A Motocross motorcycle (often shortened to MX or MotoX) is a form of motorcycle sport or all-terrain vehicle racing held on enclosed off road circuits as opposed to an Enduro. Motocross is derived from the French, and traces its origins to British Scrambling competitions. The name "motocross" is a portmanteau derived from the words "Motorcycle" and "Cross Country".
Solo machines have engines ranging in displacement size from 50cc to 650cc. In the early years of motocross, the 500cc class was considered the premier division. However, as technology progressed, the open class bikes became more powerful and fewer riders were able to ride them at their limits. The 250cc bikes also became faster with newer technology and were more manageable thus, they eventually superseded the 500cc bikes and became the premier class.
Originally all bikes were 4-stroke pre-1965, but as the two stroke engine improved they became more popular with their domination of the sport in the 1970s, 80's and 90's. The two stroke engine produced more power than a four-stroke engine of the same capacity (cc), however oil must be introduced into the crankcase space for connecting rod bearing lubrication, either with a pump or by mixing it with the fuel; this oil is burned, giving the characteristic smell of a two-stroke engine. Four-stroke continued to be raced in specialist classes throughout this period, partially in the 500cc class.
- European Class: MX1
- U.S. Class: Motocross/Supercross (formerly "250") 250cc
- Two stroke 250cc / Four stroke 450cc
- European Class: MX2
- U.S. Class: Motocross Lites and Supercross Lites
- Two stroke 125cc-144cc / Four stroke 250cc
- European Class: 85BW
- U.S. Class: Supermini
- Two stroke 85cc-112cc / Four stroke 150cc
- European Class: 85SW
- U.S. Class: Mini
- Two stroke 85cc / Four stroke 150cc (if club allows)
- European Class: 65
- U.S. Class: Mini
- Two stroke 65cc / Four stroke N/A
- European Class: Autos
- U.S. Class: Pee-wee
- Two stroke 50cc / Four stroke 50cc