Can I install a C5 Z06 leaf spring on a 98 vert ? I was going to buy a used standard spring since my front spring needs to be changed, but it looks like the deal is off. I'm now thinking of upgrading to Z06. I have already bought C6 Z06 shocks to be installed later. If the springs fit, can I change the front first and then rear later, or will the setup be all wrong like this? Is it a big difference in stiffness between Z06 and standard spring?

Thanks for tips, need to pull the plug on this now...

 

The Z springs are indeed stiffer and you should change them out as a pair. If you don't you'll end up with more push that is normal, but it isn't going to make the dangerous, it's just going to push a bit more at the limit.

If you're going to just change at one end the front is the one to stiffen. If you just change the back spring it would oversteer more and that wouldn't be good. Bottom line is go ahead and do it and plan on getting the right rear spring and you should be fine.

I don't have any data on the base suspension as to bar stiffness, but it's softer than the Z51 bars. In order to know that the balance is perfect you should use the Z06 bars with the springs, but if the base suspension bars aren't biased one way or the other you can just keep the base bars and it will probably be fine. The Z06 and Z51 use different front bars and the same rear bar, so you wouldn't want to use the Z51 front bar with these springs or it would be loose compared to the Z06 setup which is properly balanced.

 

I have the C5Z springs in my '04 Convertible. The rear is Z06 specific, the front is shared between the Z06 and FE3/Z51 as shown in the link 8VETTE7 posted.

 

Thanks for the good info. The Z06 springs are bolt on, you don't need any modifications to install it?

 

Yes. No modifications required. But you will probably need an alignment when changing out springs. You will also want to measure your ride height before you change them. The ride height will need to be adjusted to your liking.

 

The ride height and alignment should probably be set to Z06 specs after the spring change. That's what I did.

 

So Cultrag Performance just got my order. I ordered a Z06 spring and C6 Z51 swaybars with metal end links. I will se how this performs with the C6 Z06 shocks that I ordered before, and then see if I upgrade the rear spring also next winter. This should be a good handling vert, don't you think

 

With the bigger front spring and the stock rear spring the car will ride better than a Z. The bigger rear bar (C6Z51) is probably a decent match with the softer stock rear spring. If you put the Z06 rear spring with that bar the car is going to be pretty loose.

Mixing and matching parts from different packages is fraught with pitfalls unless you have some adjustment to dial it in and have the experience to recognize what it needs and how to fix it. It's just that suspensions today are well tuned and mixing and matching parts tends to make a mess of things.

Doing what you've done may work fine... or it may make the car miserable to drive. No way of knowing for sure, it may push or it may be loose. Just no way to tell. That is why it's better to install a complete package of springs and bars and you will have something that you absolutely know will work. When you go off the reservation so to speak, you really need some adjustment in roll stiffness at one end or the other or you're pretty much stuck with the parts you bought.

All that said, trading some rear bar for a softer spring is in the right direction so it may work ok and not be too far off.

If the car is loose when you get done, change the front bar bushings to poly and that may cure it. There is a lot of tuning that can be done with bar bushing stiffness so that's something you can do if it ends up a bit loose. Conversely, if it pushes try a set of poly bushings in the rear bar and that can get you a balance.

Finally, make sure when you bought the bars you get the bushings and proper clamping brackets so that the bars don't get bound up in the brackets. Otherwise it will make a mess of the handling.

 

Thanks a lot for your insightful comments. Looking at what I'm doing to my car, it looks like I'm a serious trackday driver looking to shave seconds off my time. That ain't the case. I will do a track day or 4, but I will not be "pushing". I'm a motorcycklist at hart (but my body doesn't agree anymore), so finding the twisty backroad and drive "inspired" is my thing. Just to explain where I'm at. The reason why I do these upgrades is that I think the car is too "floaty" in lack of a better word. If you look at for example a Porsche 996 (which I think is otherwise quite comparable), you will recognize a way firmer ride than the C5. I want more of that, simple as that.

As for your comments, there's a couple of terms I don't know; you talk about "push" and "loose". Can you explain what you mean by that?

Again, thanks for your enlightning help!

 

If it was the floaty feeling that you were trying to get rid of, a good set of stiffer shocks would've sufficed. You did not need to change the springs. I had the same issue with mine. The installation of Koni Sport shocks with Eibach roll bars solved the issue for me. I kept the base springs. The car is exactly where I want it to be. Decent street ride with excellent handling during aggressive driving.

 

Ok, this isn't that tough...

Push is understeer. That is, when you are in mid corner the front end isn't going where you want it to, that is you have to keep turning the wheel and the front tires are giving up, that's push..

Loose is oversteer. That is, if the back end feels like it's trying to come around and you have to "countersteer" at the limit...

If you don't understand this it probably best to get someone who has some chassis tuning experience to drive the car and help you sort it out.

 

Thanks,

I'm well familiar with the under- and oversteer consept. I'm way more happy with oversteer :-)
I will just have to set the car up and see how it works, and then adjust accordingly. And as mentioned, I will sooner or later get the Z06 rear spring also. If I have problems with the setup, maybe sooner...

Are there other differences between base and Z06 appart from spring, sway and shock when it comes to underbody?

 

When I first got my 'vert, the front spring was cracked, so I ordered a new one. Due to a part # snafu, I inadvertently bought a Z06 spring. After installing it, I found that the front end reacted quicker than the rear, due to the difference in rates. It felt like the rear was being "wagged" or delayed in response when making quick turns. I then replaced the rear with a Z06 spring and all went back to a normal balance, but stiffer/flatter than the stock, base suspension. FWIW, I also have C6 Z51 shocks and sway bars.

 

The new sways and metal links alone will make it handle like a different car.

 

Most folks that don't race are. To them it "feels" better and it feels faster.. Unfortunately it really isn't.

Just a touch of understeer at the limit is faster for the simple reason that if the car is pushing a bit you can just lift, stick the front end and not lose any time.

With an oversteering car you can't put down power on corner exit because if you try the back end will come out. Bottom line is that just a touch of understeer is consistently faster than a car that is on the knife edge of oversteer. The reason is that corner exit speed is more important than the speed through the middle of the corner...

 

I follow you on this. It's just that when the track times doesn't count, it's more fun with a tail happy car. I think the most important thing is that when the tail is letting go, it happens in a controlled manner, so that you are able to pick it up and control the powerslide before your tail is passing your nose

 

Actually if you want to drift or powerslide you want a car that pushes like a pig.. Then you can go around with your foot in it and hang out the back end, and if you lift a bit you can hook it back up.

It's dog slow, but if the traction isn't that good a car that understeers strongly can be hung out with power.. That's how drift cars are set up, with huge front bars so that when not under power they understeer like a pig.

 

It looks like I'm going to buy the rear spring quite fast then... :-)
At least we get god handling verts out of this

 

Just thought I would start the work since I have the shocks already, so I changed the rear shocks yesterday. One of them was actually shot, when I unscrewed the top bolts, it just compressed itself, no resistance in it whatsoever. Took it for a quick spin, and could of course feel the difference right away. No wonder I thought it drove like a boat :-)