Originally Posted by gman2304
Respectfully, I just googled the temperature in Charleston, W.V. and as of 11:00 am it was 86 degrees. According to the chart the 10w30 is recommended for temperatures between 10 degrees and 70 degrees. The 10w40 is good for temperatures between 10 degrees and 110 degrees. As I stated before, the 10w30 is the worst choice of those shown considering the op's location.
Precisely, the chart tells him what to do. The 10w30 mantra getting repeated is flat wrong if someone would take the time to look at what Yamaha actually recommends and where the person lives. It's not hard. I'm going to call it out every time.
With respect to oil shear, I've run both Mobil motorcycle oils (10w40 4T and 20w50 V Twin) in my shared sump on 5,000 mile oil change intervals. Both maintained excellent shift quality and analysis showed they stayed in grade with 20w50 in the middle of grade and the 10w40 right on the bottom edge.
Starting as a 30 weight it's not going to feel as good or shift as nicely as a 40 weight that may eventually drop down to a 30 weight. Fact. It's when the oil drops down to the 30 weight that the shift quality degrades.
Sounds silly but I take my shifting seriously and do not want missed shifts or poor feel at the shifter.
I have probably tried 12 different oils in my bike and done analysis on every one. 15w40, 5w40, 20w50, 15w50, 10w40.
Both oils mentioned above were the best for shift quality and still had so much TBN left they probably could have 10,000 miles unless shift quality fell off first which I suspect would have happened.