In the evolution of ride-over-anything mountain bikes, the ever-vulnerable rear derailleur—that gangly parallelogram that shifts the chain up and down the rear cogs when it’s not clogged with mud or bent by rocks—has been a glaring technical handicap. So GT (gtbicycles.com) got rid of it. With its $5,000 IT-1, GT moves gear-changing duties to an unsullied haven inside the bike frame, by way of an eight-speed internal transmission.