You're welcome! Are you still running the softest setting?

 

Yes in the softer setting.

 

I finally got around to measuring the front base bar,, 31MM give or take. Z06 front bar was 25MM so definitely softer.

 

Hi folks,

I've been using my Z51 with MCS Coilovers at 1142 lb/in front, 1256 lb/in rear, and have been happy with the way it felt at the track (except some other issues; long story). The Z07 spring rates are about 800 / 500 front/rear in lb/in (and magne ride dynamically adds onto it a bit).

I've recently switched to a C8 Z06 Z07. I've first tried the car with 18" wheels shod with Hoosier R7s 315/30/18, 345/35/18, and the car felt very numb. I've since learned that this car is really tuned for the Cup2R tires that it comes with at 20" front, and 21" rear sizes with very small sidewalls. I've heard from others using 19" wheels that they have also felt this numbness. When I switched back to OEM wheels/tires, at least during my tests at the street, most of that numbness was gone. I'll test OEM tires/wheels at the track next weekend. That said, even if it feels good with OEM tires, that's not sustainable since there's no good option at 21" for rears, and the OEM tires cost $3K, even though they don't even last one full day at full pace as far as I understand..

To mitigate the issue and use 18" or 19" wheels, I can just install the MCS coilovers I already have, but I'd like to first try and fix the handling of OEM suspension. The car is currently with stock suspension except the wheel rate (and R7s should have similar traction to Cup 2R anyway). Major components of wheel rate are spring rate, shock's spring rate, sway bar, tire spring rate, bushings, etc., probably in this order. As such, I think there's a chance to fix the wheel rate by changing the sway bars.

Assuming Z06/Z07 comes with 25mm sway bars front and same rear as base C8, I'm guessing these rates:
Base rates for OEM Z06: about 203 lb/in
Z51: 300 lb/in +50%
Eibach: ~400 lb/in +100%
AFE: 600+ lb/in +200% or more.

Since front bar is so small on Z06, Z51 bar at 30.5mm(?) might be a huge steps in itself besides the aftermarket bars. The same goes for the rear bar as well. Thoughts?

In short, my suspension is stock besides the lower wheel rate caused by lower spring rate of tires, and the car feels very numb and is very hard to drive fast; it's very hard to feel the limits and also to settle the car. I cannot use OEM tires in the long term, so I'm hoping to address wheel rate by increasing sway bar rates. Which sway bar set would you recommend?

I'm thinking about starting with Z51 sway bars, but I fear it not being enough, and considering the time it takes to swap front bars, I wonder if Eibach with its adjustable bars would make more sense. I could also switch to MCS coilovers I already have, and can actually install them in 2 hours, but I wonder if I'd lose on giving a chance to GM's highly tuned magnetic Z07 shocks...

 

Surprised you're feeling the car being numb, seems to be the opposite of every review journalist i've ever heard who claim the z06 fixes all the stingray issues. Perhaps they just needed the exhaust to be louder

I'll say from experience, popping the MCS's in is the way to go. Sway-bars transformed the car so much i didn't feel much of a difference going to the penske 2 ways, but i'd rather have the penskes as they're much easier to tune. If MCS doesn't get you the feeling you want, maybe go for some bushings? Sway bar install is a PITA and the front is really the one you want to do. I would not start with a Z51, it is inadequate imo if you're already fast. Rather hop to the AFe. However i think coilovers -> bushings -> swaybars.

 

As I mentioned, I went to track with 18" wheels, and the car didn't feel right with them. Journalists always use the cars with factory tires/wheels, so I'm sure they were feeling 'OK' : )

The problem is, unlike the journalists, we have to pay for the tires we're shredding, and Cup 2Rs are both very expensive to buy, and also have very very short life, making it not feasible for most of us...

When you switch to 19" or smaller wheels, the car starts feeling not so great as far as I understand (more discussion in the build thread here).

I know for a fact that the MCS coilovers worked well with these exact 18" tires (and Z51 sway bars at the time).. hmm..

EDIT: Just ordered Eibach sway bars. I have a feeling that they might be the ticket to my problem, and it will be a significant step from Z06 bars (similar to the step from Z51 to aFe). If it's still not as good as I'd hope, I can always install MCS on the top as well; I think MCS would work well with these sway bars.

 

I have c8 z51, I installed Afe sway bars front and rear, it made much less lean and handle better, but the softest rear setting is 100% stiffer than OEM. And the back end would step out way to much. I think installed the Eibach adjustable end links and had fitment issues with the Afe sway bar and large Heim joints, and had to switch to longer bolts in the front with spaces to get it to fit right. Furthermore, I don't think I could even get the front softest setting on the AFE to fit when combined with the adjustable end link without having the bolt hit the shock (time for some more custom thinner spacers). Moral of the story is, IMO, 100% stiffer in the rear is way to much.

And yes installing the front Sway bar is "fun" involving dropping the front sub-frame a few inches (luckily control arms hold it) and a 2nd or 3rd person to loosen the front end lift while trying to pull the sway bar out and get new one in. As noted by others the Afe looks great, is well built, but the placement of the mounting holes is different than stock creating problems for mixing and matching. And I don't see them offering their own adjustable end links (which presumably you would want to remove the preload when doing a corner balancing).

Subsequently I installed MSS Adjustable Sport springs which are much (???) stiffer than stock and include a tender spring on the rear. Now that I have stiffer springs the sway bars are way too stiff, tons of oversteer. With Afe 100% softest rear setting, I to switch to the Eibach rear sway to try their softer settings, and found a "fun" (no sarcasm this time) balance with AFE front at 100% and Eibach rear soft (40%??) when combined with these stiffer springs.

Overall I was worried about lost grip everywhere from stiffer bars (lap times can be tough to compare between different tracks, days, tire heat cycles), so I have now returned to Z51 stock rear with AFE front at 78% stiffer (again with the MSS sport springs). That resulted in slight understeer and reduced turn in. Next try will be AFE front 50% + z51 oem rear + MSS Sport springs.
2nd moral of the story, if you start making changes expect many track days evaluating results (its really difficult to tell on street unless is really really mismatched front to rear) and planning your next change as there will be one. Good news is each change was detectible.

If you plan an making and spring or shock changes, do those 1st before sway bars. Especially the front sway bar as so much is involved in its installation.

Cheers!

 

@X25 I might suggest just doing the adjustable end links to increase "feel", as that replaces the oem rubber/plastic end links with heim joints and does provide a little more feel/feedback without significantly altering spring rates or suspension geometry, although you can change the preload.

 

UPDATE: I ended up ordering Z51 sway bars front/rear, and canceled Eibach sway bars (or at least I think I canceled). Z51 bars are already a substantial upgrade with 30.5 mm over 25 mm of stock Z06 at front, and ~300 vs ~200 lb/in at the rear. The convincing statement for me was that I should try to find the least step up that fixes my issues, since once it starts getting too stiff, it would be very hard to understand where I crossed that line. Another benefit is that I already know these bars work well with my MCS coilovers from my experience with Z51, so I'd not need to remove them even if I need to switch to coilovers : )

 

Man @Kracka and I have been talking about this for awhile. He convinced me to order the rear AFE bar and now I am worried it might be to much. I am non Z51 and lowered on Eibachs. The suspension is just a bit to soft but I dont want the rear to start walking.

 

The biggest gripe with Eibach is their mounts aren't greasable like aFe's.

 

indeed! Made me sad loosing the zirc grease fitting when replacing the afe rear with eibach (and now back to oem z51). Although if it gets loud, not too bad to uninstall and regressed (the rear at least)

 

Agreed. I regreased mine once already and it only takes a few minutes. Sounds like @teddyca got his aFe installed last night and is pretty happy with how the car handles on full-soft!

 

Yes sir I am. I actually only drove the car about 10 miles but I was in the country and I hammered it and it felt 100% better. Before I could hit a bump or wave if you will in the road and the car would sway a little like a sedan. Nothing like a sports car. Now the ride is much more stiff and the concerns with the rear washing out dont seem apparent. AFe might be a little to harsh for some to be honest. As for installation the AFe is a big bar. The poly bushing is tight and I had to fight it. The kit came with a bunch of lube so I greased the hell out of the bar and bushing but I didnt hit the zirk fitting. Once it starts making noise I will get in there and grease them. I didnt want to mix the two lubes. LOL

 

Channel your inner Diddy...

 

Oh my friend I was very generous with the lube.

 

Did you, or anyone, ever measure the center to center distances or the length of the black turnbuckle on the longer set? The short ones seem to be ~80mm and the long ones ~192mm based on Eibach's instructions for install. How much adjustability did anyone need +/- from those nominal dimensions? I'm trying to figure out if I need 140mm or 150mm turnbuckles. An M12 male rod end is showing Center of eye to end of rod end to be 54mm w/ a threaded end length of 33mm. That means thread all the way into the turnbuckle I'd have 21mm to the eye. A 140mm turnbuckle with two rod ends install all the way would be 140+21+21 (182mm) and a 150mm turnbuckle would be 192mm but would not be able to go shorter. With the 140mm turnbuckle I could run those out to 192mm with still 16mm of engagement on each end which seems reasonable.

I'm all for supporting vendors, but at the same time as an engineer when I see I can build the part like this for considerable less money I'm open for doing it. Some end links and threaded couplers on McMaster is an easier solution... heck, even looking at Pegasus Racing for some Aurora end links (which from images I've found of the short Eibach link they appear to be Aurora's) it's pretty easy to build these up.

LOTS of great information on this thread. I've started to pull images and info together from here to make a reference sheet. Is there anywhere on this forum where we can upload / share stuff outside of threads? Sometimes you just want to grab a sheet that lists all the tools needed, a couple of reference photos, and torque specs all in one quick sheet.

 

@Kracka Thanks for the wealth of information on this page. Eibach was having a 15% of sale for the 4th, took advantage of it and ordered the rear bar and there Eibach lowering springs. Hopping the springs and the rear bar will make a nice combo a stiffen things up a bit on my z51 with magride.

 

Awesome! Report back with your results.

 

FWIW I've been very happy with the Eibach rear bar. I was noticing the understeer on a few key corners on my local track... one in particular is an off camber corner leading to an uphill section that becomes the back straight. With the rear bar (I also added the end links) installed I'm far more consistent through that corner with the ability to carry higher mid, and exit corner speeds. It was enough to do what I wanted without overdoing it and heading towards oversteer.