FL is a model designation used on motorcycles manufactured by Harley-Davidson from 1941 to present. Mostly applied to Harley's large-framed bikes, including the current Touring series, the FL designation is also used with their Softail series, especially on Softails with traditional styling, 16-inch front wheels, and either Springer forks or large-diameter telescopic front forks.
Early FL models
The FL was introduced to the Harley-Davidson model line in 1941. It used a 74 cu in (1,210 cc) version of the "Knucklehead" OHV engine that powered the EL in 61 cu in (1,000 cc) form. The FL shared its frame with the EL and with the U and UL, which used a 74 cubic inch flathead engine. The FL replaced the UH and ULH, which used the same frame with 80 cu in (1,300 cc) flathead engines.
The FL continued relatively unchanged until 1948, when it and the EL were given redesigned "Panhead" engines of the same capacities as before. These engines had several improvements over the earlier "Knuckleheads", including aluminum cylinder heads to reduce weight and improve cooling and self-adjusting hydraulic lifters. The U and UL flathead twins were discontinued in 1948, leaving the OHV EL and FL models as Harley-Davidson's large-frame motorcycles.
In 1949, a year after receiving the "Panhead" engine, the FL was given a new front suspension and a model name to go along with it. In honor of their first production motorcycle with hydraulically damped telescopic forks, the FL was officially called the Hydra-Glide. This name would change twice in the history of the basic large-framed FL bikes, each time signalling an improvement in the bike's technology. In addition, the Glide ending would be used on other models, based on both and FL and FX formats.
In 1952, the Hydra-Glide's transmission standard hand-shift/foot-clutch was joined by the optional foot-shift/hand-clutch. Although the original format continued to be offered as an option until 1978. 1952 was also the last year of the 61 cu in (1,000 cc) EL, making the FL the last remaining large-frame model.
Although the 1903 founding is now the basis for "Anniversary Models", Harley-Davidson's 50th Golden Anniversary was celebrated in 1954 with special paints and badges on the front fender. (1904 was the first year of production.)
A more highly tuned engine with high-compression heads, higher-lift cams, and polished ports, was offered with the FLH version of 1955. The FLH designation has continued up to the present.
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.
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.
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.
A fork-mounted fairing became available on Electra Glides in 1969. This became unofficially known as the "batwing" fairing. Although the batwing fairing was an easily removable option on early Electra Glides, it was not removable on later machines, as the instruments were moved from the fuel tank into the fairing.
The FL frame was the basis for the 1971 FX Super Glide. The FX mated the FL frame with the forks of the XL Sportster, with buckhorn handlebars and a large fibreglass tailpiece completing the Super Glide specification.
The FL was given a front disc brake in 1972.
The three-speed plus reverse option was discontinued in 1977.
A 1977 Harley-Davidson Confederate Edition of the FLH Electra Glide that featured commemorative paint and tank and fender decals was produced. The unit production was in such low volume numbers - only 44 - as to make it one of the rarest of the company's motorcycles. 
An 80 cu in (1,300 cc) engine was made optional on the Electra Glide in 1978. However, the FL designation was not changed as a result. By 1981, the 80 cubic inch engine was the standard engine; the 74 cu in (1,210 cc) engine being discontinued.
The FLT Tour Glide was introduced in 1979 as a 1980 model. Sold alongside the existing FLH Electra Glide, the FLT had a larger frame with rubber engine mounts, a five-speed transmission, the 80 cu in (1,300 cc) engine, and a frame-mounted fairing. In order that the FLT frame, which was larger and heavier than the large and heavy FLH frame, would handle acceptably, the front forks were given radical steering geometry which had them mounted behind the steering head, with the frame behind the steering head being recessed to allow adequate steering lock.
The FLHT was introduced in 1983. This was an Electra Glide based on the FLT Tour Glide frame, but using the Electra Glide "batwing" fairing instead of the Tour Glide frame-mounted fairing.
Except for the base FLH, all 1984 FLs were equipped with the new rubber-mounted Evolution engine and a five-speed transmission.
All "Shovelhead" engines were discontinued by the 1985 model year. In that year, the four-speed solid-engine-mount FLH was modified to accept rubber mounting and the Evolution engine. The FLH was discontinued in 1986; all Touring models thereafter used the FLT/FLHT frame. Ironically, the FLT Tour Glide, which introduced the current Touring frame, was dropped from the lineup in 1996. A smaller version of the frame-mounted Tour fairing would return with the FLTR Road Glide in 1998.
An unfaired version of the FLH Electra Glide, known as the FLHS Electra Glide Sport, was available from 1979 to 1982. An unfaired FLHT Electra Glide reintroduced the FLHS Electra Glide Sport name in 1987. In 1994, the FLHS Electra Glide Sport was replaced by the FLHR Road King, which continues to the present day.
2009 Touring chassis
For the 2009 model year, Harley-Davidson redesigned the entire touring range. The changes included a new frame, new swingarm, a completely revised engine-mounting system, 17-inch front wheels for all models except the Road King Classic, a 6 US gallons (23 l; 5.0 imp gal) fuel tank, and a 2-1-2 exhaust. The changes result in greater load carrying capacity, better handling, a smoother engine, longer range and less exhaust heat transmitted to the rider and passenger.
Tri-Glide Ultra Classic
Also released in the FL Touring range for the 2009 model year was the FLHTCUTG Tri Glide Ultra Classic, the first three-wheeled Harley-Davidson since the Servi-Car was discontinued in 1973. This model features a unique frame and a 103 cid engine exclusive to the trike.
Harley-Davidson introduced the Softail chassis in 1984. The original Softails used the small FX telescopic forks, but the FLST Heritage Softail with large FL telescopic forks was introduced in 1986. The FLSTC Heritage Softail Classic, with large front forks and retro styling, was in production by 1988.
Other Softails with big forks followed, including the 1990 introduction of the FLSTF Fat Boy and the 1993-only FLSTN "Cow Glide". The base FLST Heritage Special was discontinued in 1991. The FLSTN was continued after 1993 without the bovine motif as the Nostalgia model until 1997, when it was replaced by the FLSTSC Springer Classic. The Springer Classic is also designated as an FL despite using Springer forks instead of the large FL telescopic forks.
The FLSTN designation returned in 2005 with the Softail Deluxe. The FLSTN Deluxe, which was introduced in 2005, also came with an option of carb or EFI models. The year 2005 was also the last in which a carb was offered on all HD big twin models.
FLD Dyna Switchback
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