| Parameter | Specification |
|---|---|
| Engine | Milwaukee-Eight™ 117 V-Twin |
| Engine Oil | SAE 20W-50 (4.3 Liters) |
| Front Tire | 110/90B19 62H (36 psi / 2.5 bar) |
| Rear Tire | 180/70B16 77H (42 psi / 2.9 bar) |
| Battery Part No. | 66000207 |
| Spark Plug | H-D 10R12A |
Engineering Highlight: The 2025 FXLRST represents the pinnacle of the Softail chassis evolution. A little-known engineering detail is that the frame-mounted fairing was developed using Computational Fluid Dynamics (CFD) to replicate the iconic 1983 FXRT Sport Glide silhouette while significantly reducing helmet buffeting at highway speeds—a feat achieved by integrating triple splitstream vents that balance air pressure behind the fairing.
Technical Review: The 117 CUI Powerhouse
As the Editor-in-Chief of MotoSpecsLab, I find the 2025 Low Rider ST to be the most balanced ‘Tall Bike’ in Harley-Davidson’s current lineup. The Milwaukee-Eight 117 engine, once exclusive to CVO models, is now the heartbeat of this machine. With a high-performance camshaft and a Heavy Breather intake, the volumetric efficiency of this V-Twin is optimized for mid-range torque, peaking at 125 ft-lb.
The Softail chassis utilizes a hidden mono-shock rear suspension with 56mm of stroke, providing a taller ride height than the standard Low Rider S. This increase in lean angle (31.3 degrees) transforms the ST from a mere cruiser into a legitimate canyon carver.
Maintenance Guide & Vital Specs
Lubrication System
The 117 CUI engine requires 4.3 liters of SAE 20W-50 oil. For high-performance riding or extreme heat, synthetic fluids like Screamin’ Eagle SYN3 are recommended to maintain viscosity and protect the hydraulic lifters. Always check the oil level when the engine is at operating temperature on the jiffy stand.
Tires and Traction
The FXLRST is sensitive to tire pressure. To maintain the intended flickability of the 19-inch front wheel and the stability of the 16-inch rear, adhere strictly to the 36 psi (Front) and 42 psi (Rear) cold pressure settings. The Michelin Scorcher “31” tires are the factory standard, designed specifically for this load rating.
Electrical & Ignition
The electrical system is powered by the 66000207 battery. Given the high compression of the 117 engine, ensuring a high Cold Cranking Amperage (CCA) is vital. For ignition, the H-D 10R12A spark plugs should be inspected every 5,000 miles for carbon fouling or electrode wear, which can occur more rapidly in high-output V-Twins.
Frequently Asked Questions (FAQ)
A: The 117 offers a 3% increase in displacement but a more significant 10% increase in torque due to the high-lift camshaft and improved air intake, providing better roll-on acceleration in 6th gear.
A: It is not recommended. The Milwaukee-Eight engine is designed for the thermal stability of 20W-50. Using thinner oils may lead to increased mechanical noise and accelerated wear in the valve train.