Why is it so critical to use motorcycle-specific oil, and what actually happens inside the bike if someone pours standard car oil into the engine?

Answer: Motorcycles differ from cars by the fact that most bikes have a transmission & clutch that share the same oil! Add in the fact that today’s sport bikes rev twice as high as a car and you can start to see why they require vastly different oils. If someone was to put car oil in their motorcycle it would still start and run but shifting would become notchy, clutch may slip and over time, the engine would see greater wear.