concept just like with any other mechanical engine. When climate is HoT use thicker CoLd use thinner. If you run a search on the site there is prolly 123498723498723 posts.
Our little bikes are no diff than our big ones---I personally run either Rotella 15w40, or Rotella synthetic 5w40, depending on my budget. True ester synthetic is good stuff, and the more of a revver you are, the more you need it. In a sportbike, you can literally feel the reduced engine vibration when revving hard, and the engine noise is quieter...