I see some discussion on oils in older threads so thought I would bring it up again. Sorry if everyone's tired of it. I've always used plain old castrol gtx 10/40 in the cool seasons and 20/50 in the summer heat in all my bikes. But in researching oils more lately I have switched to Shell rotella t 15/40 in my little gixxer. Yamaha does not recommend deisel specified oils in the vmax despite deisel oils also having the sg, sh, or sl, gasoline ratings. I suspect they just want to peddle their overpriced 20/40. I've never tried synthetic oils because its my belief that oil gets dirty and contaminated whether its synthetic or not. I change oil often, thinking this is the safest and best thing to do for an engine. I invite others point of views on this on all bikes and the busa in particular. Thanks.