Your project sounds impressive - does that mean you'll be controlling 3x30 led outputs? are you going to need 6 TLC5940 to control the lot - or is it possible to multiplex the TLC5940 output pins?
I wasn't planning on multiplexing, so at least 6. I'm assuming that a single rotation of the wheel will have ~30 PWM periods, which means one image is (24 bytes per tlc)(6 tlc's)(30 periods) = 4.32KB. That comes out to ~231 frames per 1MB of SD card space.