CONCORD, N.C. – NASCAR updated its rule book for the 2024 Cup Series season on Wednesday, setting the rules package that will be used on a majority of the tracks that measure 1 mile or shorter as well as all road courses. 

The rule book update revealed the following details for the short track/road course package: 2023 short track/road course splitter stuffers, no engine panel strakes, a three-inch spoiler (was previously two inches), simplified diffuser and simplified diffuser strakes. The simplified diffuser will not be used for the Clash at Los Angeles Memorial Coliseum on Feb. 4. Bristol Motor Speedway and Dover Motor Speedway will also not use the new aero package. 

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The race at Phoenix Raceway on Sunday, March 10, will be the first to utilize this rules package. As a result, teams will have a 50-minute practice session on Friday, March 8, a departure from the usual 20-minute group practices held on most weekends. The 1-mile track was also the host of a two-day test in early December where six teams, including Kyle Larson and the No. 5 team, tested different aspects of a potential short-track package and provided feedback through the test sessions. 

"At the test, we noticed an improvement in traffic," Dr. Eric Jacuzzi, NASCAR vice president of vehicle performance, said in a statement. "The car did not lose rear downforce when it yawed, which is an issue we fight with the current car. The drivers would be able to slide around more on the short tracks and really have to be less careful about putting power down. We felt that would be a benefit, and that was the big takeaway from the driver feedback. At the test, they felt they could really tell that it was more forgiving. They felt they could slide the car."

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In an appearance last month on SiriusXM NASCAR Radio (Channel 90), No. 5 team crew chief Cliff Daniels offered his insight into the final portion of the December test, which utilized a package that is pretty similar to the one NASCAR announced. 

"The aero package we ended the test on everyone seemed to be favorable of, which is pretty normal splitter on the front of the car, a little taller spoiler and what NASCAR calls the simple diffuser on the rear," Daniels said. "All drivers seemed to be in favor of that. That feedback was well received by NASCAR. I think there’s been a lot of good dialogue between NASCAR and the teams."