFQ3.jpg (the black things on top of the front axle

Jaguar MkII rear suspension (can’t find a picture)

Like #3, these suspensions uses a combination of links and the leaf spring to support the axle. The Jaguar set up looks similar to a 4 bar solid axle rear suspension except the lower link is the end of an inverted leaf spring. The other end for the leaf is attached to the chassis under the passenger compartment. The middle of the upside down (frown rather than smile) spring presses against a rubber block. The end connects to the bottom of the axle. This system offers better handling and axle control than #2 but is still suffers from friction between the leaves of the springs and compared to multi-link live axles, poor control of the axle’s location.



What makes these all the same

All of the above have several things in common. First, multi-leaf springs that suffer from friction between the leaves as the leaf flexes. Second, the inherently flexible leaf spring is being asked to work as a spring AND a suspension arm. Springs (leaf, coil, torsion etc) are good at being springs. They are bad at being other things like rigid links. In those suspension designs the spring is being asked to hold the axle and be a spring. To it’s credit, the leaf spring does this much better than a coil spring. How well would a coil spring do that job? Think of a bobble head doll.



Why is the Vette different?

First, the Vette actually has double A-arm suspension like many other high end sports cars. The A-arms are used to fully control the movement of the wheels. The only difference between the Vette and other cars with A-arms is the Vette uses a leaf to pull the lower arm down rather than a coil spring to push it down. In both cases the spring is doing what it does best, being a spring ONLY.

The other problem was friction between the leaves of a leaf spring. Well the Vette uses a single piece leaf so there is no internal friction, just like a coil spring.

So what we have is double A-arm geometry just using a different type of spring.



So why does the Vette use it

To be honest, I have no idea how GM got started with the transverse leaf spring. The used to use coils in front but in 1984 they switched too leafs front and rear. I suspect it’s a tradition they maintain for the same reason Porsche keeps their engine out back even though the platform mate Boxster moved it to the middle.



What are the advantages for the Vette?

This is an article written around the time the C4 was released. It covers a lot of the reasons why GM retained the leaf suspension

http://web.telia.com/~u60113742/misc...ass_spring.gif

The big advantages are:

-It weights A LOT LESS than coil springs. One leaf replaces two coils. The two coil springs weigh 3 times as much as the one leaf. Additionally the leaf is placed at the bottom of the car. In addition to removing weight you lower the CG.

-It acts as an anti role bar. The article above explains how this works so I won’t. The advantage is you can run lighter anti-role bars because the springs are taking care of part of the job for you.

-The leaf springs never wear out. The vendor of these springs has never had to replace one due to fatigue failure. Coil springs to were out but you typically don’t notice on smaller, lighter cars. You do see it more on old, heavy Caddies and such. The improved fatigue life was really evident compared to the C3’s steel leaf spring. Thus this is an advantage over coils but not a big one.



What are the drawbacks for the Vette?

-They are expensive. We normally don’t think of leaves as the expensive suspension but in the case of the Corvette, coils would be cheaper. The Vette already has all the parts a coil sprung double A arm suspension would use. Pull the leaf off, replace the shock with a coil over and you’ve converted the Vette. Since the rest of the system is the same, the cost comes down to the price of 2 coils or one spring. Well if it was a steal leaf spring it might be cheaper (remember truck suspension is cheaper because the leaves also act as links).