These new changes were introduced to facilitate Pirelli's tyres and therefore to reduce loads, thus canceling the natural increase in downforce that the competing teams would have achieved with their cars in the 2021 season.
In addition, the initial floor change was also revised three more times at the end of 2020.
James Allison, Mercedes technical chief, through a video from Mercedes, said that the small changes made may seem minor, but when added together they mean a significant cut in downforce.
Allison declares: "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.
"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."
Furthermore, the changes made were mandatory as it was expected that the 2019 Pirelli tyre sets would be transferred for a third season in 2021.
Despite this, some other changes have been made to the construction for this year, trying to develop more resistant tyres, giving the teams the opportunity to have another variable to deal with, including a revised profile on the fronts.
So the change in tyre construction means that a 2021 tyre set is about 3kg heavier.
"We got a first glimpse of these new tyres back in Portimao in 2020,
"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." Allison added.
"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."
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