Whats not to get it? I thought this post by mmmmmmmm_cheese exsplained it pretty well. As i understand it, more surface area the greater the braking, i cant quite rememeber the forumla to prove that. But the more holes ect wehich gives less surface area give greater heat dispertion, for trials that doesnt matter to much. Also people have said that with using gothic rotars ect that arnt just circular there brake judders. I would say just go with a simple rotar design like the normal hope rotar that has a decent amount of surface area and holes to get rid of the heat.