While Formula E works towards its goal of stretching battery capacity enough for drivers to require only a single car with which to contest an entire race distance, car swaps remain a particularly unusual feature in open cockpit racing. Beyond the obvious hurdles drivers encounter in trying to escape the narrow confines of a single-seater cockpit at speed and then doing up all the various safety harnesses and restraints in the second car, the whole process requires no little input from the engineers to get right and can be critical to determining track position in closely-fought races.

The first issue to negotiate is knowing when a driver is actually going to enter the pits. Unlike in other racing series, the tyres are extremely durable and the cars are not refuelled, which means the focus of pit stop strategy is centred on one thing: energy. In each car, drivers have an imposed battery energy limit that they may not exceed (a little like having a set amount of fuel). How the car is driven will affect the rate at which the energy is used and therefore how quickly the second car will be needed. Data on remaining energy is presented on the driver’s dash and via telemetry to the FIA; due to Formula E’s telemetry restrictions, however, teams must rely on careful planning and on their drivers radioing through values on a lap-by-lap basis.

“All teams will have a pre-determined primary strategy based on simulation and modelling work, as well as a several reactionary strategies based on scenario planning,” explains Vin Patel, chief engineering at Mahindra Racing. “These are all affected by real-time data analysis. Usually, you’ll find the people running at the front will consolidate and default to the same strategy (which is to do the slightly slower, energy critical stint first) while those further back will risk more early on.”

As the race develops, it’s not just how heavy the driver’s right foot is that affects the strategy. Technical glitches, spins, wheel-to-wheel battles or powertrain temperature may all affect how the driver tackles the first stint. “We take into account any issues that may result in too much energy being used,” says Patel. “Then we plan ahead for any possible windows of opportunity, such as safety car stints or periods under a full course yellow.”

A safety car or full course yellow will dramatically reduce the speed of the cars, which in turn lowers the rate of energy consumption. This can lengthen the stint that the driver can do: “You can usually race flat out after a safety car, with powertrain thermal load being the only limiting factor.”

With the decision to pit made, the next hurdle for teams to navigate is making the swap as fast as possible without falling foul of the minimum pit stop time or pit lane speed limit that the FIA mandates at each event. For drivers, this means jumping between cars as quickly as possible (two mechanics are permitted to help each driver) before waiting for the team’s say-so to hurtle back out again. But without telemetry, how does the team know how to sequence and time all of this?

“We sort of work backwards,” Patel explains. “First, each driver’s engineering team calculates how fast the car can legally exit the box from a standing start and how long it takes to reach the FIA timing line at the pit lane exit. We simulate it, then we practice it to be sure this is accurate. We then work out how long it will take the first car to reach the box once it’s crossed the FIA timing line at the pit lane entrance. This is a little easier as we know the car will already be in motion when it enters the pit lane and because we can control the speed precisely by programming the car’s pit lane limiter. We add the two times together; the difference between that total and the FIA’s minimum pit stop time gives us the optimum car-swap window for that round.”

Simple? Not so fast. Remember that “no telemetry” rule? How does the team know when the driver has crossed the FIA pit lane timing lines? “Without telemetry, teams have had to develop various ingenious methods to solve this problem,” says Patel, without divulging any secrets. “Plus, the official timing screens have a counter next to each driver’s name which activates when they enter the pits and stops when they exit.”

To help the actual swap go smoothly, a few teams have invested in countdown clocks for their garages, sited at a height that makes them easily viewable by drivers when sat in the cockpit. Beyond this, the old saying the “practice makes perfect” finds a comfortable home here. “We practice as often as possible,” Patel confirms. “Usually on Thursday and Friday evenings, as well as ‘live’ during free practice sessions on race day. Each of the mechanics who help the drivers have to hone their skills and tailor the process to suit each driver.”

While the car swap procedures are adapted to suit each driver for maximum efficiency, like much else in Formula E, seemingly effortless success is based on meticulous planning by the race engineers and rigorous practice by the whole team.