Why would GM put leaf spring suspension on a Corvette, besides cost factor ? Leaf spings belong on trucks not cars .Try taking a curve with some washboard bumps in it and see what happens , you lose total control of steering until you hit smooth pavement. I took the same curve in a C4 with coil overs and it tracked perfect .WAKE UP GM

 

 

I'll be the first to acknowledge that I'm no expert on spring materials or technology, but I strongly suspect that the difference you felt between those two cars had a lot more to do with the freshness and/or valving of the shock absorbers in each car than it did with the spring material or design.

The fiberglass monoleaf springs in the C4 are very low mass, and I'd expect them to behave not all that differently than a coiled spring, or a torsion bar, for that matter.

Be well,

SJW

 

I think it's called "bump steer". The idea, according to John Greenwood, is that the Transverse leaf spring controls contact patch changes better & cheaper that any other conventional upper/lower A-arm + coil spring over tube shock set up. Back in the 70's he had a conversion kit for the rear of the C3's to eliminate the leaf spring. The bad effect of having a leaf spring is that over bumps the wheels are still connected via the spring and they are not truly independent of each other's movement.

I think it was a cost/design issue with the C4. The T-leaf was all the rage in the early 60's as it was a step forward from the set up that the euro cars were using back in the late 50's & early 60's. It was a live rear with a parrallel bar type set up. Look at a the 63/250GTO or an Alfa 2000 spyder from the early 70's.

Anyway, the T-leaf was carried from the C3's & put at both ends of the C4 because it worked and was a simple solution for controlling contact patch, it gave a ton of lateral G on smooth road for cheap. They could have spent a ton of $ doing something like a upper & lower un-equal lenght wishbone/ coil over set up but why do it if there was no customer protest? There is no way to build in more "compliance" if you use a T-leaf. On a coil over set up W/ wishbones you can use the shock to control tire orientation and use the spring to soften the ride, to a degree, to control bump steer. It's money, though!
JMHO

Tom

 

Exactly. Could not have said it better myself...



Larry
code5coupe

(PS Suspension geometry determines amount of bumpsteer, spring type does not.)

 

I've gotta respectfully disagree with this. The transverse leaf is solidly pinned at two points near its mid-section to the chassis, and that isolates movement at one end from movement at the other. If the leaf were free to pivot like a lever, what you've suggested would be true. If you were to disconnect the rear spring at both ends, then lift one end, you should see no movement at the other end.

A solid axle car will transmit some of the movement of one wheel to the other (regardless of whether it's suspended with parallel leaf springs, coil springs, or whatever). But a true independent suspension, with a transverse leaf will fully isolate each wheel.

It's worth noting that some C3 owners are ditching their front coil springs in favor of aftermarket transverse monoleaf fiberglass springs. They surely wouldn't be doing this if the transverse monoleaf were an inferior suspension design.

Bump Steer is caused by a mis-match in the lengths and/or arcs of travel between a tie rod and the other suspension components at a given wheel. This mis-match causes the wheel to pivot on its steering axis with suspension travel.

Be well,

SJW

 

IIRC, bump steer is defined as any change in toe angle caused by suspension travel.

 

Bullseye. And this toe angle change is caused by a mis-match in length and/or arc of the tie rod relative to the other suspension components.

Be well,

SJW

 

I just learned something, thank you very much!

Then why does the C4 front end react to wash board surfaces the same way that the rear of my C3 reacted to the same wash board surfaces? Not trying to be obtuse.

The first thing I noticed when I got my 90 was that both ends of the car behaved just like the rear of my C3? I still think that the shock of the bump on one side gets transmitted to the other side via the leaf spring because the spring is firmly attached to each wheel?

You don't have to explain, just point me in the right direction to do some reading so I can learn.

Thanks
Tom

 

My front end has acted the same way. Problem was inadequate shocks. New set of Koni's took care of that issue.

Larry
code5coupe

 

I have new bilstein shocks. No "world class sports car " should handle this way .My 87 Grand National does not even have bump steer nor did my 911.How do you remedy this problem .

 

For those of you who are disappointed with the handling of your C4s, the first thing to do (presuming the shocks and steering/suspension components are fresh and the shocks are appropriately valved for the sort of driving you want to do) is to get a four-wheel alignment done by a true expert.

Be well,

SJW

 

I am a firm beleiver in a supple suspension. The key to handling is holding the wheel in contact with the surface.

My 92 has the base FE1 with Koni shocks (new). It is better over the old Bilstiens and the replacement KYBs by a mile! However, the suspension still wants to step out on a bump. Most unsettling.

The idea behind the TLS was to remove the need for sway bars. Which tells us what the engineering basis was, and leads me to beleive that there is some residue in the geometry.

I don't like the inability to corner load the TLS, either.

Finally, the TLS will spring on an arc, not a vertical, I have always wondered if that is pulling on the suspension in some way...

Corvette is the last to use the TLS... and I think that is with good reason. If the concept was so great, why doesn't Ferrari still use it? Ferrari IS using the GM MR shock in their newest F599GTB, tho.

 

Bingo. The "World Class Sports Car" handling that is being derided by some in this thread was set up in 1984 with an ultra-stiff, tooth-loosening suspension. And it was praised to the heavens in 1984 as being a truly amazing car in terms of handling. But we must bear in mind that its handling was optimized for the conditions of a smooth race track. If you run a car that's set up this way on a rough road, it will be a harsh ride, and it will lose tire contact in the rough. Engineering inevitably involves compromises. Choose the conditions for which you want to optimize, and never forget that it will compromise performance under nearly all other conditions.

You might wish to try yet some other shocks, to see if you can find some that perform more like what you're seeking under your typical driving conditions. In any case, I'd bet that the spring rate has far more to do with this than does the spring type or material.

This is interesting. I've never heard this before. Do you know this to be true beyond any doubt?

With the TLS secured to the chassis in two places near its centerpoint, the only way that spring is gonna transmit any motion from end to end is if the lower chord of that spring stretches through the mounting points and pulls downward on the far side of the mounting point -- and/or if the upper chord of that spring compresses through the mounting points.

Yes, the TLS will describe an arc as it travels. Can you identify any other IRS (or IFS) system that does not travel in an arc, regardless of the spring type?

I can't help with this one. But it does raise a question in my mind: What are the springs in the C6 (both base and Z06)?

This is becoming an interesting thread...

Be well,

SJW

 

Agreed. It's all about reaching a balance with what the intended use is.

These are the adjustable Koni's. I am very happy with them. I don't question the material, it's the concept. My bother had a 67 with the TLS (steel) in the rear... the back end was strange, at best. Then again, the 435hp 427 would make a lot of things strange.

Yes. Read it somewhere in the Dave McClellen book, Corvette from the Inside.

Agreed. But the downside to the TLS is it's inability to deal with small imperfections. I am a big fan of the progressive coil.

Yes, the Honda double wishbone. The tire contact stays very even the entire throw. I watched my 94 Prelude VTEC go up on a lift, and the camber stayed very consistant during suspension sag.

same basic concept as the C4 and C5. I don't know about material, but I do know about idea... TLS lives.



yes, very!

 

Oh gawd I thought we were done with this conversation.

Go here:

http://forums.corvetteforum.com/show...light=coilover

 

No, bump steer is determined by the control arm lengths, steering tierod location, and castor. It has nothing to do with the spring type. Although a softer spring will allow more suspension travel, and therefore more bumpsteer.


Neither is every single other independent suspension car that has sway bars.


The Corvette front end is an unequal length double wishbone setup, minus the coil overs.


The way to build in more compliance without softening the spring rate is a progressive coil. Not all coil springs are progressive.

The shock does nothing to locate the tire on a double wishbone setup.

 

And the fact that it was a nine-leaf steel spring, with tremendous mass, had a lot to do with that, too.

Correct you are. Further research confirms this, although that only applies to the C4 and later Corvettes with TLS suspension. Thanks for educating me on this point.

Wouldn't any taper in a leaf spring provide progressive springing also? I don't think the C4 spring has any taper (going from memory here), but...

I think you'll agree that it's the unequal length of suspension components -- not the TLS -- that's actually the cause of camber change during suspension travel. And the camber change was designed in, to optimize contact patch as the car rolls in a turn...

You are correct again, Andy. I just checked this, and the C6 Z06 does still use TLS suspension. I guess maybe TLS is not so inferior, eh?

In digging into all of this a bit, I stumbled across this must-read page:

http://en.wikipedia.org/wiki/Corvette_leaf_springs

Fascinating...

Be well,

SJW

 

Zero camber change is not in anyway desireable.


Ideally, you want zero camber when going straight, and want to gain camber when loading the suspension in corners. Front castor will help there, but ultimately you need an unequal double wishbone or unparallel double wishbone setup to get camber change in back to maintain the contact patch, especially on a soft suspension like a Honda where you have more body roll.

BTW, the Prelude has unequal length control arms.

(Disclaimer, none of this applies to solid axles.)

 

Thanks for the link, CC. The title on this thread didn't interest me, so I'd missed it 'til now.

Be well,

SJW