Basics of drag racing

In a drag race two vehicles go against each other over a straight, measured distance from a standing start. The standard distances are a quarter-mile (1,320 feet/402.3 m), 1000 feet (301.5m) (contested in the highest horsepower classes only), or an eighth-mile (660 feet/201 m). A standard drag racing event involves several classes, each competing in their own single-elimination tournament of head-to-head races.

Before each race (also known as a "pass"), each driver is allowed to perform a burnout (which heats the tires and lays rubber down at the beginning of the track, improving traction), then lines up (or "stages") at the starting line. Informal drag races can be started by any means, including flag-waving and arm-dropping. Professional drag races are started electronically, with a series of vertically-arranged lights known as a Christmas Tree. A Christmas Tree consists of a column of lights for each driver/lane. In each column, the top two lights are small amber lights connected to light beams on the track, which when broken by the vehicle's front tire(s) indicate that the driver has pre-staged (approximately 7 inches (180 mm) from the starting line) and then staged (at the starting line).[2]

Below the staging lights are three large amber lights, a green light, and a red light. When both drivers are staged, the tree is activated to start the race, which causes the three large amber lights to illuminate, followed by the green light. There are two standard light sequences: Either the three amber lights flash simultaneously, followed 0.4 seconds later by the green light (a "Pro" tree), or the amber lights light in sequence from top to bottom, 0.5 seconds apart, followed 0.5 seconds later by the green light (a "Sportsman" or full tree). If the driver leaves the starting line before the green light illuminates, the red light for that driver's lane illuminates instead, indicating disqualification should no further infractions occur.

Several measurements are taken for each race: reaction time, elapsed time, and speed. Reaction time is the time from the green light illuminating to the vehicle leaving the starting line. Elapsed time is the time from the vehicle leaving the starting line to crossing the finish line. Speed is measured through a speed trap near the finish line, indicating the approximate maximum speed of the vehicle during the run.

The winner is the first vehicle to cross the finish line (and therefore the driver with the lowest total reaction time + elapsed time). The elapsed time is a measure of performance only; it does not, per se, determine the winner. Because elapsed time does not include reaction time, a car with a faster elapsed time can actually lose the race if the driver does not react to the green light fast enough. In practice, it is advantageous for the driver to "jump the gun" by a fraction of a second, starting the car during the split-second interval between when the yellow light goes out and the green light goes on. However, if the car leaves the front light beam before the green light comes on, the driver has "red-lighted" (because the red light is lit on the Christmas Tree) and should no further fouls happen during the race, is disqualified. Once a driver commits a red-light foul, the other driver can also commit a foul start by leaving the line too early but would win because he or she would leave the line slower. A driver who gets a substantial lead at the start is said to have gotten a "holeshot". A win where a driver wins a race with a higher elapsed time but lower reaction time is known as a "holeshot win".

It is also possible for a driver to be disqualified for other infractions, depending on the rules of the race, including crossing the centerline between lanes, touching a wall, striking a track fixture, failing to stage, failing a tech inspection, or running faster than expected/allowed for the assigned class. In boundary line violations, if the offending driver have made a clean start, and the red-light driver does not commit the violation unless forced by the offending car for safety reasons, the driver who committed a red-light foul wins.

In the common Eliminator racing format, the losing vehicle and driver are removed from the contest, while the winner goes on to race other winners, until only one is left. In cases where a driver has no opponent for a round, the driver makes a solo pass or "bye run" (in order to at least partially eliminate the advantage that would otherwise come from the engine having one less run on it) to advance to the next round. In most Eliminator formats, the bye runs take place only in the first round. On bye runs, some drivers may choose to drive slowly so as not to stress the car unduly, though choice of lane in the each round is often determined by time in the previous round, making this strategy possibly detrimental. Unlike the NHRA, many European events feature a consolation race where the losers of the semifinal rounds race for third place, the final spot on the podium, and standings points.

During drag racing events, vehicles are classified by various criteria that take into account the extent of modifications to the car. These criteria include engine capacity, configuration of cylinders, frame type, vehicle construction materials, wheelbase, horsepower to weight ratio, number of cylinders, whether or not power adding devices such as turbochargers, superchargers or nitrous oxide are employed, vehicle type (such as car, truck, et cetera), or even make and model for limited entry fields. The aforementioned divisions are in place to ensure that the cars are evenly matched during the race. (not all of these can apply)

Drag racing vehicles are special in that they are modified to be lighter and more powerful than in their standard form. A lighter vehicle means that the power-to-weight ratio is increased and hence a greater acceleration will be achieved. Power increases vary depending on the extent of the modifications to the engine