Lowering your car can cause your vehicles negative camber to increase. What happens when you drop your car it causes your tires to lean inward and this is what is causing your wheels to wear down irregularly if you don't take measures to fix the problem. Camber kits are necessary to correct the misalignment caused by the installation of the new springs and are also highly recommended if you are upgrading your stock wheels and tires to aftermarket ones.

When a car leaves the manufacturer's factory camber is set according to oem part specs so when you do lower your car or add a new set of rims to it you risk the chance of throwing off camber.

Camber Explained
Camber is simply the tilt of your car's tires. When adding a set of new springs or aftermarket rims you should really consider adding a camber kit at the same time to prevent any future problems with tire wear and alignment.

When someone mentions negative camber they are referring to an inward tilt. By adjusting negative camber you will improve the way your car handles on the road.

On the other hand, an outward tilt is referred to as postive camber. An adjustment of this sort will give you less tire wear and easier handling.

Lastly, when you lower your car you are more than likely going to cause excessive camber and to correct the problem you will need to make note of the following:

Car lowered 1" = -0.75 degrees of camber

Car lowered 2" = -1.50 degrees of camber

Car lowered 3" = -2.50 degrees of camber