The bumpstops have to be cut when installing any aftermarket springs. I'll try to explain this in a simplified way from the top of my head, but there are better sources that would be good to read up on this stuff with more detailed info. The idea is that cutting the bumpstops will restore some of the suspension travel lost when installing a shorter spring to lower the car. It is not good to run out of travel. What happens is the spring will fully compress and then ride on the bumpstop which makes the spring rate infinite, or basically nonexistant. This is also why it is important to have stiff springs. A softer spring will compress much quicker than a stiff spring and has that much less room for travel. That is a very unsafe situation to be in. It can make the car do some dangerous stuff like lose the rear end. The easiest way I can think of to recreate this by taking a very long sweeping corner as fast as possible. Or a skidpad. Basically and simplified, drive in circles in a parking lot and see how fast you can go maintaing a perfect circle without sliding. your suspension will compress on the inside part of the car.



MuRiX
97 Eclipse GS HRC Stage II
And a whole lot of other mods...
89 Accord LSi - yes it's mine :(
http://murix.home.icq.com/index.html