Hi,

This link http://www.bolly.com.au/book/ and other charts will get you "in the ball park" from there it is a "suck it and see" approach as various brands with the same diameter and pitch will perform in different manners. Then as you pointed out there are different flying styles and huge variety of models and weights even within the same ARF or kit depending on setup. On a 50cc 3D model I have just changed from a 19x6wide to a 21x8. Trial and error is the answer.

Cheers,

Colin