Matt_27

I put the bar that I received from you this week on my car last night, it went very smoothly.

Also Vansteel/Hyperco will do custom rates for the same price as their HPT springs, if you wanted to go higher than the HPT springs (640 lb rate). The HPT springs are only ~22% higher rate than stock Z06/Z51 springs so I could easily see quite a few of us going custom to get higher wheel rates.

ltborg

Good to know, thanks.

69autoXr

I always thought it was Street Touring Ultra.

ltborg

It is. There have been a lot of STU's in use at one point or another. Currently for the SCCA, in autocross it's Street Touring Ultra and for road racing it's Super Touring Under. I think at one point or another NASA or SCCA has a Super Touring Unlimited. Too many classes to keep track of...

ltborg

As I'm running the numbers on this, I'm not so sure we will have to go that stiff. I'm assuming I'll go stiffer than most people will just because most people will probably stick with the stock rear spring and a mildly stiffer front to keep things easy. Some of the good SSP C5Z's keep their stock spring and go mildly stiffer at the front and do great (Berry Langley's car for example that places 1-2 in class AND PAX at Wilmington), and that's with A6's.

I just personally don't like the big bar/soft spring setup people seem to be all about and don't like the idea of just throwing a stiff front spring on and calling it a day to go from BS to STU.

hklvette

What do you intend to improve by putting more rear spring in?

strano@stranoparts.com

Lane and I talked at length the other night. To be honest, I'm very skeptical about the rates of the various springs and how they are arrived at. I say this simply because there is NO WAY anyone who saw me run my Grand Sport vs. the Z06's will buy the front springs are only 10 pounds different. Maybe at some point in the range, but not functionally.

I think both Lane and I are on a similar path (which is both good and not unexpected) though personally I don't think I'd stiffen the rear spring myself, at least not very much.

Haven driven cars with the real stiff springs there is no way I'd ever.... they ride like crap and aren't ever 'in the road'. And honestly if you watch my Z06 run it's not exactly a rolly polly mess.

Matt, glad to know the bar gave you no trouble.

troyguitar

Are the OEM springs progressive? If so, does lowering the car increase preload on the spring and therefore increase your effective spring rate?

I'm still trying to decide what to do with my car (stock 04Z springs) and really have no idea at this point for suspension. I got a good deal on the pfadt JOC shocks and sways but both the JOC shocks and my stock springs feel too soft, especially in the front. That's on Bridgestone RE-11's with super stiff sidewalls too.

strano@stranoparts.com

Oh there are definitely differences. In arch, thickness, etc. And some "rates" are shown as ranges. Honestly I kind of thing everyone does something different.

Going to be honest, don't think the car needs major spring changes, and personally I think really only the front. Driven lots of C5's and C6's and quite frankly any with the Z06 front springs haven't been IMHO too soft. The Z51 stuff (that's not the same as the Z06 is a little different matter).

To be very honest what the car needs is really good shock and bar setups and the Pfadt stuff never really impressed me. I have issues even finding size information on the "JOC" bars. But their adjustable shocks weren't very good and I suspect the less ones are, well... less good. I had a customer 'get a good deal' on some of their adjustables and dumped their very early Koni reds. About two years later when he just could not get the car to feel right, he sent the car to be and replaced them with Koni Sports (the inverted yellows). The front bumpstops were completely split on the Pfadts as the are hard urethane and don't like the pounding. And hard stops like that cause spikes in spring rates which are less than fun, or ideal. And GM stops have the same issue, but at least are shorter and stay out of the way longer. I think the JOC shocks use the GM stops where the Pfadt adjustables use a generic Energy Suspension type stop nothing like a good silasto type stop the Koni's use.

strano@stranoparts.com

And yes.... if you look at the cross section of the springs and how they flex when they work the rate won't stay the same. Think of it like this, a linear coil spring is the same all they way through. A linear rate "leaf" spring like an old rear mono-spring on an early Camaro is the same all teh way. But our springs aren't the same. They change thickness and width, and even arch. And what they are doing in roll is different than what they are doing in pure compression too.

Does lowering the car change the rates? No because it's not changing the spring at all, you are just moving the bolts in the spring. Same spring, same weight sitting on the spring. Not quite like a coil-spring you might start adding preload to as it compresses as you raise ride height. See also how some coil-overs use a separate adjuster that doesn't compress the spring for height changes (not for a Corvette mind you, but they exist).

troyguitar

Yeah I come from karts so I don't know much about suspensions. AFAIK the pfadt JOC bars are just like T1 bars but a little weaker and the JOC shocks are OE sachs with different valving (they are not adjustable).

I just know the car dives a lot, it's not flat at all under braking. I assume that means I need more front spring and/or more rear brake bias.

strano@stranoparts.com

I'm not all that far away. If sometime you can make it here before the weather gets crappy we can take my Z06 for a ride. And the plan is to pick up an FRC this weekend too and you can see what the differences are.

I guess compared to a kart anything that moves will seem like it's not flat at all. I don't know that in itself is a bad thing. But the shocks do have a lot to do with how that mass moves. The roll and pitch rates are controlled by the shocks... not the amount of it, but the rate of it. Slow that down and it can feel a lot better.

troyguitar

It is definitely possible that I'm just expecting the car to feel like my shifter kart and it will never get there.

I might have to take you up on that, too bad I'm busy this weekend since it's beautiful out. I am planning to run with NEPA SCCA in Williamsport next weekend, then it will probably be snowing after that

strano@stranoparts.com

Well no, it'll never be a shifter.

I missed the last Pocono event, but was there earlier this year. Those guys know me. You know there are two days at the end of October @ Hersheypark. Big lot...and usually fun courses (I have some final say in them).

troyguitar

Cool, I'll try to make it down there if it's not snowing. I'll be the slow guy in the purple C5Z - running a street car on street tires in SSP/SSM, not sure which I technically fall into but either way it's a joke, with NEPA I just run CAM.

(sorry to hijack thread)

ltborg

Like Sam said, I'd keep the rear spring and up the front. I really think that setup will be the best for 95% of people out there.

ltborg

Better match the car to my driving style. I do best at work in cars we consider tight, probably because I do a lot of our truck testing. However as I have found out from the high number of people that have spun my car, my definition of tight and loose is a little different than most.

I DO NOT want a car that can't get into the corner and I'd rather err on the slightly looser side since I can drive around too much rotation. If the car doesn't rotate, you just have to wait.

In addition to entry, I want to be able to stab the throttle and not wait for the rear end to come around and right now, the car doesn't point power-on unless the engine is above about 3500 RPM. This should help fix that.

Lastly, raising the front spring and not the rear might put the ride rates too close together and the car will start to oscillate in pitch. I still am working on getting the math on this right, but I already am most concerned about pitch so the last thing I want to do is prop up the front, then end up with a nasty pitch oscillation into braking zones that pissed of the ABS.

l2yeP

Sam, picking up a FRC? Will you bring it to Hershey?

talon95

So what shock(s) do you recommend these days Sam?? The yellows you mention?? I have the yellows now (have since I got them from you in '07), but have considered trying to step up to something else off and on.

89BP

Any hints as to what spring rate to start with? Springs are next on my purchase list.

I got a response from VBP about testing against stock springs, he said about C5 1997 - 2004 "These varied from around 600 to 725 pounds per inch on our machine. The standard C-6 front springs we tested came our even less, at around 420 pounds per inch."

Looks like they measure high, about 150lbs.