| Component | Specification |
|---|---|
| Engine | Milwaukee-Eight 117 V-Twin |
| Oil Type | SYN3 Full Synthetic 20W-50 |
| Oil Capacity | 4.7 Liters (1.24 US gal) |
| Front Tire | 130/60B21 63H (36 psi) |
| Rear Tire | 180/55B18 80H (42 psi) |
| Spark Plugs | 6R10 (4 units) |
| Battery | OEM P/N 66000174 |
Engineering Highlight: The 21-Inch Factory Landmark
The 2018 CVO Road Glide (FLTRXSE) holds a unique place in Harley-Davidson history as the first factory touring model to be engineered specifically around a 21-inch “Knockout” front wheel. Unlike aftermarket conversions, Harley-Davidson engineers redesigned the front fork internals and triple trees to maintain the trail and handling characteristics necessary for high-speed touring stability, effectively bridging the gap between custom show-bike aesthetics and long-haul performance.
Powertrain Analysis: The Milwaukee-Eight 117
At the heart of the FLTRXSE/18 is the 1,923cc Milwaukee-Eight 117 engine, the largest displacement powerplant offered by the factory at the time. This engine utilizes a four-plug ignition system (two per cylinder) to ensure complete combustion across the large bore. Maintenance of these 6R10 spark plugs is critical; a gap of 0.76–0.86 mm must be strictly maintained to prevent high-load misfires. For lubrication, MotoSpecsLab recommends the factory-specified SYN3 Full Synthetic 20W-50, with a total service capacity of 4.7 Liters.
Chassis & Maintenance Protocol
The 21-inch front and 18-inch rear wheel configuration requires precise pneumatic management. Under-inflation on the 21-inch front (130/60B21) can lead to heavy steering and increased cupping. Always verify the 2.5 bar (36 psi) front and 2.9 bar (42 psi) rear pressures when the tires are cold. Electrical integrity is managed by the 66000174 high-output battery, which is essential to provide the cranking amps required for the high-compression 117 cubic inch cylinders.
MotoSpecsLab Verdict
The 2018 FLTRXSE remains a pinnacle of the CVO line. Its combination of the first factory-fitted 21-inch wheel and the raw torque of the 117 engine makes it a collector’s favorite. Adhering to the specific fluid and spark plug tolerances outlined in this guide is paramount for preserving the mechanical longevity of this high-performance touring machine.