Formula E strategy is unlike any other in motorsport and often produces races that throw conventional strategic thought out of the window. As the electric world championship prepares for its season finale in London, we take a look at how this unique strategy works.
The Formula E rules have been written to force teams to utilise the energy from the battery as efficiently as possible. Before each race, the FIA dictates the number of laps and the amount of energy teams may use. Typically, this is around 25 per cent less than what is needed to complete the race, which is why they need to implement energy management techniques and regenerate energy to ensure they reach the finish line.
In the Gen3 era, teams calculate lap energy targets. Essentially, these are the kWh of energy the driver should consume per lap to use all the energy available in the battery in the fastest total race time.
However, the energy consumption targets vary according to the car’s efficiency, as well as track evolution, tyre degradation and the slipstream effect of other cars. Consequently, teams spend much of their time trying to understand these influences.
These are then modelled via a frontier plot, which illustrates the relationship between energy and lap time. Engineers use this plot to identify the lap targets that allow the driver to save energy, for the least possible lap time penalty.
Past Practices
In the previous Gen2 rule set, energy management strategy was relatively simple. The key to winning was to ensure the driver utilised every kWh of allocated energy in the most efficient way possible to achieve the fastest total race time. This typically led to races where the lap energy target remained relatively constant throughout.
Most races in Gen2 went this way, so although energy management was vital, the lap energy targets were a relatively easy calculation. Only if the pace of the leaders was significantly different to what was expected did teams have to adapt their lap counts, and therefore energy targets.
The introduction of Gen3, however, turned the approach to strategy upside down. Formula E races were no longer won by simply achieving the fastest total race time for the allocated energy. Instead, the winner could have excess energy on board their car.
This made race strategy far more complex. Essentially, no driver wants to lead, so the pack bunches up as everyone jostles for position, navigating the tight street circuits three or more cars wide. Then, at a seemingly random lap, a driver will suddenly break away, triggering a near flat-out race and, if you haven’t saved enough energy by that point, you come home last. Simple as that.
‘It is similar to criterium racing in cycling,’ says Roger Griffiths, team principal of the Andretti Formula E team. ‘The leader manages the pace to build up energy, so the lap energy targets increase. Then, at around 70 per cent through the race – although it varies from track to track – once you’ve saved enough energy, you can go flat out until the end.
‘The difference in lap time between the first and last laps of the race can be as much as six seconds, so now a Formula E event really is a race of two halves.’
Power Limits
So, what is it about the Gen3 car that is causing this unique style of Formula E racing?
‘The biggest difference between Gen2 and Gen3 is the power limits, which cascades into a higher drag effect on the cars,’ explains Cristina Mañas, head of performance and simulation at Nissan Formula E Team. ‘We can now regenerate more power – 600kW compared to 250kW – and maximum power output has increased from 250 to 350kW.
‘So, for the same amount of braking torque demand, we can regenerate more power, which we can then discharge on the straights, allowing us to reach higher speeds over the same distance.’
According to data published by Formula E, the top speed of a Gen3 car is 322km/h (200mph), compared to 280km/h (174mph) for Gen2. Although some teams have commented that Gen3 cars are slightly slower than this quoted figure, it is still significantly faster than Gen2. However, the Gen3 carries more drag, which is an important factor in the racing.
Drag force is proportional to the square of speed, so the faster a car travels, the higher the drag force resisting it. Consequently, the car needs to consume more energy to overcome this drag force to achieve the same speed. In practice, this means the leader in free air experiences more drag and therefore consumes more energy relative to the drivers behind, while a driver sitting in the tow of a car experiences less drag and consumes less energy. This banked energy can later be used to overtake during the faster phase of the race.
The energy consequences for being at the front early on are so damaging that, in some cases, drivers have voluntarily moved aside to hand over the lead of the race.
‘The sensitives are so large now that you really can save a substantial amount of energy by being in the tow,’ explains Ash Willoughby, senior energy management engineer at ERT Formula E team.
‘If you are the race leader, the most efficient way to run the race is to follow the ISO energy target, which is the optimum point on the lap frontier. However, drivers behind sitting in the tow can travel at the same pace without consuming as much energy, which gives them an advantage.
‘Let’s take some simple numbers and assume that the driver behind saves 0.05kWh of energy each lap. If they spend 20 laps behind the leader in a 30-lap race, they will save a total of 1kWh, which is a huge saving. Consider that the available race energy in Gen3 is now 38.5kWh, 1kWh is almost three per cent of the total race energy that they’ve banked, simply by sitting in the tow.’
This saved energy increases the lap energy targets for the remaining 10 laps, so the driver has much more energy available for the rest of the race compared to the leader.
‘Everyone is now trying to save energy by following someone else until the point where they have stored enough energy to achieve sufficiently quick lap times that allow them to overtake and defend until the chequered flag,’ continues Willoughby. ‘It has now become a game of who can get to that point the fastest.’
The “Go Point”
Establishing the point at which a driver has enough energy to drive flat out towards the finish constantly changes, but is relatively simple for the teams to calculate for their own cars. There is no live telemetry in Formula E, so the driver updates the team with energy information each lap via coded messages, which the teams then use to adjust the lap energy targets.
The trick, however, is predicting the so-called “go point” of the rest of the field, and then using this knowledge to outpace them to the line.
‘We try to monitor the energy buffer our drivers build up throughout the race and then estimate when we can afford to spend energy on overtakes,’ says Mañas. ‘You then have to factor in that to move through the field, the drivers need to overtake and, with the pack so bunched up, there is a high potential of crashing. It’s difficult for us as engineers to define the perfect strategy, so it comes down to the drivers more to judge when they can make up positions efficiently, and when the pace of the race starts to change.’
As teams have started to get their heads around this unique style of racing, we have seen some blinding strategies come into play. At the first round of the Berlin double header, for example, Nick Cassidy for Jaguar TCS Racing qualified ninth on the grid and, by lap 21, had dropped down to 21st place. However, he had saved such a significant amount of energy that he then moved through the field to take the lead and win by a four-second margin.
Team Tactics
Another trend emerging from Gen3 racing is team tactics. To protect the leader from consuming too much energy, the team in the lead manoeuvres its second driver to the front. Once both drivers are running in first and second, the team then cycles between the drivers, giving each an opportunity to save energy in the other’s tow, making up for the energy deficit of leading.
Other strategies involve defensive driving from the car behind, helping to protect their team mate ahead from an optimistic lunge, or rivals triggering the flat-out phase of the race. Team tactics are particularly influential when it comes to taking Attack Mode. This requires a driver to go off the racing line and drive through an activation zone containing three transponder loops. This triggers an extra 50kW of power the driver can then deploy over the next two, four or six minutes. Each driver must take a total of eight minutes of attack across two activations during a race.
‘We’re seeing teammates now working together to hold up the rest of the field so the driver in front can take Attack Mode without losing places,’ notes Mañas. ‘We saw this with the Porsches in Monaco. [António Félix] da Costa climbed through the field up to protect [Pascal] Wehrlein when he took his Attack Modes. More and more teams are starting to understand this so, if teammates are running together, they now work together more to protect each other from overtakes.’
The limited amount of race energy drivers have at their disposal, combined with this now more powerful slipstream effect, is making Gen3 the most strategically challenging era of Formula E so far.
‘Race strategy in Formula E now is like a game of four-dimensional chess,’ concludes Albert Lau, chief engineer at NEOM McLaren Formula E team. ‘You start with the basic energy targets defined by the frontier plot, which is the most efficient way to complete the race in free air. Then you add a second dimension that covers factors such as track evolution and tyre degradation. The third dimension is this “Gen3 effect” of saving energy in the tow.
‘On top of all that, you also have to manage the temperature of the batteries as well, which is like the fourth dimension.
‘This is where it gets super exciting as an engineer, because there are so many factors you have to consider to be successful, and nobody has got it completely right yet. In Gen2, races were temperature limited. That was the main thing we worried about. We didn’t also have to consider driving in a peloton race. Now, the drivers need to save energy, manage battery temperature and be aware of the race pace in case the leaders break away, all whilst battling for position around tight street circuits. It’s an interesting time to be in Formula E right now, for sure.’
