I used to have big rooster tails of mud and gunk from the road after driving up part of the front doors and then the rears up to the windows. After installing the front guards it never seemed to be a problem again. The big thing is that these are just big enough to stick out to be flush with the tire to catch that extra spray. I'll update if I don't think the rears are doing what they should, but I'm expecting it to be the same.
08 Focus SE Ice Blue
Steeda CAI and Strut Brace, 17" Racing Dynamic wheels, Big 3 w/ TB wire, other goodies on the way!