Here is an interesting article regarding the Transverse Composite Leaf Springs in our (C5, C6, C7) Corvettes. It explains a large part of why race cars need Coil-Overs, and why drivers might prefer Coil-Overs. It has to do with the Ride Rate. Our Leaf Springs provide no more than 500 lbs per inch of movement, while racing Coil Springs provide from 800 to 1200 lbs per inch movement:

https://grassrootsmotorsports.com/ar...-deep-talk-se/

I have some experience in Composite Fabrication, for both small parts and for large. For instance, a typical large component for our composite airplanes is the one-piece Main Landing Gear Bow. It uses higher-performance S-type Glass Fiber. Our airframes generally use less-expensive E-type glass fiber, except for the Main Spar where once again the better S-type glass fiber is used.

I may put some thought toward how I might FABRICATE MY OWN CORVETTE LEAF SPRING. A primary difficulty will be obtaining a Press which can Apply and Measure up to 1,000 pounds or more. I'll check on Amazon ...

Here are images of Composite Springs that I have made recently, these being replacements for Steel Coil springs for the Roll and Pitch Trim controls:
(The motivation is Failure Mode. If that Steel Trim Spring EVER BREAKS ... my airplane could suddenly become UNCONTROLLABLE. Composite has a much more BENIGN failure characteristic.)

Rate Testing of Steel Coil Trim Spring and Composite replacement. Composite is MGS L335 Resin and E-glass in Tapered layers.


Standard Approved application as Roll Trim Spring in a Cozy MkIV 4-seat Canard Homebuilt.


Size comparison of Steel Trim Spring and Composite replacement.


German Industrial Medical Device Spring, designed for a lower extremity Prosthesis.

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So I have discovered a scientific paper which provides equations for designing fiberglass leaf springs:

https://www.researchgate.net/publica...site_Materials

This research used E-glass, there is some discussion of glass weave orientation, but no specific Epoxy Resin/Hardener system is named. If the Martin G. Scheufler (MGS) L335 System is not up to the task, I can always try the L287 System which I also have. The combination of 287/S-glass is stronger than the 335/E-glass. There are also advantages to combining Bi-Direction weave with Unidirectional weave. Carbon fiber would not be suitable because it is too brittle and way too stiff. Kevlar would not be suitable because its ability to stretch is simply counter-productive to making a Stiffer spring for a Corvette.

Beyond this, I have discovered a good-quality 1,000 lb cap Crane Gauge for $110 each on Amazon (will need two, left and right.) And I do believe I can fabricate a test jig for Leaf Springs using my Engine Hoist at my hangar. That is good for up to 2,000 lbs. Hendrickson states they offer after-market composite leaf springs for Corvettes with Spring Rates from 180 lbs/in to 850 lbs/in.

I am thinking of shooting for 600 lbs/in ... but I wonder what the FE3 spring is. Evidence so far is that it is no more than 500 lbs/in. A spring with a Rate of 600 lbs/in (Per Wheel) would flex 1-1/2 inches with the full weight of a Corner (of a Corvette) ... ALL OF IT, 800 pounds ... in a turn.

If the OEM FE3 spring is really only 500 lbs/in or less, this means that the spring is already flexed quite a bit at each end just sitting there parked.

 

Yes they are flexed at rest, and yes you have to bend them to install them

this sounds like a fun project, but with so many aftermarket leafs and coils in the market, make sure you are doing just for the experience.

I won a world challenge race and set a track record in VBP leafs, but they are longer gone and their products developed a reputation for cracking.

 

Well the article written by Lane Borg of Borg Motorsports shows that for real racing, you cannot buy a truly stiff set of leaf springs for a Corvette. Compared to 700 lb/in coil springs, both the Hypercos and the VBPs just can't keep up, in terms of Wheel Ride Rate. And some race cars have 900 - 1,200 lb/in rated springs. Note that a 700 lb/in coil spring has about 300 Wheel Ride Spring Rate. This seems counterintuitive to me, considering that the wheel has a longer Moment Arm. Oh, wait ... a longer arm would decrease the value.

Now, I don't really want a 1,200 lb/in equivalent spring in my car. But if I can make a 600 lb/in spring, I will be able to make a 1,200 lb/in spring. Just in case YOU decide that you want one.

For our airplanes, it is important to have an accurate Weight & Balance calculation. I mean, this is REALLY important. So there is always a pilot/builder among us who has a set of Race Car Scales. We usually only need 3 of the scales for an airplane. But the Set of course has all four. For the final phase of testing a DIY Leaf Spring, I have realized that we could Raise the car on my set of QuickJacks and place Rick's four race car scales under the wheels. Then we would lower the car, measure the Leaf Spring Deflection, and note the Weight readout on each scale during the process. This would give us the actual Wheel Ride Spring Rate.

A crucial factor would be finding white lab coats to wear.

 

Well, remember that coil springs act at an angle to the arm when viewed from the front or rear of the car. That removes a good amount of their effective rate compared to a leaf spring that acts directly in the downward direction on the control arm. So even though a coil spring acting through the shock mounts has better leverage on the control arm in terms of its distance between the chassis mounts and ball joint, it's acting at an extreme angle, so a lot of its force is acting laterally on the car, which really does nothing other than adding some tension force to a portion of the control arm and preloading the bushings slightly in the lateral direction.

If you do end up making something yourself, remember that the spring is preloaded when you mount it on the car. Like @davidfarmer said above, you have to bend them to get everything installed. If you place the car on the scales and measure the wheel deflection from full droop to the resting height, you won't get the proper value for ride rate if you don't know the preload on the spring. When I ran that test you quoted above, I loaded the car with steel and sandbags on the axle I was measuring and would lower the car in approximately 1" increments at the subframe, take a reading on the scales, and repeat until it bottomed out (or I ran out of weight). This will generate a spring curve for you. Some of the springs were more linear than others. As I'm sure you know from your time in composites, the shape of your spring and the layup you use for your fibers will have effects on how linear the spring behaves.

I looked into offering a custom leaf spring and even talked with the manufacturer of the Corvette OEM springs (they also make Hyperco's Corvette leaf springs and the leaf spring for the front of the Mercedes Sprinter vans). They had major concerns about going as stiff as I wanted to based on their experience with the resin they use. Their main concern was the huge increase in internal stresses from thickening the spring. Thickening the spring is easily the most efficient way to increase stiffness, but the stress increase causes a high likelihood of delamination. You can make the spring wider, but there isn't that much room between the subframe mounts to make a huge increase in stiffness.

Since most people put coil springs on their cars, I put the idea of a custom leaf spring on the back burner. Now that just about every race class that allows different springs also allows switching Corvettes to coils, it's not something we plan on offering. It is a cool engineering project though!

 

I strapped my car down and did direct load/eflection measurements back in the early 2000's, as I was converting from VBP leafs to Coils. I have nothing against fiberglass, but coilovers are so nice from a packaging standpoint. Back in the early 2000's, there were NO off-the-shelf Corvette coilovers, so leafs made sense. My first coilover Vette had Penskes, and it took multiple return trips before they got the sizing correct. I'm not sure how, but they didn't seem capable of reading their own custom build forms. Now, we have tons of options.