For most of the 1950s and 1960s, four-stroke engines dominated Grand Prix racing at all displacement levels. The transition began in the smaller classes as two-stroke technology advanced to the point where the inherent power advantage of two-strokes — producing a power stroke on every rotation of the crankshaft rather than every second rotation — became decisive.
In 1969, the FIM introduced rules restricting all classes to six gears and limiting most to two cylinders, with four cylinders permitted in the 350 cc and 500 cc classes. The regulation change, intended to reduce development costs for private entrants, provoked a mass withdrawal by Honda, Suzuki, and Yamaha. This temporarily left MV Agusta as effectively the sole works competitor in the 500 cc class, and the Italian marque dominated in the absence of Japanese opposition.
Yamaha returned to Grand Prix racing in 1973 with a new two-stroke design, and Suzuki followed in 1974 with the RG500 square-four. By this point two-stroke machines had completely eclipsed four-strokes across all classes. The first two-stroke victory in the 500 cc class had been achieved by Jack Findlay on a Suzuki TR500 in 1971, signalling what was to come.
From the mid-1970s through to 2001 the rules allowed 500 cc displacement with a maximum of four cylinders, with no separate limits distinguishing two-stroke from four-stroke engines. In practice this meant all competitive machines were two-strokes. Honda made a sustained attempt to reverse this dominance with its four-stroke NR500, introduced in 1979, but the project failed to produce competitive results. By 1983 even Honda was winning races with a two-stroke 500.
The two-stroke 500s were notoriously difficult to ride. Power delivery was intense and concentrated in a narrow rev band, requiring riders to manage the engine's characteristics with great precision. The absence of engine braking relative to four-strokes, and the sensitivity of chassis balance to throttle inputs, made these machines demanding at the limit. Riders who mastered them — Kenny Roberts, Freddie Spencer, Eddie Lawson, Wayne Rainey, Mick Doohan, Valentino Rossi — became defining figures in the sport.
Yamaha's dominance with the YZR500 and Honda's rivalry through the NSR500 shaped competition through the 1980s and 1990s. Honda's introduction of the big-bang engine configuration on the NSR500 in 1992, firing two cylinders in quick succession rather than at even intervals, proved to be a development milestone that altered how engineers thought about rear-wheel traction.
Mick Doohan won five consecutive 500 cc championships from 1994 to 1998. Valentino Rossi took the final two-stroke premier class title in 2001.
Rule changes introduced for the 2002 season opened the premier class to four-stroke machines of up to 990 cc, renamed the category MotoGP. Manufacturers could choose to continue with two-stroke 500s during a transitional period, but the superior performance of the new four-strokes rendered them obsolete almost immediately. The last two-stroke machine was started in a MotoGP round at the 2003 Czech Grand Prix. The 125 cc and 250 cc classes continued with two-stroke machinery until their replacement by the four-stroke Moto3 and Moto2 categories in 2012.
The two-stroke 500cc era left a lasting mark on the culture and technical memory of motorcycle racing. The distinctive exhaust note, the demanding riding style required, and the extreme power-to-weight ratios of those machines remain points of reference for riders and engineers who experienced them. The era is frequently cited as the most technically demanding period in the history of Grand Prix motorcycle racing, producing a generation of champions whose skills were forged under uniquely unforgiving conditions.