Mercedes tech chief Allison expects return to 2019 F1 downforce levels

The changes were introduced to reduce loadings on Pirelli's tyres by negating the natural increase in downforce that teams would have made with their 2021 cars, given that aero development is not restricted by the freeze that impacts other aspects of the package.

An initial change to the floor was followed by three smaller tweaks that were agreed late in 2020.

In a Mercedes video, Allison says that what appear to be four relatively minor changes add up to a significant overall cut in downforce.

"The combination of those four effects in their rawest form just cut-off and trim back in a way that the rules require brings the performance of the car way back to sort of somewhere near 2019 levels.

"It's been our challenge over the weeks and months since those rules were set in stone to try to recover as much of the performance as possible.

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"That has been quite an entertaining ride in the wind tunnel and in CFD to try and make sure that we get that performance as far as possible back onto the car."

"There has been a triangular cut-out to the edges of the floor in front of the rear wheels which when you see it you'll think, 'that doesn't look that big,' but on its own in its rawest form if you just chop that area off your car it'll take about a second a lap away from the car.

"At the back of the car underneath in the diffuser area the fences were reduced in height so that they can't go as near to the ground, [and] they can't create as good of an aerodynamic seal to the ground as they did previously. And again, they shed a bunch of downforce when they are trimmed upwards.

The changes were mandated because it was anticipated that Pirelli's 2019 tyres would be carried over for a third season in 2021.

However in the end there was a change to the construction for this year, in an attempt to make the tyres more durable, giving the teams another variable with which to deal, including a revised profile on the fronts.

The change in construction also means that a set of 2021 tyres is around 3kg heavier.

"We got a first glimpse of these new tyres back in Portimao in 2020," said Allison.

"We've had two other occasions where we could test them, and they were in Bahrain and then in Abu Dhabi the last race of last year.

"That's not really very much opportunity to take on board a new tyre and get ready for a new season with it because these tyres will affect the way that the car performs, and they affect the way that you have to design the aerodynamic platform, and the way that you have to set up the car.

"So it's been a big challenge for us to try and stretch out that testing data that we had at the tracks last year and to try and make as much as we can out of the tyre data supplied to us by Pirelli."