ok so we are saying that 2 FG leafs weigh less than 4 steel coils would on the Corvette. I don't necessarily disagree with that but I'd like to see a source of that information because FG is not that light and those leafs aren't that small. but that would be one good reason for GM to favor FG leafs.
When GM first used the fiberglass spring on the C4 McLellan said (in Michael Lamm's book on the subject) that the single front leaf spring weighed but 1/3rd of the pair of coils used on the front of the C3. GM's SAE published paper "Design Synthesis of the Suspension Architecture for the 1997 Chevrolet Corvette" had this to say on the subject:
GM paper said:
Ride Spring - The first C5 suspension concepts were conventional coil over shock absorber for both front and rear suspension. One proposal utilized a horizontal coil over shock actuated by a bell crank upper control arm, and was evaluated in a mule vehicle.
A composite transverse leaf spring was selected for efficient packaging and low overall mass. Shock towers may be lower and smaller for hood height and less intrusion in the engine compartment. The shock absorber may be placed further outboard on the lower control arm than is possible with a coil over shock unit. The improved shock lever arm ratio provides efficient damping authority and reduced jounce bumper loads.
From that we can infer a few things. First, GM certainly wasn't wed to the leaf spring when developing the C5. The C6 and C7 might be stuck with it because they are derivative platforms but it also might be that the choice that made since for the 1997 car still makes sense now. We can also assume that GM found the overall weight to be an advantage. Do consider that it's not just a comparison of the weight of coils vs the leaf, though I think the leaf would still win. Because the leaf and it's dual mounts have significantly more roll resistance than traditional coil springs the anti-roll bar can be smaller and lighter for a desired roll rate. The passage also implies the shock towers could be smaller and lower thus saving more weight and lowering the CG of the car.
Finally, I would point out that the strain energy density, that is the amount of potential energy that can be stored in a spring of a given mass, is higher for fiberglass springs than for steel springs.
And aftermarket coil-over shocks, like Pfadt, will either suffer from reduced overall travel or premature sagging. I'd like to hear what Pfadt would say about that. Because that would be another good reason to use FG leafs for this application.
I would too. However, I would also be careful with some of their "facts". I don't question the quality of their product. That many happy customers aren't likely wrong. I do question some of their marketing claims. One of the Corvette vendor mouth piece rags talked about the leaf and aftermarket coils. In the first part of the article they correctly explain how the leaf spring's mounting allows it to act like an anti-roll bar. They then interview a guy from Pfadt who promptly contradicts the early explanation and incorrectly states that the spring works like a see-saw thus implying that you need a THICKER, not thinner swaybar because of the leaf spring. Pfadt has also heavily used the negative sounding "cross talk" term to describe this behavior. They fail to use that same term to describe the way their stiffer than factory swaybars do the EXACT same thing. Clearly they understand that many of their customers don't understand how things work.
And apparently there are no performance disadvantages with FG leafs. So can designers alter/control the variable-rate characteristics of FG leafs as broadly and effectively as they can coils? Or does using a FG leaf somewhat limit the designer's flexibility in this area? I really don't have a clue on that.
For the most part yes, the only drawback is cost. As with a coil spring, depending on the mount the factory engineers can make the thing fixed rate, rising rate, falling rate etc. What it does do is limit the abilities of the aftermarket tuners. While the Pfadt marketing guy was spewing out BS, their engineer is more honest about it. He doesn't see the leaf spring as a bad idea but he also says that HE can do a better job with HIS tuning using coils. I would assume that's in large part because he can readily select the rates he wants since it takes almost nothing to get a run of coils with custom vs off the shelf rates.
Someone else said that GM shouldn't spend any time/money explaining why they chose FG leafs. I disagree with that assertion if GM wants to promote the image and sales of the Corvette. They spend a lot of time and money highlighting the Corvette's positive attributes. And if FG leafs are the right choice its one more positive attribute to tout. Maybe they have touted it but i haven't noted it.
GM already explained it but most haven't read the article I quoted from since it's not readily available. I really think were it not for the "leaf" part of the name no one would think anything of it. We all associate leaf springs with outdated live axle rear ends. That old live axle had all sorts of issues and basically none apply to the Corvette setup. The old school setup had a heavy axle (high unsprung mass), the Corvette does not. They used the leaf as a type of suspension arm, the Corvette does not. The individual layers of the multi-leaf steel spring had internal friction (ask the C3 guys about this), the FGS does not. We can accept that the BMW M3 and Porsche 911 use McPherson struts up front instead of "proper" double A-arms but somehow it must be a problem when GM uses a different kind of spring. I think it's basic human nature. The Corvette's rear is skittish so people look for the thing that makes it "different". They fixate on the spring type rather than the details that mater like damping, tire selection, unsprung vs sprung mass, tire width etc.
I agree GM gets a lot of crap for it even though none of it's deserved.
But really, I've just been critical and curious about the FG leafs for a long time because I'm a Corvette fan and have seen the car get repeatedly dissed for this feature (although possibly without merit).
You are right it has been dissed and often without merit by people who don't have sufficient knowledge to discuss the subject. Hell I caught the Motor Trend tech editor describing the spring's anti-roll properties as similar to a see-saw, ie 100% wrong! This guy was the tech editor!
I also find well-designed products very desirable. And I'm very happy to find that FG leafs may have performance virtues and aren't a cost-cutting measure. Like most on this board i love Corvettes regardless of their springs but always want it to be the best it can be. :thumbsup:
:thumbsup:
Having said all that I wonder if TI coils wouldn't resolve the previously-stated issues with coils and be even better than FG leafs for a high-dollar model like the ZR1. :laughing: TI coils, which are used in racing, are of course much lighter than steel, but they are also thinner, have greater travel, and have greatly reduced sag over time.
Most racing springs would be a bad choice on a road car. I doubt they have the needed corrosion resistance. Cost of course is HUGE on road cars. The mag dampers are even larger in diameter than the standard dampers. The coils that fit around those things probably couldn't fit in the suspension. When it comes down to it people have been using steel coils because steel is VERY good spring material, better than TI IIRC though not as light. I can't imagine any race car having to worry about spring sag over time. That's the sort of thing that affects cars that are driven over 100,000 miles, not race cars that might see 5000 on a set of springs. Incidentally, I suspect the FG springs are better yet when it comes to sag. Heavy trucks and MB Sprinter vans have used them in part because they do hold up better than traditional steel leaf springs.