List of smallest winning margins in American open-wheel car racing

American open-wheel car racing, commonly referred to as Indy car racing, is a category of professional open-wheel auto racing in the United States. Since 1996, the highest class of American open-wheel car racing is the IndyCar Series, sanctioned by IndyCar.^[1] The "Indy" in the name refers to the series' premier event, the Indianapolis 500.^[2] The IndyCar Series schedule consists of purpose-built circuits, such as superspeedways, short ovals, and road courses, along with temporary street circuits.^[3]

The Indianapolis 500 played a crucial role in shaping the evolution of timing and scoring in American open‑wheel car racing. In the earliest years of the event, cars had to drive over a wire an inch off the ground, which would record the time of the lap into a paper card system.^[4] Yellow and green lights were installed around Indianapolis Motor Speedway in 1935 to warn drivers of an incident and mandate them to hold their positions until the track was cleaned.^[5] After many drivers found loopholes in this system,^[6] the United States Auto Club (USAC) introduced the Electro-PACER light number board system in 1972 to prevent passes under caution periods.^[7] By 1978, most Indy car races on oval circuits utilized a pace car to keep drivers from passing during cautions, and the Indianapolis 500 implemented the same rule a year later.^[5]

Computerized timing and scoring was first used by MCA TV in the 1969 Indianapolis 500 to present intervals between drivers during their closed-circuit broadcast of the race.^[8] USAC began using computerized scoring in the 1982 Indianapolis 500 with the introduction of the Dataspeed system, designed by IBM,^[9] which kept track of the amount of laps completed, running order, lap times, and fastest lap of the race down to a thousandth of a second, by manually pressing a button.^[10] The Dataspeed system was eventually replaced by the Dorian Automatic Timing Apparatus (DATA-1), the first fully-automated timing and scoring system in Indy car racing history, in the 1990 Indianapolis 500.^[5] With a network of radio transmitters, antennas, and computers, DATA-1 was capable of simultaneously tracking 40 cars and was accurate to a ten-thousandth of a second.^[11] Meanwhile, in 1991, Championship Auto Racing Teams (CART) adopted Electronic Data Systems (EDS)' scoring system, known as EDS Track, which was implemented on 14 of the series' tracks by the end of the season.^[12]

The Indy Racing League (IRL) was initially sanctioned by USAC upon its debut season in 1996, but after scoring blunders in the 1997 Indianapolis 500 and True Value 500, the IRL took over officiating duties for their events.^[13] While CART and its successor—the Champ Car World Series—scored to a thousandth of a second, the IRL began scoring every race down to the ten-thousandths digit in 2001, becoming one of the few motorsport series to do so.^[14] In 2004, the IRL acquired a camera which was positioned on the tracks' start-finish line and snapped photos every ten-thousandths of a second, acting as a backup to the electronic system already in place.^[15] The camera has since played a vital role in determining the winners of photo finishes, such as Buddy Rice in the 2004 Argent Mortgage Indy 300 and Hélio Castroneves in the 2008 Peak Antifreeze Indy 300.^[16][17]

As of 2026, the smallest margin between the first- and second-place finishers in Indy car racing occurred in the 2002 Delphi Indy 300 at Chicagoland Speedway, with Sam Hornish Jr. beating Al Unser Jr. for the victory by 0.0024 seconds.^[18] The high amount of downforce in IRL open-wheel cars created intense pack racing and photo finishes,^[19] eight of which took place in the 2000s decade and are currently included in the top-ten smallest winning margins in series history.^[20]