50% good, 50% not so good. My daily 2010 Cobalt SS with not quite 70G mile on the odometer, needed replacement front end links, said my local repair shop. My last purchase with ZZP to get new front rotors, calipers, braided brake line kit went well enough, so I proceeded to add to my cart the replacement end links(nicer than stock ones). I then went ahead and added the front and rear kyb struts and shocks then proceeded to look at springs, and since I did not want to brake the bank, and based off of certain spring selections being out of stock, I opted to forgo stock spring heights for a more fun aggressive lowered look, and based off the site's description, it seemed to me the ZZP lowering springs and KYB shocks and struts would work well together.
Once purchased and delivered, I had the local shop do the install. When I picked up the car, they warned me that I may not have as much travel with this new setup. Not sure what they were exactly referencing, until I got in the car and drove home. Right away, the back passenger side started to produce an **** solid clunking noise over bumps, not every bump, but a good chunk of the bumps that were in the road on my way home. I tested the car over the next few days, over a weekend , etc, the clunking noise was almost unbearable on some roads that had those fixed road cracks where as the car hit them, the noise would occur. I conversed with someone on the ZZP support, no indications as to what that would or could be, just stated they had no issues with this setup for the many others who purchased this setup.
The following week, I had the local shop try out the rear bump stop cutting. Of course, that did not do anything. Then I mounted a gopro underneath the car to capture the noise. The local shop took another look underneath the car after seeing the video. They still could not figure out where the noise was coming from. Rest of the suspension checked out, according to the shop. I was almost heading down the path to buy a prothane bushing kit for the car, in case any bushings was causing the clunk. The local shop did not find anything wrong with the bushings. At that time, I still had the old springs. I had the shop put the original stock springs back on the rear of the car only. The clunk has gone away with the original rear springs.
Afterward, the local shop indicated that maybe the rear shock, or shocks, maybe the culprit to this setup/clunk. They suggested that the shock was bottoming out on that side, but were unable to validate that theory.
In the ZZP description for the springs, it suggests the rear of an SS will drop about 1 1/4 inch. From my perspective, it appeared to drop the car about 2 inches. So not sure if that amount of drop would have made a difference.
I still have the ZZP front lowering springs in front. They seem to be holding up and not causing any grief or noise, so the rating for this spring setup will be good for the front, not so good for the rear (plus the extra cost to put the stock ones back on)
For a daily driver, stickling with the stock setup may be the better route, at least on an 2010 SS, IMO.