Grand Prix motorcycle racing refers to the premier categories of motorcycle road racing. The category is commonly referred to simply as GP racing. GP motorcycles are generally prototype racing machines and are not available for general purchase (although road-going versions of the machines are available). This contrasts with the various "production" categories of racing (such as World Superbikes ) that feature modified versions of motorcycles currently on the market to the buying public.

Currently there are three engine displacement categories of Grand Prix motorcycles—125 cc, 250 cc and MotoGP (up to 990 cc). The premier class of GP motorcycle racing has changed in recent years. From the mid-1970s until 2002 the top class of GP racing was restricted to 500 cc 2-strokes. However in 2002 manufacturers were also allowed to enter 990cc 4-stroke machines. While a 500cc two-stroke machine should (in theory) deliver the same power as a 990cc four-stroke, it rapidly became apparent that the four-stroke machines could outperform the two-strokes in almost every area and by 2003 there were no two-stroke machines remaining in the field. The 125 cc and 250 cc classes still consist exclusively of two-stroke machines.

The 125 cc machines are restricted to a single cylinder and a minimum weight of 80 kilograms and the 250 cc machines to two cylinders and a minimum of 100 kilograms. The MotoGP bikes are permitted to have from 3 to 6 cylinders and have variable weight limits depending on the number of cylinders (to account for the fact that, generally, having more cylinders for a given capacity means more power). In 2004 there were motorcycles entered with three-, four- and five-cylinder configurations, but not six.

GP motorcycles, much as with Formula One cars, exist not only to be raced but also to demonstrate the technical prowess of the manufacturers. As a result the GP motorcycles, particularly the MotoGP machines, are generally made out of lightweight and expensive materials such as titanium and carbon-fiber-reinforced plastic. Additionally, they regularly feature technology not available to the general public. Examples of this include sophisticated electronics, including telemetry, engine management systems and traction control, and advanced engine technology such as Honda's V5 engine configuration and Aprilia's RS3 which employs a Cosworth-designed pneumatic valve actuation system, as seen in Formula One racing cars.

One of the main challenges that confronts a MotoGP motorcycle rider and designer is how to translate the enormous power generated by these engines, rumoured to be around 240 horsepower, (179 kW) through a single tyre-contact patch roughly the size of a human hand. For comparison, Formula 1 cars can make up to 800 bhp from their three-litre engines but have 10 times the tyre contact surface. Because of this difficulty, MotoGP is perhaps unique in modern motor sport in that teams will often deliberately detune their engines to allow their riders a chance to control them, with most not making more than the 180 to 190 bhp of the front-running two-stroke bikes.

The best riders, of each category of machine, travel the world to compete in the annual World Championship series, with each category run on a point-scoring basis similar to most other racing championships. The circuit is perhaps most closely followed in Spain and Italy, home of many of the more successful riders at the moment.

Until recently, the 500 cc class was seen as similar to Formula One car racing, given that one man (Michael Doohan and, later, Valentino Rossi) and one team (Repsol Honda) were almost totally dominant. A new generation of riders and the shift to 4-stroke bikes has seen the racing become as exciting as the fairing-bashing antics of the Superbike competition (while WSB began to be seen as dull and uncompetitive as Ducati began to utterly dominate it) and the older formula is now considerably more popular.

Notable riders of the past include:

• Giacomo Agostini
• Michael Doohan
• Mike Hailwood
• Libero Liberati
• Eddie Lawson
• Toni Mang
• Angel Nieto
• Wayne Rainey
• Jim Redman
• Phil Read
• Kenny Roberts Sr
• Kevin Schwantz
• Freddie Spencer
• Egbert Streuer (sidecar)
• John Surtees
• Jock Taylor
• Tetsuya Harada
• Daijiro Kato

Some of the more successful of the present riders include:

• Valentino Rossi
• Max Biaggi
• Sete Gibernau
• Kenny Roberts Jr
• Garry McCoy
• Steve Jenkner
• Yuichi Ui
• Makoto Tamada
• Shin-ya Nakano

While the MotoGP motorcycles are raced only at World Championship level, slightly less powerful 125 cc and 250 cc bikes are available at relatively reasonable cost for purchase (the 125 cc bikes are available for about the same as a small car) and are thus raced in national championships around the world.

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