Auto Racing is competitive racing using automobiles. There are as many kinds of racing as there are kinds of automobiles, with divisions for every age and type of wheeled vehicle. Every kind of car from the tiniest utility truck (Like the Daihatsu Midget) to full-size big rig tractors, both with and without trailers. Probably the world's most famous types of racing are drag racing, so-called stock car racing including NASCAR, GT/Grand Touring, F1, and rally racing.
There are forms of auto racing for all levels of involvement, both in terms of time and money expended. For example, the SCCA operates several divisions of racing including autocross in which one competes against the times of other racers, and one car is on a track at a time, as well as touring car racing, orienteering and off-road rallycross. In the lower divisions, the rules allow nearly no car customization, and very little safety gear is required.
At the other end of the cost spectrum we have the open-wheel Formula 1 (F1) Grand Prix racing series which follows a tradition spanning a century. The FIA Formula 1 series itself goes back fifty years. Cars themselves often cost many millions of dollars, and are created, maintained, and piloted by a crew of hundreds. Expensive racing events like Formula 1 are generally run exclusively by factory teams. F1 cars must be powered by a three liter naturally aspirated powerplant, and meet various restrictions on minimum weight and maximum dimensions. The engines themselves often cost in excess of $300,000, and competition is carried out on tracks worldwide. The first race known as a "Grand Prix" was held at Le Mans in 1906, and it has come to be associated with powerful cars.
While most racing series attempt to group competitive cars together, through handicaps if necessary, none put more effort into it than stock car racing. The primary example of this is the IROC or International Race of Champions, an American race in which all teams drive cars engineered and tuned to be as close to identical as possible, putting all of the emphasis on the driver. Other racing series tend to use the addition of ballast weights and intake restrictor plates to control performance.
Not all racing is done on a roadlike surface. Many tracks in Rally racing are made of tarmac, but the majority of them are some combination of dirt, sand, mud, and gravel. One of the most famous rally races is the Pikes Peak Hill Climb, an exhibition race featuring the most highly designed and oddly constructed race cars you will ever likely see, including six wheel drive vehicles and off-roading semis. Without doubt, however, the best-known rally event is the World Rally Championship, or WRC. The world rally championship features four cylinder turbocharged cars with approximately 300 horsepower, running on and off road in countries throughout the world. Teams get three days to scout the course, which must be done in stock vehicles from the same manufacturer as the car itself. Teams get 20 minutes between stages to work on the cars, and only 45 minutes to work on them at the end of the day.
Drag racing is a direct competition of speed in a straight line. Vehicles used for drag racing can be of any type, but the kind we're most familiar with are dragsters, cars built specifically and only for drag racing. Top fuel dragsters run in the neighborhood of 6,000 horsepower out of a mere 500 cubic inches or so. The engines consume themselves rapidly in the course of racing, and must be rebuilt or replaced between events. Slower vehicles are generally placed in groups to keep them essentially competitive, though the point is generally to see who has the faster car. Still, all wheel drive vehicles have a distinct advantage over other cars, for example, and cars using nitrous oxide are generally in their own class.
There is a type of drag racing called bracket racing in which cars compete against their own time. Several trial runs are made to determine a baseline best time, and then drivers compete to see who can get closest to their best. This is probably the most common type of speed trial outside of professional competition.
Many people have been known to take part in illegal street racing, recently made excessively popular and in fact glamourized by the movie The Fast and the Furious. Whether in classic American muscle cars or highly tuned Japanese sports cars, street racing has always been a favorite past time of tuners and hot rodders. Of course, racing on open streets is quite dangerous, since you never know who or what you will find on the roads, and it is naturally illegal. If you get caught keeping time while driving excessively fast on the street, it is often considered "exhibition of speed" which carries serious penalties. Modern street racing is arguably more dangerous than what the hot rodders were up to in the fifties, since they were mostly looking for relatively deserted and quite straight strips of road upon which to drag race, whereas imports emphasize handling and that means twisty roads, though that is almost a whole different kind of racing - "canyon racing". Import street racers are just as likely to engage in an impromptu competition through the downtown area of your local metropolitan center or have a 100+ MPH highway battle in traffic as they are to pull a simple drag race in a quiet industrial area.
Auto racing is, to some, the ultimate competitive sport. It is faster, stronger, louder, and more dangerous than any other competition outside of war that is open to the average person. Drivers wear heavy protective gear, but for many it has not been enough. This risk does not dissuade those who hear the call of a sweet exhaust note wound way up high, because no rush is as strong as crossing the finish line first.