Originally Posted by ???
long story....
but its because they built the motor to need it. stock bikes are not, for the most part.
its all about knock resistance, if its not needed then the extra octane just slows the flame front in the combustion chamber for no reason.
Basically what he said, It has alot to do with load, cars because of weight etc, will see more. Thus high compression and big boost cars need higher octane. Lowest you can use is the fastest.