| Component | Specification |
|---|---|
| Production Years | 2012 – 2017 |
| Engine Oil | SAE 20W-50 (2.8 L) |
| Tires (F/R) | F: MT90B16 72H / R: MU85B16 77H |
| Tire Pressure | F: 36 psi / R: 40 psi |
| Battery Model | 65989-97E |
| Spark Plugs | H-D 6R12 |
Engineering Heritage: The Post-War ‘Bobber’ Aesthetic
The Harley-Davidson Softail Slim (FLS) represents a unique engineering milestone for the Motor Company. Unlike other Softails that leaned into chrome and excess, the Slim was intentionally ‘narrowed’ to evoke the post-WWII era of home-built bobbers. A distinct engineering highlight is the inclusion of the ‘Hollywood’ handlebars, characterized by their wide profile and cross-brace, a direct homage to the customized bikes of the late 1940s. This model successfully integrated the hidden rear suspension of the Softail chassis with a minimalist profile, stripped of all non-essential components to maximize the power-to-weight ratio of the Twin Cam 103B counterbalanced engine.
Technical Performance & Powertrain
Between 2012 and 2017, the FLS was powered by the Twin Cam 103B™ engine. Because the engine is rigid-mounted to the frame, Harley-Davidson utilized internal counter-balancers to mitigate vibration, providing a smoother ride than the rubber-mounted Touring counterparts while maintaining the ‘connected’ feel enthusiasts crave. The 1690cc displacement delivers peak torque at low RPMs, making it an ideal platform for urban cruising and light touring.
Maintenance Guide & Technical Data
Lubrication System
For optimal thermal stability in air-cooled V-Twin environments, MotoSpecsLab recommends SAE 20W-50 synthetic or mineral oil. The system requires 2.8 Liters for a standard oil and filter change. Periodic inspection of the primary chaincase and transmission fluids is also critical, typically every 5,000 to 10,000 miles depending on riding conditions.
Chassis and Contact Patch
The FLS utilizes a specific tire combination to maintain its vintage ‘fat’ look without sacrificing modern handling. The front MT90B16 and rear MU85B16 must be maintained at 36 psi (Front) and 40 psi (Rear) respectively. Under-inflation on this specific chassis can lead to ‘wobble’ in high-speed cornering due to the narrow rear profile of the Slim’s design.
Electrical & Ignition
The electrical system relies on the 65989-97E battery. Given the high-compression nature of the Twin Cam 103, ensuring a high Cold Cranking Amp (CCA) rating is vital for cold starts. Ignition is handled by H-D 6R12 spark plugs; these should be gapped to factory specifications to prevent misfires under heavy load.
MotoSpecsLab Verdict
The Softail Slim FLS remains a favorite for purists. Its low seat height and balanced center of gravity make it accessible, while the technical simplicity of the 2012-2017 era (before the transition to the Milwaukee-Eight engine) makes it a prime candidate for home mechanics and customizers alike.