Open-wheel car, formula car, or often single-seater car in British English, describes cars with the wheels outside the car's main body and, in most cases, one seat. Open-wheel cars contrast with street cars, sports cars, stock cars, and touring cars, which have their wheels below the body or fenders. Open-wheel cars are usually built specifically for racing, frequently with a higher degree of technological sophistication than in other forms of motor sport.
A typical open-wheeler has a minimal cockpit sufficient only to enclose the driver's body, with the head exposed to the air. In modern cars the engine is often located directly behind the driver, and drives the rear wheels. Depending on the rules of the class, many types of open-wheelers have wings at the front and rear of the vehicle, as well as a very low and virtually flat undertray that helps achieve additional aerodynamic downforce pushing the car on to the road.
Some major races, such as the Monaco Grand Prix (sanctioned by Formula One) and the Long Beach Grand Prix (sanctioned by the IRL), are held on temporary street circuits. However, most open-wheel races are on dedicated road courses, such as Watkins Glen International in the US, Nürburgring in Germany, and the Bahrain International Circuit in the Middle East. In the United States some top-level open wheel events are held on ovals, of both short track and superspeedway variety, with an emphasis being placed more on speed and endurance than the manueverability inherently required by road and street course events. The most well-attended oval race in the world is the annual Indianapolis 500 (Indy 500) in Speedway, Indiana, sanctioned by the IRL; in the United States, it is common to refer to open-wheel cars as Indy Cars because of their recognizable appearance at the Indy 500.
Open-wheeled racing is among the fastest in the world. Formula 1 cars can reach 360 kilometres per hour (220 mph). At Autodromo Nazionale Monza, Antônio Pizzonia of BMW Williams F1 team recorded a top speed of 369.9 kilometres per hour (229.8 mph) in the 2004 Italian Grand Prix. BAR Honda team recorded an average top speed of 400 kilometres per hour (250 mph) in 2006 at Bonneville Salt Flats with unofficial top speed reaching 413 kilometres per hour (257 mph) using modified BAR 007 Formula 1 car. Speeds on ovals can range in constant excess of 210–220 miles per hour (340–350 km/h), and at Indianapolis in excess of 230 miles per hour (370 km/h). In 1996, Paul Tracy recorded a trap speed of 256.948 miles per hour (413.518 km/h) at Michigan International Speedway. In 2000, Gil de Ferran set the one-lap qualifying record of 241.426 miles per hour (388.537 km/h) at California Speedway. Even on tight non-oval street circuits such as the Grand Prix of Toronto, open-wheel Champ Cars attain speeds of 190 miles per hour (310 km/h).
Driving an open-wheel car is substantially different from driving a car with fenders. Virtually all Formula One drivers spent some time in various open-wheel categories before joining the F1 ranks. Open-wheel vehicles, due to their light weight, aerodynamic capabilities, and powerful engines, are often considered the fastest racing vehicles available and among the most challenging to master. Wheel-to-wheel contact is dangerous, particularly when the forward edge of one tire contacts the rear of another tire: since the treads are moving in opposite directions (one upward, one downward) at the point of contact, both wheels rapidly decelerate, torquing the chassis of both cars and often causing one or both vehicles to be suddenly and powerfully flung upwards (the rear car tends to pitch forward, and the front car tends to pitch back.) An example of this is the 2005 Chicagoland crash of Ryan Briscoe with Alex Barron.
The lower weight of an open wheel racecar allows for better performance. While the exposure of the wheels to the airstream causes a very high aerodynamic drag at high speeds, it allows improved cooling of the brakes, which is important on road courses with their frequent changes of pace.