To explain the wheel sizes a bit more, I should point out that, as I understand it, "triathlon" and time trial bikes sometimes come with the smaller 650c wheels, due (I think) to the fact that the bikes are built for time trial riding and the smaller wheels work better with the frame geometry, which is slightly different from standard road bikes. Your normal road bike comes with the standard 700c wheels. Some of the bike manufacturers who have come out with a women-specific line of bikes have incorporated the 650c wheels in the design (and even 24" wheels in the front, as is the case of some of the Terry bikes) to allow for clearance on the smaller frames.