The first letter of the model designator reveals the engine series:
G - Servicar three wheeler, 1932 to 1972
E - Overhead valve 61 cubic inch "big twin" (Engine/trans separated)
F - Overhead valve 74 or 80 cubic inch "big twin"
K - Side valve 45 and 55 cubic inch sports bike that replaced the WL in
1953 and was replaced by the sportster in 1957. It had many design
features that were carried over to the Sportster.
U - Side valve 74 or 80 cubic inch "big twin"
V - Side valve 74 cubic inch made prior to 1936
W - Side valve 45 cubic inch made 1934 to 1952
X - Sports and special construction. Applied to 1918-1922 opposed twin
Sport, 1944 military opposed twin, and 1957 to present Sportster.
There were others, such as the J series (a very nice looking bike that was about
the hottest thing around in the 20's) but you're not likely to see them in daily use
L - high compression. Omitted on low compression early models, and not
indicative of compression on current models.
Model descriptions, eg WG - Wide Glide. Some generalizations:
A - Military (Army) version (except GA, Servicar without tow bar)
B - Battery start (early models), Belt drive (some later models).
C - Classic, Competition, Custom, various others meanings.
D - Dyna, the newest frame and engine mount design.
E - Electric start
F - Foot shift (when the standard was hand-shift)
H - varied between High performance and Heavy duty. The early FLH for
example produced 5 more HP than the FL and was used primarily for
touring and sidecar applications.
LR- Low Rider (though many Low Riders don't include LR in the model ID)
P - Police version
R - Rubber mounted engine (some models) racing version (other models) e.g.
the FXR is a lowrider with rubber mounted engine, WLR is the flat
track racer that was very hard to beat in the 30's, 40's, and 50's.
ST- Soft Tail
S - (without following T) Sports version eg FLHS is an FLHT without the
T - Touring
WG - Wide Glide
Sportsters: Models beginning with X are Sportsters. These descend from the K series, 1952-56. The XL series started in 1957. They are "unit construction" (engine & transmission share a common case). X was in the normal series, following the U and V used for flathead Big Twins. L stood for high compression (7.5:1 in 1957). In 1958 came the XLH with H meaning Higher-power or High-compression (9:1) or Hot. Also in 1958 was the XLCH: The C in XLCH was intended to mean "Competition", but the late Hal Robinson used to claim the CH on his bike stood for "Charley Horse" because it was highly modified and had enough initial ignition advance to kick back rather severely.
The Sportster engines were originally actually 53.9ci. (883cc) but were designated as 55ci. This was upgraded (in 1970?) to 61ci (1000cc), redesigned in '73 but still 61" and stayed relatively unchanged untill the 74" evo version. The 883 and 61" were both produced the first year of the 883. Options for Sportsters abounded but these same letters have been used since 1958 in various combinations, plus the XLCR (a "cafe racer" style, with bikini fairing) and the XLT (Touring, with bigger tank, thicker seat, and hard bags straight off the FLHS), both produced 1977-1978 only.
Big Twins: Models beginning with F are Big Twins. These all descend from the 61E in 1936. Knuckleheads 1936-47, Panheads 1948-65, Shovelheads 1966-84/85, and Evolutions 1984/5-present. The Evolution (block head) was introduced in '84 on the Soft Tail and Tourglide Ultra, with the last Shovel built in mid '85. Until 1978, these were mostly 74's (~1200cc). In 1978, the 80ci (~1340cc) was introduced.
In 1971 was the first FX model, with an F engine and assorted Sportster (X) parts, notably forks - these were initially Super Glides. In 1974, FXE was Electric start. In calendar 1977 came the FXS Low Rider, with shortened shocks and scooped seating position. Also in 1978, the FX Super Glides got belt final drive. 1979 brought 80ci Shovelheads and the FXEF Super Glide Fat Bob (not Boy), for bobbed fenders and fat tank. In 1980, FXWG (Wide Glide) andthe FXB Sturgis with belt drive (primary and secondary).
1984 brought the Softtail FXST, with the look of an old hardtail but some suspension for comfort.
In 1991 came the FXD Dyna Glide series, starting with another Sturgis model. This brought many frame and engine mounting changes, a relocated oil tank and moved crossover pipe.
Touring: In 1980, the FLT designation was introduced for the Tour Glide. This model introduced the vibration-isolation mounted engine (rubberglide) and also a slightly different frame from other FLs and a fixed fairing. FXR (originally called Super Glide II) arrived in late 1981. The R had rubbermount engine and 5-speed tranny, as opposed to rigid-mount and 4-speed in other models. FXRS maybe meant Sport, with cast wheels and a small sissy bar. The Sport Glide FXRT (Touring) arrived in 1983, with the fixed fairing and air adjustable anti-dive forks.
The only really reliable letters now are at the beginning of the model: X=Sportster, F=Big Twin, FL=Big Twin with big forks, FX=Big Twin with Sportster-style (smaller) forks, FXST=Softtail, FXD=Dyna Glide. At times, different models have even shared the same letter-designation; witness the FLHTC Electra Glide Classic/Ultra Classic Electra Glide in 1993 models.
THE BASICS FROM THE PAST
E the basic version of the big twin
EL the E with more power
F basic, enlarget from 61 to 74 big twin
FL the F with more power
FLH still more power built as pan shovel and evo
K sidevalve middleweight circa '52
KK tuned version of K
KH the K stroked from 45 to 54
KHK tuned version of the KH
XL basic sportster
XLC stripped Calif. model
XLH higher performance
XL '58 XLCH high performance XL (w/ kicker)
FX original Super Glide form F and X parts
FXE original Super Glide form F and X parts with electric start
XLR hot stripped XL
XR-750 iron and alloy 750 racing only
XLCR road race style XLH
XR-1000 alloy XR top end and dual carbs on the XLH cases
XLT XLH with larger tank
XLX stripped XLH
XLS fancy XLH
XLH most current Sporty 883 and 1200
XL '96 1200C (Custom) and 1200S (sport) Sportsters
FXS the original Low Rider
FXEF the first Fat Bob F=Fat
FXWG FL forks w/o covers and 21" front wheel aka Wide Glide
FXB original sturgis B=belt drive
FXR Super Glide II original rubber mount
FXRP P=police equip.
FXRS FXR with cast wheels, extra trim aka Low Glide
FXSB Low Rider with belts
FXRDG FXRS with solid disk rear wheel
FXRT R=Rubber mount T=touring aka Sport Glide
FXRC Low Glide Custom w/ wire wheels
FXRT/P FXRT P=police equip.
FXRD FXRT w/ trunk aka Grand Touring
FXRS-SP Low Rider Sport edition
FXRS-CONV Low Rider w/ detachable windshield and bags
FXDB Dyna Glide, latest chassis ('91 Sturgis) two-point engine mounting
FXDC FXDB with goodies C=Custom (NO 21" front wheel)
FXD Dyna Super Glide
FXDS-CONV Dyna Glide w/ detachable windshield and bags
FXDWG Dyna Wide Glide
FXDL Dyna Low Rider
FXST original Softail
FXSTC Softail Custom
FXSTS Springer Softail
FXSTSB Springer Softail Badboy
FLST Softail with 16" front wheel
FLSTC Heritage Softail
FLSTN Fatboy/Heritage with different goodies(N for Nostalgia)
FLT Tour Glide, has frame-mounted fairing
FLTC FLT with extras (C for Classic)
FLTC U FLT with even more extras (U for Ultra)
FLTC U I FLTC U with fuel injection (I for Injection)
FLHT Electra Glide, has fork-mounted fairing
FLHS FLT with windshield and less goodies S = Sport
FLHTC FLHT with extras (C for Classic)
FLHTC U FLHT with even more extras (U for Ultra)
FLHTC U I FLTC U with fuel injection (I for Injection)
FLHR Road King, factory customized FLHT