NASCAR announces technical and testing updates to 2026 rulebook

NASCAR made a host of technical rulebook updates on Friday, with some of the most notable changes regarding increased horsepower next season, as well as testing guidelines.

To begin, five racetracks in 2026 will use the short-track/road-course aero package as Cup Series teams compete with an increase to 750 horsepower – a change from previous use of the intermediate aero configuration: Bristol Motor Speedway, Darlington Raceway, Dover Motor Speedway, Nashville Superspeedway and World Wide Technology Raceway.

All tracks under 1.5 miles will see the increase in horsepower.

Concerning testing, NASCAR established new rules for all three national series:

• A maximum of three tests for new manufacturers (manufacturers may be considered "new" if they have not competed in the series during the previous five seasons)
• Each test can have a max of two consecutive days (inclement weather consideration)
• Testing completed by March 1
• Each test is limited to a maximum of three affiliated organizations, with a maximum of two cars each
• Testing is not permitted at tracks that are repaved, new to the schedule, or within 60 days of an event

NASCAR also will mandate A-post flaps at all Cup Series tracks next season. The flap, which runs along the sides of the windshield, is designed to work with the roof flaps to reduce the possibility of a car lifting off the ground. NASCAR did not mandate them in 2025 as they were introduced with the summer event at Daytona International Speedway.

As it does each year, NASCAR will release its full rules brief to the media in January.