Dirt bike is a type of motorcycle designed for off-road driving. Dirt bikes are also called trail bikes and off-road motorcycles. They are used for recreation and competition. Compared with other motorcycles, dirt bikes tend to be lightweight and have smaller engines. They can travel on rough country trails, climb hills, and cross streams.
Dirt bikes range from 88 pounds (39 kilograms) to 346 pounds (156 kilograms), depending on the type of engine, engine volume, and size of the bike. The average dirt bike weighs 214 pounds (97 kilograms).
Parts
Dirt bikes have five major parts: (1) the engine, (2) the transmission system, (3) the wheels, (4) the brakes, and (5) the controls. A frame of steel or aluminum tubing holds dirt bikes together. Aluminum frames are more common because they are lighter. 
The engine of a dirt bike has one or two cylinders. It operates on either a two-stroke or four-stroke cycle (see ). The gas tank is relatively small because dirt bikes are not designed for long-distance travel. The average dirt bike gas tank holds about 1.6 gallons (3.7 liters).
The front fork, an extension of the frame, helps hold the front wheel in place. It serves as a suspension system that cushions the rider against bumps. A rear swing arm allows the rear wheel to move up and down, providing additional stability when riding over bumps. Dirt bikes require a strong front fork and rear wheel suspension system to enable the bike to absorb the impact of jumps and rough terrain.
Dirt bike tires have knobs and deeply grooved ridges that provide traction on gravel and other loose or uneven surfaces. They enable the bike to navigate sand, dirt, and other rough terrain in all weather conditions. Unlike street motorcycles, many dirt bikes have rubber tubes inside the tire to hold compressed air.
Types
There are many different kinds of dirt bike. Trail bikes are designed to handle multiple terrains for longer rides. They tend to have a softer suspension, lower torque, and more fuel capacity. Torque is the amount of twisting effort that a force or forces exert on an object. Motocross bikes are faster than other dirt bikes. They are lightweight with a smaller gas tank and hard suspension. Enduro bikes combine the features of motocross and trail bikes. They are heavier than motocross bikes and made for short races. Enduro bikes have a stronger suspension and higher torque compared with trail bikes. They are a combination of motocross and trail bikes.
Dual-sport bikes are heavier and taller than other dirt bikes. They can be used for off-road and street riding. Trials dirt bikes are designed to test the ability of dirt bike riders and do not have a seat. They are short and light with a small gas tank. Supermoto bikes are designed for both street and off-road riding, with smooth tires like those of road bikes. Hill-climb bikes have an extended swing arm and more powerful engines for climbing slopes. Flat-track bikes are a combination of supermoto and motocross bikes, with a softer suspension, smooth tires, and a powerful engine.
For various terrains and competitions, dirt bikes may need to jump or ride further. Seat height varies for different uses. For trail riding, riders generally favor a shorter seat height. Suspension and ground clearance also varies with a bike’s intended use.
Racing
Dirt-bike enthusiasts enjoy racing as a pastime as well as a spectator sport. Different types of dirt bikes are used for various races.
Motocross racing is the most popular type of motorcycle competition. It includes races run on difficult courses that feature jumps, hills, and other obstacles. Supercross, an indoor competition, started in the United States in the early 1970’s. The races take place on artificial dirt tracks in arenas. Supercross courses are shorter than motocross courses but often have more obstacles and longer jumps. Hare scrambles are speed races run on courses laid out among rugged natural terrain. Other types of racing include Grand National Cross Country (GNCC) races, enduro races, vintage racing, track racing, and snow bike racing. 
Safety
Dirt bikes can be hazardous. Manufacturers warn that riders should wear helmets and not carry passengers. They also warn that younger people should ride only smaller, less powerful dirt bikes, under adult supervision.
Dirt bikes often lack the brake lights, headlights, rearview mirrors, and turn signals needed to be safely ridden on public streets. In the United States, it is illegal to drive dirt bikes that lack such equipment on roads. Dirt bikes also do not typically comply with emission standards.
History
Dirt bikes originated in the United Kingdom. Siegfried Bettmann, a German bicycle, motorcycle, and automobile manufacturer, modified motorized bikes for off-road use in Coventry, United Kingdom, around 1914. Motocross began shortly after. The first scramble was held in Camberley, Surrey, in 1924. The popularity of dirt bikes increased in the 1940’s and 1950’s. The bikes became popular in the United States in the 1970’s. The first mass-produced electric dirt bikes were developed in the 2000’s.
