In their first season as a team, Brawn racing surprised everyone with their car design, upsetting the likes of Ferrari and McLaren to the 2009 title. This was all due to their unique diffuser design.

At the end of 2008, Honda entered administration after the world reeled following the global economic crisis. From the ashes arose Brawn GP with Jenson Button and Rubens Barrichello as their two drivers. Due to the fact that they were using the previous year’s designs, as they had no money, they had to be innovative in order to make sure they could keep up with all the other teams. Major regulation changes aerodynamically were introduced for the 2009 season, almost halving the amount of downforce that could be produced by the car, meaning every team wanted to gain as much of it back. Brawn GP, along with Toyota and Williams, came up with the idea of using a double diffuser.

2009 Regulation changes

Major aerodynamic regulation changes were introduced in 2009 with front and rear wings being altered to try and create closer wheel to wheel racing, a bit like what has been done now from 2021 to 2022. Any winglets or front wing devices used to increase downforce were banned as well as the structural wing made lower and wider. Rear downforce had been decreased by the use of a higher and thinner rear wing.

The Double Diffuser solution

Toyota Williams and Brawn racing created the double diffuser in order to gain back some of the lost downforce. Essentially, they created a small cut out in their diffuser to create a larger area for air to exit the floor. This meant that there was larger space for air to be accelerated out of the back of the car creating more downforce as a result. This meant their car could be faster around the corners without the need to increase drag by using a larger angle of attack on their front or rear wing.

Another factor that isn’t seen, but is major, is the use of the Mercedes engine in 2009. Previously, the Honda engine used at the back of their car was not powerful and unreliable with 9 DNFs in total that season. The Mercedes engine was the best on the grid in 2009, and with only 2 DNFs next to their name in the 2009 season, it was reliable.

Legality issues?

The issue the double diffuser had depended on law 3.17.2 of the F1 regulations:

No bodywork which is visible from beneath the car and which lies between the rear wheel centre line and a point 350mm rearward of it may be more than 175mm above the reference plane. Any intersection of the surfaces in this area with a lateral or longitudinal vertical plane should form one continuous line which is visible from beneath the car.

Designers from Brawn Williams and Toyota found a loophole through this with the double diffuser. Brawn GP did this better than Williams and Toyota as their design effectively had two floors to it with their unique cut out shape, boosting the effectiveness of their double diffuser. When other teams found this trick they missed, their only option was to try and get it banned as it cost money and time to create what was, essentially, a B-spec car. The diffuser produces almost half of the car’s total downforce and is such a key structure that re-designing it would mean the complete re-design of the rear of the car and maybe even the floor.

With 8 wins out of 17, including wins in 6 out of the first 7 races, the genius of Ross Brawn and his team was made clear as they won both constructors and driver’s titles in their first season as a team.