When I first took off the running boards on mine I had ordered them and put them on. They are HARD and will also fill with snow, ice and mud. They fillled so bad that it would create a pack of snow or mud in between the mudflap and the tire. Then grind as you drove. I would have to get out of the car and kick the snow and ice that had built up between the tire and mudflap. I tried to alter them to provide tire coverage but not hang below the car but they never looked right , kept filling with snow and mud, and then went in the garbage. I replaced them with inexpensive, flexible nylon ones (smooth on both sides) and mounted them in the stock location using stock bolts. I found these to be superior.
Those stock flaps worked great in most conditions, but they filled with snow or mud easily. They are shaped like a bucket on the tire side of the flaps. They also are not flexible so they can bend and damage the mounting points when they drag on the ground like mine did.
But it does give a clean look if that's what you are after.
