Motocross is a form of off-road motorcycle racing held on enclosed off-road circuits which evolved from motorcycle trials competitions.
Such bikes are raced on short, closed off-road tracks with a variety of obstacles. The motorcycles have a small fuel tank for lightness and compactness. Long-travel suspension allows riders to take jumps at high speed. Motocross engines are single-cylinder two-stroke or four-stroke units, which vary in size from 50cc up to about 500cc. At the professional level, bikes are spilt up into two levels based on their displacements: MX and MX Lite. The MX Lite class contains 125cc two-stroke engines and 250cc four-stroke engines, while the MX class pits 250cc two-stroke engines against 450cc four-stroke engines. The differences in power, displacement, torque, and weight are all variables that balance the competition between two-stroke and four-stroke engines.