Cycling cleats are specifically shaped pieces of metal that are mounted to the underside of cycling shoes. These cycling cleats lock into pedals designed to work in unison with the cleats; a rider is then clipped into the pedals, meaning more of the cyclist's pedaling power will be transferred to the pedal and in turn to the drivetrain. The pedals designed to work with cycling cleats are known as "clipless pedals" because they replaced toe clips, which were metal or plastic cages into which the cyclist slipped his shoes during cycling activities.
The advantages of cycling cleats that lock into clipless pedals include more pedaling power transferred directly to the drivetrain, and easier clip-in and clip-out capabilities. One of the biggest dangers of toe clips was the need to cinch them down over the cycling shoes, which could make exiting the pedals difficult, especially in emergency situations. Clipless pedals and cycling cleats eliminate this problem by making exit from the pedals extremely easy: the cyclist needs to simply kick his heel outward and the cleat and pedal will release. To get back into the pedal, the cyclist will position the cleat over the pedal so the toe of the cleat slides into the pedal, then push down at the rear of the cleat. The motion is quick and easy.
Cycling cleats come in a variety of shapes and sizes, and they are not always necessarily made of metal. Road cycling cleats are usually much larger than mountain biking cleats; mountain biking cleats must be much smaller, since a mountain biker is more likely to get off his bike often to walk or run through a section of trail. Cycling road cleats tend to be much larger, though the pedals themselves are much smaller. Road cleats are more likely to be made out of plastic rather than metal for weight savings.
Mountain bike cycling cleats are made of metal for durability. The cleat can wear out fairly quickly, especially if the cleats are made from softer metals, so plastic cleats are out of the question for a mountain biker who is likely to hit rocks and other obstructions regularly. Cyclists must be careful to clean the cleats regularly, as grit and grime can quicken the wear of the cleat. Moisture can also work into the cleat bolts, which can then seize up, meaning the cleats must be cut off in order to be replaced.
