A component of two wheeled transportation vehicle frames (primarily motorcycles and bicycles) which spans between the seat tube and the rear dropout creating (with the seat tube and chain stay) a triangular structure by which to suspend and harness the rear wheel of the vehicle. Newer rear suspension bicycle frames, and nearly all modern motorcycle frames employ a slightly different design, in that the seatstay does not directly interface with the seat tube, rather a suspension device that then either interfaces with the seat stay or another section of the frame.