This is the claim on the front label of the 20-50 Valvoline 4 stroke motorcycle oil I just bought. I have read numerous posts concerning different oils for the primary drive. One of them, by Vince, was quite adamant about using 20-50. Wouldn't it be prudent to adhere, as closely as possible, to the factory specified requirement, IE, 15-40? I had a choice between the Valvoline 10-40 and the 20-50. Are there any thoughts on this, based on 'scientific' studies? Rotella was the only 15-40 I could find. It is, course, not specifically for motorcycle use. Cheers!