froggy47

Here are some from an old thread:

Springs:
C5 Z06: 526# Front, 714# Rear
C6 Z06: 531# Front, 782# Rear
C6 Z51: 526# Front, 645# Rear
T1 (C6): 582# Front, 850# Rear
C6 Base: 420# Front, 657# Rear (VBP: 400-420 F / 600-620 R)
T1 (C5): 582# Front, 793# Rear
Pfadt Coil-overs: 425# Front, 575# Rear (Remember: Wheel rates!)
Hyperco HPS (Street): 565# Front (12405HPS), #765 Rear (12406HPS)
Hyperco HPT (Track/Solo): 625# Front (12407HPT), #850 Rear (12408HPT)
VBP Sport 990# Front, 650# Rear
VBP Extreme 1050# Front, 855# Rear

As you can see almost every spring PAIR has a higher rear rate?

Why?

Then at the bottom you have some VBP springs that flip to the opposite.

Why?

I had a great phone discussion with a highly regarded forum member just a few days b4 my last event (yesterday) about changes to my c5z (for autox) and he recommended trying springs in the 900-1200 front and 700-800 rear.

Not only much stiffer than stock c5z but stiffer on the opposite end.

So the MAIN QUESTION is what about the car handling CHANGES when you go opposite of what GM and MOST of the aftermarket spring vendors suggest?

I would like to understand more on the setup dynamics of this before/if I throw an ultra stiff front/rear on.

Is that what the ASP cars run? 1200F/800R?

I have some T1's to try and after looking at the chart, I guess they would be "safe" to try for autox as they are not "that" much higher. Unless it like richter scale?



Your thoughts?

gkmccready

Motion ratios. Go calculate wheel rates. Those "stiffer" rear springs are actually about the same, or a little less, wheel rate than the fronts they're paired with. As for "most" vendors... every coilover -except- DRM and maybe some Pfadt packages go with a stiffer front than rear. For leafs VBP always recommends a stiffer front than rear.

I'm interested to hear some direct feedback from folks that have experimented with various configurations. I like my 475/575 DRM set up better than my 800/650 set up I had prior to it... also curious what swaybar combination people are running with the leafs since it feels like a big heavy front leaf should negate some of the need for big bars.

JRL

I'm running 1200/front, 900 rear w revalved Bisteins. The car works well on track (NASA TTS), and autox (ASP). I thought the high front rates would create understeer but the car is balanced and it rotates real well.


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John

John Shiels

mountainbiker2

I had a 966 front, 750 rear. Henry B. with last years winning ASP car, had something real close to that.

Steve A.

froggy47

Why is VBP the opposite of all others? What does it do to the car?

froggy47

Thanks guys,

I am having trouble figuring out VBP being so totally opposite of all the other leaf spring vendors.

We would all agree, I think, that stock the c5z/c6z handles pretty darn well. With stiffer rear than front.

Wouldn't common sense dictate that making the front spring stiffer than the rear would "upset" the whole suspension package of the car?

Does that setup require some other compensating adjustment to work?


Does VBP explain their theory anywhere?

RacePro Engineering

Bob,

At the risk of making a bunch of enemies, I'll take a stab at it:

Street Corvettes, with OEM suspension components, handle pretty darn well FOR A STREET CAR. The "stock" suspensions are made to accomidate --- well, of course you know all that. Taking these on the track begins to highlight their shortcomings. Also, I believe the design engineers continue to build to the "lessons learned" from the 1984 Z51, where the complaints of a harsh ride can still be heard echoing.

So, let's shift from the street to the track:
Suspension Design 101: Support the chassis weight proportionally.
A trip across the scales will reveal that more than 50% of the Corvette's weight rests on the front axle. Ergo, the front springs need to be a higher rate.

Why is VBP the only popular vendor to implement this? Well, a percentage of their sales is from simple, after-market "better performance" replacement parts. Indeed, most people who have tried their products report "better than ever" handling. But, a very large percentage of their trade is to racers, and they know that doing it "backwards" will not keep them in business very long.

Some might be tempted to argue that, inherently, the "stock" Corvette understeers, and that is very true. So, wouldn't raising the front spring rate just make this characteristic worse? Perhaps - but that is not what is needed FOR THE TRACK. The entire suspension package needs to be stiffened - springs, anti-roll bars, and dampers - and not just a little.

Once the worst part of pitch and roll has been conquered, then one can fully benefit from "supporting the chassis weight proportionally", which typically would mean a slightly higher rate spring in the front.

Glen mentioned wheel rates, and it is generally thought that, for competitive autocross, one should attempt to match the chassis' static corner weights. This is probably better handled on a seperate thread, but VBP, with their Extreme Line, begins to move in that direction.

Not a 'Vette, but for reference, each of the front corners on our Reynard weighs 205 pounds, and each is supported by a 450 pound/inch spring. (Stiff !)

Ed LoPresti

[EDIT] - I just checked with Bill Dearborn, and the C6Z is only 49.3% front static weight. He also mentioned that some of the small block C3s may have been slightly less than 50% front weight bias.

redtopz

LG coilover rates are very similar to the vbp leaf rates I think (both stiffer in front). The stiffer front springs make the car easier to drive at high speed. The car turns in quicker and doesn't exhibit the "corvette flop" as Randy Pobst once called it while driving my car. That's when you hit the brakes and turn in and the rear of the car flops up and forward while the front end squats. The T1 kit overcomes this with stiffer sway bars and it works quite well. However, I prefer the stiffer spring rates with softer bars if I had to choose. The stiffer front springs will set the suspension quicker once you turn in and keep the rear planted to let you get back on the gas earlier coming out of the turn.

trackboss

I run really stiff VBP front spring and the softer of the two hyperco rear springs. I'd say the car handles extremely well. IMO, the factory front spring rates are much too soft. The car seemed to roll all over the place. Part of that of course is the dampers. It is much easier to drive/control with the stiffer springs.
On street tires it is a bit oversprung (VBP does have a wide variety os springs and something in the 900-1000 range would probably be ideal)and causes loss of grip, but on track tires that I've tried the car really sticks and is easy to drive. I'm going to wider rear wheels and tires so some day I might try a slightly stiffer VBP rear spring because I am assuming the car may begin to understeer with so much rubber in the back.

RX-Ben

What do you guys run for bars with such (relatively) stiff springs?
Seem like you will have huge wheel rates if coupled with the typical big bars.

trackboss

I've got the hotchkiss bars with no adjustment. They seem to work well, but I have nothing to compare them to.

JRL

Stock C5Z06 bars


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John

froggy47

Thanks Ed & everyone else. Starting to make sense of it. Jeez, fixing the (intentional) shortcomings of a street car does get ya thinking about a purpose built racer.

AU N EGL

Would not too much spring rate cause the car to bounce too?

Not all tracks are smooth, or drivers use curbing

93ASP

I'm sure my ASP setup was in the minority... I purchased an ASP car that was already setup and had a 990# front / 714# rear setup. The handling was fairly balanced but the performance over bumps was less than stellar with the front spring frequency so much higher than the rear. I switched to Hypercoil HPT springs front and rear (635# front / 850# rear). Those rates with my weight distribution resulted in spring frequencies ~8% different between front/rear with front lower.

With the Hypercoil spring setup I did win 2 ProSolo ASP national championships... and the springs are for sale since I've moved up to SSM and coilovers.

Eric

travisnd

I've always heard the rear spring rates are stiffer because of how much the shock is angled inward. I.e. the resulting effective spring rate isn't necessarily what's stamped on the spring due to the suspension geometry. Any merrit to this?

varkwso

I run VBP 1100 front 800 rear and love the grip in the car. Best stick of any I have driven. It is not fond of bumpy pavement but is predicatable.

varkwso

I use the ones Raftracer advised me to. Do not recall the exact sizes now. Bigger then stock - smaller then T1.

RX-Ben

Thanks.

Also - I recall reading that VBP uses a different rating method on their springs than GM, correct? Anyone know how they relate?

And here is a tangent - how about just monster bars instead of the stiffer springs? Still brake dive, but should hook up better on bumpy tracks (if both wheels hit the bump).