• Most spring manufacturers put a lot of research into their springs and what will or will not work in each application, it is very important to follow their instructions and guidelines.
• When upgrading your springs you you should also upgrade your struts/shocks. The old struts/shocks are designed to work with the original springs, and leaving them on could damage the springs and the suspension.
• How low is too low? Again the spring manufacturers spend time and money to research what works best. In our shop, we have installed lowering kits that brought the cars down over 80mm, but the car wasn’t designed to be that low, damage to the underneath of the car is likely to occur in these cases. We have also seen holes caused by the tires in the metal inner fender well, and conversely, tires torn by fender lips and the inner fender well. We once test drove a car and tore a hole in the engine's oil pan by hitting a tiny bump in the road. Being low has its advantages but being too low has its consequences.
• Tire rubbing: it’s going to happen, especially if you plus-size the wheels.
  • Most of the time it’s the inner fender well lip hitting the tire. If it is excessive you should have your fender lips rolled.
  • If it is the inner fender well plastic hitting the tire, don’t just rip it out, it’s there for a reason, sometimes you can trim a little away to stop it from hitting. You can also try a heat gun to soften the plastic and bend it out of the way. CAUTION: be very careful with the heat gun, make sure you know what’s behind the liner before applying heat, the charcoal canister may be located behind it, and its purpose is to collect fumes from the gas tank to burn in the engine. This could cause a potential fire hazard to you and the car if it is damaged by the heat gun.
  • If you have a charcoal canister behind the inner fender well we recommend removing the fender well and working on it away from the canister. And always follow the heat gun's directions.
• Alignment: after any suspension work a quality alignment should be performed. When you lower a car you also change the camber adjustment which changes the toe alignment. The camber will go negative, which is not a bad thing for handling. Cars set up for road racing run a high negative camber, but they don’t care about tire wear, but I will bet you do. On some newer cars you have to change parts to adjust camber. These parts, depending on the car, are available from the dealer, or if they don’t make one some of the aftermarket make “camber plates."
   

H&R Springs make a universal camber bolt for certain style strut housings called “Triple C camber adjusters.” Check out this link for applications:

In some cars, you cannot do any camber adjustment at all. As noted above, negative camber is not a bad thing—camber up to -1 degree from original specs shouldn’t cause tire wear, it should increase handling.

As always, you must adjust your toe setting as it will change with lowering. Toe out of spec will destroy tires fast.