The term "wheel guard" can refer to several devices that essentially perform the same duties. The wheel guard protects the wheel from debris, and it also protects the user from debris that may shoot off the wheels of a vehicle. A chain wheel guard is a structure that covers the chain wheel of a motorcycle or bicycle, protecting the teeth of the chain wheel from impact damage and protecting the user from contact with the teeth of the chain wheel. Wheel guards are often known as fenders or fairing as well, especially on motorcycles. The design will vary from vehicle to vehicle.
A motorcycle will feature a few different types of wheel guard. The chain wheel will have its own guard to protect it from impact. This chain wheel is part of the motorcycle's drivetrain, or collection of components that drive the motorcycle forward. The chain wheel and chain are the two most recognizable parts of the drivetrain, and both of these components are very often protected from damage and from contact with the rider. A motorcycle will also feature fenders or fairing that act as a wheel guard for the front and rear wheels. These guards can be made from metal, fiberglass, ABS plastic, and sometimes from other composite materials. Their purpose is to keep debris from flying off the wheels and striking the rider or other vehicles. They will also protect the wheels from impacts from outside debris, and add an element of aerodynamic performance to the motorcycle.
Bicycles sometimes feature one ore more wheel guard as well. Some riders choose to install fenders that protect the rider from debris, moisture, mud, and other materials that can fly up off the rear tire and onto the rider's clothing. A front fender will protect the rider's face and chest from debris or moisture flying off the front wheel as well. Like motorcycles, a bicycle may also feature a wheel guard that protects the front chain wheel of the bicycle. This guard is usually made from plastic or other composite materials, and it is affixed to the outside of the chain wheel to protect the teeth of the gear from impacts with rocks and other obstacles a rider may pass over.
On a car or truck, a wheel guard may be called a hubcap. Such caps protect the lug nuts that secure the wheel to the axle from dirt, grime, road salt, and moisture, thereby helping to prevent the lug nuts from seizing up. When lug nuts seize, removing the wheel from the automobile becomes extremely difficult. Such guards can be made from metal or plastic and they come in a wide variety of designs.