A stock car, in the original sense of the term, is 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 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
suspension, engine, etc. are architecturally identical on all vehicles. For example, Monster Energy NASCAR Cup Series race vehicles now require
fuel injection. 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. In Australia there was a formula that was quite similar to NASCAR called
The Racecar-Euro Series began in 2009 and was sanctioned by NASCAR as a touring series in 2012, currently operating as the
NASCAR Whelen Euro Series.
There are several classes 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.
Street stock and pure stock
"True" stock car racing, which consists of only street vehicles that can be bought by general public, is sometimes now called "street stock", "pure stock", "hobby stock", "showroom stock", or "U-car" racing. In 1972,
SCCA started its first showroom stock racing series, with a price ceiling on the cars of $3,000. Some modern showroom stock racing allows safety modifications done on showroom stock cars.
Super stock classes are similar to street stock, but allow for more modifications to the engine. Power output is usually in the range of 500–550
kilowatts). Tire width is usually limited to 8 in (200 mm).
Some entry level classes are called "street stock", and are similar to what is often called "banger racing" in England.
A late model car on a dirt track
Late models are usually the highest class of stock cars in local racing.
 Rules for construction of a late model car vary from region to region and even race track to race track. The most common variations (on paved tracks) include super late models (SLMs), late model stock cars (LMSCs), and limited late models (LLMs). A late model may be a custom built machine, or a heavily modified street car. Individual sanctioning bodies (like NASCAR,
ACT, PASS, UARA, CRA, etc.) maintain their own late model rule books, and even individual racetracks can maintain their own rule books, meaning a late model that is legal in one series or at one track may not be legal at another without modifications. The national touring series, the
NASCAR Late Model Sportsman Division, originated from local late model races in the east coast of the U.S. This division was later called the "Busch Series", the "Nationwide Series" and the "Xfinity Series" as its