Very few custom motorcycles are identical, making it difficult to find a seat that not only compliments the motorcycle, but fits it as well. This leads many bike builders to fabricate their own seat from fibreglass, due to the material's low-cost and relatively easy-to-use nature. Making your own seat starts with moulding the seat's base to the contours of your motorcycle. Doing this will ensure a solid foundation to support you while you ride. Preparation is critical to the success of this project.
Fill in the empty space between your motorcycle's seat rails, the portion of the frame's tubing that supports the seat, with cardboard.
Cover the motorcycle's fuel tank, seat rails and rear fender with blue painter's tape to provide an easily removable layer of protection. Cover the blue tape layer with a second layer of aluminium tape.
Cover the rest of the motorcycle with plastic dust sheets secured with blue painter's tape.
Cut a piece of paper into the rough shape of your desired seat. You will use this as a template. Shape it using scissors. Lay the paper template onto the motorcycle's seat rails to check the template's size. Remove the template from the motorcycle.
Cut four pieces of fibreglass cloth into the shape of your paper template, leaving a minimum of three inches of extra cloth from the edge of the template.
Coat the layer of aluminium tape with a high-quality automotive wax, using a minimum of four coats.
Use a paintbrush to coat the aluminium tape layer with fibreglass resin. Lay the first piece of fibreglass cloth onto the resin. Dab the cloth lightly with the tip of your paintbrush until its is completely saturated with resin.
Spread another coat of resin over the first piece of fibreglass cloth. Lay the second piece of cloth onto the resin. Dab the cloth lightly with the tip of your paint brush. Repeat until you have created four successive layers of resin and fibreglass cloth.
Allow the fibreglass seat base to cure for 12 to 24 hours. Lift the seat base off of the seat rails.
Use a permanent market to trace the outline of your paper template onto the fibreglass seat base. Cut the excess fibreglass away, using an angle grinder.
For best results, have the seat base upholstered by a professional upholsterer. Read all preparation instructions provided by the fibreglass resin's manufacturer before beginning.
Don't cover your motorcycle with fabric dust sheets, which will absorb spilt resin and damage painted parts. Work in a well-ventilated area to prevent overexposure to the fumes emitted by fibreglass resin.