The Harley-Davidson Fat Boy has never been a subtle motorcycle. With its massive stance, solid wheels and unmistakable Softail silhouette, it has always been one of Milwaukee’s most recognizable machines.
But this Harley-Davidson Fat Boy FLFBS 114 “Bad Boy”, modified by Killer Custom, pushes that attitude considerably further. The goal is not to reinvent the Fat Boy, but to sharpen its proportions, lower its stance and give the big Softail a more aggressive custom-bike presence.
The result is a muscular, blacked-out Fat Boy with a distinctly low-slung profile and a collection of carefully chosen aftermarket parts.
Lower, Longer, Meaner
The standard Fat Boy already has plenty of visual weight, but Killer Custom’s modifications make the FLFBS 114 look even more planted.
A Harley-Davidson M8 Softail rear lowering kit works together with a Progressive Suspension front fork lowering kit to bring the motorcycle closer to the ground at both ends. This changes more than the ride height: it gives the Fat Boy a tighter, more aggressive silhouette.
The custom stance is complemented by the Avenger rear fender kit, designed for the Fat Boy, Breakout and FXDR. The matching Avenger seat helps create a clean transition between the rider and the shortened rear section.
At the front, the “Fatty” custom front fender adds another layer of visual bulk, reinforcing the Fat Boy’s characteristic wide-shouldered appearance.
A Blacked-Out Softail
The “Bad Boy” name makes sense when you look at the details. Killer Custom has used a broad selection of black components to eliminate visual clutter and give the motorcycle a darker, more cohesive appearance.
The package includes black front and rear brake rotors, axle covers, fork end caps and a black front wheel spacer kit. Even smaller details, such as the M8 Softail swingarm axle cover set and rear axle cover set, contribute to the finished look.
The result is a Fat Boy that feels less like a factory cruiser and more like a purpose-built custom.
Avenger Rear End
One of the most important changes is the rear section.
The Killer Custom “Avenger” rear fender kit dramatically changes the visual character of the FLFBS 114. Combined with the dedicated Avenger seat, the conversion creates a compact rear end that works particularly well with the lowered suspension.
A Softail M8 back frame spoiler further cleans up the area around the rear frame, while the dedicated licence plate bracket and licence plate holder keep the tail section visually tidy.
The result is a rear profile that looks considerably more compact than the standard Fat Boy.
1¼-Inch Fat Drag Bars
The cockpit is another major part of the transformation.
Killer Custom fitted its “Avenger” 1¼-inch Fat Drag handlebar, paired with a 3-inch riser set for 1¼-inch handlebars. The combination gives the Fat Boy a broader, tougher front-end stance without losing the unmistakable cruiser ergonomics.
The handlebar setup also incorporates a dedicated instrument cluster and speedometer relocation housing, designed for 2018–2023 M8 Softail models using 1¼-inch handlebars.
For contact points, the bike uses Avon Air Cushioned Fly-By-Wire grips, adding a little extra comfort to an otherwise uncompromising cockpit.
The finishing touch comes from Booster mirrors, which keep the handlebar area compact and contemporary.
A Cleaner Front End
The original Fat Boy front end has plenty of presence, but the “Bad Boy” treatment gives it a more custom appearance.
A 7-inch DOT- and EC-marked headlight with parking light provides the central focal point, while the Turbo LED turn signals, also DOT and E-approved, keep the indicators compact.
The front brake setup is upgraded visually with a black 300 mm “Dislike” brake rotor, while the corresponding 292 mm rear “Dislike” rotor continues the blacked-out theme.
The M8 Softail fork end caps and front axle covers complete the lower part of the front end, making the whole assembly feel more deliberate and finished.
Harley-Davidson Fat Boy FLFBS 114 “Bad Boy” by Killer Custom: Specifications
Base motorcycle: Harley-Davidson Fat Boy FLFBS 114 Platform: M8 Softail Custom builder: Killer Custom Style: Custom cruiser / blacked-out Softail Key conversion: Avenger rear fender and seat Suspension: Rear lowering kit + Progressive front fork lowering kit Handlebar: Avenger 1¼-inch Fat Drag Risers: 3-inch, for 1¼-inch handlebars Headlight: 7-inch DOT/EC approved unit Turn signals: Turbo LED, DOT/E-approved Front brake rotor: Dislike, black, 300 mm Rear brake rotor: Dislike, black, 292 mm
Killer Custom Parts Used
H-D Softail 3-inch Riser Set for 1¼-inch Handlebar
H-D Rear Lowering Kit All Softail M8
H-D Licence Plate Holder with Lightning, All Countries
H-D M8 Softail Back Frame Spoiler
H-D Custom Front Fender “Fatty” Softail Fatboy FLFBS
H-D Softail “Turbo” LED Turn Signals, DOT and E-Approved
