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.
Today most 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 car racers 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. In addition, the Ford Fusion, Dodge
Avenger, Chevrolet Impala, and Toyota Camry competing in the 2009 NASCAR
Sprint Cup Series are front-wheel drive sedans, but the NASCAR versions
continue to use rear-wheel drive.
There are several categories of stock car racing, each with slightly
different rules, but the key intention of cars that look like production
cars, but with near-identical specifications underneath, remains true.
Stock car racing compared to other forms of motorsport
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 the 1980s, the high speeds attained at superspeedways (Daytona
and Talladega) forced NASCAR to implement power-reducing measures, resulting
in the unique style 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 stress on the driver's body. Stock cars are much heavier than open
wheel cars and are generally slower as a result. They cannot produce the
g-forces of an open wheel car, but a stock car's weak handling and high
power output places more emphasis on car control.
Source: http://en.wikipedia.org/wiki/Stock_car_racing
