most 4stroke motorbikes including japanese and chinese recomend a minimum SG grade oil(standard car oil)for engine and gearbox but in a 10w40 or a sae 30 but they do not recomend any friction modified type oils as they damage clutches,these oils are recomend as best for all round conditions,i have often thought as too our hot summer climate that a slightly thicker oil as a 15w 50 would be more suitable as it wouldnt thin as much on our hotter days dropping lubrication properties,would be interested too hear seans opinion