had no clue that racing trikes exsisted. was just looking for a more convinent way to travel about in the neighborhood. i knew that single speed kits were available and have seen two speed factory trikes pass by my home. i wanted a bit more; something out of the ordinary and to see if my ideas would work. there isnt a differential. the trike uses an axel that is common to both rear wheels. ive been researching trike m/cs and have found several that appear to use a primitive rear differential. research has also revealed an easy and inexspensive way to make suitable hubs. the cage like structure that surrounds the rear axel housing provides, i believe, enough strentgh so as not to require additional frame tube members. the bridge like structure is not unknow to bike builders. i probibly will never figure out the entire nature of the "push" and will just live with it. i dont have many miles on the trike, but have toured the neighborhood. the bike is pleasent enough to ride and is only problematical when sharp cornors are encountered. refining the idea is left to others to do. ill ride the trike as time and weather allow. for me the greatest pleasure was the doing not the trike. thanks to all who have responded to this post. micheal