And with friction comes heat, which is why nearly all modern bikes use wet clutches that are bathed in engine oil. The oil cools the clutch pack, keeps the plates clean, and in general provides smoother and quieter operation and longer service life than dry clutches. The oil isn’t needed to lubricate the plates, but it does lower the friction between them, necessitating stiffer springs and/or grippier clutch plates. A dry multi-plate clutch handling the same power can be smaller since oil isn’t reducing the friction between the plates, plus there’s no fluid drag slowing things down. That’s the primary reason Ducati stuck with a dry clutch design for so long, but with ever-increasing engine horsepower (causing issues with smooth engagement and wear) and increasingly stringent noise-emissions requirements, even Ducati has switched to wet clutches.