Grand Prix motorcycles(Now called MotoGP)are almost completely unrestricted in their design, except for minimum weight and engine capacity requirements. Their engines have some of the highest power per litre ratios of any engines made, and the lightweight, tiny machines have better power to weight ratios than any vehicle short of dragsters.
As of the year 2002, there are three categories of Grand Prix motorcycles - 125cc, 250cc, and the 500cc class which is changing to 4 stroke machines of about 1000cc, both are currently racing in the same class. The 125cc machines are restricted to a single cylinder and a minimum weight of 80 kilograms, the 250 cc machines to two cylinders and 100 kilograms, and the 500cc bikes to four cylinders and 130 kilograms. While four stroke engines are permitted, two-stroke designs have been universal since the 1970's due to their far greater power than a similarly-sized four-stroke design. The motorcycles, particularly the 500cc machines, are made out of exotic and expensive materials, including titanium and carbon fibre, and are equipped with sophisticated electronics including telemetry, engine management, and traction control, though most machines still use carburettors because fuel injection's throttle control is not precise enough for the riders.
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.
Compared to Formula One car racing, as many riders are competing on near-identical bikes, and trailing riders usually have an aerodynamic advantage over the leaders, the racing is usually close and entertaining, with much overtaking. Rider ability (though this includes the ability to figure out which suspension and tyre choices are appropriate for the conditions) is usually the determining factor in races and world championships.
Notable riders of the past include:
As fewer and fewer road motorcycles have two-stroke engines, and development of the category has stagnated somewhat, there has been some agitation by motorcycle manufacturers for a change back to four-stroke machines. In 2002, 1000cc four-stroke motorcycles will ride alongside the 500cc two-strokes. The future for the 250 and 125 classes, with this change, is also uncertain.