| Specification | Data |
|---|---|
| Production Years | 1999–2006 |
| Engine Type | Twin Cam 88 (V-Twin) |
| Oil Specification | HD 360 20W50 / SYN3 20W50 (3.8 L) |
| Front Tire | MT90B16 72H |
| Rear Tire | MT90B16 74H / MU85B16 77H |
| Battery | 66010-97C |
| Spark Plug | HD 6R12 |
Engineering Highlight: The Birth of the Twin Cam
The transition from the Evolution engine to the Twin Cam 88 in 1999 marked a pivotal moment in Harley-Davidson’s engineering history. While the Evo was beloved for its simplicity, the FLHTCUI required a more robust thermal management system and increased torque to handle the substantial weight of the Ultra Classic’s touring amenities. The Twin Cam 88 introduced a dual-cam design and a significantly larger cooling fin surface area, increasing the oil capacity and structural rigidity of the engine-to-transmission interface.
Technical Review: Performance and Handling
The FLHTCUI represents the pinnacle of the ‘Batwing’ touring era. Utilizing the Magneti Marelli (1999-2001) and later the Delphi (2002-2006) Electronic Sequential Port Fuel Injection (ESPFI), the bike offered improved cold-start reliability and throttle response over its carbureted predecessors. The chassis features an air-adjustable rear suspension system, allowing riders to fine-tune the preload based on luggage and passenger weight—a necessity for a machine with a dry weight exceeding 800 lbs.
Maintenance Guide & Critical Service Data
Lubrication System
For the Twin Cam 88 engine, MotoSpecsLab recommends Harley-Davidson 360 20W50 for standard climates or Screamin’ Eagle SYN3 20W50 for high-performance or high-heat environments. The total refill capacity is 3.8 Liters. It is vital to check the oil level when the engine is at operating temperature to ensure an accurate reading on the dipstick.
Tires and Traction
The FLHTCUI requires specific load-rated tires to handle its touring capacity. The front uses an MT90B16 72H, while the rear can accommodate either the MT90B16 74H or the wider MU85B16 77H (introduced in later years for better longevity). Pressure management is critical for handling: 36 psi (2.48 bar) for the front, and 40 psi (2.76 bar) for the rear when carrying a passenger.
Electrical and Ignition
The ignition system relies on HD 6R12 spark plugs. Given the heat generated by the rear cylinder of the Twin Cam, regular inspection of the plug gap and ceramic insulator is recommended every 5,000 miles. The electrical system is anchored by the 66010-97C battery, which provides the high cold-cranking amps (CCA) required to turn over the high-compression V-twin.
Expert Verdict
The FLHTCUI 1999-2006 is a robust touring platform. While early Twin Cam models should be inspected for cam chain tensioner wear, the overall mechanical integrity of the Electra Glide Ultra Classic remains a gold standard for long-distance comfort and American engineering heritage.