NOSLO6

Hi folks,

I'm looking for some suspension setup advice for my C6 coupe (has Z51). I switched over from a C5Z06 and notice quite a bit more body roll and float over bumps and elevation changes. I'd like to tighten her up a bit and am quite happy to sacrifice ride for handling.

Add to this that I'm going to swap to a rear widebody setup and Z06 wheels and I'm wondering if the larger rear wheel/tire setup will warrant more than a simple shock mod and alignment are in order.

I get to 2-3 autocross events a year, 1-2 HPDE events, but the primary use will be as a driver and lots of spirited back roads driving.

I don't think my limited use justifies the expense and adjustability of coilovers, so I'm particularly interested in feedback on swaybar / leaf spring changes that might be beneficial.

Of course, any other feedback is more than welcome. I'm a drag racer first and foremost, so this turning stuff is out of my element a bit.

avizandum

Unless you are or want to be competitive in AutoX or Road Racing, it's unlikley you will out drive the stock Z51 suspension - especially with street rubber.

Just go have fun.

NOSLO6

Thanks, good general advice. I'll be running Michelin Pilot Sport Cups with the widebody (and currently run Toyo R888s), and am just interested in feedback on whether the wider rear setup will change the balance.

I've seen numerous posts from folks here that their Z51 setup got twitchy when they switched to the wider rear wheels / tires. Switching to some cheap takeoff z06 sways & springs is one option, but I'm interested in thoughts on other things to consider (including the 'do nothing' option as noted above).

Thanks,
Scott

gkmccready

I would expect adding rear grip with wider wheels and tires would, if anything, take the looseness out of the back end. Without wider front tires to match the new rear tires the added rear grip will make the car want to understeer. The C6Z front sway is the same as your C6 Z51 front sway. Understeer is "safer" than oversteer. I'd run the Z51 parts and see if you feel any balance issues. I've run 3 different rear bars, and 2 different front bars, one set front/rear is adjustable (Pfadt Pfattys). After a lot of experimenting with combinations I'm back to my stock C6 Z51 bars... the balance issue I was chasing turned out to be more alignment related than anything else (more rear toe-in was needed)...

EvilBoffin

- GK -

If you feel that the Z51 bars are the best balance, then what do you feel a stock Z51 suspension DOES need - to reduce the inherent float and softness that Scott refers to? Different shocks (maybe Pfadt adjustables), different leaf springs (like C6 Z06) or BOTH, etc.??

To me, the car feels under-damped. And, my DE instructor at VIR commented that my '08 coupe was far too soft for the power it has, to the point that the unsettled rear made him nervous several times when braking down from 140-150MPH at the end of the straights. He is an ex-Corvette Challenge driver, and knows how stiffness can help in these situations, but doesn't know the particular needs of a C6.

And Yes, I know that the passenger seat is going 15MPH faster then the driver's seat, especially when I wasn't always doing exactly what he was telling me...

BTW - I'm referring to a realistic compromise setup between autocross, street use AND HPDE.

gkmccready

I had KONI 3013Sports on the car for several months and a few events. I didn't really like them. Just as with the stock shocks I worked through some swaybar combinations and went back to C6 Z51 sways. I *did* notice that extra rebound dampening in the rear helped the car under braking compared to stock. But I was never happy with the overall grip the car had with these shocks.

I sucked it up and spent the money on the HardbarUSA Penske Double-adjustable shocks with dual-rate coilover springs. They are amazingly compliant on the street until you lean on them and then when you do lean on them it is night and day. The extra spring rate compared to stock means I can still run my stock sways and get better roll control.

I've tried a lot of brands of single-adjustable shocks on various cars over the years and the Penskes are just so much better. Even if you're not willing to go coilover, the Penskes would be a phenominal upgrade when combined with some higher rate VBP springs... it may also be worth talking to RAFTRACER about KONI 2812s in combination with the VBPs...

Again, stock shocks, KONI 3013s, and the Penske 8100s... the sweet spot -for me- is stock sways. With the right alignment I feel like I get more grip with the stock sways than any other combination; I have even experimented with a base model swaybar in the rear.

The soft spring (stock leaf) and big bar (Pfadt Pfatty) set up was definitely easier to drive than stock when I didn't have enough rear toe-in... once I added rear toe-in, though, I got more grip from the car by going to a softer bar set up.

Short version is you need to drive the car and decide what you need. Everybody likes a bit different set up. If you think you need more stiffness in the car in straight line situations (like braking) then you have to look at springs and not bars. You might get away with shocks as a bandaid, though...

gkmccready

BTW, I wouldn't waste my money putting a C6Z suspension on a C6... look around and you'll see the C6Z guys are all upgrading their suspension, too. If I was going to do a leaf spring replacement I'd definitely call VBP or Hyperco, and I'd buy the best shocks you can afford... IMO, they're where all the difference is... and a really really nice shock will let you run large spring rates without feeling all the pain.

I -definitely- wouldn't bother with C6Z swaybars on a C6 Z51... the front bar is already the same, and the C6Z rear bar is likely way too much for any tire you'll fit.

EvilBoffin

That's good info, GK.

I completely agree about the C6Z bars. My only interest was in the higher-rate Z springs. I have no desire to ruin the balance by adding MORE oversteer with a big rear bar. My car turns in quite well and is very predictable - it's just too floppy & soft. Whether in an autocross or HPDE, mild oversteer is all I'm getting, along with the noted instability during hi-speed braking. It really hasn't understeered obviously yet - at least with 275/305 Toyo RA1's on the car for all events so far (I'm still waiting for a hitch to be built to be able to tote some Hoosiers around...).

That was my first impression of this car - that a well-tuned set of shocks could be a great first step towards improving the handling and reducing the tendency of the rear to get twitchy when cornering over uneven pavement, or during hi-speed braking. My primary concern is to ensure that it makes sense to upgrade the shocks when still using the stock springs.

For cost reasons and to stay in SuperStock for now, I'm considering Pfadt's new shocks and SS-legal adjustable FRONT swaybar. The Big-Daddy Penske's or 2812's are out for now ($$$), and most user reviews posted about the Koni 3013's have NOT been favorable, including yours.

BTW - here's my current alignment settings, courtesy of David Farmer's efforts:

Front -
1.95 negative camber per side
1/16th toe OUT total
7.5 degrees caster

Rear -
1.1 negative camber per side
1/8th toe IN total

Do you think a little more rear toe IN is called for, to further neutralize the oversteer? Maybe more rear negative camber?

Thanks for sharing your wisdom & experience, guys...
Robert

NOSLO6

Great responses here folks! As Crystal wonders above, how should I best think about matching springs to a shock replacement?

Would even the good bang-for-buck swap to Bilstein sports benefit from a Z06 spring? Given the responses here and elsewhere I'm tempted to approach this in two stages: (1) Try a cheap but proven shock swap to Billy sports (also considering the Pfdat adjustables) and consider a spring change to complement them at the same time. (2) See how this works and consider coilovers if still unhappy.

I'd again echo the experiences above about the need for additional dampening. With the C5Z06 I agreed with the 2nd poster's comment "I'm not going to out drive this suspension for a good while"; I beat the heck out of it for a multi-day Evo school and just loved the general setup. I don't have the same feeling about the C6.

gkmccready

Push harder. :-) I have that same tire but with 295mm fronts on CCWs and I can make it understeer at will. At Spring Mountain being a goof chasing somebody on Hoosiers I understeered my way right off track...

So long as you can match the shock valving to the springs, upgrading the shocks is always a good choice. And if you get a shock that can be revalved (Penske, Bilstein) they can stay with you even as you upgrade your springs.

If you're already neutral with very slight oversteer DON'T SCREW WITH YOUR SWAYBARs... if you don't feel neutral then the bars are a good tool to balance with. The new Pfadt shocks are single adjustable, rebound adjustment only, and could be a good choice. I do not know their adjustement range or if they are revalvable. You may save money in the long run looking at a non-adjustable Penske, or single-adjustable Penske since they last forever... wasn't Monks selling a Penske set up for $1200 or so? Versus the $860 (?) for the Pfadts and the Penskes can be revalved and live a long, long time. And the Bilsteins are revalvable if you send them to Bilstein. I'm remembering $399 shock cost and $50/shock for revalving to your specs (which they will work with you on).

Given what you've said about your current balance, I'd put the swaybar money in to the shock money and see where I ended up...

This set up should work well for you, it's pretty close to what I was running last season -- I just have more rear camber now. Since you say slight oversteer I wouldn't messing with it but you're starting to get in to where I don't have personal experience to draw on with the Corvette -- but having read and talked to a lot of folks, for autocross some guys run up to 1/4in toe-in out back. That is definitely not a streetable setting so you'd have to get good at changing the toe at the events... which isn't rocket science.

gkmccready

* C5 Z06: 526# Front, 714# Rear
* C6 Z06: 531# Front, 782# Rear
* C6 Z51: 526# Front, 645# Rear
* T1 (C6): 582# Front, 850# Rear
* C6 Base: 420# Front, 657# Rear
* T1 (C5): 582# Front, 793# Rear
* Hyperco HPS (Street): 565# Front (12405HPS), #765 Rear (12406HPS) $521ea
* Hyperco HPT (Track/Solo): 625# Front (12407HPT), #850 Rear (12408HPT) $521ea
* VBP Sport 990# Front, 650# Rear $500ea
* VBP Extreme 1050# Front, 855# Rear $500ea
* VBP 750-900 lbs/in Front, 700-800 lbs/in Rear $500ea

Would seem to me that there's just not enough difference between the C6 Z51 and Z06 spring rates to bother with that change. If you want more spring rate you're going to want to step up to a Hyperco or VBP and make sure you get your shocks valved for the new spring rate. Call the shock vendors and see what spring rates their rebound valving was done for...

A suspension that can keep the wheels firmly on the ground works better than one that skips. Don't think soft is bad. Sometimes soft is exactly what you need to get maximum grip -- ask any racer that runs in the rain... I've driven some racecars that felt floppy or looked like they had a tonne of body roll, but once you get in and just deal with it, it's amazing how much grip they have, and how much they lose when you increase roll resistance (with bars)...

OCCOMSRAZOR

I put a wide rear on my 2005 Z51. Add Z06 sways with Bilstein sport shocks. Get an alignment and check your rake.

After doing these things, my car feels like it's on rails, plus the cost was reasonable.

Aaron Pfadt

NOSLO6,

I think Glen makes a lot of good points above as does CrystalRacer. It is true that damping should be matched to your springs, but also to your unsprung mass (tire and wheel weight primarily) and vehicle weight, among a million other things. The bottom line is that you should get a package that works well together and you can tune to your driving style as you get faster.

There are options for improving your suspension from simple inexpensive bushing changes to $10000 coilovers and everything in-between.

My personal opinion is that one of the shortcomings of the Z51 suspension is lack of spring rate. For that I like to see someone go to upgraded leafs or a set of coilovers. The leafs need to work with your shocks, so something adjustable is great. One of the nice things about our Pfadt adjustable shocks is that you can tune compression and rebound with our adjustment. The adjustment is rebound biased (about 3:1) but does change both.

A package that we have that you might consider is our Pfadt Threat Level 1 package. It combines our Street sways (about 1.5x Z51 sways) with a nice increase in spring rate from the Hypercoil HPS springs. Those two components are combined with the Pfadt Shocks to complete the package.

In a similar price range you could also install Pfadt Coilovers and Street sways. You'll have more spring rate in the coilover package and more ride height adjustment options. However, some competition classes don't allow the use of coilovers so we have both packages available.

Either of these options will eliminate the shortcomings that you are feeling with your stock suspension.

Here is a description of our Threat Level 1 package:

If you are not looking for adjustable ride height and spirited driving is the cars main focus then I would suggest the following package...

Threat Level 1

Pfadt Sport Shocks
The Pfadt Sport Shocks will rid the car of the infamous rough corner nervousness that seems to plague the Corvette. The Pfadt Sport Shocks are also adjustable so you can tailor the balance between cornering performance and ride quality to suite your taste, even if your taste changes during the day. The adjustments are simple and can be changed in a matter of minutes, with no tools necessary.


Retail: $890

Pfadt Street Sway Bars
The Pfadt Street Sway Bars are the perfect sway bar for the street driven Corvette that may see one or two track days in a year. They offer a rate that is about twice what the stock sway bars are. They are also fully adjustable, so you can change the overall balance of the car to your particular setup and driving style.


Retail: $845

Hyperco HPS Leaf Springs
The Hyperco HPS Leaf Springs will give you about a 10% increase in spring rate which will lead to faster transition times from corner to corner. These are a great complement to our Street Sway Bars!


Retail: $1050

Package Price: $2685

This would be an exceptional kit for what you are describing to me. This kit will provide an obvious improvement in road holding capability over stock without noticeably impacting the ride quality of your Corvette.

We are currently working on releasing a complete list of Pfadt Race Engineering packages. So keep your eyes peeled for the release.

Please do not hesitate to call us if you have any questions!