The traditional field of 33 starters arranged in rows of three is among the most recognizable conventions in motorsport. The field size was fixed at 33 in 1912, one year after the inaugural race, and has remained at that number ever since. The starting grid of eleven three-wide rows is itself a visual icon of the event. The full-time IndyCar Series typically contributes approximately 25 to 27 cars to the field, with the remaining spots filled by part-time or Indianapolis-only entries, known colloquially as "Indy-only" or "one-off" entries. These may be extra cars from full-time teams, returning former professionals, or entries from drivers who compete exclusively at Indianapolis.
Qualifying takes place over two separate days in the weeks leading up to the race, with practice sessions and a dedicated Fast Friday session preceding the time trials. Each qualifying attempt consists of four consecutive timed laps, a ten-mile distance that has been the standard since 1939 and was first introduced in 1920.
On Saturday, all entries are guaranteed at least one qualifying attempt. The fastest twelve drivers from the Saturday session advance to a shootout on Sunday to determine the pole position and the first four rows of the grid. Drivers who qualify between approximately tenth and thirtieth place have their grid positions locked in from Saturday and do not re-qualify. Drivers who fall to thirty-first place or below on Saturday enter a separate last-chance session on Sunday, from which the fastest three cars claim the final three grid positions.
For drivers who choose to improve their Saturday time, two re-attempt lanes are available. Lane 2 is designated the "no risk" lane, where a driver may keep a previous time if the new attempt is slower. Lane 1 is the "priority" lane, which gives priority access to the track but requires the driver to withdraw any previous times regardless of the outcome. This creates a meaningful strategic decision for teams near the bubble of the field.
On Sunday, the twelve drivers who advanced from Saturday's session qualify in reverse order of their Saturday times. Each car makes exactly one attempt. The fastest six from this session advance to the Firestone Fast Six, the final round that determines the pole position. In the Fast Six, each of the six remaining cars makes exactly one attempt, with the fastest time winning pole.
The shootout structure creates multiple layers of competitive tension across the two qualifying days. A driver who sets the fastest Saturday time goes into Sunday's session as the overall leader but faces the uncertainty of knowing that all twelve advancing drivers must beat or match each other in reverse order before the ultimate final six attempts.
Cars are allowed two warm-up laps before an attempt begins. A team member stationed at the north end of the main straight waves a green flag to signal the start of a timed attempt; if no flag is waved, the car is waved off without penalty. An attempt can be aborted at any point by the team, the driver, or race officials, though if the car is on track when the abort occurs, the attempt is counted and any previous time is forfeited unless officials called the wave-off due to weather conditions. At the end of each session, a ceremonial gun signals time expiration; any attempt already in progress may be completed, but no new attempts are allowed.
Before and after each qualifying attempt, cars undergo technical inspections. The pre-qualifying inspection is relatively brief and focused on safety, conducted in the pit lane queue. The post-qualifying inspection is more rigorous and takes place in the garage area, focused on detecting any deviations from the performance regulations. Cars can be fined or disqualified if they fail the post-qualifying check.
The multi-lap, multi-day qualifying format distinguishes Indianapolis from virtually every other major race. Formula One, for example, uses a single-lap knockout format conducted in one afternoon. The Indy procedure preserves a tradition of extended time trials that dates to the earliest years of the race, when the "month of May" at Indianapolis included extensive practice and multiple qualifying days spread across the weeks before the race.
The 25/8 Rule controversy of 1996, in which Tony George reserved 25 of the 33 grid positions for IRL points leaders, was precisely so disruptive because it broke the fundamental assumption that all starting positions were open to qualification on merit. Returning to fully open qualifying was one of the symbolic restorations of the pre-split tradition after the IRL-CART reunification in 2008.