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No more leaf-springs?

10K views 34 replies 12 participants last post by  spd98 
#1 ·
I was watching the latest C7 video when I caught this...



Now I may be looking at this wrong, but is it just me or are am I not the only seeing the leaf-springs missing here???
 
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#4 ·
They are too invested in the long-standing story about the greatness of the leaf springs to abandon them now. They won't go away until someone at GM comes up with a story about how they always were awesome, but now they found a way to make coils as good. /sarcasm, but its heartfelt sarcasm at least.

We're stuck with them. Yes I know they lower the Cg by .000001 inches, similar to the amount the Cg is lowered if you simply don't have lunch before driving.

I sure hope the car isn't as jumpy as the C6 Z06 was. Its the greatest flaw of the car. Also, in a way, thrilling, truly. Also, in a way, endearing. I guess thats how old school Porsche lovers felt. The knowledge that your car may try to kill you at this very corner is very very truly thrilling and invigorating. But it is a flaw, not a virtue.
 
#8 ·
The leaf springs are a great idea. "Just because nobody else" is a pitiful excuse for an argument. There are no contenders that match the Corvette in it's performance for it's price range period.

If you look at the pic it seems to share the same attachment area as the sway bar now.
 
#22 ·
Not making an argument. Asking why GM made the very deliberate a-typical design choice of using leafs when NO ONE else does, including their own C6-R racecar. Its a curious feature of the road-going Corvette and one that I've heard criticized many times.
 
#10 ·
simple answer... corvette's have to make a profit... with many other cars, such as the LFA or the GT-R, they are sold below the cost point since they are considered flagship cars. Corvettes compete against cars costing twice as much and are still sold with a profit margin for GM, so that dictates everything that goes into that car.
Everytime GM has a serious shot at the corvette, there is always some kind of financial crisis either for GM or for the US economy in general and that affects the cost of the design.
with the expect 9% increase, it better look and perform light years better than the current C6 but everything i can see points to simple incremental improvements.. call it a C6.8
 
#13 ·
This sounds like a good argument, however the leaf springs cost more then coil springs.....

The C6 Corvette stood up to the best that the world had to offer, how is that not serious. Actually the areas where the Corvette falls behind happen to be with the areas that have nothing to do with performance. The interior was its biggest short coming, after all I would not call suspension that allowed the Corvette with an engineer to run the ring in 7:19 bad....... You can count the amount of cars that have run faster lap times on one hand....... BTW This Corvette didn't cost $500,000....

I actually agree with Blast....

It seems that every time a new Corvette is coming out everyone wants GM to just build a Ferrari clone. Then you have people bitching that the car doesn't look like a Corvette...... The Corvette community is very schizophrenic in that way.

People want a Ferrari 458 Italia, however they think that just slapping a Chevy badge on it would result in a $50,000 price. They can't seem to understand that the 458 Italia simply can not be built, sold, and sustained at $50,000.

This new C7, the base car will go from 0-60 in 3.9 seconds and probably have a top speed around 200MPH. Its probably going to pull 1.0G in base form, and stop from 60MPH in about 100 feet.

This is where I agree with the Germans, some people seem to be obsessed with how the Corvette is made. However at the end of the day its the end results that we are after and the Corvette is a great end result.

The C6 Z06 has in stock form pulled 1.12Gs on a skid pad, name me one production street car that can match that......
 
#23 ·
I would assume that most of us here prefer the OHV SBC for the Corvette instead of an OHC engine -- because OHV is smaller, lighter, torqyer, responsive, powerful, reliable, and sounds incredible. But I've never heard that FG leafs are superior in performance to coil-over shocks.

Bottom line: In its own interest GM should demonstrate why FG leafs are better and end the debate for its customers and potential buyers.
 
#16 ·
Guys, there's not even a firm definition of what qualifies as a "Sports Car." Some insist that a v6 mustang and a Subaru Impreza WRX sedan are sports cars. Where is the line drawn?

If enthusiasts can not agree on the most basic of descriptors for performance vehicles, there is almost no chance in agreeing on the definition of the subcategories of "sports cars."

There is an element of subjectivity in these terms that will probably never be eliminated. JMHO
 
#17 ·
Can anyone show me a real cost comparison between the leafs and coils?

I fail to imagine that leafs can cost more. Please prove me wrong.
 
#19 ·
I might be able to come up with something lol.


I can tell you the manufacturing process of a steel spring is much much simpler and can be done many more places than the gfe springs. The biggest benifit isn't cost, it's the amount of weight reduced combined with the allowable stress on the gfe spring.

The weight reduction between a steel leaf and a gfe leaf is about 65-70%. They typically can handle more than 50% more stress as well. One of the most unique and least talked about attributes to gfe springs is the increase in natural frequency. In similar applications they can have a natural frequency about 2x as high as steel. The good thing about this is that you can use less damping and not have to worry about vibration issues.

Keep in mind I'm talking in generalities about the springs in automotive applications but not about Corvette specifically.

I wouldn't be surprised to see the technology in the trucks at some point. Primarily due to the weight reduction needed to enhance MPG. They are already in use in some vans and commercial bus applications.

There are also some other emerging technologies out there that could be neat. There are now better ways to manufacture carbon reinforced coil springs.
 
#20 ·
Personnally, I don't really feel that strongly about the FG vs. coilover wars. I just look at the results, which have been pretty good for corvette.

BTW, didn't someone mention that the FG expected life is much longer than coilovers?

Vettes tend to to have long lives. Perhaps this is weighed into the FG decision. :huh:
 
#27 ·
Ah, the old leaf debate...

OK, a couple of things here.
1. I don't think GM would consider the use of the leaf spring to be part of the core of what makes the car a Corvette. Lose the V8 for say a turbo V6 and I would say that radically changes the Corvette. Lose the leaf and most wouldn't notice. I mean how often do you hear someone bitch about the leaf spring in the rear but fail to mention the leaf spring under the nose?

2. With the C4 the leaf setup was picked because it was very innovative AND solved some packaging issues. The C5 design team did not start off with the intent of keeping the leaf spring. It is after all more expensive than a set of coils (more on that later). When it came time to package a spring into the tight confines of the chassis GM felt normal production car coils (not the highly stressed aftermarket ones that likely wouldn't last the life of the car without some sag or a reduction in suspension articulation) couldn't do the job. They simply didn't have the space to package the length of spring wire needed to do the job. The leaf spring, which has NO inherent disadvantages as a spring, just simply fit better. Mind you GM was considering using pushrods and bell cranks with coils springs. They were clearly concerned about packaging.

3. The C7 is an evolution of the C5 chassis so it's not surprising that the design choices that were valid then are valid now.

4. Cost. The fiberglass spring is significantly more expensive to make. Period. Bosch recently showed a prototype economy car suspension using the fiberglass leaf. They said the leaf was more expensive than coils. The only way it made sense for an economy car was by making the leaf a control arm as well AND using the dual pivot mount, like the Corvette, to act as a sway bar to save the cost of adding a sway bar. The reason why the leaf spring setup under the Chevy truck costs less than the coils under the Tahoe is NOT because the leaf spring costs less than the coils. It costs a lot more. It's because the leaf spring does lots of jobs at once. The 2 leaf springs replace 5 links + 2 coils. The same is true in the Bosch setup. That is NOT true of the Corvette. Finally, the cost argument completely fails when you ask a simple question, if the leaf was cheaper then why does GM only use it on the expensive cars? GM used it on the W-body cars which were more upscale than say the J-body cars. They use it on the Corvette but not the Cobalt. Somewhere I think on this site a manufacture of both coil and FGS posted in reply to a thread of mine confirming the manufacturing cost difference.

5. Others have used it. It's not commonly used due to the added cost and because it's real advantage is packaging, not performance (though it has no performance loss). The packaging of other cars is different and thus their solutions are different. So far Mercedes, Smart, Volvo and VW have all used he design. Ford, Honda and Porsche all have patents on similar designs.

6. What works on race cars doesn't always work on road cars. The C6-R team needs custom springs for the cars. They couldn't use the stock springs any more than a racing 911 would use the car's stock springs. Since the fiberglass springs are molded a new spring would be VERY expensive to tool up while coil race springs are all but interchangeable between various car makes as most are using the same dampers. I've known Formula Ford owners using ex Indy car shocks. Just change the valving and the spring rate and you are good to go. Race springs and dampers are largely interchangeable thus the C6-R team will use what the market provides. Also they can use highly stressed race springs which would again either limit travel or sag after years of use. Most high end race cars use torsion bar springs these days. Would we think it's cool if GM used torsion bars like a '78 Chevy Van (or the Audi LMP cars)? Most high end race cars use third spring setups. I don't hear anyone begging for something like that just because a race car uses it. Oh, those torsion bar setups also mean most high end race cars aren't using coil overs.

As Carroll Smith said, cost aside, the FGS is an ideal road car spring because it's lighter and can be used to provide more inherent roll resistance than a traditional set of coil springs. It has NO inherent performance disadvantage. The down sides are cost and that the small reduction in weight can be recaptured elsewhere in the car for less money thus the cost benefit isn't that great unless you are stuck with respect to packaging.

I suspect the biggest issue with the Corvette suspension has always been the dampers. Look at the gain GM sees when using the mag shocks. OK, time to go.
 
#28 ·
There is a TON of truth in this. Though I suspect dampers are one of the problems they are not the only problem. Suspension dynamics are complex, there are some "real" measures of performance and a lot of just "feel".

Spring rates can be constant or variable by design (just like the dampers). Then you have to factor in geomerty. As the geometrey of the suspension changes through it's travel, so do the forces applied to the springs and dampers.Then you also have to realize the development guy's are also having to hit a bunch of targets (weight, cost, ride quality, handling) and some of them are subjective.

If you just want a car thats easy to control without electronics I would suggest something longer and heavier than the Corvette lol. It's really poised on a knife edge in the handling department. It's powerful, light, and fairly short in the wheelbase department.
 
#30 ·
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.

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.

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.

The explanation given about why the C-6R doesn't use FG leafs seems very plausible to me and I thank the person for explaining that.

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.

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). 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:

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.
 
#32 ·
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.
 
#33 ·
I think the biggest problem here is not the different setups, its the lack of technical knowledge on how these things work. Really its not always a matter of which setup is better then another, as all of the setups have their merits and demerits to go along with them.

People also are all too willing to use anecdotal evidence to support a claim such as I got rid of the leafs in my car for coil overs and that proves it. As if the only vehicles that have the stock suspension swapped out for after market parts are cars that use leaf springs. Fact is that car makers try to tune their suspension to appeal to a a wider market segment. People buy after market suspension components to alter the way the car drives. To have different spring rates, thicker sway bars, and a lowered ride height no matter what the stock suspension setup is.

Also for race cars its about having the ability to quickly adjust the suspension for that race track.

Its not to say that the leaf spring is superior or inferior, just that the evidence often brought forward to support that idea often just isn't reliable. Its just like how people will sit there and point out what car reviewers stated about the C6 Z06. However they also state that the Z06 with the mich. tires, or with the magnetic shocks, or with the R tires do not do this. Also the even more powerful ZR1 Corvette was not also mentioned to have this problem. So the leaf springs in the Z06 with the old GY tires had this problem and it was the leaf springs. Even though all Z06 have leaf springs from the factory as well as the ZR1 Corvette.

Once more I am not trying to claim that one setup is better then another, just that there is a lack of evidence to support what the car mags have pushed.
 
#34 ·
Actually this reminds me of a review comparing someones C5 Z06 that has been modified (including an after market coil over setup) and a C6 GS. He states that the abandoned the leaf spring suspension which is incorrect as the Grand Sport Corvette still uses leaf springs. This just shows that car reviewers are not always the best source of technical data on any car.
 
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