Editing Indianapolis 500 (section)

===Technical regulations===
[[File:PenskePC23.jpg|thumb|[[Penske PC-23]] [[Mercedes-Benz|Mercedes]], [[1994 Indianapolis 500|1994]] winning car]]

Technical specifications for the Indianapolis 500 are currently written by [[IndyCar]]. Rules are generally the same as every other IndyCar race. In the past, particularly during the era in which USAC sanctioned the Indy 500 (but CART sanctioned the other Indy car races), rules at Indy slightly differed at times. The result, for example, would be a particular chassis or engine configuration being legal at Indy, but not so at the CART-sanctioned events. This was rather commonplace in the 1980s and early 1990s, when "stock-block" engines (namely the V-6 Buick) were allotted an increased level of turbocharger boost by USAC at Indy, compared to the purpose-built V-8 quad-cam engines. While the "stock block" engines were technically legal in CART competition, they were not given the increased boost advantage, which effectively rendered them uncompetitive, and precluded their use by teams. The most famous manifestation of the USAC rules disparity was the [[Ilmor]]-built [[Ilmor#Racing in the USA|Mercedes-Benz 500I]] engine fielded by [[Roger Penske]] in [[1994 Indianapolis 500|1994]].<ref name="INDY31">{{cite news|title=The Penske-Mercedes PC23-500I|publisher=forix.autosport.com|url=http://forix.autosport.com/8w/penske-mercedes-pc23.html|access-date=May 27, 2010|archive-date=September 22, 2022|archive-url=https://web.archive.org/web/20220922091434/http://forix.autosport.com/8w/penske-mercedes-pc23.html|url-status=live}}</ref>

Teams may enter up to two machines under a given car number—the "primary" car and a "backup" car. The backup car is identified by the letter "T". For example, the two cars for the #2 team would be numbered #2 and #2T. Both cars may be practiced during the month, but due to engine lease rules, they must share the same engine. It is not uncommon for teams to prefer their backup car, if it is deemed faster, or for other strategic reasons. Additionally, as the month wears on, a "T car" may be split off into a separate entry, and reassigned a new number, or be sold to another team.

All cars must pass a rigorous technical inspection before receiving a sticker signifying that the car is eligible to practice. Various criteria include minimum weight, dimensions, and approved parts, particularly safety equipment. Before and after qualification attempts, cars must pass another inspection. The pre-qualifying inspection is focused on safety aspects and is done on the pit lane qualifying queue. It is relatively brief, due to the time constraints of the qualifying procedure. The post-qualifying inspection is much more stringent and lengthy, taking place in the garage area. It is to detect deviations from the performance guidelines set forth by the league, and cars can and have been fined or outright disqualified if they fail inspection.

During the race, work on the car is permitted, but it is usually limited to routine pit stop work (changing tires and refueling) and minor adjustments (wing angles, etc.) Pit stop activity is rigorously rehearsed by the crews and in modern times, routine pits stops are regularly completed in under ten seconds. Other more involved work, such as replacing damaged bodywork (wings, nose cones, etc.), can also be completed quickly by the crews. More lengthy repairs are allowed, and since 1998 teams are permitted to return to the garage area to make heavy repairs. However, there are limitations to the extent of repair work allowed and the practicality of such work. Teams are not allowed to change engines, and since 1933<ref>{{cite episode|series=The Talk of Gasoline Alley|series-link=Donald Davidson (historian)|station=[[WFNI]]|airdate=August 5, 2020}}</ref> a rule has been in place where teams are not allowed to add [[Motor oil|oil]] once the race has begun. In addition, the officials designate a certain lap after which off-track cars being serviced/repaired are no longer permitted to return to the race.