With the 4300 you get alum bars and stem, 3700 has steel, better fork (not much, but a little) and a slightly better alum frame. It has disc mounts, but if you really want disc brakes I would get a bike that already has them. Would be cheaper in the long run. I think the 3700 has dick mounts too now that I think of it. The 4300 also comes with better wheels and tires, hubs are the same. The 4300 also has a removable/replaceable rear der hanger if I remember