Traditional trikes use 2 wheels in the rear and 1 wheel in front. The front wheel can be a standard front wheel, and the rears wheels can either be a comnination of a front wheel and a coaster wheel or 2 hollow hub wheels. Recumbant trikes now are made that use 2 wheels in front and 1 rear wheel. Trike conversion kits can be used to turn a standard bicycle into a 3 wheel trike for fun or for work.