Is my bike compatible with the Xtracycle FreeRadical?

We'll be updating this checklist, but here's a starting point.

1. Rigid or front suspension bicycle. Full-suspension mountain bikes are most often not compatible.
2. Rear brakes on your bicycle are either V-brakes or disc brakes. (Disc, the rotor size should be 203mm. If your rotor is 160mm, you buy a replacement rotor.