[joedoh]

you wouldnt really notice if they were missing on the front, I think they were to keep the fenders stiff rolling over mud heaps in fields, a lot of trucks (and I have seen a LOT of trucks haha) they are missing bent or broken.

but the rears, they go from the fender edge to the frame and if they are missing you will hear the fenders shimmying and dancing around while you drive, they really need that rear support. on an s10 swap if the factory one is there I usually cut the frame side shorter and bend it up and weld the end to the bed side, leaving the fender side bolted. if they are missing completely I use the same part from an s10, bolted to the fender and welded to the bed side up under.

I also notice that the rear ones have a profound impact on the SHAPE of the rear fenders, so if your rear fenders are a little out of whack proportion wise, the supports usually help a lot. sometimes the front is the same way, if your fenders are bent up getting that lower support back in makes a difference.