The owners manual:
http://www.trekbikes.com/pdf/owners_...OM_english.pdf
Trek used to offer/sell an optional hitch that came with a variety of inserts/spacers so it would fit a majority of bike tube sizes.
It basically turns your bike into a tandem and (should) only allow an up and down movement.
Last edited by Sci-Fi; 07-19-08 at 02:31 PM.