I am on my 39th motorcycle. I have used M1 15W-50 for a number of years now. It seems to be about the best motorcycle oil available and is thin for a 50.
Motorcycle engines are hard on oil, period.
Higher viscosities do increase fluid drag and reduce HP slightly.
One thing to keep in mind is the fact that big bore sport bikes are really not run very hard for long. Smaller bikes like the 600's actually have to be tougher because they are pushed to the limit much more often. This fact allows those big engines to be made very light. When I was in Japan, I learned the percentage of time spent at max output/load is well less than 1% of total engine life for big bores, compared with about 3% for smaller bikes. A 250 Ninja engine spends a whopping 6-7% of it's life at max load, that is more than 10 times the big bore sport bike level.
Chris
Motorcycle engines are hard on oil, period.
Higher viscosities do increase fluid drag and reduce HP slightly.
One thing to keep in mind is the fact that big bore sport bikes are really not run very hard for long. Smaller bikes like the 600's actually have to be tougher because they are pushed to the limit much more often. This fact allows those big engines to be made very light. When I was in Japan, I learned the percentage of time spent at max output/load is well less than 1% of total engine life for big bores, compared with about 3% for smaller bikes. A 250 Ninja engine spends a whopping 6-7% of it's life at max load, that is more than 10 times the big bore sport bike level.
Chris