Before an F1 car turns into a corner, it needs to be slowed down, so braking is the first part of any corner phase. So if a driver doesn't get the braking right, he will usually mess up the entire corner and lose valuable time. From an engineering point of view, a corner presents a bit of a contradiction. Under braking, the car should be as stable as possible, requiring the least amount of driver steering correction.
However, once you reach the turning point of the corner, you want a car with a great turning capability that is very reactive to steering input. Ideal straight-line braking stability would require a rather numb front end with lots of front downforce; however, that would make turning into the corner very difficult. So the engineers have to fine-tune the car and try to find the right balance. The two main areas they will look at for this compromise are aerodynamics - mostly the front wing - and the suspension set-up.
Monza is a relatively fast track, so the drivers have to slow down their cars from very high speeds. Additionally, they will be running the lowest downforce configuration of the year, which makes braking at the Autodromo Nazionale Monza even more tricky.
Most of the track in Monza is wide open throttle and only limited by the drag characteristics of the car and the performance of the Power Unit, making the eleven corners of the circuit particularly important, as that's where a driver can easily gain or lose a chunk of lap time over his competitors.
That is especially true for the two major braking events at the Autodromo - the Variante del Rettifilo (Turns 1 and 2) and the Variante della Roggia (Turns 4 and 5).
On his fastest race lap in 2017 (Lap 50), Lewis Hamilton was going over 205 mph (330 km/h) before he hit the brakes going into Turn 1, shedding over 160 mph (260 km/h) and slowing down to under 44 mph (70 km/h). On the straight before Turn 4, he was doing 192 mph (310 km/h) and decelerated to under 68 mph (110 km/h). At both events, the drivers will easily pull over 4G.
To put this in comparison: a high-performance road car with special tyres can achieve a little over 1G. The heavy braking is not just demanding for drivers, but also for the brakes themselves: On the long straights, brake discs will cool down to about 200 degrees Celsius. But when the driver hits the brakes, temperatures will rise to over 1,000 degrees within a second. Managing the brake temperatures is therefore an important job of an F1 driver as brakes that are too hot are prone to fading and might cause reliability issues.
In reality, in terms of braking, road cars and F1 cars cannot be compared. F1 cars have lots of downforce available - and the amount of downforce increases the faster they drive. The more downforce the car produces, the higher the grip level - which means that the cars have more stopping potential at high speeds than they have at low speeds. This makes braking an F1 car quite challenging as the grip levels change. While, for example, it would be quite difficult to lock the wheels under braking when the car is going at speeds of over 300 km/h, it is in fact quite easy to do so at 60 km/h.
So F1 drivers have to brake very hard at the start of braking when they have the most stopping potential and then fade it as they get towards the turning phase of the corner to prevent potential lockups.
But that's not the only difference between an F1 car and a road car when it comes to braking. F1 cars also use brake migration - a dynamic change of the brake balance as a function of the brake pressure.
Here's how it works: Under braking, there's a weight transfer happening in the car. It's the same kind of weight transfer you can experience when you stop any vehicle abruptly - in a road car, you're thrown into your seat belt, on the underground you might end up on your neighbour's lap. F1 cars use this kind of weight transfer to their advantage and shift the brake bias towards the front of the car when the drivers first hit the brakes. When they then slowly come off the brakes to prevent locking up, the weight transfer to the front is reduced. At that point, the brake power is migrated rearwards - by how much depends on the track and the type of corner. Drivers can adjust the brake migration on a corner-by-corner basis through a rotary switch on their steering wheel. Just before the turning point you could move the brake bias almost entirely to the rear to give the car a bit of oversteer, allowing it to turn more quickly - similar to the effect of pulling the hand brake in a road car.
Since 2014, Hybrid engines have given the engineers the chance to harvest kinetic energy under braking and use that energy to propel the car forwards again when the driver accelerates. But in addition to harvesting energy, the introduction of hybrids and brake-by-wire systems gave the engineers another avenue to fine-tune the car and further advance braking by improving brake migration.
In the pre-hybrid era, the teams used mechanical systems to change brake balance through a corner or a braking event. To quickly adjust the brake balance between corners, they would use a hydraulic system. Both of these functions can now be operated with a switch on the steering wheel - in fact, a total of five buttons and rotary switches on the wheel. This means that the drivers can access those functions much faster.
Another benefit of the system is that the engineers can compensate for how the power unit behaves under braking and downshifting. Every time the driver opens the clutch, he loses the engine braking. In the pre-hybrid era, that would mean that there were sudden shifts in brake balance and brake power every time the clutch would open and close. Today, the cars can counteract that with a little spike of brake pressure every time the car loses the engine braking. This means that the rear brake torque is more continuous, allowing the driver to operate closer to the peak of the tyre slip.
Generally speaking F1 drivers generate a lot of brake pressure. When they hit the brakes, they basically stand up on the brake pedal. As they brake at 4G, they will apply roughly four times their body weight to the pedal. At the same time brakes - like almost everything else in an F1 car - are highly customisable and depend very much on driver preferences. The brake pedal can be adjusted to how hard a driver usually hits the brakes as it works as a lever upon the master brake cylinder. So if a driver feels that he has not enough power in his legs, the brake pedal can be manipulated to generate peak pressures more easily; however, this would also mean that the pedal will travel further. For that reason, training his legs is part of every driver's fitness programme.
The ideal braking point will change over the course of the race - depending on fuel loads, compound choice, tyre degradation and how much the drivers have to manage the tyres. So the drivers have to vary their braking during the race, keeping in mind all the parameters that influence it.
In qualifying, the braking points stay more or less the same as the car goes out on similar amounts of fuel and on fresh rubber. If you look at telemetry overlays from qualifying, you can appreciate that the drivers are able to repeatedly hit the brakes at roughly the same spot. Usually, they will brake within a couple of metres or less; five or six metres are a significant difference. This is all the more impressive if you consider that a car that's going 205 mph (330 km/h) travels almost 92 metres in a single second. So being able to hit the perfect braking point is a matter of fractions of a second.
Drivers determine the ideal points for braking over the course of the weekend. They will start conservatively, braking early and allowing for a small margin of error. As the track builds up grip, they will push the braking points deeper and deeper towards the corner, changing it by a few meters at a time and pushing it all the way to the limit.
But there's always one braking point that is extremely tricky to get exactly right: braking into Turn 1 on the opening lap of the race. There's no practice on Sundays, so drivers have to estimate the grip levels as best as they can from the few laps to grid they do before the race. To make things more challenging, the brakes will be cold, making it even harder to estimate where to brake. Additionally, the other drivers might be willing to take a bit more risk going into Turn 1 as the field is bunched up and one can easily gain a position, so you don't want to brake early as you might be overtaken. All those circumstances make it very difficult to determine when to brake into Turn 1. However, the drivers do get a bit of help from their engineers who will suggest brake balance and brake migration settings to them based on historical data.
Check out our Thursday gallery from Monza, here.