Fat Boy (FLSTF/FLSTFB/FLSTFBS/FLFB/FLFBS)

The Harley-Davidson FLSTF Fat Boy is a V-twin motorcycle and one of the best selling models produced by Harley-Davidson. Designed by Willie G. Davidson and Louie Netz, their prototype Fat Boy was built for the Daytona Bike Week rally in Daytona Beach in 1988 and 1989. The Fat Boy is unusual for having solid-cast disc wheels.

Softail frame
The frame used on the Fat Boy originated with the 1984 Softail which appears like a rigid chassis but has hidden springs. Engineer Bill Davis began experimenting with the idea and was originally turned down by Harley-Davidson, who later bought the rights and redesigned the frame in-house.

In 2017, Harley unveiled a completely redesigned Softail frame for the 2018 model year along with the new Milwaukee-Eight engine and new Showa suspension, the first major change since the introduction of the Twin Cam engine in 2000. The 2018 Softail frame uses a differently shaped swingarm suspended by a single rear shock absorber, mounted underneath the seat in a similar fashion to the original Haubert and Davis designs. Harley claims that the new chassis is significantly stiffer and lighter than the previous-generation Softail and Dyna platforms, the latter of which was discontinued with some of its models being carried over to the new Softail chassis. The new model is offered in two variants the FLFB 1,746 cc (107 cu in) and FLFBS 1,868 cc (114 cu in).

Development
In 1994 though the exhaust was changed to a seamless type and the master cylinder and switch gear were improved in 1996. A new twin cam 1450cc engine was introduced in 1999 and in 2002 bullet-style indicators were added with an alarm and immobiliser. The 15th anniversary in 2005 was marked with a custom version for one year only with custom paint options, custom wheels, screaming eagle engine and added accessories. In 2006 the engine was upgraded to a larger twin cam 1584cc model[8] and a six speed gearbox.

The Fat Boy Lo FLSTFB
The Fat Boy Lo introduced in 2010 featured the lowest seat height on any Harley motorcycle.