[ericcumbee]

It's called a run down test. You accelerate to a certain speed, and then coast and the way the car slows down is where you get the data from.

It's not a new idea. Teams including Audi's Le Mans squad use it. Teams have rented the Shuttle landing facility at Cape Canaveral to do the same thing. The advantage of the Tunnel is there are less variables to contend with such as things like wind.

[Gracana]

That's not the only thing they were doing. The article also mentions braking tests, and pulling all kinds of telemetry. These things aren't new, but being able to do all these tests and measurements on a full-sized car in a controlled environment is rather unique.

[mwg66]

It is also common place in F1, particularly during winter testing and occasionally FP1.