What's the difference between a restrictor plate and a spoiler in NASCAR?

The NASCAR Cup Series circuit returns to Atlanta Motor Speedway this Sunday for the opening race of the 2024 Playoffs. In recent years, fans have seen a major difference in the racing at Atlanta ever since NASCAR required the cars to have restrictor plates.

As at Daytona International Speedway and Talladega Superspeedway, the restrictor plates have forced drivers to run in tight packs and utilize the draft at Atlanta.

For fans new to the sport, there could be some confusion about what a restrictor plate is, what its purpose is, and how it differs from a spoiler. Here's a little bit of information about the two parts.

Restrictor plate

A restrictor plate is a small, square, thin sheet of aluminum with four holes in it that goes in the engine of a NASCAR stock car. The purpose of a restrictor plate is in its name—to restrict the engine's power and slow the car down. This is done primarily as a safety precaution. NASCAR stock cars can reach dangerously high speeds on tracks and it is on such tracks that restrictor plates are used.

Because the engine's power is limited at tracks such as Atlanta, drivers are forced to run together in packs to keep their pace up and find the best speed possible. Pack racing has created some of NASCAR's closest finishes, most recently when Daniel Suarez captured the win at Atlanta last February in a three-wide finish over Ryan Blaney and Kyle Busch.

Spoiler

A spoiler is a completely separate piece that's used on every NASCAR stock car at every track. The spoiler is a long, thin piece of metal that is attached to and extends across the car's rear. The purpose of the spoiler is to prevent unnecessary airflow across the back of the car, which gives the car downforce and can prevent dangerous crashes, such as flips.

The height of the spoiler varies depending on the track. NASCAR will sometimes host test days which allow drivers and teams to show up at a racetrack and log laps to get a feel for how the car handles and thus make adjustments to pieces such as the spoiler. NASCAR went to Charlotte Motor Speedway in 2021 for a test day and experimented with variations of spoilers at different heights. When NASCAR came out with the "Next Gen" car, which debuted in the 2022 season, the initial height of the car's spoiler was eight inches. Later, prior to the cars' debut, the spoiler was reduced to seven inches and then reduced again to four inches.

Thus, while the spoiler and the restrictor plate work to change the dynamics of the car, their specific purpose and their frequency of use differ significantly.

Meanwhile, fans can catch the NASCAR action at Atlanta Motor Speedway on Sunday at 3 p.m. EST by watching on USA Network or listening to the Performance Racing Network (PRN).