Mach2

I have a 2010 1LT, MN6 C6. Since buying it in October, used with 6900 miles from previous owner, I have made upgrades to the base suspension. Did not change the transverse springs but added Z51 front/rear swaybars & polyurethane bushings and Z06 front/rear shocks. I have Firestone Wide Oval RFT tires @ 30 psi cold. After installing these upgrades all was well untill I was going onto a freeway onramp, turning right, and the onramp had a slight off camber and it was choppy from the asphault being beat up. As I entered the onramp in second gear I started to accelerate, not full throttle, and the rear end stepped out very quickly. Had the default traction & active handling nanny's on and between them and my lifting the car straightened and I went on my way. Kinda dismayed that the suspension upgrades let that happen. Couple days later going around a 90 degree left flat left turn, I accelerated exiting the turn and the rear end stepped out again. I posted a thread about this situation and a forum member PM'ed me saying that the Z06 rear shocks were too stiff for the stock rear spring and rear Z51 sway bar and poly bushings. Didn't have any issues with the front suspension pushing or anything due to the Z06 shocks in front though. He suggested I put Z51 rear shocks on in place of the Z06's in the rear. I just installed the Z51 rear shocks and after two days of driving, and going back to both the corners where I had rear end stepping out issues, the Z51 shocks allow the rear end to squat and move and the stepping out issue is gone. The suspension is working.

For those with the base C6 I would suggest that when you upgrade your suspension to go with Z51 front/rear springs, Z51 front/rear sway bars and poly bushings and Z51 front/rear shocks. I'm going to leave my base springs and existing combo of sways and shocks as it is for now and continue to drive in a safe but spirited manner and change the stock springs and front Z06 shocks if I feel these items are hampering the suspension from working to my liking.

DSOMC6

You will never completely get rid of the rear getting skittish, stepping out etc over bumps at speed untill you get rid of the leaf springs and upgrade to a coil over suspension. It may improve somewhat, but still remains unfortunately by the nature of the design.

johnodrake

Your changes have made for more oversteer (loose).

Here is some good suspension information regarding swaybars.

http://www.houseofthud.com/cartech/swaybars.htm

el es tu

I definitely suggest redoing the springs

I run a z06 front spring with the base one in the rear
and z06 shocks front and rear - this has really reduced the rear end stepping out issue.

also if you want something a bit closer matched to your z06 shocks you might try the gs rear shocks:

the grand sport has its own shocks for the rear but uses z06 shocks up front. This is with Z51 springs (front and rear).

peter pan

I do not have any issues on our base upgrade, I went with Koni FSD shocks and Z sways to go with the 325 rubber I have out back

wayback

No problems here either. I also have the Z sways but I have Pfadt adj sport shocks set at 6 for DD.

Pfadt Racing

The bolded section is key to what is likely going on here. In our testing the Z06 shocks have a really high amount of high speed rebound built into them. What happens when you dial a bunch a high speed rebound into your rear shocks is over road irregularities the shocks prevent the tire from actually following the road surface and this decreases the amount of overall grip. This was one of the situations we was looking to cure when we valved our Johnny O'Connell shocks.

By dropping the high speed rebound damping in the shocks you can expect increased traction over rough road surfaces with our Johnny O'Connell shocks.

rwillitt

So I put the JOC stage 1 shocks and bars on my base C6. What springs would you recommend if I were to swap the base springs?

bud miller

interested too...with the JOC stage 1 would spring change really be necessary for street??

el es tu

The base springs are very soft up front. At a minimum Id change out the front spring for reduction of brake dive.

Spring balance front to rear is driven by personal preference.

The factory runs stiffer springs in the rear, while some racers and tuners choose stiffer springs up front.

factory Front/Rear:
base 420/657 (.639 ratio)
z51 525/645 (.814 ratio)
GS 525/645 (.814 ratio)
z06 531/782 (.679 ratio)
T1 racing 582/850 (.685 ratio)

Z06 or Z51 front will both work well with the base rear spring

383 Z06

LOVE my Z51...though I never really "test" the limits....the feel is sharp

Fiss

I have a 09 base suspension C6 and am looking at doing the JOC Stage 1 kit. What springs do you suggest? I dont track the car but just drive it like it was meant to be driven

Gearhead Jim

There is a reason why GM, and everyone else, designs a suspension as a complete package.
Springs, shocks, sways, wheels/tires; all should be designed and tested to work together. When you just start throwing parts at the car using a "stiffer is better" approach, bad things can happen. And they may not be apparent in normal driving, only when you approach the limits and can least afford a surprise.

Generally, stiffening the suspension at one end of the car will provide more grip at the other end.

The factory Z51 setup uses a stiffer front spring to counter the stiffer rear sway bar.
If it were my car, I'd install the Z51 front spring and lose the Z06 shocks.
GM Z51 and Z06 shocks are regarded by many (including me) as being harsh on the ride, without providing commesurate improvements in handling. Depending on roads and driving style, I'd go for one of the good aftermarket shocks. But remember stiffer isn't always better, especially on the street.

Mach2

Gearhead Jim. I posted this thread last year and shortly after posting it I realized, thanks to you and others here on the Forum, that the Z06 shocks in the rear was wrong. If I had it to do over, and may if I can find an 09 C6 Coupe with a manual trans and Z51 suspension, I will leave the Z51 suspension alone. If I don't find a Z51 suspension C6 Coupe, I will change to Z51 springs, shocks, sways. With my previous C6, in my avatar, after adding the Z51 sways, Z51 front shocks and Z06 rear shocks, the rear was WAY too stiff and in got spooky sometimes thru the center and exiting turns in a sporting manner, becaust the rear shocks were overriding the front stock spring.. I then changed the rear shocks to Z51's and the handling improved to where it handled turns better. I still knew I should have changed the front & rear springs to the matching Z51 parts. Like modding an engine, you don't just throw a cam in it and expect great things. It's the complete package. Either leave the stock C6 1LT Coupe suspension as is, or change everything to all Z51 suspension parts.

LFZ

Oversteer is fun...but it sounds like you need some better balanced shocks. I'd recommend the DRM Bilsteins or the complete JOC Stage 1 kit.

not08crmanymore

I miss my z51 cars.The base car really is noticeably different!I never would have thought that until NOW,BECAUSE THIS IS MY FIRST BASE SUSPENSION C6.

ATC399

Have yet to notice this on my Z with the MRSC/PTM

Pfadt Racing

So sorry for the late reply! We should be clear, while the base springs are pretty soft up front, there is not any cause for concern that your new package won't be ideal. The damping curves on our shocks encompass the whole range of spring rates, which front to back only vary about ~350lb (not including T1). But with that said, we are going to recommend the Z06 spring set up. We prefer the stiffer setup with the larger rear bias. This works well because the JOC1 sway bars have a front bias to them, and this gets the car back to being much more neutral overall, and you don't have to sacrifice any serious ride quality to attain it since the front spring is not a significant bump in rate. . The Z06 springs are the most optimal from a performance perspective and ride quality perspective. Hope that helps

I wouldn't consider a spring change necessary at all for someone who is doing mostly street driving. If you find yourself tracking the car more often, again we will recommend the Z06 springs.

This is good info, thanks for posting it!


As I mentioned above, I don't think you need to change springs at all! If you were interested in added performance, I would certainly install the Z06 springs since they are a stiffer package overall. But for cruising around on the street the base setup is going to be perfect!

Gearhead Jim

Duh, I failed to notice the date on your original post. Glad you got things working better.

If you do want to put Z51 springs on a base car, the base and Z51 rear springs are almost identical. You could probably get by with doing just the front spring. I have no personal experience there, just looking at the specs.

C U IN REARVEIW

i loved mine as well....until i went phadt featherlight coilovers and z06 bars.....now its just sick handling....