on much older bikes you may see them on the downtube. By using the shifters, you can change gears by altering the chain's position across the different cogs and chainrings. To change gear ...

Engineers at SRAM came up with a solution that's hard to imagine for other bikes but not too hard to grasp. A freewheel in the back has two cogs, with a high gear for cruising and a low gear for ...