Wind tunnel and CFD limits

Every F1 team is limited in how much aerodynamic testing it can do. The rules, known as the aerodynamic testing restrictions (ATR), cap the number of wind tunnel runs and the amount of computer simulation each team is allowed. Since 2021 those limits have been on a sliding scale: the better a team finished in the Constructors' Championship, the less testing it gets.

Aerodynamics is where most of a car's lap time comes from, so this is one of the most important rules for how fast teams can improve.

#The two tools being limited

A wind tunnel blows air over a scale model of the car while sensors measure the forces on it. F1 models can be no bigger than 60% of full size, and the air speed is limited too. Teams are restricted by the number of runs they can do, and by how long the wind is actually on.

CFD (computational fluid dynamics) is the computer version. Teams simulate the airflow over a digital model of the car. The limit here is on the number of simulations (sometimes called items) and on the computing power used.

Teams use both. CFD lets them try lots of ideas quickly, and the wind tunnel checks the promising ones against something physical.

#How the sliding scale works

The FIA sets a baseline allowance, and each team gets a percentage of it depending on where it finished in the championship. The champion team gets the least, and each place further down gets 5% more.

So the champions get 70% of the baseline and the last-placed team gets 115%, which is well over one and a half times as much testing.

The allowances are reset twice a year. The first half of the season uses the final standings from the year before, and at the midpoint they're recalculated from the current standings. That means a team climbing the table during the year loses some testing time in the second half, and a team sliding down gains some.

To give an idea of the numbers: when Haas dropped from sixth to eighth at the end of 2025, its 10% increase was worth 32 extra wind tunnel runs and 200 extra CFD items for the period.

#New teams

A new team gets the same allowance as the last-placed team. Cadillac was put under these limits during its build-up to joining the grid in 2026, so that it couldn't do unlimited testing before its first race.

#Why it matters

The idea is to stop the most successful teams pulling further and further ahead. A team at the front still has the best car, but the teams behind get more chances to catch up.

The ATR has also been used as a penalty. When Red Bull broke the cost cap in 2021, part of its punishment was a 10% cut to its wind tunnel and CFD time.

There's a separate limit on when teams can work on new rules. Before the 2026 regulations, the FIA banned wind tunnel and CFD work on 2026-style cars until 1 January 2025, so that the richest teams couldn't get too much of a head start.