Few riders realise that many motorcycles run a shared sump: the engine, gearbox and wet clutch use the same oil. Gear sets impose intense mechanical shearing that can break down viscosity improvers, while the clutch demands a stable friction profile to avoid slip yet remain progressive. Short Nordic rides and damp storage add another stress: condensed moisture and some fuel dilution, which can weaken film strength and disturb clutch feel if oil changes slip. These combined demands are why a purpose‑made formulation such as 4T SAE 10w30 is used instead of passenger‑car oil.