I8URSVT

Hey guys, I've got a '99 coupe thats my daily driver. I wasnt happy with the way it handles (before this car, I had a ls2 CTS-V, and that thing felt like it was on rails compared to the c5), so I picked up a VBP front spring, stock c5z rear spring, c6z shocks. While it is my daily driver, I would like to start taking it to the track maybe a couple times a year

What I havent decided on yet, was which sway bars to get? I have been reading a bunch about the c6z51 sways and those seem to be great. My question I guess is, will those work well with the VBP/c5z springs? Would the c6z sways be an option because of the spring rates? (In reading I've seen that c6z sways should really be used unless running a 345 tire, but I was assuming that was using stock springs f/r). Tires will be 275 front, 295-315 rear.

What do you guys think? Thanks for the advice, help

Ramo7769

If you're not using slicks, I'd think a good setup would be the Johnny O'connell or Pfadt Light Rate Racing bars.

crimlwC6

I've run the pfadt Johnny O'connell bars for two years. I'm very happy with them. I ran them on a streetcar and now on my race car. The racecar has pfadt old school single adjustable invert shocks and stock springs. You can see some videos here: http://www.youtube.com/user/awlittle13/videos
I usually list any changes I make to setup in the video...which is rare. I run the softest rear setting usually. I wouldn't bother with stock bars. 2 cents.

96CollectorSport

Bar selection depends more on tire selection than anything, most people will recommend what they use on there race car running r-compound tires, and it probably works for them. However what works for them may not work as well for you. Looking over Pfadts famous sway bar chart may help a little.


According to this the C6Z51 front bar and the C6Z06 front bar are the same and I think you would be fine with either that or the C6ZR1 front bar. As far as the rear bar goes I have customers running slicks that perfer the C5Z06 rear bar so I think the C6Z06 bar or the JOC bar would be a bit much for street tires, that would leave either the stock C5Z06 bar or the C6Z51 bar. So if you want the car a little stiffer try the C6ZR1 front and C6Z51 rear and if you want to stay softer try the C6Z51 front and C5Z06 rear. Softer isn't necessarily a bad thing, especially when running street tires. Honestly if you have the scratch I'd get all 4 and mix and match to find out what works best for you (I'd assume that used C6Z51 bars have to be floating around for a good price).

Since the car is dual purpose I think you will be much happier with the ride with either of those set-ups than a stiffer set-up like the JOC bars.

It would help to know what VB&P spring you put on the front (Replacement, Sport or Xtreme)

redtopz

Are rear sway bars interchangeable between C5 and C6's?

RDnomorecobra

yes

I8URSVT

Thanks for the input! I've got the VBP Xtreme front spring. Does that change your suggestions?


I was thinking that since its a street car, I would like try to staying with the OE swaybars (c5z, c6z51, c6z06, c6zr1) since they will tend to be cheaper to pick up used, unless i found a screaming deal on aftermarkets. If I end really enjoying the track (I dont see how I wont), then I would dig more into the setup as I grow as a driver.

Also, I notice that all the racing ones (GM T1, JOC and Pfadt racing bars) all have stiffer fronts that the rears. However, stock the c6z06 and zr1 have stiffer rears than the fronts. Why is that?

mountainbiker2

With stiffer springs in the front, I would go with the C6Z51 or C5Z06 front sway bar. Then buy a rear Hotchkiss sway bar only. Then adjust according to understeer vs. oversteer.

Steve

RX82Z06

If you go with any of the C6 front OE bars, they are only about $100 new so I wouldn't bother with used unless you can get a used one delivered for say $50...

C6Z and ZR1 have massive rear tires...

crimlwC6

Swaybar stiffness won't impact ride quality if that is a concern.

96CollectorSport

Ok first and foremost it doesn't matter what sway bars you install I really don't think that your going to get the car to handle well until you balance out the spring rates.

If you are running a VB&P Xtreme front spring and a C5 Z06 rear spring you are either way over sprung in the front or way under sprung in the rear. Here are what the typical spring splits are.

C5 Z06 Front 525 Rear 715
C6 Z06 Front 530 Rear 780
GM Racing T1 (C5) Front 580 Rear 795
GM Racing T1 (C6) Front 580 Rear 850
Hyperco Race Front 625 Rear 850
Vette Brakes Sport Front 990 Rear 650
Vette Brakes Extreme Front 1050 Rear 855

Now you can see that all of the factory (and Hotchkiss) run higher spring rates in the rear than in the front - that's because when you go over a bump the rear end has to "catch up" to the front end so the car feels smooth going over the bump. Vette brakes are the only ones that do not stick with this system, it works for some but I think it requires a very aggressive driving style to get that set-up to work. Running the Xtreme spring in front and running 275 street tires is not going to give you the best performance IMO.

There are two schools of thought when it comes to springs and bars the old traditional theory was larger springs with smaller bars, now there are some who perfer larger bars with lighter rate springs. Either way they end up at a similar place.

Since your car is a dual purpose car I would think you would want something kind of in the middle of the road - my thought would be Hotchkiss or T1. And since you are running street tires I would stick with a C6Z51 or C6 ZR1 front bar (I think the Hotchkiss front bar is in a similar range as the C6 ZR1 bar as well). Then stick with a softer rear bar like a C5Z or C6Z51. But I really think you should sort out the springs first before trying to select bars that will work with these springs. Because to balance the car out with bars you would probably have to run a base C5 front bar and a T1 rear bar to get your wheel rates back into the ball park.

Just some info on the Pfadt graph, it doesn't accurately depict the true rate of a front bar with the true rate of the rear bars it should be used to compare one front bar to another and one rear bar with another - but not a front bar to a rear bar.

The actual spring rate of a T1 front bar is somewhere around 800 lbs per inch where the T1 rear bar is around 375 lbs per inch and a C5 Z06 is somewhere around 300 lbs per inch front and 200 lbs per inch rear.
So it's just a comparison between front bars and a comparison between rear bars they just happen to be on the same graph.

Hope this helps

mikeCsix

I have a '12 GS I've tracked last year and am interested in firming up the suspension. According to what I've read so far, the front spring between the GS and Z is very close, the rear spring in the GS is about 125lbs lighter. The rear sway bar is a larger diameter bar but being hollow, there isn't a way to tell if its stiffer and unfortunately, with its larger diameter I can't get poly bushings for it. I offer this info as alternative considerations for the OP. The GS is very comfortable on the road, exhibits less roll and brake dive than my '08 Z-51 while achieving a better ride.

What I want to do is firm up the ride a bit and I don't have plans to go to R-compound tires. One of the issues I have on the track is hitting the front air dam on compression from a short down-hill drop on the track.

Current thinking is to increase the compression of the front shocks, necessitating a shock change (I'm on OEM shocks). I also want to reduce body roll on sweepers without increasing skipping on bumpy turns.

How best to go about making these changes? Adjustable shocks? I've been thinking about installing a rear Z-06 (C-6) spring but don't want to go with the Z-06 shocks as the compression may be too stiff.

I've also read in the forum where pfadt changes the bias/balance of the car from understeer to try to hit neutral with the JOC package and their light rate racing sway bars, but don't know how that works out with the GS suspension setup (which IMHO is already pretty good).

From what I've also read, the sequence of suspension tuning is to get the springs right first, then fine tune with shocks and sways. Also, you can make the car too stiff where the inside front tire lifts off the ground, not good because you lose the traction ability of the lifted tire.

I8URSVT

96, sorry i miswrote, i actually have the sport springs, 990 spring rate.. I was looking on their website and quoted the wrong ones.

So my spring rates are actually 990/715, which doesnt seem too far off from the VBP f/r setup. So maybe if i went with c6zr1 and then c6z51 in the rear (like you are saying) that would be best. Knowing the the correct front spring now, do you still think I should consider a different rear spring?

Thanks for all the help! I'm learning

96CollectorSport

That looks a lot better, after all it all comes down to how it feels to you.

I think that would be a good place to start, what sways do you currently have on the car? The base model bars?
If you go with the C6ZR1 front bar and C6Z51 rear bar you are basically tripling the stiffness of the front and rear bars.

For rough numbers the stock C5 front bar is 110 lbs per inch, the stock rear bar is 67 lbs per inch.
The C6ZR1 bar (and here I'm guessing as I've never physically measured one - but we can extrapolate based off the Pfadt graph) is probably around the 330 lbs per inch and the C6Z51 rear is around 225 lbs per inch.

I would think that you should notice a differance that large.

After you try it post back in the thread and let us know how it worked out.

96CollectorSport

You are correct about the sequence of suspension tuning, starting with springs then shocks and sways - but only you know what you will be happy with. Matching springs with shocks with sway bars becomes complicated, especially with a dual purpose car.

That being said, you may be surprised what a good set of adjustable shocks will do for the car. You can dial them up at the track and soften them up for the street. That may all you need, if that doesn't do enough you may want to put a set of bars on the car to help control body roll.

But you have to be comfortable making those changes, some want to just install and forget, but that obviously limits your adjustablity.

BTW - I wouldn't worry about the air damn that's it's job, so what if you have to replace it every could years, that just means that your pushing your car harder than 99% of the other guys out there.

I8URSVT

Thanks alot 96!

The car currently has the stock base springs/shocks/sways on it. Im collecting the parts to do everything at one time around april, that way i can get 1 good alignment and hopefully be "done".

So I think its going to be a huge difference from what im working with now (at least i really hope so!).

I will definitely post about once i get everything regarding how the setup is and my impressions.

I8URSVT

Just figured i would update this thread as i put everything on a couple weeks ago.

I did the following:

VBP Sport composite front leaf
C5Z rear leaf
C6Z shocks front and rear
C6ZR1 front swaybar with metal endlinks
C6Z51 rear swaybar with metal endlinks

At the same time i lowered the car about 1.5" up front and 1" in the rear. It handles like a Completely new car. I have so much more
Confidence in how it is going to behave in corners, and i dont think the ride is too stiff or harsh.

Big thanks to 96collectorsport for the advice! The car is so much more fun to drive!

Heres a quick pic of the stance: