The factory rear already has adjustable camber eccentrics that typically will provide enough adjustment for most lowering springs. On our
Project TriloG car we were able to lower the rear to almost 1.5" and still fall within the -.2 to -.6 degree alignment spec. If you remove the eccentric washer as shown below their is actually 14mm of adjustment in the rear cradle. This roughly translates to about 3-4 degrees of total adjustment at the wheel. That does not mean that you can get -3 to -4 degrees of camber in the rear, just that you have somewhere around 1.5 to 2 degrees of adjustment in either direction, assuming you are starting off in the middle of the range (each car will be a little different).
Camber bolts are an option and will give you a little more adjustment, one sometimes 2 degrees, depending on the application. In some situations these work great. The issue with camber bolts is that the only way to build more adjustment into an existing slot is to either reduce the diameter of the camber bolt or make an offset bolt. Either way, it compromises the strength of the bolt. For lightweight imports, this may not be an issue but this car weighs 3800 pounds and their is a reason GM uses 14mm bolts. This is one of the main fulcrum points for the rear suspension that serves double duty, it not only acts as a camber adjustment but has the majority of the spring load applied. It is not our recommendation to compromise this bolt in any way.
In our testing we have found that this new platform loves negative camber, front and rear. If you plan to autocross or road race your car with R compound tires, chances are you will not be able to get enough negative camber with the OE eccentrics. On the other end of the spectrum, we have determined that when drag racing, these cars like a little positive camber. On a typical launch, the car wants to compress the suspension to a point that it enters negative camber resulting in decreased tread contact. By setting the static camber a little positive, it keeps it closer to zero during compression on launch.
Keep in mind that these examples are both extremes in two different areas but if you plan to do either or both, you will probably not have enough camber adjustment. This is why we are developing lower control arms with up to an inch of adjustment. 50-75% of people just wanting the lowered "look" will probably be fine with the factory adjustment, for everybody else our control arms should be available within the next few weeks.
