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This article is about leaf springs used on the GM Chevrolet Corvette. While most other cars use coil springs, the Corvette uses leaf springs.

In suspension designs where leaf spring systems are tasked to hold the axle and function as a spring (modern truck suspension), multi-leaf springs suffer from friction between the leaves as the system flexes. 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 not good at being rigid links. To its credit, the leaf spring does this much better than a coil spring. For example a coil spring may be viewed as a bobble head doll in the same tasked assigned to truck-style leaf spring designs.

The Corvette 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 Corvette and other cars with A-arms is the Corvette 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 only a spring.

Another problem with leaf springs arises from friction between the leafs. The Corvette however uses a single piece leaf in its design so there is no internal friction, just like a coil spring.

So the Corvette's leaf springs design is similar to double A-arm geometry just with a different type of spring.

Leaf springs on the Corvette

GM began using a transverse leaf spring type suspension in the Corvette in 1984, replacing the traditional coil springs.

Advantages

• Leaf spring suspension weighs much less than coil springs as a single leaf can replace two coils. The two coil springs weigh three times as much as the one leaf.
• Leaf springs help by lowering the center of gravity of the vehicle by being placed at the bottom of the Corvette.
• Leaf springs act as an anti-roll bar allowing for lighter anti-roll bars because the springs perform part of that role.
• The leaf springs never wear out. The vendor of these springs has never had to replace one due to fatigue failure. Coil springs do wear 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.
• They are easy to adjust. One or two hand tools are all that's required to adjust ride-height, and some people are able to adjust the springs with the car on ramps and without removing the wheels.
• They allow the shock to be mounted as far out as possible. Coilovers allow it as well, but require the springs to be mounted at the top of the assembly, which is bad for the center-of-gravity. They also allow for a non-existent shock tower, which in turn allows for a lower fender/hoodline.

Drawbacks

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. Coils are usually easier to install as well. In the C5/C6, the lower ball joint must be popped on one side for the spring to be pulled out. It's also impossible to run stiffer springs left-to-right, so a transversely leaf sprung car would be a poor choice for oval tracks.

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 steel leaf spring it might be cheaper (remember truck suspension is cheaper because the leaves also act as links).

It is also susceptible to damage from chemicals and heat, so extra care must be taken that spilled fluids do not remain left on the springs long enough to eat thru the outer coating. The rear springs can be destroyed by heat from cutouts or catback removal. When these springs start to fail, they fail very quickly and completely!

Street cars

1. You must design them into the car in the first place. This seems obvious but consider these springs span across the bottom of the car. In the front they have to clear the engine oil pan and in the back they have to stay out of the way of the differential. Basically, you can retro fit coils on the Vette because the mounts can be shared with the shock mounts. For the most part you can't retrofit Corvette style leaves onto other cars because you would have to add mounts that don't exist on the regular car.
2. GM and their supplier spent a lot of time and money developing the Vette's composite spring. Currently they are the only manufacture with the knowledge and understanding to make the springs work. On the other hand, coil springs are common and well understood. Lots of vendors can make them in a wide variety of configurations. It's easier for the other manufactures to stick with what they know. Other manufactures would have to study the design and manufacture of composite leaf springs before they could pop them on the next Supra-NSX-Type-GT. GM did that work years ago. Toyota could certainly afford to develop their own composite springs if they wanted. The same may not be true for smaller companies like Ferrari and Porsche.
3. Engineers like to stick with what they know. Lots of suspension engineers are familiar with using coil springs. They could experiment with leaves if they wanted or they could stick with coils and get the job done. See the point about undertaking a research project.
4. Coils are cheaper. This automatically keeps them off lower cost cars (Miata, Civic) and cars that share platforms with lower cost siblings (Audi TT). Porsche isn't worried about saving every last dollar but there suspension and chassis design may not allow packaging a Corvette type leaf. Even if packaging isn't a problem they still have to pay for tooling to make the springs. Unlike the GM who spreads that cost over 30,000 Vettes a year, Ferrari would spread that over maybe 2000 cars a year. Conversely I can get coils made with relatively low setup cost and a cheaper per part cost. So not only would they have to spend more per car, they have to spend a lot more up front.
5. Perception. Just like pushrods, the leaf spring has a stigma attached to it. The reasons for the stigma are legit (key component to heavy and typically poor handling suspension). However the reality is the sum of the older parts was the problem, not a specific part of it.
6. Some Do! Volvo used a transverse leaf spring on the 960.

Race cars

Not all race cars use coil springs, some F1 cars (Ferrari and others) use torsion springs instead. Years ago Indy and F1 cars DID use leaf springs but those days are long past.

The current design of open wheel racecars places great restrictions on suspension packaging. The Corvette's transverse leaf spring must span from one side of the car to the other. Also, to be most effective the links between the spring and suspension arms should be under tension. This makes a bottom mount spring most effective. This packaging doesn't work well on an open wheel car because the spring would have to pass though the gear box around the dif (or the gear box would have to be raised and hurt the car's CG). At the front the driver's legs would get in the way. Additionally the spring is wide and would have to extend past the body work where it would hurt the car's aero package.

NASCAR rules dictate coil springs on the rear axle. They probably originally used leaves but given the option any car designer (modifier back in the day?) would have replaced the leaves with a multi-link set up. As I said before the multi-link offers better control of the rear suspension.

Another good reason is only a few companies understand the technology necessary to make the springs. Hypercoil is currently the top race spring manufacture. They can make very precise, matched spring pairs. The level of precise spring rate control and matching may not exist in the composite bow springs.

Coil race springs are not car specific. You select rates, diameters, length etc but you don't have a specific spring for a specific car. If you want to order a custom spring Hypercoil will wind it to your specifications on the same machine they use for the next custom spring. A custom Porsche, Formula Ford and LMP car spring can all be made on the same machine. By the time the C6 evolves into a C6-R (they don't start off with a production Corvette) the suspension geometry is so different that they couldn't just mount a C6 leaf spring. It's far too expensive to have a few custom leaf springs tooled up (you would have to buy the tooling as well as the springs) so they use readily available coil springs.

This type of universal tooling isn't availible for the composite leaf spring. Only the Vette currently uses the spring so you are making a Vette only part. This seriously reduces the market for aftermarket composite leaf springs (still there are after market leaf springs available for the Vette). The business case for custom equipment to make Vette springs is harder to justify since it's a smaller market.

Why don't other cars retrofit leaf springs? Well they also don't retrofit torsion springs despite the fact that F1 cars use them. Put simply it would be VERY difficult. The Vette was designed to have them. It has mount points under the car where the springs fit to the suspension sub frames. It's not easy to just add that to a car that was designed to use a coil spring. All of the cars you mentioned would have to be re-engineered to add leaf springs. Replacing the factory spring with a racing is easy by comparison.

The other VERY significant reason is racers will use what they know. They will put effort into learning about new technology (torsion springs in F1) but ultimately it is too there advantage to stick with what they know.

• Chevrolet vehicles
• Automotive suspension technologies