Loads of threads with the tier requirements in basic form as I am sure you are aware. Winning credits / beating higher tiers can also become part of the calc, and WGT do not reveal their methodology for that, but threads discussing it all over too.
BG20bball:If I am stuck on the tour master level I have no choice but to give up as there is no point in playing if i cant win any credits.
You never get to go down.
Have a look around (if not done so) at all the discussions on equipment / new green speed etc to help do well.