| Component | Specification |
|---|---|
| Production Years | 2008–2017 |
| Engine Oil | SAE 20W-50 (H-D 360 or Syn3) / 2.8 Liters |
| Tires (Front) | 130/90B16 67H |
| Tires (Rear) | 180/70B16 77H |
| Battery | 65989-97C |
| Spark Plug | HD-6R12 (Gap: 0.97–1.09 mm) |
The Engineering Legacy: A Dyna Built for Muscle
The Harley-Davidson FXDF Fat Bob, introduced in late 2007 for the 2008 model year, represents a significant engineering departure from the traditional Dyna lineage. While most Dynas favored the ‘skinny’ 19-inch or 21-inch front wheel, the Fat Bob was the first production Harley to utilize a massive 130mm front tire paired with a distinctive dual-headlight assembly. This ‘Tommy Gun’ aesthetic wasn’t just for show; the dual-disc front brakes and beefy 49mm forks were designed to provide superior front-end stability and stopping power compared to its stablemates.
Technical Review: Performance and Handling
At the heart of the FXDF/13 is the Twin Cam engine (96 or 103 cubic inches depending on the specific year). The rubber-mounted engine design allows for significant vibration at idle, which smooths out remarkably once under load. From a technical perspective, the Dyna chassis provides a more ‘connected’ feel than the Softail counterparts, thanks to the external twin rear shocks. The Fat Bob’s geometry, featuring a 29-degree rake, offers a balance between straight-line cruising stability and surprisingly agile cornering for a bike of its mass.
Maintenance Guide: Keeping the Beast Healthy
Lubrication System
For optimal thermal stability, MotoSpecsLab recommends SAE 20W-50 (Harley-Davidson 360 or Syn3). The system requires 2.8 liters. Given the air-cooled nature of the Twin Cam, regular oil changes every 5,000 miles are critical to prevent oil breakdown and protect the valvetrain.
Tire Pressure & Safety
Handling on the Fat Bob is highly sensitive to tire pressure due to the wide contact patches.
- Front: 2.5 bar (36 psi)
- Rear: 2.8 bar (40 psi) for solo riding, increasing to 2.9 bar (42 psi) when carrying a passenger or heavy luggage.
Electrical & Ignition
The Fat Bob utilizes the 65989-97C battery, which must be maintained with a tender during off-seasons to prevent the security system from draining the charge. For ignition, use HD-6R12 plugs. Ensure the gap is precisely set between 0.97 and 1.09 mm to ensure consistent combustion and prevent misfires under high-torque demands.
Editor’s Verdict
The FXDF/13 remains a high-water mark for the Dyna line. It combines an aggressive stance with genuine mechanical capability. For owners, adhering to the strict fluid and tire specifications outlined above is not just about longevity—it is about preserving the unique handling characteristics that define the Fat Bob experience.