A trailer bike (also known as a trailer cycle, and trademarked names such as Trailerbike, Trail-a-bike, Half wheeler or Tagalong) is a one-wheeled, or sometimes two-wheeled, bicycle trailer designed to carry one or more children in positions that closely resemble that of a bicycle rider. It can be described as the, "back half of a bicycle." The rider of a trailer bike usually has a saddle, handlebars, and pedals. Some fold for more compact storage.
The trailer bike was patented by Canadian entrepreneur Delbert Adams. Adams started the first manufacturer of trailer bikes, Trail-a-Bike, and began selling them in the early 1990s.
Trailer bikes have come in a variety of configurations. These include upright, bicycle-like configuration, and the seated passenger position as with the Weehoo iGo. Trailer bikes may have just one gear or more than one. They seldom have brakes.
A trailer bike is attached to a bicycle at either the seatpost or on a special rear rack by a linkage that allows for pivoting. Alternatively, the hitch mechanism may rotate using the seatpost as the pivot. The attachment may include a quick-release option. Trailer bikes have been available in single-seat and tandem configurations. The Trail-Gator tow bar converts a kid's bike into a trailer bike.