The FIM Road Racing World Championship Grand Prix is the premier class of motorcycle road racing, held since 1949.
Grand Prix motorcycles are purpose-built racing machines that are neither available for purchase by the general public nor able to be ridden legally on public roads. This contrasts with the various production-based categories of racing, such as the Superbike World Championship and the Isle of Man TT Races that feature modified versions of road-going motorcycles available to the public.
The championship is currently divided into three classes: MotoGP, Moto2 and Moto3. All three classes use four-stroke engines. In 2010 the 250cc class was replaced by the new Moto2 600 cc four-stroke class. In 2012 the 125cc class was replaced by the Moto3 250cc four-stroke class with a weight limit of 65 kg with fuel, and the engine capacity for MotoGP increased from 800 cc to 1,000 cc.
Previously, the championship featured a 50cc class from 1962 to 1983; an 80cc class from 1984 to 1989; a 350cc class from 1949 to 1982; and a 750 cc class from 1977 to 1979.
Unlike races such as the TT Formulae, or Moto-Cross, where two and four strokes had different engine size limits in the same class, until 2002 GP racing set the upper limit the same for both types of engines in all its classes. After that, MotoGP gave the four-strokes a 490cc advantage over the two-strokes. A 2 stroke engine produces power with every rotation of the crank, where as the 4 stroke engine produces power every second rotation. In theory, a 500cc 2stroke produces the same power as a 1000cc 4 stroke, however there are many differences between the two configurations. Carburation vs fuel injection, engine mapping, power/torque curves, and throttle response are a few major differences. Practice showed the 4 strokes generating 10 to 15 more Hp and turning in much faster lap times than their 2 stroke counterparts. 4 stroke engines would be the obvious choice for years to come. Moto2 and 3 are four-stroke only. - Source : MediaWiki