| Component | Specification |
|---|---|
| Engine | Milwaukee-Eight 117 V-Twin |
| Oil Type | 20W50 HD 360 or Syn3 (3.8 L) |
| Front Tire | 130/60B19 61H (36 psi) |
| Rear Tire | 180/55B18 80H (42 psi) |
| Spark Plug | 6R10 |
| Battery | 66000643 |
The Harley-Davidson Road Glide’s iconic “Sharknose” fairing represents a pivotal moment in motorcycle aerodynamics. First introduced in 1980 as the FLT Tour Glide, the design was revolutionary for being frame-mounted rather than fork-mounted. This engineering decision decoupled the fairing’s weight and wind resistance from the steering assembly, significantly reducing handlebar inertia and enhancing high-speed stability—a legacy that the 2024-2025 FLTRX/25 continues with refined wind-tunnel-tested contours.
The Milwaukee-Eight 117 Powertrain
At the heart of the FLTRX/25 is the 117 cubic inch (1,923cc) Milwaukee-Eight engine. This iteration features precision oil/air cooling and, in recent configurations, liquid-cooled cylinder heads to manage the thermal loads generated by its high compression ratio. For the MotoSpecsLab technician, maintaining this powertrain requires strict adherence to fluid specifications. The system requires 3.8 liters of 20W50 lubricant; while HD 360 mineral oil is acceptable, MotoSpecsLab recommends the full-synthetic Syn3 for superior shear stability in high-temperature touring environments.
Chassis and Contact Patch Integrity
The Road Glide 117 utilizes a heavy-duty touring chassis designed for stability under load. Tire maintenance is critical for the Skyline OS infotainment-linked traction control systems to function correctly. The front 130/60B19 and rear 180/55B18 tires must be maintained at precisely 36 psi (2.48 bar) and 42 psi (2.90 bar) respectively. Deviations in pressure can adversely affect the lean-angle sensitive ABS and linked braking systems.
Electrical and Ignition Systems
The 2024-2025 models utilize the high-output 66000643 battery to support the extensive electronics suite. Ignition is handled by 6R10 spark plugs, which should be inspected for gap erosion during scheduled intervals. The move toward more integrated digital architecture means that battery health is no longer just about starting power, but about maintaining the voltage stability required for the bike’s Controller Area Network (CAN bus).
Maintenance FAQ
Which oil should I use for the 117 CUI engine?
Harley-Davidson 360 or Syn3 20W50 is the standard. Total capacity is 3.8 Liters.
What are the correct spark plugs for the FLTRX/25?
The engine requires 6R10 spark plugs, specifically designed for the Milwaukee-Eight’s combustion chamber geometry.
What is the recommended tire pressure for two-up riding?
Even when loaded, Harley-Davidson recommends maintaining 36 psi in the front and 42 psi in the rear to ensure carcass integrity and heat dissipation.