| Specification | Detail |
|---|---|
| Production Years | 2004–2007 |
| Engine Oil | SAE 20W-50 (HD 360 or SYN3) |
| Oil Capacity | 3.3 L – 3.8 L |
| Tires (Front/Rear) | MT90B16 72H / MU85B16 77H |
| Tire Pressure (F/R) | F: 36 psi / R: 36-40 psi |
| Battery Model | 66010-97C |
| Spark Plug | HD 6R12 |
Historical Engineering Highlight: The Harley-Davidson FLHRS Road King Custom represented a significant pivot in the Touring family’s design philosophy. Introduced in 2004, it was the first factory “slammed” bagger, featuring a lowered rear suspension and a clean, streamlined profile that removed the traditional windshield and passing lamps. This model effectively bridged the gap between the utilitarian touring line and the custom cruiser aesthetic, predating the modern “Special” and “ST” trends by nearly a decade.
Technical Overview: The Twin Cam Evolution
The FLHRS utilized the Twin Cam 88 engine (and later the Twin Cam 96 in 2007), integrated into the classic rubber-mounted touring frame. This configuration was designed to isolate the rider from high-frequency vibrations while maintaining the structural rigidity required for heavy-duty touring. The “Custom” designation brought unique 1-inch thick stainless steel beach bars and hidden hardware, requiring specific cable routing and internal wiring that differs from the standard FLHR.
Maintenance Guide & Fluid Specifications
Proper lubrication is critical for the longevity of the air-cooled V-Twin. MotoSpecsLab recommends SAE 20W-50 oil, specifically Harley-Davidson 360 or the synthetic SYN3 variant. The capacity fluctuates between 3.3 L and 3.8 L depending on whether the oil cooler is drained. Always check the level with the bike on its jiffy stand (lean position) as per the service manual for this specific era.
Tires and Chassis Stability
The FLHRS relies on a specific tire combination to manage its 700lb+ curb weight. The front MT90B16 72H and rear MU85B16 77H must be maintained at precise pressures to avoid “high-speed weave.” We recommend 36 psi (2.48 bar) for the front and 36 psi for the rear for solo riding, increasing to 40 psi (2.76 bar) when carrying a passenger or heavy luggage.
Electrical System
The charging system on the 2004-2007 models is robust but sensitive to battery health. The 66010-97C battery provides the necessary cold cranking amps (CCA) to turn over the high-compression cylinders. Ensure the terminals are torqued correctly, as loose connections on this model frequently lead to ECM error codes or stator failure.
FAQ
Q: Can I use 10W-40 oil in the FLHRS?
A: Only in emergency cold-weather situations. For standard operation, 20W-50 is required to maintain oil pressure and provide adequate film strength at high operating temperatures.
Q: What is the spark plug gap for the HD 6R12?
A: The gap should be set between 0.038 and 0.043 inches (0.97 – 1.09 mm).