I'm searching for a suspension kit for my daily driver. I'm looking for better handling and look without sacrificing too much ride quality. I'm currently torn between the Cobb Tuning kit and the Hotchkis kit. I'm looking at these because I hear great reviews on the sway bars and hear they are almost identical. I'm sure either sway set would be fine. Springs are where I am at a crossroads. I'm sure many of you are aware that the 05+ Zs have dramatically higher rear spring rates (around 430 lb/in) as opposed to the earlier Zs around (340 lb/in). The hotchkis kit is said to have springs that are SOFTER than the early Zs, to match the shocks better. This concerns me for a few reasons when considering what to put on my '06. I dont know how the dramatic spring rate drop would go with my shocks which are valved for a 430lb spring. I lean more toward the Cobb for that reason, as I think it might be a better match with my stock shocks, but they use a rear spring that looks much higher than anything else ive seen offered for the Z. I can deal with increased stiffness, but I don't want to get my fillings knocked loose every time I drive my car. As you can see though, my concerns here are the same as the hotchkis spring being too soft, but rather concerned that these would be too hard instead. Could someone lead me in the right direction on this? Maybe I need some lessons in suspension dynamics...

 

What's the rating of the Cobb's springs? I don't think they have ever given a number other that their '15% stiffer', but compared to what. Are you sure is compared to the 05+ suspension?
I'm in the same position as you, and also considering the RSR's.

 

-

 

2007 Stock
Spring rates F314/R427

Cobb Tuning
Spring rates F345/R438

Post edited for proper spring rates

 

Those numbers sound good. Let's see what others say.

 

Willing to bet , those numbers will destroy your stock shocks very fast.

 

Hmm, nobody knows anything about this?

 

PMed

 

I believe Cobb said they developed it with the stock dampers in mind. But id probly go with Koni Yellows with this setup.

 

Post #4 updated with correct spring rates. Original problem isn't an issue anymore, and these look like a great match for those of us with Zs with the later spring rates. There was some incorrect info posted in other threads about the spring rates of the Cobbs. I think I'm sold on them actually.

 

Well just like any lowering spring, i would believe they would wear the factory shocks out pretty quick, Koni Yellows would be a great match.

I would buy the Cobb springs for my car before Hotchkis, much better spring rates, great drop , probably just better matched for the car. Anyone know the sway bar rates ??

 

The only reason that I have not gotten the Cobb springs is because of a review on them I read that explained how the bottom of the spring was slightly bigger than the mount causing part of the bottom coil to not seat properly. And the customer uninstalled them because he thought they would be unsafe. Every time I ask this, I never get an answer as to if this is the case with these springs.

 

And how often do you read post from people on here that actually have not a clue in the world about mechanical parts,some can't even figure out to remove the bolt on the front rotors to install aftermarket wheels. Have you seen the way our springs mount in the control arm ??? Take a look, then think about how how they sit in the bucket. They would have to pretty dam oversized to become unsafe IMO.

Disclamer, they could be pretty dam oversized.

 

As I would normally agree in this situation since I understand completely what you are saying. But, the OP of the thread that installed the springs provided pictures showing the spring somewhat overlapping the edge some around the mount base. So its hard to deny that, unless he somehow completely installed the springs wrong.

 

Here is the thread that I am referring to. The OP never posted a picture, but another member posted a picture confirming that there is some overhang. Is it a big deal? Im not an expert, but that would make me uncomfortable.

 

I saw that too. I havent seen repeated posts of it though, and several other members have them installed and don't seem to be having any problems, so I figured it was just someone who got the wrong springs by mistake or didn't really know what they were doing.

 

I'm still rolling strong with my Cobb springs. Not sure what sort of failure you are expecting.. I will definitely post up if my car explodes.

 

I'm curious where you got the springs rates from? I provided some calculated measurements on driver, but they were solely based on a scientific spring rate equation and at the time I didnt have an OEM spring to compare them to. Also I could not account for the material type so what I provided wasn't completely accurate.

I just want to know where your data came from so i could update my driver post.

As for sway bars, this is what I have found out about the rates:
Front:
Position 1 = 25% Stiffer over stock
Position 2 = 50% Stiffer over stock
Position 3 = 85% Stiffer over stock
Position 4 = 135% Stiffer over stock
Rears:
Position 1 = 85% Stiffer over stock
Position 2 = 130% Stiffer over stock
Position 3 = 190% Stiffer over stock

I have my Cobb sways set at 3-front and 2-rear on OEM suspension. I hope to have my Cobb/Dspec combo installed by spring.

 

Mikel pm'd me with them. He got them directly from shayne@cobbtuning.com.

 

Yes, I'm on the same boat as Wheelman, wanting to drop the car just a little but not going softer as with the Hotchkis. I e-mailed their tech support asking for the rate of the springs and surprisingly they answered back.