<P> The FL model was given a new frame in 1958 . This frame included a rear swingarm suspended by a pair of coil - over-shock suspension units . In honor of this fully suspended chassis, the FL's model name was changed from Hydra - Glide to Duo - Glide . </P> <P> Unlike OHV configuration, aluminum heads, and telescopic - fork front suspension, however, this improvement in technology was applied to the small - frame bikes first, the K - series having received rear suspension in 1952 . </P> <P> The third and final change given to the name of the basic FL model would occur in 1965, the final year of the "Panhead" engines . These last "Panheads" were the first "big - twin" Harley - Davidson engines to be equipped with electric starters, the Servi - Car having received electric start the year before . This innovation for Harley - Davidson was greeted with the new model name of Electra Glide . </P> <P> In 1966, the "Panhead" gave way to the "Shovelhead", gaining a ten percent increase in power in the process . </P>

What does fl stand for on harley davidson