1985 Harley Davidson Softail

Bill Davis, an avid Harley rider and engineer from St. Louis, Missouri, designed the softail in the mid-1970s. His first design, which he worked on in 1974 and 1975, had a cantilever swingarm pivoted at the bottom and sprung at the top with the springs and shock absorber hidden under the seat. Davis then built a prototype based on his 1972 Super Glide. He patented the design and arranged to meet Willie G. Davidson August 1976. Davidson was impressed, but made no commitments, and six months later, said Harley-Davidson was interested but would not use the design at that time.

Davis continued to develop the design, switching the pivot and the springing points around so that the springs and shock absorber were under the frame and the pivot point was at the top of the triangular swingarm. This allowed the traditional Harley-Davidson oil tank to be placed under the seat. Davis attempted to produce the new design independently as the Road Worx Sub-Shock, but the partnership he had put together for this purpose collapsed. Harley-Davidson executive Jeffrey Bleustein contacted Davis shortly afterward and began negotiations to buy Davis's design. Davis sold his patents, prototype, and tooling to Harley-Davidson in January 1982. After further testing and development, Davis's design was introduced in June 1983 as the 1984 Harley-Davidson FXST Softail.

In April 1980, Harley-Davidson started work on its own rear suspension design that would have the look of a hard-tail motorcycle. The job was given a low priority until later in the year it was transferred to Jim Haubert Engineering, a firm that Harley-Davidson contracted yearly to custom build motorcycles and prototypes. Haubert built a prototype using his own rear suspension design that closely followed the look of the earlier Harley rigid frames. This version was completed enough for review by Harley-Davidson in January 1981.[better source needed]

In 2017, Harley unveiled a completely redesigned Softail frame for the 2018 model year, 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 being discontinued with some of its models being carried over to the new Softail chassis. The 2017 Street Bob 103 ci was dyno tested and made 65 hp (48 kW) and 88 lb⋅ft (119 N⋅m) at the rear wheel. The new 2018 Street Bob 107 ci makes 77 hp (57 kW) and 101 lb⋅ft (137 N⋅m) at the rear wheel. The 114 ci motor such as in the 2018 Heritage Classic produces 81 hp (60 kW) and 108 lb⋅ft (146 N⋅m) at the rear wheel.