This diagram is with a 52cm LHT with 26" wheels and the small backrack deluxe. The large and small versions of the Bontrager backrack deluxe have the same platform and rail dimensions, but the small version sits back on the bike a bit further. You can clearly see how far the rack sits back over the rear wheel.



The top rail is 15" long, the bottom rail is 12.5" long and the top of the rack is about 5.5" wide. I forgot to note in the picture, the bottom rail starts about 4" behind the forward lip of the top platform. I thought the other measurements might be of use to someone since I wanted them when shopping but they weren't available at the time.

For the record, the bottom rails work very well with Arkel's pannier mounting system but the upper rails don't work so great since the aluminum brackets Arkel uses are slightly too tall. I don't know how this rack would work with other pannier mounting systems, but I wouldn't anticipate any serious problems.