Guide
Formula E explained: energy limits, Attack Mode and duels
Formula E races are decided by a fixed energy allowance, not outright speed. How the kilowatt-hour budget, Attack Mode, Pit Boost and qualifying duels work.
By CricketTaken EditorialPublished Guide18 min read
Two cars cross the line at a city-centre circuit half a second apart, and the one that lost was quicker all afternoon. It was quicker in practice, quicker in qualifying, and in front for most of the race. It also arrived at the last corner with nothing left in the battery, and the car behind had been saving for twenty minutes precisely so that this would happen.
Formula E explained properly starts there, because the constraint that shapes everything in this championship is not speed. It is energy. Every car is given the same fixed allowance of electricity for the race, the distance is set so that allowance will not cover it at full pace, and the entire competition is an argument about how to spend it. A driver who leads from the front is paying for the privilege in kilowatt-hours, and the drivers behind know exactly what it is costing.
That single design decision explains the odd things you notice on a first viewing: the queue that nobody wants to lead, the sudden dive off the racing line into a marked corner of the track, the car that surges past four rivals with three laps left, and the leader who slows visibly on the final lap and is swallowed. None of it is a gimmick bolted on. It all falls out of a fixed budget in a finite battery.
- 38.5Usable energy in kilowatt-hours
- 300Race power limit in kilowatts
- 600Maximum regeneration in kilowatts
- 25Points for winning a race
Specification figures for the Gen3 Evo car used in the most recent season.
What a fixed energy allowance actually does to a race
Start with the number. The car raced through the most recent season, the Gen3 Evo, carries a battery with 38.5 kilowatt-hours of usable energy. That is the whole afternoon. There is no refuelling in the conventional sense, no way to carry more, and every car has the identical figure.
Now set a race distance that consumes rather more than that at racing pace. The result is that no driver can drive flat out from the start, and the gap between the energy required and the energy available has to be found somewhere. It is found in three places: lifting off the throttle early and coasting to a braking point, braking harder and earlier to recover more energy through the motors, and sitting in another car's wake where the air resistance is lower.
All three cost lap time when you do them and save energy that buys lap time later. The strategic question is therefore not how fast a driver can go, but when to be slow.
That is why the leader's position is uncomfortable. A car in clean air is pushing through undisturbed atmosphere and using more energy per lap than the cars queued behind it. In practice a lead group forms and nobody wants the front of it, so drivers surrender positions deliberately, tuck back into the queue, and wait. Watching the leaderboard alone, this looks like drivers going backwards for no reason. Watching the energy readout, it is the most rational thing on the track.
The consequence is that the order at half distance tells you very little. The car in eighth with a two per cent energy advantage over the leader is often in the stronger position, and the closing stages of an ePrix regularly rearrange the top ten in a way that has nothing to do with anybody suddenly finding pace.
Laps, not minutes, and what an added lap really costs
For several seasons Formula E ran to a clock, forty-five minutes plus a lap, and that produced an odd distortion: a long safety car period ate race time without consuming much energy, so the finish became a sprint on a full battery.
With the arrival of the Gen3 car the series went back to a set number of laps. Neutralisations are now handled by adding distance rather than by stopping a clock. Roughly every four minutes spent behind the safety car or under a full course yellow adds a lap to the race.
The mechanism is neat because it keeps the sum honest in both directions. A caution saves energy, because the cars are circulating slowly. It also adds laps, which need energy to complete. Whether a safety car helps or hurts a given driver therefore depends on where they sit in the queue, how much they had saved already, and whether the extra distance is worth more than the extra allowance.
It also produces one of the cruellest outcomes in the sport. Attack Mode cannot be activated while the race is neutralised, and a driver who has just armed one and then sees a full course yellow has effectively burned it while everyone crawls. Races have turned on exactly that, with a driver holding an unused allocation while rivals wasted theirs behind a slow zone.
Regeneration: the reason the brakes barely need to work
A combustion car throws its kinetic energy away as heat every time it brakes. An electric one can send a large part of it back into the battery, and Formula E has pushed that harder than any other championship.
The current car can recover up to 600 kilowatts under braking, split between the front and rear axles. That is double the car's own race power limit, and it is why the Gen3 generation was designed without conventional friction brakes on the rear axle at all. The rear motor does the work.
The scale of that recovery is what makes the whole format viable. The series has stated that regenerative braking can supply around forty per cent of the energy a car uses across a race. In other words, the 38.5 kilowatt-hours in the battery at the start are not the total energy the car will use. They are the shortfall the driver has to manage on top of what the circuit gives back.
That inverts a normal racing instinct. In most categories, braking later is the aggressive move. Here, braking earlier and harder can be worth more than the tenth it costs, because it fills the battery for a later phase of the race. Drivers talk about the brake pedal as an energy control rather than a deceleration control, and the balance between motor braking and mechanical braking is one of the few genuinely difficult things a Formula E driver has to master. The power unit engineering that Formula One built around energy recovery started from a similar idea, but with a combustion engine still doing most of the propulsion.
Attack Mode: buying power with track position
Every driver has to use extra power during a race, and to get it they have to go somewhere slow.
Attack Mode is armed by steering off the racing line and through a marked activation zone, usually a widened section on the outside of a corner. Driving through it costs time, normally enough to lose a position or two. In exchange the car is released from the normal race power limit and runs at a higher output for a set number of minutes.
The allocation is fixed before each race by the officials, and it is set late so that teams cannot model it for weeks in advance. A driver is given a total amount of Attack Mode time and a set number of activations to split it into, with the choice of how to divide it. Take two even blocks, or a short one early and a long one late, or the reverse. All of the allocation must be used during the race.
That produces the most watchable strategic pattern in the championship. A driver takes Attack Mode, loses two places going through the zone, then spends the next two minutes with a power advantage over cars that do not have it and takes back four. A rival holds theirs, absorbs the loss of position, and waits for a moment when the extra power is worth more, such as immediately after a restart when the field is bunched.
Where it becomes genuinely intricate is when two drivers have different amounts left. A car with six minutes remaining behind a car with two minutes remaining is in a strong position, because it can afford to wait. The commentary on a Formula E race spends more time on remaining Attack Mode than on lap times, and rightly so.
Unlike the movable rear wing that Formula One uses to assist overtaking, Attack Mode is not conditional on being within a gap of the car ahead. It is available to everyone, it must be used by everyone, and the only cost is the detour.
Pit Boost: thirty seconds and ten per cent more energy
The other lever is a stop, and it took years to arrive.
Pit Boost is a mandatory pit stop used at selected races, during which the car takes a thirty-second charge at 600 kilowatts. That adds roughly 3.85 kilowatt-hours to the allowance, about ten per cent more energy for the rest of the race. The stop has to be taken inside a window announced before the event, only one car from each team may take it at a time, and no other work on the car is allowed while it charges.
The strategic effect is larger than the number suggests. A ten per cent increase in available energy is enough to change how hard a driver can push for the remainder of the race, so the timing of the stop becomes a genuine choice. Stop early and you race the rest of the distance with more energy but you rejoin in traffic. Stop late and you spend most of the race managing a tighter budget while cars around you have already topped up.
Because both Attack Mode and Pit Boost have to be fitted into the same race, the two interact. At races that use Pit Boost, the current rules require drivers to take only one Attack Mode activation rather than two, which stops the race becoming a sequence of mandatory detours. Drivers use the pit window to try overcuts, taking Attack Mode first and running hard while rivals are stationary.
- Free practiceTwo sessions, usually forty minutes each, run at full qualifying power so teams can gather data on grip and energy use.
- Group qualifyingThe field is split into two groups by championship position. Each group has ten minutes at reduced power, and the fastest four from each advance.
- DuelsEight drivers face off head to head at full power through quarter-finals, semi-finals and a final. The winner takes pole and three points.
- Race startEvery car begins with the same usable energy and the distance is a set number of laps.
- Attack Mode windowDrivers detour through the activation zone to arm extra power, choosing when to take each block of their allocation.
- Pit Boost, where usedA mandatory thirty-second charge inside an announced window adds about ten per cent to the energy allowance.
- Closing lapsWhoever has energy left attacks, whoever does not defends. Positions change late and often.
The order in which sessions and race elements run at a standard single-header event.
Qualifying duels, and why the championship leader has the harder job
Formula E qualifying is unusual in a way that has a specific competitive purpose.
Drivers are divided into two groups by their position in the championship. Those in odd-numbered places go into one group and those in even-numbered places into the other. Each group gets ten minutes to set a lap at the reduced race power setting, and the fastest four from each group progress.
Those eight then meet in knockout duels, run at full power. Quarter-finals, then semi-finals, then a final. The winner of the final starts on pole and takes three championship points. The loser of the final is second on the grid, the losers of the semi-finals take third and fourth, the beaten quarter-finalists fill fifth to eighth, and everybody else lines up alternately from ninth according to their group times.
The design solves a track evolution problem. A street circuit built on public roads is filthy at the start of a session and gets faster as rubber goes down, so a straightforward one-session shootout would hand a large advantage to whoever ran last. Splitting the field in two and then settling the front of the grid in head-to-head runs on a rubbered-in track reduces that. It is a different answer to the same question that produced the three-part knockout used in Formula One qualifying.
It also has a deliberate edge to it. Because the groups are set by championship position, the leading drivers are distributed across both groups rather than concentrated, and a driver who is doing well in the standings can find themselves in the group that runs on the dirtier track. Nobody in the paddock pretends that is accidental.
The scoring beyond pole follows the standard international scale, 25 points for a win falling through 18, 15 and 12 to a single point for tenth, with one further point for the fastest lap provided the driver finishes in the top ten.
Why the calendar is built on city streets
Formula E was designed around a venue strategy before it was designed around a car.
The founding argument was that electric racing belongs where electric cars belong, which is in cities, and that a championship able to build a circuit on closed public roads over a few days does not need a host country to fund a permanent facility. That put races in the centres of Rome, Berlin, Monaco, London, Tokyo, Jakarta, Sao Paulo and Seoul, in front of audiences who mostly do not travel to racetracks.
There is a technical fit as well. A street circuit is short, typically between about two and three and a half kilometres, tight and slow. Low average speeds mean lower energy consumption per kilometre, frequent heavy braking means plenty of regeneration, and narrow roads mean overtaking is difficult enough that the energy game decides positions rather than raw straight-line pace. A high-speed permanent circuit with long full-throttle sections would flatten all of that.
The commercial case follows the same logic. A city-centre race is a hospitality and brand event in a downtown location for a manufacturer with an electric road-car range to sell, which is a very different proposition from a weekend at a rural circuit and a large part of why sponsorship and manufacturer deals in this series have looked as they have.
The calendar has broadened since. Recent seasons have used permanent venues including Mexico City, Shanghai, the Miami autodrome and Jarama alongside the street tracks, and the most recent season ran seventeen races, the longest in the championship's history. The street circuit remains the core of the idea rather than the whole of it.
Published usable energy for each generation. The Gen3 and Gen3 Evo cars share the same figure.
Show the numbers
| Item | Usable energy |
|---|---|
| Gen1 | 28kWh |
| Gen2 | 52kWh |
| Gen3 | 38.5kWh |
| Gen3 Evo | 38.5kWh |
| Gen4 | 55kWh |
The car itself, and the odd shape of its power figures
The Gen3 Evo has run since season eleven and it is worth understanding why its numbers look the way they do.
Peak power is 400 kilowatts, but the race limit is 300. Attack Mode releases 350. Qualifying duels run at 350 as well, while the group stage runs at the race figure. So the car has more capability than it is normally allowed to use, and the regulations meter that capability out as a competitive currency.
The car weighs around 863 kilograms including the driver, has a front motor as well as a rear one, and takes tyres from Hankook that are used in both wet and dry conditions. The front motor is not a permanent drive: it is there for regeneration and for the specific high-power modes, which is why all-wheel drive appears in qualifying and Attack Mode and not in ordinary racing.
Notice, too, that usable energy went down rather than up between Gen2 and Gen3, from 52 kilowatt-hours to 38.5. That was not a step backwards. It reflects a car built to recover far more energy while running, so it needs to carry less. The battery is lighter, the car is lighter, and the racing depends more on how well a driver harvests than on how much they were handed at the start.
The manufacturer case for being in Formula E
Manufacturers do not enter championships for the trophies alone, and the case here has three parts.
The first is engineering transfer. In Formula E a manufacturer does not build the chassis, the battery or the tyre. It builds the powertrain, which means the motor, the inverter, the gearbox and the software that governs energy deployment and recovery. Those are precisely the components a road-car business needs to be good at, and the efficiency problem the regulations set is the same problem an electric road car has: cover a distance on a fixed amount of energy. A win here is a claim about efficiency rather than about outright power.
The second is cost. Formula E is a controlled-spend championship with spec elements everywhere the money would otherwise go, which lets a manufacturer run a factory programme at a fraction of what a top-level campaign costs elsewhere. That is a very different bargain from the prototype racing at Le Mans, where the halo is bigger and so is the bill.
The third is position. Racing in city centres, in front of urban audiences, with a product that is itself electric, is a marketing alignment few other categories can offer.
The most recent season carried powertrains from Porsche, Jaguar, Nissan, Mahindra, Stellantis under both the DS and Citroen names, Lola with Yamaha, and Cupra, across ten teams and twenty cars. Porsche took the manufacturers' title, Jaguar the teams' championship and Pascal Wehrlein a second drivers' crown. The roster has churned over the years, and that churn is the honest measure of whether the case above is holding.
What changes with the Gen4 car
The next car is a substantial step and it arrives for season thirteen.
The published specification gives it 600 kilowatts of peak power in qualifying and Attack Mode and 450 kilowatts in the race, with all-wheel drive available all the time rather than in selected modes. Usable energy rises to 55 kilowatt-hours and maximum regeneration to 700 kilowatts. Bridgestone replaces Hankook as tyre supplier and brings a dedicated wet tyre, which lets the dry tyre be built with a more aggressive compound instead of compromising for rain.
The car is heavier at around 1,012 kilograms and considerably longer, both consequences of a bigger battery and stronger crash structures for the higher speeds. Friction brakes return to the rear axle for the same reason, and the car gets power steering for the first time in the championship's history.
What that does to the racing is the open question. More energy and more power do not automatically mean less energy management, because the FIA can set race distances to keep the budget tight. The lever the series has always had is the relationship between the allowance and the distance, and that lever does not change with the car.
Who builds what, and why customer teams can win
The entry list looks like a manufacturer championship, and it is not quite one.
The chassis is common to every car and comes from Spark Racing Technology, which also supplies the front axle motor generator unit. The battery is a single supplied item rather than a competitive one. Tyres come from a single supplier and are the same for everybody, in the wet and the dry alike. What a manufacturer designs is the rear powertrain: the motor, the inverter, the gearbox and the control software that decides how energy leaves and returns to the battery.
Those powertrains are then sold on. Andretti has raced with Porsche equipment and Envision with Jaguar equipment, which means a team with no manufacturing arm can beat the factory that built its hardware, and has. Because the differences between packages are narrower than in a series where teams design the whole car, operational quality carries a lot of weight: the simulation work that predicts energy use at a given circuit, the calls made on the pit wall, and the driver's discipline in following an energy target lap after lap.
That is also why the championship tends to produce close fields. A pre-season test in the most recent campaign put the entire grid inside a second, with the top four separated by hundredths. When the machinery is that tightly bunched, the strategic layers described above stop being decoration and become the whole competition.
The counterpart is that a bad software season is harder to hide than a bad aerodynamic one. There is nowhere to spend money to escape it, no development race to win over the winter with a larger budget, and the fix has to come from the same engineers who got it wrong.
What running out of energy looks like
The failure mode in this championship is unlike any other, and it is worth recognising because it happens in public.
A driver who has misjudged the sum does not blow an engine or spin off. They simply slow. The car is still running, still on the racing line, still apparently racing, and cars begin streaming past it in the final two or three laps. Drivers have lost podium finishes in the last kilometre of an ePrix having led comfortably a few minutes earlier.
Sometimes the misjudgement is not the driver's. A late safety car adds laps that were never in the calculation, and everybody who had planned to finish on an empty battery now has to find another lap's worth of energy from somewhere. That is the moment when the queue at the front dissolves, because the drivers who had spent the race conserving suddenly have a surplus and the drivers who had committed to attack have nothing.
The other version happens on a drying track. When rain gives way to sun, cars that started on a wet setup are slower but easier on energy, cars on a dry setup are quicker and thirstier, and the race becomes a race between two entirely different plans. Mixed conditions in this championship rearrange results more violently than in almost any other, and the reason is not grip. It is the budget.
None of this is failure in the ordinary sense. Finishing a Formula E race with a comfortable margin of energy in hand usually means a driver was too cautious, and the ideal race ends with almost nothing left. The skill being measured is the accuracy of a running calculation under pressure.
From mid-race car swaps to world championship status
The format did not arrive fully formed, and knowing where it came from explains several of its current rules.
In the first four seasons the battery could not last a full race, so drivers stopped halfway and got into a second car. That was an honest admission of the technology's limits at the time, and it ended with the second-generation car in season five, which carried a battery large enough to complete the distance. Races then ran to a clock, forty-five minutes plus a lap.
The energy rules under neutralisation went through their own evolution. For two seasons the series simply deducted a kilowatt-hour from every car's allowance for each minute spent behind the safety car, which was a blunt way of stopping cautions from turning the finish into a free sprint. Then came an added-time system, and finally the current added-lap system that arrived with the return to lap-counted races.
The championship gained full FIA world championship status from the 2020-21 season, making it the first single-seater series outside Formula One to hold that title. That mattered for manufacturer boardrooms, because a world championship is a different thing to sign off than a series.
Each of those changes was made for the same reason: to keep the energy calculation binding. Every time a loophole appeared that let a driver finish a race without having managed anything, the regulations closed it. That is the through-line, and it is the best single test to apply to any future rule change the series announces.
How to watch an ePrix without missing the point
A few habits make the format legible.
Watch the energy figures rather than the gaps. Broadcast graphics show remaining energy as a percentage, and a driver two per cent up on the car ahead with ten laps to go is winning the race even while losing it on the timing screen.
Watch who refuses to lead. A leader who lets a rival through into clean air has not made a mistake. They have handed over the expensive job.
Count Attack Mode. Note who has taken what, how much is left, and how it is split. A driver holding a long block for the final phase is planning something, and a driver forced to take theirs behind a queue has usually lost it.
Watch the restarts. Neutralisations add laps, block Attack Mode activation and bunch the field, and more Formula E races are decided in the ten minutes after a safety car than at any other point.
And judge a drive by what a car had left at the flag rather than by how it looked at half distance. A driver who arrives at the last corner with the energy to defend has solved the problem the championship actually sets.
For how the same efficiency arguments are playing out in prototypes and single-seaters, the motorsport section has the neighbouring explainers, and the wider archive covers the rules that decide results across the rest of the sporting calendar.
Common questions
How does energy work in a Formula E race?
Every car starts with the same usable energy allowance, currently 38.5 kilowatt-hours on the Gen3 Evo car, and the race distance is set so that allowance will not comfortably cover it at full pace. Drivers therefore lift and coast, slipstream and brake early to recover energy, and the car in front usually burns more than the car behind. Running out before the flag is a real and regular outcome.
What is Attack Mode in Formula E?
Attack Mode is an extra power setting a driver arms by steering off the racing line through a marked activation zone. It raises the car's output above the normal race limit for a set number of minutes, and every driver must use their full allocation during the race. Because the activation zone costs time to drive through, taking it usually means losing a position before gaining several.
Why are Formula E races a set number of laps rather than a fixed time?
Formula E ran to a clock for several seasons but moved back to a lap count with the arrival of the Gen3 car. Neutralisations are handled by adding laps rather than stopping the clock, with an extra lap added for roughly every four minutes spent behind the safety car or under full course yellow. That keeps the energy sum honest, because a caution both saves energy and adds distance.
What is Pit Boost?
Pit Boost is a mandatory stop, used at selected races, in which a car takes a thirty-second charge at 600 kilowatts and receives roughly 3.85 kilowatt-hours of extra energy, about ten per cent of the race allowance. It must be taken inside a window set before the event, only one car per team may stop at a time, and no other work on the car is permitted.
How does Formula E qualifying work?
Drivers are split into two groups by championship position, with odd-numbered places in one group and even-numbered in the other, and each group has ten minutes to set a time at reduced power. The fastest four from each group advance to knockout duels, run at full power over quarter-finals, semi-finals and a final. The winner of the final takes pole and three championship points.
Why does Formula E race on street circuits?
The series was founded to bring racing to city centres that would never build a permanent circuit, which puts electric cars in front of the audience most likely to buy one and lets a race be staged without a year-round facility. Street tracks are also tight and low-speed, which suits a car with a limited energy budget. Recent calendars have added permanent circuits alongside the street venues.
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