Stock car racing is a form of automobile racing found mainly in the United States, Canada, New Zealand, Great Britain, Brazil and Argentina. Traditionally, races are run on oval tracks measuring approximately 0.25 to 2.66 miles (0.4 to 4.3 kilometers) in length. NASCAR (National Association for Stock Car Auto Racing) is the world’s largest governing body for stock car racing, and its Sprint Cup Series (named for its sponsor, Sprint Nextel Corporation) is the de facto premier series of stock car racing. Top level races are 200 to 600 miles (322 to 966 km) in length. Average speeds in the top classes are usually 70–80% of comparable levels of open wheel racing at the same tracks. Some stock cars may reach speeds in excess of 200 mph (322 km/h) at tracks such as Daytona International Speedway and Talladega Superspeedway. These tracks have come to be known as “restrictor plate tracks”, a name that is derived from the “restrictor plate,” device that was designed to limit top speeds to approximately 192 mph (309 km/h) on such tracks.
A stock car, in the original sense of the term, described an automobile that has not been modified from its original factory configuration. Later the term stock car came to mean any production-based automobile used in racing. This term is used to differentiate such a car from a race car, a special, custom-built car designed only for racing purposes.
The actual degree to which the cars conform to standard model specs has changed over the years and varies from country to country. Today most American stock cars may superficially resemble standard American family sedans, but are in fact purpose-built racing machines built to a strict set of regulations governing the car design ensuring that the chassis, suspension, engine, etc. are architecturally identical on all vehicles. Ironically, these regulations ensure that stock cars are in many ways technologically less sophisticated than standard cars on the road. For example, NASCAR (the largest stock car organization in the U.S.) requires carbureted engines in all of its racing series, while fuel injection is now universal in standard passenger cars. The closest European equivalent to stock car racing is probably touring car racing. In the UK and New Zealand there is a racing formula called stock cars but the cars are markedly different from any road car you might see. In Australia there was a formula that was quite similar to NASCAR, but it has now closed down, and a form of touring cars has taken its place.
Stock car races take place predominantly on oval tracks of 3 or 4 turns, with all turns to the left. Oval tracks are classified as short track (less than 1 mile), intermediate or speedway (1 to 2 miles) or superspeedway (over 2 miles). Road courses are any tracks having both left and right turns. Depending on the track, typical race speeds can vary from 90 miles per hour (140 km/h) at Martinsville to over 200 miles per hour (320 km/h) at Talladega. In 1987 Bill Elliot’s asphalt blistering 212.809 mph (342.483 km/h) qualifying time at Talladega brought about a change at superspeedways (Daytona and Talladega).Such high speeds and Bobby Allison’s car going airborne into the catch-fence and injuring fans forced NASCAR to implement power-reducing measures, one of which was the mandated implement of below carburetor restrictor plates. This later became known as restrictor plate racing.
Oval circuits differ from the rough terrain and sharp turns of Rally, and the complicated twists and turns of Formula One tracks that put up to 5 or 6 g of horizontal stress on the driver’s body. Stock cars are much heavier than Formula One cars, and as a result they are generally slower. Additionally, they cannot produce the g-forces of an open wheel car. A stock car’s weak handling with high power output places more emphasis on car control.