I have done this a couple of different ways. I have removed them completely (creates a huge mess if driven daily or in the rain). I have slightly trimmed the outer edges and removed the metal support that helps attatch to the wheelwell opening (but you still get a fair amount of rubbing). I have cut the outside from the center to the fender opening to clear the tires, but you always get any and all dirt/rain that travels around the outside edge of your tires slung up in the compartment almost as easy as not having the fenderwells in at all. I'll try to describe what I've done on the set that's in my car now. First I removed the metal backing from the wheel opening area. You will need to make slits in the fenderwell between the center mounting holes and the outside edge. I used an angle grinder with a thin cutting wheel to cut slits parallel to the opening maybe a foot long. Finally I cut one slit through the middle 4 or 5 slits to allow the "fingers" to rise when the tire comes up in fenderwell. The "fingers keep most of the dirt and rain out from under the engine compartment.