I've used the Shell Rotella Syn in a few bikes, works good. I switched to Mobil 1 15w-50 cause they are the same price at Wal-Mart here now. Mobil shifts a bit smoother, maybe higher weight or different additives? The Mobil is a non energy-conserving oil also.
This is interesting to me because I've been riding dirt bikes, ATV, motorcylces 15 years. When I was a kid I would sometimes put in auto oil. Then I got to riding where I started noticing clutch slip on off road, pull it apart and the clutch was still in spec. Changed to riding with motorcycle oil and the slip went a way. Maybe street bikes don't abuse the clutch like on dirt bikes and quads and you can get away with auto oil, but from my experience it will cause some slippage so I don't use it.
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