dirt bikes

Motocross first evolved in Britain from motorcycle trials competitions, such as the Auto-Cycle Clubs's first quarterly trial in 1909 and the Scottish Six Days Trial that began in 1912. When organisers dispensed with delicate balancing and strict scoring of trials in favour of a race to become the fastest rider to the finish, the activity became known as "hare scrambles", said to have originated in the phrase, "a rare old scramble" describing one such early race.

Though known as scrambles racing (or just scrambles) in the United Kingdom, jthe sport grew in popularity and the competitions became known internationally as "motocross racing", by combining the French word for motorcycle, motocyclette, or moto for short, into a portmanteau with "cross country".

The first known scramble race took place at Camberley, Surrey in 1924. During the 1930s the sport grew in popularity, especially in Britain where teams from the Birmingham Small Arms Company (BSA), Norton, Matchless, Rudge, and AJS competed in the events. Off-road bikes from that era differed little from those used on the street. The intense competition over rugged terrain led to technical improvements in motorcycles.

Rigid frames gave way to suspensions by the early 1930s, and swinging fork rear suspension appeared by the early 1950s, several years before manufacturers incorporated it in the majority of production street bikes. The period after World War II was dominated by BSA, which had become the largest motorcycle company in the world. BSA riders dominated international competitions throughout the 1940s.

FIM Motocross World Championship

FIM Motocross World Championship The FIM Grand Prix Motocross World Championship is predominantly held in Europe, but also includes events in North America, South America, Asia, Australia, and Africa. It is the major Motocross series worldwide. There are three classes: MXGP for 450cc machines, MX2 for 250cc machines, and Women's MX. Competitions consist of two races which are called motos with a duration of 30 minutes plus two laps.

AMA Motocross Championship Main article: AMA Motocross Championship The AMA Motocross Championship begins in mid May and continues until late August. The championship consists of twelve rounds at twelve major tracks all over the continental United States. There are three classes: the 250cc Motocross Class for 150–250 cc 4-stroke machines, the 450cc Motocross Class for 251–450 cc 4-stroke machines and a 250cc Women's Class, using the same rules as men's 250cc. Race events take place over two motos of 30 minutes plus two laps each.

From the late 1970s to early 1990s, Japanese motorcycle manufacturers presided over a boom period in motocross technology. The typical air-cooled two-strokes with twin-shock rear suspension and telescopic front forks gave way to machines that were water-cooled and fitted with single-shock absorber rear suspension and "upside-down" (or inverted) front forks. Although the advancement of two-stroke engine technology was the primary focus of the major Japanese motorcycle manufacturers well into the mid 1990s, a rekindled interest in engineering a competitive, lightweight four-stroke motocross race bike was expressed among several brands, including Yamaha Motor Corporation.

To further inspire the research and development of four-stroke motocross racing technology, the American Motorcyclist Association, America's leading motorcycle sport governing body, increased the allowable displacement limit for four-stroke powered machines in the 125 and 250 AMA Supercross and Motocross championships. Due to the low relative power output of a four-stroke engine compared to the then-dominating two-stroke design, the displacement limit of a four-stroke power motocross bike was raised to 250cc in the 125 class and 550cc in the 250 class.