The Xtracycle modular rack system allows you to customize your S.U.B. to your specific needs. The base FreeRadical frame comes with cables, chain and installation parts, but leaves your accessorization options wide open. The frame can accept any of the accessories listed below. Alternately you can make your own custom load-carrying system out of conduit and 2x4's...
The Free Radical frame has two sizes: the 26" and 700c. The only difference is in the location of the brake post mounts. The 26" style is for most mountain bikes, and the 700c will fit most road and cyclocross bikes.
Both sizes will accept disc brakes. They will not accept cantilever brakes - if you have cantilever brakes you will need to convert to a V-brake or disc brake arrangement. Bear in mind that a regular V-brake won't work correctly if you previously had cantilever or road caliper brakes on your bike. You will need a special BMX style V-brake or a regular V-brake plus a Travel Agent to correct the pull of the cable.
If your bike lacks a chainstay bridge, you will need an extra Front Attachment Plate to grab onto the frame.
If your rear dropouts flare out more than about 8mm, directly above the rear axle, they may interfere with the fit of the bike.