The pedals transfer human muscle power to the drive train of the bicycle. Some pedals, such as the metal rat-trap design used on utility bicycles and old ten-speeds and the more recent ATB (all-terrain bicycle) or platform design used on some mountain and BMX bicycles, allow the feet to simply rest on them. The pedals convey motive force only when the feet push down during the front half of each pedal stroke.
Much mechanical advantage is gained, however, if a cyclist’s feet are attached to the pedals so that the cyclist can also use muscle power to pull up on the pedals in the back half of each pedal stroke. Two of the oldest ways of attaching the feet to the pedals (originating in the early 20th century) are toe clips and cleats.
Toe clips are curved, springy cages, commonly made of metal or high-impact plastic, that are bolted to the front of a counterweighted pedal to enclose the toes of the cyclist’s shoes. Using a leather or fabric side strap, the toe clips may be cinched down to grip the shoe. The optimum gripping force holds the foot on the pedal with minimum play but still allows the cyclist to free the foot as needed when coming to a stop. Toe clips work with virtually any type of ordinary walking shoe, so cyclists can walk around once they stop riding.
Cleats are permanent attachments that project from the soles of special hard-soled cycling shoes. These attachments lock the feet in place against the pedals. Cleats enable a cyclist to deliver power to the pedals more efficiently than is possible with toe clips alone, making them popular for racing. However, toe clips without cleats have long been preferred in touring, commuting, and ordinary recreational cycling because walking in the shoes with the projecting cleats is virtually impossible.
Manufacturers since the 1970s have devoted much attention to developing clipless or uncleated systems. The cyclist must still wear special shoes, but the shoes attach to devices that replace conventional pedals and toe clips. The cyclist inserts or removes the foot from the attachment by a twisting motion of the ankle. Unlike cleats, however, the attachment mechanism on the shoe is recessed into the sole instead of projecting from it. Such clipless or uncleated systems yield the efficiency of cleats without impairing the cyclist’s ability to walk, an innovation that has been widely embraced. By the 1990s some manufacturers had developed shoes for clipless pedals that were nearly indistinguishable in appearance from normal sneakers or loafers. The only disadvantage to the clipless system is that the attachments that replace the pedals make it difficult or impossible to ride the bicycle while wearing ordinary shoes.