Matt_27

Wow that is a lot of variation, I have a hard time believing GM has a 20% difference in spring rates leaving the factory- that would cause a lot of handling differences between cars that are otherwise exactly the same.

I am currently on the path of HPT front spring/ Z06 rear spring until I find a reason that won't work. Strano 33mm front bar, Z06 rear bar. If the HPT front spring makes for too much % front TLLTD I can still go up to a Strano 25.4mm rear bar or a HPS rear spring.

Lane, do you think pitch oscillations will really be a problem with those fancy MCS shocks you have? Plus isn't the ride rate already higher in the front than the rear, even with stock springs? Rear spring rate is higher but the motion ratio is worse afaik.

strano@stranoparts.com

Nope. I like my R's... and my Z06... and I have no time to really mess with much before then anyway. And SSR will be hefty in Hershey, like a mini-nationals.

strano@stranoparts.com

Largely personal taste. I carry a number of shocks. The Koni's, MCS, Ridetech which are made by Fox (and someone I trust says the valving is good but I've never run them), KW (and you can run the KW's without coil-overs on a car with leaf springs but it's kind of a pain. Hard to beat a Koni to be honest. I can even get Penske's, but I don't tend to since I've been so pleased with the MCS stuff in the high end arena (no leaks, etc.).

ltborg

Agreed. I really liked my Konis (bought through Sam). I like the MCS's too just because they are easier to adjust.

ltborg

They probably won't be, but I don't want to be putting myself at a disadvantage from the start.

Make sure you are looking at natural frequency, not wheel rate. I'm talking about having a higher rear frequency than the front, not necessarily rate.

The delta in frequencies is mainly aimed at preventing ride oscillations like I mentioned and as far as I know, pretty much all cars come with this split from the factory. You design the rear ride frequency slightly higher than the front because the front will encounter bumps first. Having the rear frequency higher results in the car settling out to ride oscillations instead of pitch. Pitch oscillations tend to cause more issues like motion sickness, but can also mess with things like the ABS under braking.

ltborg

Based on my conversation with Sam, I think this is the best start for everyone that wants an STU C5, except maybe add the Strano 25mm rear bar. Extra suspension adjustment is always good on these things, especially since the rear suspension is so easily accessible in grid.

troyguitar

What makes you choose HPT over VBP? The claimed rates are all over the map so it's hard to figure out what the actual difference is between the two (or 4 I guess, each manufacturer has 2 options).

I'm seeing these as the only options on the market:

VBP 97310 "775-875" rate http://www.vbandp.com/auto-parts.htm...category_id=59
VBP 97320 "900-1225" rate http://www.vbandp.com/auto-parts.htm...category_id=59

Hyperco HPS "Z06+10%=579" rate http://www.vansteel.com/index.cfm?fu...p=1949&ID=2873
Hyperco HPT "T1+10%=641" rate http://www.vansteel.com/index.cfm?fu...p=1949&ID=2874

or GM T1 "582" rate at a significantly higher cost, in theory that should be about the same as the HPS.

strano@stranoparts.com

I'm a Hyperco distributor and the pricing is nice... like less than $500 a spring. But I also don't think you need that much spring rate (or want it on street tires).

hklvette

I agree with this. To make adjustment even easier, use something like the Borla XR1 exhaust so that the over-axle pipes run straight out the back instead of through a 180 like the factory system. This gets the mufflers out of the way, making disconnecting the rear links easier while the car is on the ground.

I have a VB&P front leaf that measures "1115lbs/in" according to what is written on the leaf itself. I find its street manners to be quite nice in combination with the Z51 rear leaf. In my observation the rear leaf will make the biggest difference in ride quality on the street. I think this is because where you sit is very close to the rear axle and quite far away from the front.

markdaddio

Maybe this is a stupid question, but is there an automatic transmission version of a c5 that would put the car in a better place gearing wise within the STU rules?

strano@stranoparts.com

Not unless you wanna ream 1st gear all the time. But I think it's mostly a non-issue. The way headers and a tune woke up my 2001 Camaro I think the power will be more than adequate to exceed the grip of the tires most of the time. MHO

rotis

Lane, what are you actually targeting for ride frequency? I haven't gone back through all my math, but plugging numbers into my setup sheet says the HPT (625/850?) combo is ~2.06/2.25Hz. Seems a little on the soft side, but is a pretty reasonable spread. Enough front bar ought to make that work?

A 2.2/2.4Hz setup would require 715f/975r springs measured the not-VB&P way, nobody does anything like this so I imagine there is good reason?

The HPT Front, Z06 rear setup comes out to 2.06/2.06Hz using my corner weights. I'm sure that'll work fine handling-wise, you'll just have a little more oscillation on bumpy lots.

89BP

Wheel offset question.

What offset will we need to fit 18x11" wheels? Will we need different front offset than the rear? Can we get the wheels and tires completely inside the fenders?

hklvette

Probably because the autocross crowd is so small and everyone else usually switches to coilovers is why you don't see more options for stiffer leaves on-the-shelf. Its been mentioned here that stiffer leaves can be custom-made by Hyperco, and I know that VB&P can do the same. If memory serves, VB&P can go up to around 1400lbs using their method of measurement. It would be nice to round up a bunch of different springs and get them all measured with the same machine to get a feel for what's what.

stl1

Jumping in to follow along. After 10 years in F125/KM I need something less abusive on the body. Carry on...

troyguitar

You want a ~65mm offset in the rear and it will pretty much sit inside the fenders. I'm not sure about the front. My 73mm offset 11" wheels appear to fit up front but I did not test how far the wheels can be turned before anything rubs.

89BP

What brand/style rims are you using? When can you find out if they rub up front?

Anyone want a set of Forgestar F14 Gunmetal 18x11" 40mm offset? I have a feeling these are a better fit for a C6 Z06/Grand Sport. I bought them from a C5 owner, and figured they would be right for my car, boy was I wrong. Fronts stick out, over an inch, rear stick out, but are close, I would say half an inch out.

Matt_27

Dang that sucks. I have rear C5 Z06 all around on my car and the fronts stick out maybe a quarter inch, it's pretty close. Rears obviously fit fine, so if you get the offset of those wheels you can add in the extra half inch for 11" wheels and you should be good to go.

ltborg

I'm hoping I can keep this type of setup (which is what I have now, at least in terms of pipe orientation), however headers and race cats are going to make it LOUD so I think we'll all need something once we go the power route.

ltborg

Hypercoil is the standard in spring design and quality. If I'm buying parts, I want to buy the best. Nothing against VB&P, I know a lot of people that are happy with their products and they have been helpful with some of my questions. As an added bonus, Sam sells the Hypercoils and I plan on buying as many of my parts through him as possible since that's how you get his setup help.