Waiting time in Mexico: Formula E race stewards investigate suspected traction control at Porsche

Even several hours after Pascal Wehrlein was presented with the 2024 Mexico City E-Prix winner's trophy on the podium in the Foro Sol stadium, it was still unclear whether the German would actually be travelling home as the winner of the race. It was not until 6.51 pm local time that the FIA announced that there would be no penalty against the race winner.

The race was just six minutes old when a message from race control flickered across the timing monitors and the international TV signal: a suspected technical infringement involving Jake Dennis, Norman Nato and Pascal Wehrlein was being investigated. While race control gave the all-clear for Nato just three minutes later, it announced shortly before the end of the race that it would continue the investigation into Dennis and Wehrlein after the end of the race.

It took more than three and a half hours after the chequered flag fell before the all-clear was finally given: Wehrlein retained the race win, Dennis was classified ninth. The official documents revealed that irregularities in the throttle pedal map were the reason for the investigation.

As reported by the colleagues at The Race, the FIA noticed suspicious behaviour from the Porsche cars at the start of the race. The race stewards subsequently "took the necessary time to conduct a comprehensive investigation as per process", an FIA spokesperson is quoted as saying. FIA employee Thomas Chevaucher, former engineer at DS and Stellantis and at times also team boss of DS Techeetah, was involved in the investigation and was seen in the Posche garage during the investigation.

Technical digression: The best possible acceleration

In an ideal situation, exactly enough torque is transferred to the driven wheels during acceleration so that they have no or only minimal slip. Too little torque ensures that the available grip of the tyres is not fully utilised. Too much torque, on the other hand, causes the tyres to spin, the force transmitted to the ground decreases and the tyre surface quickly overheats. It is therefore important to find the right spot.

A traction control system that automatically reduces or even prevents wheel spin when the car accelerates is prohibited by the technical regulations of Formula E. The torque output to the wheels may only be controlled by the driver using the throttle pedal. After there were indications in the Gen2 era of Formula E that some teams were preventing the wheels from spinning with a software solution of the powertrain, the FIA made torque sensors mandatory from the 2021 season onwards.

At the same time, the manufacturers had to homologate the throttle pedal map: Before the season, it was specified in a binding manner how much torque the powertrain delivers to the wheels at which throttle pedal position. This meant that automatic intervention by the software, where the driver leaves their foot on the throttle pedal, could be recognised in the FIA data logger.

However, it is suspected that some teams have further developed their software in such a way that wheel spin is actively prevented, especially during a stationary start, without the driver intervening by changing the position of the throttle pedal. To do this, the teams are supposed to exploit a weakness in the torque sensors used by the FIA.

How does a torque sensor work?

Classical torque sensors work by measuring the strain on the surface of the shaft that occurs during torsion. Put simply, the drive shaft deforms minimally when it transmits force to the wheels. The greater the force, the greater the deformation.

However, unlike in some laboratory set-ups, oscillations and vibrations occur in a Formula E car, which can distort the measurement result. These vibrations have been reduced with larger drive shafts and further developed control systems, but they still occur. This makes it difficult for the FIA to determine whether deviating sensor readings are "natural" or actually indicate some kind of traction control.

It is more than questionable whether the race stewards' decision in Mexico has now put an end to the issue. It can be assumed that Porsche's competitors are very interested in finding out the exact technical background. It is possible that the FIA will clarify before the Diriyah E-Prix which measured values were recorded by the sensors and why these were not categorised as an infringement of the rules. The double-header in Saudi Arabia will take place on 26 and 27 January.