I have a grad student friend at the local Uni that had a Z5 until the frame broke and Felt replaced it with the Z4. He's a big guy, think offensive lineman big boned 240#, and he loves his bike. He breaks lots of gear, crank arms, wheels, frames, so don't think it was a Felt issue. He likes the higher position, tends to ride a short cockpit even though he is my height or taller. The guy can climb too for as big as he is so the bike doesn't seem to hold him back.