I bought three 84" rails and one 48" rail because I had seen the system in a neighbor's garage. The 84" rails are great because, with 16" on center framing, you can mount it so that there are only two inches on either end that are unsupported. It's a different situation with the 48" rail - you can have as much as 16" on both ends that are unsupported. That should have been a 50" design.