From 1936 to the 1947 the production of Bigtwin is supplied with knucklehead 1000 and 1200 cc. engine.

With the advent of the engine 1200 cc. the Factory decided to adopt 16” rims and tires.

In the 1948 Harley Davidson Motor Co. introduced the new Panhead engine.
Only the 1948 production was built with Springer front fork. 

In the 1949 was introduced, as a prototype, a new front end with hudraulic system.
For the first time Harley Davidson Motor Co. assigned a name to the model, in this case the name came from the forks: Hydra Glide. 

In the 1958 started the production of a new model that substituted the Hydra Glide, the new one is called Duo Glide which means the use of the new frame with rear shocks absorbers to male driving more confortable compare to the old rigid frame. 

In the 1965 debut the Electa Glide model, the frame was edited to insert a  bigger battery, 12 volts, and also the starter housed between the transmission and the oil tank. 

In the 1966 Harley Davidson Co. edited the Classic Electra Glide with a new shovelhead engine. Essentially same look with small changes as the position of the front drum brake that move from the left to the right side of the bike! 

In the 1971 Willy G. Davidson project a bike with sportive design obtained from a Big Twin base. The FX Super Glide 74ci born with kick starter only, equipped with Sportster front end and drum brake,  19” wheel, 3.5 gallons gas tank with a dashboard as the FL and rear fender Sportster style. 
The floorboards are replace by footpegs, relocated backword and attached to the primary transmission outter cover on the left side and to the transmission side cover on the right side but still mantain the gear shift in the same position, this caused the inverse gear shifting with the first gear up and all the others pushing the lever down. 

The first year of the Boat Tail was supplied in "Sparkling America" color, white with blue and red stripes.

1972 Harley Davidson add six  more colors to chose from.

1973 Harley Davidson Motor CO. dismiss the drum brakes system and adopt  the new disc brakes system, from now even the FX series came with electric start beside the kickstar. 

On 1977 the company introduced the Low Rider, derived from the FX base, they add a second front disc brake, alloy rims, lower seat from the ground, strait handlebars (Dragbar) and stratched fork tubes.

1980 Harley Davidson Motor CO. introduced the FXB80 Sturgis, where "B" is for belt, a fine limited edition due to the experimental changes made. On the FXB was replace the primiry and secondary chains with belts.

​Inspired from classic choppers on 1980 the company disigned a new model. Using a bobtail rear fender, 5 gallons gas tank and a 21 inches front wheel installed on FL stretched front end with 41mm fork tubes, the FXWG Wide Glide intruduced on the market a new bike style since today available.

FXDG is the last version of FX serial with Shovelhead engine and old style frame. "DG" is for Disc Glide. This bike close the production of classic models.