There is a special rule called the World Champion's Exemption, where any former PBR World Champion can compete in any 5 events he chooses (and they don't have to be consecutive), except for the PBR Finals (he still has to earn his way there). He can then stay on tour if he accrues enough points; if not, he'll have to earn his way back on via the lower tours. Before 2007, this rule allowed former champs to compete in as many or few events they chose, with the only stipulation being that they still had to qualify for the PBR finals like everyone else. (The old rule was implemented in 2000.)
This tour was called the Bud Light Cup (BLC) tour until 2003. It started off with 8 events in its inaugural season of 1994, increasing the number of cities visited over the years, with 28 starting in 1999, and increased to 30 in 2005. There will reportedly be 34 BFTS events in 2008.