Formula 1 2017: How the balance of power is shifting between Mercedes and Ferrari
Sky F1's Mark Hughes examines how and why the balance of power has fluctuated between Mercedes and Ferrari this year...
Last Updated: 31/07/17 11:33am
Mercedes has now won twice as many 2017 races as Ferrari - and Lewis Hamilton's dominance of the British GP was total, the Ferraris destroying their tyres in trying to keep up.
So are we seeing Mercedes grind ahead in the development war as it better understands its intricate diva of a car? Or have we just had a run of circuits that happen to suit the Merc's concept better than the Ferrari's?
Perhaps a little of both. But there's a third factor too.
The FIA's various rulings on technologies that each team has been using in attempting to gain a definitive advantage. There have been three key rulings this season, one hurting Mercedes, two directed at Ferrari.
1) The pre-season banning of the hydraulically-operated heave spring Mercedes had conceived the W08 around.
2) Technical directive 22, issued on the Tuesday prior to Azerbaijan, but essentially underlining the pre-season TD04 banning of oil burning in the combustion chambers.
3) Ferrari being requested before the Austrian race weekend to stiffen the slot attached to the front of its floor.
The Ferrari and Mercedes: Compare and contrast
To more fully understand how these rulings have impacted upon the competitive picture, it's as well to recap on the key differences between the two cars.
The Mercedes W08 and Ferrari SF70-H are quite different in concept. The long wheelbase of the Mercedes is a significant factor in its better aerodynamic efficiency (ie for a given downforce it has lower drag).
The airflow around the shorter wheelbase Ferrari has less length in which to re-attach efficiently as it makes its way around various obstacles, such as the wheels. However, the shorter wheelbase allows the physically smaller Ferrari to be lighter - and thus the team can use more ballast to vary its balance from one track to the next without as much compromise, giving it a bigger set-up window and more flexibility in getting the tyres to work front and rear. Mercedes can now use ballast (having been over the weight limit for the first four races), but still not as much as Ferrari (which is reportedly 7kg under the minimum weight limit, pre-ballast).
In terms of aerodynamics, the Mercedes is a low-rake car, the Ferrari an increasingly high-rake one (following the example set by Red Bull). Generally, the closer to the ground the leading edge of the floor runs, the more downforce is produced thanks to the principle of ground effect.
As the speed of the car increases, the downforce acting upon it increases, pressing the car down harder on its springs and reducing the ride height (and further increasing the downforce). As the speed decreases, so it rises on its springs and the aerodynamic load provided by the floor reduces again.
A high-rake car (with ride heights set to make it downward-sloping towards the front) amplifies the ground effect of the floor. The slope means the floor has a bigger expansion area behind the tiny gap between the floor's leading edge and the track. The bigger this expansion area is, the faster the air is sucked through the gap and the greater the downforce.
The key disadvantage of a high-rake car is that at low speeds, with the already high rear end at its highest as the loads bleed off it, it is very difficult to keep the airflow attached to the diffuser at the rear of the floor, potentially losing you a lot of downforce at those speeds.
The Mercedes W08 in focus
Over the years, the Mercedes concept has been to try to get the best compromise by having a low-rake car (thereby retaining more downforce at low speeds) but with a very powerful forward floor, with a highly intricate arrangement of under-body vanes guiding the flow to it (to compensate for the less extreme, low-rake, slope of the floor).
A potential downside of this philosophy has always been that as the speed falls as the car enters into the corner and the ride height increases, it causes a big balance change - because the gap between track and the leading edge of the floor has increased, but there is not much compensation from the increased rake (as you get with a high-rake car - ie a high-rake car is even higher-rake as the speed comes down).
So the balance of downforce changes between having plenty of front end upon turn-in, to having less so as the speed falls, potentially giving you mid-corner understeer. Merc's hydraulically-controlled heave spring of 2016 allowed the leading edge of the floor to remain low even as the speed decreased (through stored energy from asymmetric valving).
It enabled the Mercedes to have its aero cake and eat it. Then it was banned - on the eve of the season, after Ferrari questioned it by outlining to the FIA how they believed it worked and how it was therefore primarily an aerodynamic device.
What that ban left Mercedes with was a car that had been designed around a feature that was no longer permitted. So it became quite a tricky beast to set up. You could have it with a good front end but a poor rear - or vice-versa. Getting the two ends joined up was very difficult.
That made for run-on difficulties with getting the very sensitive 2017 tyres into their temperature operating window, front and rear at the same time. For much of the season, the Merc would work well on only one compound but not the other, a real disadvantage against the more flexible Ferrari, one that the initial lack of balance-altering ballast only exacerbated.
But when working well within its tightly-defined window, the Mercedes was a faster car. Its greater body surface and underfloor allowed it more total downforce; it was just that its powerful forward floor - without the compensating hydraulic heave spring - made for a big balance change as the speed reduced.
It has taken Mercedes much of the season to tame that - but now that it has, the W08 is flying.
The Ferrari SF70-H in focus
The Ferrari features a particularly powerful diffuser and rear underbody (with clever flexing ahead of the rear wheels thanks to trick carbon lay-up) that delivers a lot of downforce at high speeds. It tends therefore to have a very strong rear end (something that Sebastian Vettel loves).
As the speed decreases it becomes less powerful (partly because of the high-rake) and the aero balance shifts forwards. So giving an understeery sort of turn-in, with the rear then rotating the car into balance as the speed bleeds off.
So what we saw at Silverstone was exactly that: Mercedes drivers turning in late and positively, with the car just following its nose, the Ferrari drivers sliding the front of the car into the turns, with the rear then rotating the car into balance.
Around the high-energy fast corners of Silverstone, that balance absolutely killed the front tyres of the Ferraris - until there was no tread left and they delaminated. The Merc's natural balance, borne of its different aero concept, was much better suited than the Ferrari to Silverstone.
Previously, Ferrari might have altered that balance by tweaking the traits of the front of its floor. But the ruling introduced in Austria prevented them being able to do that. A slot at each side of the floor's leading edge would flex as the downforce built up, and it appears that the degree to which it would do so was controlled by the slot's exit.
It's believed to have flexed the floor down at speed, increasing its aerodynamic power. Together with the powerful diffuser at the rear, it worked well. But with Ferrari having to close the slot's exit and put a stiffening bar across, the front end became less aerodynamically powerful. For the balance required at the Red Bull Ring, that was fine. For that required at Silverstone, it meant a car that ate its front tyres.
There are many ways to skin a cat and both teams will find further ways around whatever restrictions are placed upon them. Furthermore, the Hungaroring's layout might be expected to favour Ferrari.
But the effect of the off-track technical rulings on the dynamic of the title fight should not be under-estimated.
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