Corvette ZO6 vs Porsche 997 GT3 RS

[GoCougs]

Thanks a lot for that Cougs.? I'm not a huge Vette fan so I don't pay a lot of attention to the suspension setup like I would on say a Mustang.? Frankly I don't see the inherent issue if the car handles and performs as well as it does.? I would like to see GM try coilovers on a test mule to see how the handling changes though.

The inherent issue is that there is one single suspension memeber acting as two. This creates two problems. First, beam theory tells us that deflection on one side of the spring gives us deflection on the other (though in practical terms solidly clamping the spring in the center counteracts this). Second, the interaction of these two deflections can induce a harmonic(s) into the spring (causes resonance).

Corvette suspenion engineers are very smart, so I've confidence that a portion of these issues (and others) have been addressed to some extent, but the design is far less than optimal, and no doubt responsible for the Corvette's reputation for a brittle ride and twitchy handling. Just as with the 911's rear engine, BMW's in-line 6, and other vestiges that other car makers left behind, leaf springs on the Corvette are a legacy hold-over dating back to the early '60s and the C2.

[r0tor]

one would ask if the leaf springs truely has no performance drawbacks, why is an adjustable coil-over used in the C6-R... http://www.corvetteracing.com/cars/c6r/chassis_specs.shtml

[Raza]

The GT3 in Germany is 110.878,00  Euros. The Z06 in America is 70K USD. At todays exchange rate, that makes the Corvette 54,110.4883 Euros. The GT3 is more then twice as much as the Corvette. Even if you tack on, lets say, 20 grand for shipping and such, the Vette is still a bargin.
And given how close the times were and given the fact that the testor attributed the slower cornering TO THE TIRES, it is LOGICAL to say that with BETTER RUBBER, the Vette can make FASTER TIMES.
It is pretty easy.

You have to use in-market prices, you can't use exchange rates.  If you do that, then every 3 series in Australia costs 900 thousand dollars.

[southdiver1]

You have to use in-market prices, you can't use exchange rates.? If you do that, then every 3 series in Australia costs 900 thousand dollars.

And while I agree with that, I really have no way of really knowing what these cars are going for in Germany. Even if they are going to 100K Euros, it is STILL less then the GT3

[565]

one would ask if the leaf springs truely has no performance drawbacks, why is an adjustable coil-over used in the C6-R... http://www.corvetteracing.com/cars/c6r/chassis_specs.shtml

You answered your own question. 

The adjustable coil overs are used because they are... adjustable, while leaf springs are not.  On a race car, you need to be able to change spring stiffness to adapt to changing conditions.  If the C6-R used leaf springs, they'd have to swap out different stiffness leafsprings, which would be a pain.  On a roadcar, the coils provided usually aren't  adjustible anyway, so it makes no difference.

The MORE interesting question is the flipside.  If coil overs from the C5-R/C6-R really did provide some performance advantage, why didn't they make their way into the C6? A myraid of developments made on the C5R racecar later influenced the design of the C6 and C6 Z06, including exposed headlamps, longer wheelbase, and 7.0 liter smallblock and dry sump for the Z06.  One would think that with all the racing success of the C5R's with coil overs, and considering how cheaper they are, they'd be the obvious C5R derived improvement to be carried over to the C6.

Continued use of the transverse leafspring on the Corvette is not a cheap proposition.  It's pretty much the only car in GM's lineup that uses the setup.  All of GM's other cars use cheap conventional steel springs.  It would be extremely cost effective for GM to eliminate the complex composition transverse spring setup.  GM has ample testing of coilovers used in a Corvette application with the C5R and C6R racing projects.  GM chooses to continue the transverse composite leafspring design because there must be benefits that outweigh the obvious costs.

[Raza]

And while I agree with that, I really have no way of really knowing what these cars are going for in Germany. Even if they are going to 100K Euros, it is STILL less then the GT3

Considering neither Chevrolet's German or UK sites have the Corvette or Z06 listed, it will probably have to be imported through a third party, and that could potentially even up the prices more than you think.  Look at what we have to do import a car that isn't sold in the US.  Some C&D columnist said it would cost over a million dollars to import a Fiat Panda (this, admittedly, is because no one had ever imported the Panda before, so he would have to buy at least a dozen for crash testing).


EDIT:  A search on Evo.co.uk has them pricing a 2005 Z06 at 59K GBP, which is not really that much compared to the GT3 RS, which taps in at 94K GBP. 

[GoCougs]

GM chooses to continue the transverse composite leafspring design because there must be benefits that outweigh the obvious costs.

Legacy hold-over is my vote; just as with the 911's rear engine or BMW's in-line 6.

I have a tough time buying the expense argument ("they must be better because Chevy could've saved money on coils"). The Corvette is all about bargain performance. Further, a good portion of "expense" is labor for installation. Two mono leafs look quite a bit easier to install than four coils.

If the advantages were there, Porsche, Ferrari, et al., and race series with flexibility on suspension types, would use 'em.

Lastly, I don't know if one can get variable spring rate with leafs. If so, I don't see how. If not, that explains it.

[southdiver1]

Considering neither Chevrolet's German or UK sites have the Corvette or Z06 listed, it will probably have to be imported through a third party, and that could potentially even up the prices more than you think.? Look at what we have to do import a car that isn't sold in the US.? Some C&D columnist said it would cost over a million dollars to import a Fiat Panda (this, admittedly, is because no one had ever imported the Panda before, so he would have to buy at least a dozen for crash testing).


EDIT:? A search on Evo.co.uk has them pricing a 2005 Z06 at 59K GBP, which is not really that much compared to the GT3 RS, which taps in at 94K GBP.?

http://www.corvette-europe.com/index.aspx?ChapterID=2837&FilterID=998
It looks like to me that you need to actually contact a local (German) dealer to get a price. I admit Mein Deutch is not that great so I might be missing it somewhere...

[r0tor]

You answered your own question.?

The adjustable coil overs are used because they are... adjustable, while leaf springs are not.? On a race car, you need to be able to change spring stiffness to adapt to changing conditions.? If the C6-R used leaf springs, they'd have to swap out different stiffness leafsprings, which would be a pain.? On a roadcar, the coils provided usually aren't? adjustible anyway, so it makes no difference.

The MORE interesting question is the flipside.? If coil overs from the C5-R/C6-R really did provide some performance advantage, why didn't they make their way into the C6? A myraid of developments made on the C5R racecar later influenced the design of the C6 and C6 Z06, including exposed headlamps, longer wheelbase, and 7.0 liter smallblock and dry sump for the Z06.? One would think that with all the racing success of the C5R's with coil overs, and considering how cheaper they are, they'd be the obvious C5R derived improvement to be carried over to the C6.

Continued use of the transverse leafspring on the Corvette is not a cheap proposition.? It's pretty much the only car in GM's lineup that uses the setup.? All of GM's other cars use cheap conventional steel springs.? It would be extremely cost effective for GM to eliminate the complex composition transverse spring setup.? GM has ample testing of coilovers used in a Corvette application with the C5R and C6R racing projects.? GM chooses to continue the transverse composite leafspring design because there must be benefits that outweigh the obvious costs.

Leaf spring stiffness is just as easily chaged as coil spring stiffness - you just need to change the springs.    Of course with the leaf spring you are more or less stuck with equal spring rates on both sides.  An adjustable shock can be used with either, and ride height can be adjusted with either.

My best guess is (as another poster stated) the transverse leaf spring is just a legacy hold-over like the the pushrod engine.... you can throw buckets of money to make something work well, but at the end of the day there are better alternatives.

[Raza]

http://www.corvette-europe.com/index.aspx?ChapterID=2837&FilterID=998
It looks like to me that you need to actually contact a local (German) dealer to get a price. I admit Mein Deutch is not that great so I might be missing it somewhere...

Well, either way, there's no doubt anymore that the Z06 is wildly cheaper and just as fast around a track (although I imagine this has a lot to do with the track; around Bedford West, the Z06 ran a 1.24.45, with a peak of 118.1 mph, which is only slightly quicker than a Carrera S, which ran 1.24.60, with a peak of 108.2).

For me, though, it's still the 911.  It always has been, and I assume it always will be.  And that is my bias, and I don't mind if anyone quotes me on that. 

[heelntoe]

bedfore west, eh? did you read their fastest track test.

[Raza]

bedfore west, eh? did you read their fastest track test.

I might have.  I don't have the newest issue, I have to get that still.  The last issue I had was eCOTY, and I'm still fuming about that. 

[565]

The inherent issue is that there is one single suspension memeber acting as two. This creates two problems. First, beam theory tells us that deflection on one side of the spring gives us deflection on the other (though in practical terms solidly clamping the spring in the center counteracts this). Second, the interaction of these two deflections can induce a harmonic(s) into the spring (causes resonance).

Corvette suspenion engineers are very smart, so I've confidence that a portion of these issues (and others) have been addressed to some extent, but the design is far less than optimal, and no doubt responsible for the Corvette's reputation for a brittle ride and twitchy handling. Just as with the 911's rear engine, BMW's in-line 6, and other vestiges that other car makers left behind, leaf springs on the Corvette are a legacy hold-over dating back to the early '60s and the C2.

There is no issue with a single leaf spring secured at two points rather than two seperate leaf springs.  First off, in middle section of the spring is arched and flush with the metal crossmember.  Any resonance or harmonics generated by one portion of the spring must be transfered to the other side by vibrational motion in this middle portion.  Also the magnitude of motion transfered (if any) would depend on the maximum limit of motion allowed by the portion of the spring that transfers the energy.  Yet this middle portion already is permantly held in a flexed position, and there is no further motion possible. 

The faults of the Corvette's handling is not in the springs, but rather in rather lackluster shock tuning and in less on track testing than their German and Japanese counterparts to dial in the finer points of the suspension.  Case in point,  GM spent just 2 weeks at the Nurburgring testing their Z06, and only after it was almost completed.  Nissan on the other hand has been at the Ring for years with their upcoming GTR, testing at each step in the mule process.

In your mention of BMW and Porsche, you have brought up two interesting ways of justifying the keeping a traditional design.  Automakers don't hang onto a particular design when others are doing something else unless they have strong reasons to.


1) BMW hangs onto the inline 6 because it's the best balanced engine.  They keep the design for it's obvious advantages over the disadvantages.  BMW's make their living off making the ultimate driving machine, and the advantages of the smoother engine outweigh the packaging advantages of a V6.

2) Porsche's 911's flawed engine placement is kept because 911 lovers demand it (and they are a forceful bunch).  Porsche engineers wanted to kill off the 911's rear engine, because every aspect of its design was compromised by it's VW beetle roots.  But Porsche accountants reasoned that the 911 was their best selling design and alienation of their strong an base would bring financial ruin. So the 911 slaved on with the rear engine, and Porsche did their best to make the most of the recipe (and they have done very well).   Thus it is no wonder that the 911 evolves so conservatively.   911 lovers were offended even when the 996 introduced water cooling.  But notice that with the exception of the 959, Porsche has never introduced another rear engined sports car.  924's, 944's, 928's, and more recently, the Boxster, Cayman, and Carrera GT, have been either front or mid engined.

Since no Corvette lovers have ever really pushed one way or another for the leafsprings, and the general stigma on leafsprings is negative, GM had no reason to keep the leafsprings to keep it's fan base.  GM rather follows BMW's reasoning.  The unspring weight advantage of the leafsprings outweighs the cost over coils.

[565]

Leaf spring stiffness is just as easily chaged as coil spring stiffness - you just need to change the springs.? ? Of course with the leaf spring you are more or less stuck with equal spring rates on both sides.? An adjustable shock can be used with either, and ride height can be adjusted with either.

My best guess is (as another poster stated) the transverse leaf spring is just a legacy hold-over like the the pushrod engine.... you can throw buckets of money to make something work well, but at the end of the day there are better alternatives.

To adjust the stiffness on a leafspring you'd need to change out an entire leafspring, that no where as easy as simply adjusting the spring rates on an adjustable coil setup like the one on the C5R-C6R.  And that also means you have to stock about 20 different leafsprings with different stiffnesses.  They are alot bigger than say, 20 different coil springs.  So on a pitstop where the driver wants the rear springs a bit softer, you'd have some guy climbing under the car and trying to swap out a 3 feet long piece of plastic.

Legacy hold-overs only make sense if it somehow saves you money, or preserves your fan base.  GM uses the pushrod engine because it has extensive infrastructure built upon this engine.  It's basic structure is used in many engines including portions of its truck line, a version is used in the Impala, and various cars overseas.  Also many Chevy fans swear by the pushrod smallblock V8.

The transverse leafspring doesn't benefit from any of these reasons.  There is no intrastructure for it, the Corvette is the only car that uses it.  It would be far more cost effective to switch the Corvette onto the same steel coils on every other car.  There is no fan demand for it.  But rather just the opposite, as there is a rather negative stigma aganist it.

GM chooses to continue to use the transverse leaf spring because they feel the advantages outweigh the costs.

[JYODER240]

2) Porsche's 911's flawed engine placement is kept because 911 lovers demand it (and they are a forceful bunch).? Porsche engineers wanted to kill off the 911's rear engine, because every aspect of its design was compromised by it's VW beetle roots.? But Porsche accountants reasoned that the 911 was their best selling design and alienation of their strong an base would bring financial ruin. So the 911 slaved on with the rear engine, and Porsche did their best to make the most of the recipe (and they have done very well).? ?Thus it is no wonder that the 911 evolves so conservatively.? ?911 lovers were offended even when the 996 introduced water cooling.? But notice that with the exception of the 959, Porsche has never introduced another rear engined sports car.? 924's, 944's, 928's, and more recently, the Boxster, Cayman, and Carrera GT, have been either front or mid engined.

Not really, the accounts wanted to kill of the 911 because it wasn't selling. The public felt they were too expensive and they had quality control issues. No one wanted to pay that much for a car if it wasn't going to function properly. The engineers never wanted to kill of the design. In fact morale was very low because they knew that Ernst Fhrmann who was running the company at the time was planning on killing it off after 1981.

Porsche may not have built another rear-engine car but they don't need too. The 911 is unique and has character. It's not just about the performance numbers it can put up but about the unique experience you get from driving one. Sure the weight distribution is off and they're prone to snap oversteer but guess what the owners don't mind because they're loving every minute of it. It's not about the bragging rights of setting the fastest lap times it's about whats happening along the way. 

[GoCougs]

There is no issue with a single leaf spring secured at two points rather than two seperate leaf springs.? First off, in middle section of the spring is arched and flush with the metal crossmember.? Any resonance or harmonics generated by one portion of the spring must be transfered to the other side by vibrational motion in this middle portion.? Also the magnitude of motion transfered (if any) would depend on the maximum limit of motion allowed by the portion of the spring that transfers the energy.? Yet this middle portion already is permantly held in a flexed position, and there is no further motion possible.?

Good points, but the theory of harmonics and beam theory state that the transverse leaf spring, at its core, has fundamental drawbacks that in practical terms, have been mitigated somewhat.

The faults of the Corvette's handling is not in the springs, but rather in rather lackluster shock tuning and in less on track testing than their German and Japanese counterparts to dial in the finer points of the suspension.? Case in point,? GM spent just 2 weeks at the Nurburgring testing their Z06, and only after it was almost completed.? Nissan on the other hand has been at the Ring for years with their upcoming GTR, testing at each step in the mule process.

That would do it, but why would GM's suspension engineers spend a bunch of (supposed) extra cost on such a unique (and non-scalable) design as transverse leaf springs and then stumble on the industry standard practices of shock tuning and track testing?

In your mention of BMW and Porsche, you have brought up two interesting ways of justifying the keeping a traditional design.? Automakers don't hang onto a particular design when others are doing something else unless they have strong reasons to.


1) BMW hangs onto the inline 6 because it's the best balanced engine.? They keep the design for it's obvious advantages over the disadvantages.? BMW's make their living off making the ultimate driving machine, and the advantages of the smoother engine outweigh the packaging advantages of a V6.

In the days of old perhaps, but V6s and V8s what with dynamic engine mounts and a whole host of other NVH mitigation techniques have matched an in-line 6's smoothness, and eliminatied the inherent packaging and crank strength issues of in-line 6 (and 8) configurations. This is a legacy hold-over of the history kind. (read: "What, a BMW V6?!").

2) Porsche's 911's flawed engine placement is kept because 911 lovers demand it (and they are a forceful bunch).? Porsche engineers wanted to kill off the 911's rear engine, because every aspect of its design was compromised by it's VW beetle roots.? But Porsche accountants reasoned that the 911 was their best selling design and alienation of their strong an base would bring financial ruin. So the 911 slaved on with the rear engine, and Porsche did their best to make the most of the recipe (and they have done very well).? ?Thus it is no wonder that the 911 evolves so conservatively.? ?911 lovers were offended even when the 996 introduced water cooling.? But notice that with the exception of the 959, Porsche has never introduced another rear engined sports car.? 924's, 944's, 928's, and more recently, the Boxster, Cayman, and Carrera GT, have been either front or mid engined.

I agree, a legacy hold-over of the styling kind.

Since no Corvette lovers have ever really pushed one way or another for the leafsprings, and the general stigma on leafsprings is negative, GM had no reason to keep the leafsprings to keep it's fan base.? GM rather follows BMW's reasoning.? The unspring weight advantage of the leafsprings outweighs the cost over coils.

I disagree; it's a legacy hold-over of the stubborn kind.

[r0tor]

To adjust the stiffness on a leafspring you'd need to change out an entire leafspring, that no where as easy as simply adjusting the spring rates on an adjustable coil setup like the one on the C5R-C6R.? And that also means you have to stock about 20 different leafsprings with different stiffnesses.? They are alot bigger than say, 20 different coil springs.? So on a pitstop where the driver wants the rear springs a bit softer, you'd have some guy climbing under the car and trying to swap out a 3 feet long piece of plastic.

I'm not familiar with any coil-over setup that allows for adjusting spring rates.  You can adjust the ride height and the shocks, but i've never seen an adjustable spring rate.  The closest thing I can think of is Nascar people chucking spring rubbers in between the coils during the race to effect spring rate... and thats not something you see done in road racing.

also, the leaf spring beam will abosulety have several resonant frequencies that will cause modal bending if excited correctly (which may or may not be a problem).

[565]

Not really, the accounts wanted to kill of the 911 because it wasn't selling. The public felt they were too expensive and they had quality control issues. No one wanted to pay that much for a car if it wasn't going to function properly. The engineers never wanted to kill of the design. In fact morale was very low because they knew that Ernst Fhrmann who was running the company at the time was planning on killing it off after 1981.

Porsche may not have built another rear-engine car but they don't need too. The 911 is unique and has character. It's not just about the performance numbers it can put up but about the unique experience you get from driving one. Sure the weight distribution is off and they're prone to snap oversteer but guess what the owners don't mind because they're loving every minute of it. It's not about the bragging rights of setting the fastest lap times it's about whats happening along the way.?

The 911 was due to be replaced because engineers deemed it was "too hard to drive" and couldn't meet the emissions regulations.  It was supposed to be replaced by the front engined water cooled 928 in 1981. Here are some interesting facts from a site dedicated to 911's from that era

http://www.adelgigs.com/911schistory.shtml


"The 911 was due for replacement in the early 1980s, but demand continued strongly with the 911SC outselling its declared successor, the 928, by nearly 50 per cent."


Here is a similar quote. from
http://www.answers.com/topic/porsche-911


"In 1979 Porsche made plans to replace the 911 with the 928, but the 911 still sold so much better than the 928, that Porsche revised its strategy and inject new life into the Type 911 European editions. Those cars (1981?1983 911 SCs) were massaged to yield 204 bhp @ 5900 rpm from their 2994 cc powerplants. North Americans would have to wait for the replacement 3.2 L 911 Carrera in 1984 before seeing any extra horsepower."


So pretty much Porsche engineers already made a modernized car to replace all of the 911's faults, but the 911's strong sales over the car that was suppose to replace it, saved it from the cutting block.

[565]

I'm not familiar with any coil-over setup that allows for adjusting spring rates.? You can adjust the ride height and the shocks, but i've never seen an adjustable spring rate.? The closest thing I can think of is Nascar people chucking spring rubbers in between the coils during the race to effect spring rate... and thats not something you see done in road racing.

also, the leaf spring beam will abosulety have several resonant frequencies that will cause modal bending if excited correctly (which may or may not be a problem).

Yes you'd have to swap out the coil springs, but still as I said before 20 coils is alot smaller and more compact than 20 leaf springs (actually more cause you can't swap them around like you can coils, and you pack coils into each other).? Also can you imagine them changing a 3 foot long piece of plastic on a pitstop?


Here is another post found on Corvette Forums that is rather interesting.? Interesting thing of note.? Older Corvettes used coil springs for the front before.? So the all around transverse composite leafspring isn't exactly tradition at all.


"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).

Part 2
**********************************************

If it?s so good why don?t other people use it?

It?s legitimate to ask, does GM know something that Ferrari, Porsche etc don?t know or are the people at GM just being pig headed and sticking with ?outdated? technology.



Street cars:

-You must design them into the car in the first place. This seams 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.

-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.

-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.

-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. The same is probably true of Ferrari. 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. Porsche would be somewhere in between. 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.

-Perception. Just like pushrods, the leaf spring as 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.



What about race cars? (this section is almost verbatim from another post of mine.

To start off, 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.



Would the Vette be better with coil springs?

Well that depends. As I said before, there are a lot more options available in coil springs. If I want to substantially change the Vette?s spring rates then I will need to go to coils. Also, if I want to totally get rid of the Vette?s anti roll I need to dump the leaves because they provided some roll resistance.



BUT?

If for some reason I just lost my leaf spring (maybe someone stole it to make a very strong bow and arrow) and had to replace it with coils. I want the same ride quality, the same spring and roll rates etc. Basically I want the car to be the same as before but with coil springs. Assuming you didn?t change anything but the springs (same tires, shocks, ride height, same spring rate and effective roll rate, etc) the Vette would unquestionably be SLOWER with coils instead of the leaf setup. Basically if all else is equal, the coils are heavier and raise the CG of the car. One other small advantage is the shocks on the leaf sprung car will move more freely than the car with coilovers. When used as a coil over, coils impart a bending load on the shocks that cause them to bind a bit. On a street car you will never notice but on a race car it can cost a tenth of a second or so. (Hypercoil markets a pivoting spring perch to reduce the effects of side loading in coil over shocks).

Again, if I decide I really want to race I will likely dump the leaves because I have more options with coils. For a reasonable (in racing terms) price I can get custom coils made. The same isn?t true of the composite leaf spring."

[JYODER240]

The 911 was due to be replaced because engineers deemed it was "too hard to drive" and couldn't meet the emissions regulations.? It was supposed to be replaced by the front engined water cooled 928 in 1981. Here are some interesting facts from a site dedicated to 911's from that era

http://www.adelgigs.com/911schistory.shtml


"The 911 was due for replacement in the early 1980s, but demand continued strongly with the 911SC outselling its declared successor, the 928, by nearly 50 per cent."


Here is a similar quote. from
http://www.answers.com/topic/porsche-911


"In 1979 Porsche made plans to replace the 911 with the 928, but the 911 still sold so much better than the 928, that Porsche revised its strategy and inject new life into the Type 911 European editions. Those cars (1981?1983 911 SCs) were massaged to yield 204 bhp @ 5900 rpm from their 2994 cc powerplants. North Americans would have to wait for the replacement 3.2 L 911 Carrera in 1984 before seeing any extra horsepower."


So pretty much Porsche engineers already made a modernized car to replace all of the 911's faults, but the 911's strong sales over the car that was suppose to replace it, saved it from the cutting block.

"Dealers in the United States and Europe had two consistent complaints: The cars were too expensive, and they had serious quality control problems. To Schutz, this was one issue: No one objects to paying a price for something if it functions perfectly. He heard morale a Porsche was poor because the company planned to discontinue the 911 and push the 924 and 928. ... 'Every Monday, Porsche's top managers have lunch together,' Schutz said. 'This had been going on forever. So the first Monday I was there, I went to the lunch. It was a mixed bag of engineers, sales people, manufacturing, and I listened to their converstaions. After a while I asked these folks one question: "What is going on in this company right now that is so exciting that you can hardly wait to come to work?" You could hear a pin drop."

Porsche 911: Perfection By Design. By Randy Leffingwell P.166-167

[nickdrinkwater]

http://www.stratstone.com/StratstoneWebApp/NVDetails.aspx?capcode=COZ670%20%20%202CPIM

Official Corvette dealer lists it at ?59,895, though it's not available in RHD (It's not sold as a Chevrolet here).

The 911 comes in, like Raza said, at about ?94,000.

It's definitely an interesting comparison.  Personally I think the cars are good at different things.  The ZO6 has a beast of an engine which makes it lightning quick and I'm sure is pretty decent on the road. 

The 911 is more finely focused but I'm sure would be harder to live with every day and pricier.  It does look a hell of a lot better than the Corvette IMHO, which reminds be a bit of a big yellow bathtub.  But then it's only two thirds the price...you get what you pay for I guess...

[r0tor]

Yes you'd have to swap out the coil springs, but still as I said before 20 coils is alot smaller and more compact than 20 leaf springs (actually more cause you can't swap them around like you can coils, and you pack coils into each other).? Also can you imagine them changing a 3 foot long piece of plastic on a pitstop?

and so on and so on...

When is the last time you saw a spring replaced during a pit stop?  This is an immense pain in the ass to change - especially if its a coilover.  Also, I don't see how unbolting a coilover is easier then a leaf spring.  Realistically, during a race if you want to adjust the spring rate of your suspension, you would adjust the tire pressure.  I noticed in the article they mention that F1 cars have moved towards tortion bars - what they didn't mention that the flex in the tire of an F1 car is accountable for over half of the suspension travel and they use air pressure to adjust that.

I see other rather weak arguments in the article like money (when GM has millions invested in that team) and manufactureablity (they are a composite material - its no harder to make then making the carbon fiber bodywork on the C6R).  Then they go on to precision, but this time fail to mention some F1 cars have carbon aero components designed to bend in a specific way during loading from drag at certain speeds.... talk about precision.

the article was rather not suprisingly biased.

[565]

the article was rather not suprisingly biased.

Are there any articles out there that prove that the Corvette's transverse leaf springs are a decesive deficit to handling?  Outside of a few articles from Corvette fans, it's all just speculation and prejudice.  Absent minded thinking that goes much along the lines of "since trucks use leaf springs, and most cars use coils, Corvette's transverse leaf springs must be junk."

The fact is, Corvette's transverse leaf springs are unlike anything out there on the market.  I'm sure people here are gonna speculate about energy transfer or harmonics or other stuff they learned in Physics 101, but at the end of the day the fact remains that they have no idea how it would truly impact the characteristics of the suspension in real world application.

The performance advantages of the transverse leaf spring have been listed already, less unspring weight, lower CG.

Can anyone here find any evidence (aka not your own speculation) of the performance superiority of coils over the Corvette's leaf springs?


This isn't like the debate of pushrods over OHC engines.  There have been hundred upon hundreds of pages written by automobile engineers about why OHC offeres advantages over OHV designs.

Can anyone find me even 1 page devoted to all the wonderful performance advantages of coils over Corvette's transverse leaf springs?

So far all the advantages of the coil springs have been practical rather than performance,  cheaper cost, easy of implementation, etc.

[r0tor]

sorry, but things like this is rediculous

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.

I'll be willing to bet that the vette designers road tested a couple dozen different spring rates before deciding on the production rate and the C6R team has a bunch more money in the budget then they do...

[GoCougs]

Can anyone here find any evidence (aka not your own speculation) of the performance superiority of coils over the Corvette's leaf springs?

Fixed rate.

Limited wheel travel.

"Absorbtion confusion" via double duty as anti-roll bar (absorbing forces from both lower A-arms and body roll simultaneously).

[565]

Fixed rate.

Limited wheel travel.

"Absorbtion confusion" via double duty as anti-roll bar (absorbing forces from both lower A-arms and body roll simultaneously).

I wanted evidence, not speculation.

[93JC]

Just wanted to clarify that as far as I know one of if not the single biggest reason the C6-R uses coil springs in place of the production leaf springs is that most of the rac series it competes in have specific rules which govern suspension set-up, and along the line there's more than likely quite a few which mandate that the cars have to have coil springs, performance advantage or not.

[GoCougs]

I wanted evidence, not speculation.

IMO they're perfect examples of attributes as evidence.

[565]

IMO they're perfect examples of attributes as evidence.

I want evidence as in automotive engineers or reputable sources that have said, yes we tried corvette like transverse leaf spring setup and we ran into these problems, or we found the design was lacking in this area or that area.


All you have is speculation based on a photograph and an idea of a design, and none of it arises from experience or real world tests.  How do you know what the limit of suspension travel is?  It might be actually much higher than coil spring. Nor do you know whether using a leaf spring design and a softer antiroll bar actually transfers more or less motion than using coils and a stiffer antiroll bar.

You have done none of these experiments and yet speculate that the data will fall in your favor. 

[GoCougs]

I want evidence as in automotive engineers or reputable sources that have said, yes we tried corvette like transverse leaf spring setup and we ran into these problems, or we found the design was lacking in this area or that area.


All you have is speculation based on a photograph and an idea of a design, and none of it arises from experience or real world tests.? How do you know what the limit of suspension travel is?? It might be actually much higher than coil spring. Nor do you know whether using a leaf spring design and a softer antiroll bar actually transfers more or less motion than using coils and a stiffer antiroll bar.

You have done none of these experiments and yet speculate that the data will fall in your favor.?

I disagree.

Tell anyone with a smidge of automotive experience that given the choice between two performance suspension set-ups, which is preferred soley on its inherent attributes:

1.) Limited wheel travel, fixed rate, same spring works the suspension and controls body sway

2.) More wheel travel, variable rate, spring separate from anti-roll bar.

Taking it any further would necessitate quantitative tests that GM no doubt peformed, but sure as heck isn't going to make public whatever the results owing to IP concerns on testing and design methodologies.