Whilst there are differences in motorcycle engines and those of cars the oils are broadly the same.

Demonstrated by having the same specification and grading systems.

The shear forces in gearboxes exist but the m/c oils are not rated as EP. If they are, the data sheets consistently fail to mention it.

Interestingly, a number of cars I've owned specify standard engine oil as gearbox lubricant.

The issue of additives affecting clutch operstion I can only say I have never experienced it having used standard car oil in many different wet clutch m/c engines for over 25 years.

Either way, it's down to the individual.

My advice would be to make sure the oil meets the specified API rating and is changed regularly (and filters).

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Simon

Brighton, UK