Strategizing Pit Stops: Bahrain F1's Multi-Faceted Challenge

The Bahrain Grand Prix is a Formula 1 race held in the Sakhir desert in the Middle East. The race was first introduced in 2004 and has since been held annually, except in 2011 when it was cancelled due to local protests. The race usually takes place in April but has also been held in November and March. The track has a variety of layouts, with Formula 1 having raced on three different variations. The number of pit stops in the Bahrain Grand Prix can vary depending on the strategy chosen by the teams and drivers. Factors such as tyre degradation, track temperature, and fuel consumption play a role in determining the number of pit stops. In the past, both one-stop and two-stop strategies have been utilised by drivers in the Bahrain Grand Prix.

Tyre degradation and overheating

Rubber, the material used in tyres, is viscoelastic, which means that once it has been deformed, it does not return to its original shape immediately. During this delay, energy is absorbed and converted into heat. The total amount of energy absorbed depends on the number of times the rubber is stressed and its temperature. When rubber is overheated, it can boil, rupturing the surface of the tyre and removing large chunks of rubber. This is known as "blistering", which significantly reduces the contact patch and, therefore, the grip of the tyre.

On the other hand, if the rubber is too cold, it becomes brittle and the surface starts to break away, leading to "graining". Both blistering and graining can lead to an extreme, non-linear loss of performance, which is a nightmare for strategists. Therefore, maintaining the optimal temperature range for tyres is crucial to maximising grip and performance.

There are several factors that contribute to tyre degradation and wear, including track temperature, surface abrasion (how rough or smooth the track surface is), cornering speeds, elevation changes, and length of the corners. High track temperatures, friction from the track surface, and lateral forces from high-speed corners are particularly likely to induce tyre degradation.

Teams and drivers put a lot of effort into trying to understand, predict, and manage tyre degradation and wear. This includes tactics such as warming tyres effectively before a session and during safety car and yellow flag periods, as well as in-race techniques such as adjusting brake bias and lift-and-coast to reduce the load on the tyres.

Pit-stop strategy

The Bahrain Grand Prix is a demanding race for both drivers and their cars. The track's high traction demands and high temperatures can lead to rear tyre overheating. Tyre degradation is a significant factor in the race, and teams must carefully consider their pit-stop strategies to manage this.

Teams typically have a choice between a one-stop and a two-stop strategy in Bahrain. The rear tyres endure a battering due to the dry desert heat, the abrasive track surface, and several traction events around the lap. This often results in high levels of degradation, and those unable to manage their tyres effectively will be forced into a two-stop strategy.

The fastest strategy, according to Pirelli, involves two stops: one stint on supersoft for 15 laps, followed by two stints on soft tyres for 21 laps each. The second-fastest strategy is also a two-stopper, involving two stints on supersofts for 17 laps each and finishing with a stint on softs to the flag.

The one-stop strategy involves a long first stint on supersofts for 24 laps, followed by a switch to softs for the remainder of the race. However, this strategy makes cars vulnerable to attack as their tyres age towards the end of the race.

The pit lane length at the Bahrain International Circuit is 426 metres, which is 59 metres longer than average. This means that a typical pit stop will cost a car around 24 seconds compared to those running at full speed on the track.

The decision between a one-stop and two-stop strategy is influenced by several factors, including the car's performance, tyre degradation, and the potential for overtaking. Teams must carefully monitor tyre conditions and race dynamics to make the best strategic choices.

In addition to pit-stop strategies, teams must also consider fuel-saving tactics. For example, in 2018, the Ferrari was particularly marginal on fuel consumption, and the team may have opted to control the pack at a slower pace to conserve fuel.

Overall, the Bahrain Grand Prix presents a strategic challenge, requiring teams to balance tyre management, pit stop timing, and fuel consumption to optimise their race performance.

Track temperatures

The Bahrain International Circuit, located in the Sakhir desert, presents unique challenges for both drivers and their vehicles. The tyres experience high degradation due to the dry desert heat, an abrasive track surface, and several traction events throughout the lap. As a result, teams must carefully strategize their pit stops to manage tyre wear effectively.

Pirelli's data suggests that a two-stop strategy is typically the fastest approach for the race. The theoretical quickest pit-stop strategy involves one stint on supersoft tyres for 15 laps, followed by two stints on soft tyres for 21 and 21 laps, respectively. This strategy optimizes tyre performance and helps maintain competitive lap times.

The track temperatures in the afternoon are significantly hotter than during the night race. Therefore, FP1 and FP3 practices are less representative of race conditions, making FP2 more crucial for teams to understand tyre behaviour with high fuel loads during the hotter part of the day.

To cope with the high temperatures and demanding braking zones, Brembo has increased the number of holes on the carbon discs and developed new calipers for the Bahrain Grand Prix. These modifications are essential for managing the heat and ensuring the safety of the drivers and their vehicles.

Braking demand

Braking is the first element in a Formula One car's cornering phase. If the car isn't slowed down at the right time and with the right pressure on the pedal, it will compromise the remaining phases of the turn. Braking is crucial to a driver's lap time.

How Braking Works in F1 Cars

When the driver steps on the brake pedal, they compress two master brake cylinders (one for the front wheels and one for the rear), which generate fluid pressure. At the front, the system is simple and direct. The fluid pressure is delivered to the front brake callipers, where six pistons clamp pads against the disc, creating the friction that slows the car down.

At the rear, things are more complex. The wheels can be decelerated by three separate sources: friction from the brakes, resistance from the spinning engine (or "engine braking"), and electrical braking from the hybrid electric motor (the MGU-K, or Motor Generator Unit - Kinetic). When the driver presses the brake pedal, these three systems act in concert via the Brake By Wire (BBW) system to provide the overall retardation required.

The Demands of Braking on Drivers

Drivers need to be very strong to press the brakes with enough force. They stand up in the car to press the pedal with their full weight, generating a force of over 100kg. At the same time, they must modulate their effort with great precision to coax the car through the corner.

The perfect spot to hit the brakes depends on many variables, including fuel load, tyre compound, tyre degradation, and management. This means that the braking point is constantly shifting as fuel burns off and tyres wear down, and drivers must be reactive.

The Demands of Different Circuits on Brakes

Some circuits pose particular challenges for brakes. For example, the Canadian Grand Prix is considered the most demanding circuit on the F1 calendar for brakes. The Circuit Gilles Villeneuve in Montreal requires effective cooling of the brake calipers due to multiple, regular braking events, even though cars are not travelling at high speeds.

In contrast, the Monaco Grand Prix poses a different challenge: keeping the brakes cool despite low car speeds and a lack of high-speed running. Teams must run the maximum size of the brake duct to keep the brakes from overheating.

Braking Technology

Over the past 20 years, F1 brake systems have evolved significantly to meet the demands of increasingly complex circuits. Major progress has been made in brake disc materials, with Brembo, a supplier to multiple F1 teams, at the forefront of development.

In 2013, Brembo introduced the new CER material, which offered gains in performance and wear and reduced maximum wear on the hardest tracks. Ventilation has also improved, with the number of holes in brake discs increasing over the years, from 100 to the current maximum of 1400 for 32mm discs.

Braking and Strategy

Braking is a key area where the driver can extract performance from the car. If a driver brakes too hard or too late, they will likely miss the apex and carry less speed through the corner, resulting in a net loss despite a better braking phase. On the other hand, if they brake too early and with too little deceleration, they will lose time to their adversaries.

Braking and Safety

Braking systems are crucial to the safety of F1 cars. In 2009, the halo device was introduced to protect drivers from serious injury in the event of a crash. Romain Grosjean's terrifying crash at the 2020 Bahrain Grand Prix demonstrated the device's effectiveness, as he was able to walk away from the burning wreckage of his car, which had split in two and set alight after a high-speed collision.

Fuel consumption

The choice of tyre compounds plays a strategic role in fuel consumption. In 2018, the mandatory compounds were medium, soft, and supersoft, a step softer than in 2017. Pirelli's data suggests that a two-stop strategy is the fastest approach, with one stint on supersoft for 15 laps followed by two stints on soft tyres for 21 laps each. A one-stop strategy is also viable, but it requires longer stints, such as 24 laps on supersoft followed by a switch to soft tyres.

The length of the pit lane at the Bahrain International Circuit is 426 meters, which is 59 meters longer than average. A typical pit stop results in a time loss of approximately 24 seconds compared to cars running at full speed on the track. However, the potential for overtaking in Bahrain may encourage teams to opt for a two-stop strategy to minimise the impact of losing time in the pits.

The track temperatures at night races like the Bahrain Grand Prix continue to fall during the race, affecting tyre behaviour and grip levels. As a result, FP2 becomes more critical for teams to understand tyre behaviour in representative race conditions.

The high-temperature conditions and demanding braking zones of the Bahrain Grand Prix also impact fuel consumption. To manage the heat, Brembo has increased the number of holes on the carbon discs and developed new calipers. Overall, the Bahrain Grand Prix is rated a severity of 9 out of 10 in terms of braking demand, with only Montreal, Mexico City, Abu Dhabi, and Singapore ranking higher.

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