wishihad1-2

So recently I noticed a claim regarding the rear suspension on a Corvette.
http://www.speeddirect.com/index.php...ving-c2-c3-irs
Does that explanation strike anyone else as wrong?
Basically the site makes a few claims which are, well wrong. First, they claim that coil sprung cars have basically zero roll resistance (presumably minus the roll bar). This isn't at all true.
Second they claim the C2-C4 rear suspension has more roll resistance due to the leaf spring vs a pair of coil springs. This is also wrong. Finally they lump the behavior of the C5-C7 rear leaf spring (and by implication the front suspension of the C4-C7) into the same category as the C2-C4. This is also wrong.

I think all buyers should be VERY wary of buying from an organization that offers "engineer talk" that is just plain wrong. I would certainly avoid a doctor who was telling me things that were wrong while selling me a treatment. Fortunately for the doctors I don't know about medicine to know when I'm being had

OK why is the above wrong.
1. The first claim implies that cars without rear anti-roll bars but with coil springs have what the Formula Vee guys call a zero-roll resistance rear end (zero roll rear end). That is NOT true when you have coils.

So lets use a very simple example. Let's assume we have 400 lb/in springs and 1600 lbs on the rear axle. Also assume a 1:1 wheel to spring motion ratio. So when the car is static on the ground each spring is compressed 2" (2*400=800lbs per spring). Now we roll the car so the left wheel is compressed one more 1" (3"*400lb/in=1200 lb on the left). The right wheel gets the rest of the 1600 lb (1200-1200=400lb, 400lb/(400lb/in)=1" total compression). Notice that when we roll the car enough to get 1" of compression on one side the left side suspension is pushing up with 800lb more force than the right side. That 800lb is effectively the force/torque (depending on how you look at it) that is trying to keep the car from rolling. That is NOT the zero roll that was claimed in the ad copy. I can't think of ANY modern cars that would have a zero roll resistance rear even if you pulled the roll bars off.

So we start off with a claim about coil spring suspension that is wrong.

Next let's talk about the leaf spring claim. I know a lot of people are confused by the fiberglass spring with two pivot points like the C5+ cars have in the back. The C4 and earlier stuff is much easier to understand. Because the spring is RIGIDLY attacked to the cent er of the frame the spring acts like two separate springs*. The motion of the right spring does not move the left spring. So in this regard the leaf spring is EXACTLY like a coil spring.

*Two exceptions. One, this assumes the diff housing is rigidly mounted into the chassis. It isn't. This means the diff housing rolls a bit when the chassis rolls. This actually reduces the roll resistance of the chassis just slightly. Thus, ironically, the thing the ad says makes coils better is actually more true for the leaf setup vs coils. The other exception is that coils do not have inner leaf stiction. The mono-leaf also avoids this inner leaf stiction because, well it doesn't have many leaves. You will read about people going from the steel springs to the mono-leaf needing extra damping because they no longer have the damping effect of the multi-leaf spring's internal friction. Either way, the ad claims are false.

Third, the rear leaf spring behavior of the C5+ cars is different than the earlier cars for several reasons. I mean the suspension design is much different as the half shaft is no longer a suspension arm. Also the later cars use a double pivot mount form the spring in order to gain more roll resistance. The C3 does not and the position of the left wheel does not affect the effective spring rate of the right wheel.

Looking at the actual design of the kit I see a falling rate bell crank setup. Aside from making sure people can see your springs I don't see how this is going to be better than just putting a coil around the damper. I certainly can't see how this would be better than converting the car to a monoleaf and upgrading the dampers. Then again I'm not trying to sell the kit.

69427

A few of us have issues with some of their claims. You're not alone.

jb78L-82

A very nice writeup and good explanation of the inaccuracies. I have never agreed with the naysayers who feel that coilovers are a better mouse trap to a mono leaf.

7t9l82

but it looks cool

wishihad1-2

I'll say that I don't believe coils are inherently better than a mono-leaf spring. The multi-leaf spring does have some serious limitations (inner leave sticktion, weight - may not be all bad as removing weight makes the car more nose heavy). However, I think far too many people can't get their heads around the idea that leaf spring doesn't have to mean old pickup or 1960s domestic car. Once you stop asking the leaf to be a suspension arm (1963 in the Corvette's case) the biggest problem with the leaf is gone. The next biggest problem went away when GM created the fiberglass spring. A system like the one in question does fix the inner leaf stiction problem and I do believe people who say their car handles better after the change. Of course that change might not be apple to apples. Take a car with worn shocks. Replace them. Hey the car handles better even though the type of spring is unchanged.


More disturbing to me is when I see a company that claims to have "engineered" their product producing marketing claims that are clearly false and based on misinformation that any undergrad mechanical engineer should be able to understand. Sadly this vendor isn't the only guilty party. I know at least one vendor of C5 and C6 coil overs who has repeatedly made false (ie marketing) claims regarding the way the C6 suspension works. Their marketing guy even made the claims in a Corvette magazine that shamefully didn't call out his BS. The magazine had little excuse given that earlier in the same article they explained exactly how the leaf spring setup worked. Their explanation would contradict the marketing talk of the vendor.

gkull

To the poster: You can find fault in nearly every item in the way it is marketed. They have a novel system. So what? Just let it go.


jb78 - Monos major draw back is lack of easy adjustability. It is also a little expensive to be buying a range of spring rates in your rear monos. I was going to have some customs made because my tires get into my flares with a 420# The coil over is a better solution

ddawson

Yes it does, and while I haven't done an autocross it works great of on the street.

I think it rides better.

wishihad1-2

It's one thing to perhaps overstate. It's another thing to present information that is flat out wrong. The link in question is 100% wrong in it's description of the C3 suspension operation. Would you trust a doctor that told you something that is flat out wrong? If their engineers can't understand rather basic spring function how can you trust them to make a complete suspension system? Perhaps they do understand these things. In that case they are lying to their customers in hopes that they won't understand.

As consumers and forum member it doesn't hurt to call out companies that use snake oil in their sales even if the product isn't a bad product. The product's might be good but either the company don't understand what they are changing (a very scary thought!) or they figure the buyers are too dumb to know the difference.

I've worn many hats over the years and I have done just a bit of suspension design. Aside from looking trick I really can't see what this would deliver over a mono-leaf and a good set of dampers. I can think of a few things it wouldn't deliver.

A can believe it might work better than the factory setup due to the inner leaf stiction but the mono-leaf fixes that.

lionelhutz

Even the C5 springs don't have much effect side to side. I've jacked one side of my C5 springs and there was little movement beyond the first mount. Sure, there is some effect but it's way over stated if you believe some people.

Still, what you're complaining about is nothing more than typical marketing BS.

Gale Banks 80'

When I saw the Shark bite I was a little surpised that somebody would spend the time to engineer something like this with what I would consider a limeted market for our 30-40 year old Cars. Exspecialy since the Market is flooded with proven Suspension componets. And offset Trailing Arms as well. I would consider the biggest advantage of this system would be for circle track racing by being able to put stiffer Springs on one side. But how many C2s and 3s are still doing that. And making the Car less Corvette like and more simaler to Most Sports Cars with Coil Overs for Tuning. I do however think its great that people are still inventing tech for our Cars.

MIKE80

I run VBP Performance Plus full kit. The front dual mount spring has 4 adjustable spring rate settings and the rear dual mount spring has 6 adjustable spring rate settings, just move the bolts at the inner mounts inboard (soft) or outboard (firm) to adjust. Also, all 4 corners can be raised and lowered by adjusting the outer spring bolt lengths. It's a very easy suspension to adjust. I run Bilstein Sport shocks with it and even on the softest setting I'm not feeling the body roll.

redvetracr

what was it that PT Barnum used to say???

gkull

Yes, your setup is adjustable in very light spring rates. It is a usesless item if you require 550+ front and 450+ rear














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mrvette

That jacked up coil spring gig has been royally panned, as noted right off in this thread, and I mean by guys who know MUCH more than I do....

but in another group....