I think it is the frame & parts that my body connects with - frame, saddle/seat post and bars. Even when I am working hard to climb that hill, or that headwind that just wont stop and won't allow me to coast downhill...I do feel "at one" with my bike. She connects me to the world around me and forces me to be in the present moment - I can't get lost in some future or the past, and riding her gives me joy.

Sure there is some anthropomorphism in this, and that is ok. Interestingly enough, though my cars have always had at least a general name, I've never had the same connection with it.