after market wheels
 

will 15x8 wheels with 4" back spacing fit our trucks? and our bolt pattern is 5.5 correct? thanks.

Yes, those should work on both front and rear, assuming you are running stock suspension. 4" would be the max backspace I would use. 3" BS would look better. I would prefer 15X6 in the front, unless you are running power steering. I wouldn't try to put anything bigger than P275 tires on the rear, as those (with 4" BS) will just barely clear the bed walls.

Yes, our F100's run the "big Ford" pattern of 5 X 5-1/2 bolt circle. The studs are 1/2-20.

Randy is right on! I just want to add, if you buying new rims, it is best to have a tire guy measure your offset just to make sure. I'd hate to see you pay money for a 4" offset and find that they rub. Better safe than sorry. I'm running 17" wheels with a 4" offset in the rear and 4" offset in the front. I'm running 7" wide wheels in the front because of the reason RJ explained. I DON'T HAVE POWER STEERING! Rear wheels are 10" wide. Offset changes with width of wheels. Just to add, there are few other vehicles that use the 5.5 lug pattern, a few that come to mind is the Jeep and Dodge truck. Not many though.

thanks for the info guys, i am planning on installing the smoothies sold by summit racing, stock # 52-5815.