Understanding FLFB on Harley-Davidson Bikes: What It Signifies

Decoding the Harley-Davidson FLFB: A Deep dive into the Fat Boy‘s Designation

Published: October 8, 2025 | Updated: October 8, 2025

The Harley-Davidson Fat Boy, a motorcycle synonymous with power and iconic design, carries a model code – FLFB – that reveals a rich history of engineering and stylistic evolution. Understanding this code unlocks a deeper appreciation for this American classic.

The origins of ‘FL’: A Legacy of Big Twin Engines

Harley-Davidson’s use of the ‘FL’ designation dates back to 1941, initially signifying the Big Twin engine family. This lineage continues today with the modern Milwaukee-Eight V-Twin engines, a testament to enduring design principles. The ‘F’ component historically indicated models equipped with a 16-inch front wheel, a feature that established the wide-front aesthetic. Conversely, ‘FXST’ models typically featured taller, thinner 19 or 21-inch front wheels.

In 1949, Harley-Davidson further cemented its identity by introducing the Hydra glide hydraulic fork, instrumental in defining the brand’s signature front-end style for decades to come.

From ‘FLSTF’ to ‘FLFB’: A Transformative Shift

The Fat Boy’s designation wasn’t always FLFB. A significant turning point arrived in 2018, marking Harley-Davidson’s most significant engineering overhaul in 115 years. This pivotal update led to the transition from the FLSTF code to FLFB. Prior to 2018, the “ST” in FLSTF represented “softail,” denoting the bike’s concealed shock frame architecture.

Though, the 2018 redesign introduced a radically new chassis-stiffer yet lighter-replacing the customary dual-shock system with a single, hidden monoshock positioned beneath the seat. This innovation dramatically improved handling and overall performance. the reconfiguration also expanded lean angles, surpassing those achieved by previous Softail or Dyna models.

Designation	Meaning	Era
FL	Big Twin Engine Family	1941 – present
ST	Softail (Hidden Shock Frame)	Prior to 2018
FB	Fat Boy Model	1990 – Present
FLFB	Fat Boy with Modern Softail Frame	2018 – Present

The Fat Boy’s Design and Evolution

The Fat Boy, conceived by Willie G. Davidson and Louie Netz and unveiled in 1990, quickly became iconic for its robust, wide stance and distinctive solid-cast aluminum disc wheels. Its vrey name – “Fat Boy” – aptly captures its visually imposing, broad profile when viewed head-on.

Did you Know? the FLFB designation now prioritizes the core elements-the Big Twin engine and classic styling-with the understanding that the advanced frame technology is standard across modern Harley-Davidson cruisers.

Modern Performance and Technology

Contemporary FLFB models are high-performance machines blending classic aesthetics with cutting-edge technology. The 2025 Harley-Davidson Fat boy is equipped with the Milwaukee-Eight 117 Custom engine, delivering 126 lb-ft of torque at 3,000 rpm from its 1,923cc powerhouse. The FLFBS variant features the 114-CI engine.Prior to 2025, the base FLFB models had a 107-CI engine.

Beyond brute power, the latest FLFB incorporates advanced safety features, including Anti-lock Braking System (ABS), Cornering Enhanced Traction Control, and Tire Pressure Monitoring. The 49mm front forks utilize dual-bending valve technology for refined damping, while the hidden rear monoshock offers a 43mm stroke with adjustable hydraulic preload.Despite weighing 694 pounds, the redesigned chassis enables an impressive 25.6-degree lean angle, showcasing the cruiser’s modern agility.

Pro tip: Regularly check tire pressure and ensure all safety systems are functioning optimally to maximize the riding experience and safety of your harley-Davidson Fat Boy.

The Future of the Fat Boy

Harley-Davidson Continues to Innovate. As of late 2024, Harley-Davidson is investing heavily in electric motorcycle technology, with plans to expand its LiveWire all-electric lineup. While the future of internal combustion engines remains a topic of discussion, the Fat Boy’s enduring appeal suggests it will continue to evolve and captivate riders for generations to come.

Frequently Asked questions about the Harley-Davidson FLFB

1. What does FLFB stand for on a Harley-Davidson? FLFB signifies a Fat Boy model with a Big Twin (F) engine and classic styling (L), built on the modern Softail platform.
2. What was the code for the Fat Boy before 2018? Before 2018, the Fat Boy’s code was FLSTF, where “ST” denoted the Softail frame design.
3. What is the milwaukee-Eight 117 engine? It’s a 1,923cc V-Twin engine producing 126 lb-ft of torque, now standard on the 2025 Harley-Davidson Fat Boy.
4. What improvements were made in the 2018 Fat Boy redesign? The 2018 redesign included a new chassis with a hidden monoshock rear suspension, improved handling, and increased lean angles.
5. What safety features are included in modern FLFB models? Modern FLFB models include ABS, Cornering Enhanced Traction Control, and Tire Pressure Monitoring.
6. What is the significance of the ‘S’ suffix in FLFBS? The “S” indicates that the model was originally equipped with HD’s 114-CI engine.
7. How does the FLFB compare to other Harley-Davidson models? The FLFB stands out for its muscular appearance, wide tires, and classic cruiser styling, differing from sportier models like the FXST with thinner wheels.

What are your thoughts on the evolution of the Harley-Davidson Fat Boy? Share your experiences in the comments below!

what does teh ‘F’ designation in the FLFB model code signify regarding the motorcycle’s chassis?

Decoding the Harley-Davidson FLFB Model

The Harley-Davidson FLFB, often referred to as the Fat Boy 117, is a highly sought-after model within the Softail family. But what exactly does “FLFB” signify? It’s more than just a random string of letters; it’s a code that reveals key characteristics of the motorcycle. Understanding this code unlocks a deeper recognition for Harley-Davidson’s meticulous naming conventions adn the bike’s specific features. For enthusiasts looking to buy a used Harley or simply understand the lineage of their ride,deciphering these codes is crucial.

The Harley-Davidson Model Code Breakdown

Harley-Davidson uses a standardized system to designate its motorcycle models. Each letter in the code represents a specific attribute. Let’s break down FLFB:

* F: Represents the motorcycle’s chassis type – in this case, a Frame designed for touring and larger builds.

* L: Indicates the engine type – a Large displacement engine.

* F: Again, signifies the frame type, reinforcing its suitability for larger engines and comfortable riding.

* B: Denotes the model within the series – the Batwing fairing or, in the case of the FLFB, the Fat Boy style.

Thus, FLFB essentially translates to a large-engine, robust-framed motorcycle in the Fat Boy style.This system applies across many Harley-Davidson models, allowing riders to quickly identify core features. understanding this code is helpful when researching different Harley models like the FLH, FLHT, or even older models like the FL series.

FLFB: A Deep Dive into the Fat Boy 117

The FLFB specifically refers to the Fat Boy 117, introduced in 2018 and continuing as a popular model. The “117” designates the engine displacement – a Milwaukee-Eight 117 cubic inch (1923cc) V-Twin engine. This engine is known for its substantial torque and smooth power delivery, making it ideal for both cruising and spirited riding.

Here’s a closer look at key features of the FLFB:

* Engine: Milwaukee-Eight 117 V-Twin

* Transmission: 6-Speed Cruise Drive

* Brakes: ABS Standard, Disc Brakes

* Suspension: Standard Softail Suspension

* Wheels: Distinctive Fat Boy Solid disc Cast Aluminum Wheels

* Styling: Classic Fat Boy aesthetics – wide tires, low-slung profile, and abundant chrome.

Evolution of the Fat Boy: From FLSTF to FLFB

The Fat Boy has a rich history, evolving over the years. Originally introduced as the FLSTF in 1989,it quickly became an icon.

Here’s a brief timeline:

1. FLSTF (1989-2017): The original Fat Boy, featuring a 80 cubic inch (1340cc) Evolution engine, then upgraded to a Twin Cam 95, 103, and finally a 107.
2. FLFB (2018-Present): The transition to the Softail chassis and the powerful Milwaukee-Eight 117 engine marked a significant upgrade.This change brought improved handling, reduced weight, and increased performance.
3. FLFB 117 (2023-Present): Continued refinements to the Milwaukee-Eight 117 engine and styling updates.

This evolution demonstrates Harley-Davidson’s commitment to continually improving its iconic models while retaining their core character.Comparing the FLSTF to the FLFB highlights the advancements in engine technology and chassis design.

Benefits of Owning an FLFB (Fat Boy 117)

Choosing an FLFB offers several advantages for riders:

* Powerful Engine: The Milwaukee-Eight 117 delivers impressive torque for confident passing and effortless cruising.

* Comfortable Ride: The Softail chassis provides a smooth and controlled ride, even on rough roads.

* Iconic Styling: The Fat Boy’s distinctive look turns heads wherever you go.

* Customization Potential: The FLFB is a popular platform for customization, allowing riders to personalize their bike to their exact preferences. Numerous aftermarket parts are available for the Fat Boy, including exhausts, handlebars, and seats.

* Resale Value: Harley-Davidson motorcycles,particularly iconic models like the Fat Boy,generally hold their value well.

Practical Tips for FLFB Owners & Prospective Buyers

* Regular Maintenance: Follow the Harley-Davidson recommended maintenance schedule to ensure optimal performance and longevity. This includes oil changes, filter replacements, and valve adjustments.

* Tire Pressure: Maintain proper tire pressure for optimal handling and tire wear. The Fat Boy’s wide tires require specific pressure settings.

* Storage: If storing the FLFB for extended periods, use a fuel stabilizer and battery tender to prevent fuel degradation and battery discharge.

* Used Bike Inspection: When purchasing a used FLFB, thoroughly inspect the bike for signs of damage or wear. Pay close attention to the engine, transmission, and suspension.A pre-purchase