Oscar Piastri and George Russell lost ground to their respective team-mates during qualifying at Spa-Francorchamps because of a remarkably similar power unit issue, according to McLaren team principal Andrea Stella. His analysis highlights a little-known characteristic of the current Formula 1 power units: electrical deployment can create meaningful performance differences even between two theoretically identical cars.
The difficulties separating Oscar Piastri from Lando Norris appeared to share the same origin as the gap between George Russell and Kimi Antonelli. After studying McLaren’s data, Andrea Stella identified power unit behaviour that closely resembled what had emerged inside the Mercedes garage. Although the size of the losses was not identical, both teams experienced a substantial performance difference between their two drivers.
This was not the first time such a pattern had appeared. Oscar Piastri and George Russell have both struggled at times to reproduce the level of performance achieved by their respective team-mates. However, the most striking element at Spa was that the telemetry traces from McLaren and Mercedes reportedly aligned in an almost identical manner.
Electrical deployment explains Oscar Piastri’s Spa deficit
Andrea Stella highlighted the issue while discussing why Oscar Piastri could not use the Mercedes power unit as effectively as Lando Norris. The difference becomes particularly visible at power-sensitive circuits such as Spa-Francorchamps, where the available electrical energy is not sufficient to complete an entire qualifying lap with maximum deployment at every point.
Managing that limited energy reserve is therefore crucial. Teams must determine where electrical assistance will produce the largest lap-time benefit, while also ensuring that deployment does not fade too early on Spa’s long full-throttle sections.
“If we compare Oscar’s best lap in Q3 with Lando’s, it is clear that Oscar loses time on the final straight, in the Blanchimont area, for reasons that have nothing to do with his driving,” Andrea Stella explained. “It is only a small difference in the way the power unit was used. I think it is the same reason behind the gap we saw between the two Mercedes cars. When I compare the data from Kimi Antonelli and George Russell, it looks like the data from Lando and Oscar.”
The comparison is particularly significant because Mercedes had specifically worked on improving the W17’s performance at Spa. The team introduced a revised front wing designed to improve straight-line efficiency, but aerodynamic optimisation alone could not eliminate the differences produced by power unit deployment.
Andrea Stella says Oscar Piastri lost around two tenths
According to Andrea Stella, the power unit behaviour may have cost Oscar Piastri approximately two tenths of a second during qualifying. That is a significant amount on a single lap, especially when the difference was not caused by a driving error or an obvious setup weakness.
“In Oscar Piastri’s case,” Andrea Stella continued, “I think he could have been a couple of tenths faster if the power unit had behaved as we expected. These differences are mainly related to electrical deployment and, when we try to analyse them, we are faced with a very complex situation.”
Andrea Stella explained that modern Formula 1 power units do not operate through a simple open-loop system. Under such a system, engineers could complete an offline simulation, establish precisely how the electrical energy would be delivered and expect the same deployment pattern to be repeated every time.
Instead, a considerable proportion of the power unit controller relies on calculations performed in real time. Its behaviour is constantly adapted according to several parameters detected while the car is running.
“To operate these power units, we do not work in an open-loop mode in which it would be possible to complete an offline simulation and say, ‘This is how the electrical power will be delivered,’ while knowing that it will always behave in exactly the same way,” Andrea Stella said.
“A substantial part of the controller managing the power unit is instead based on real-time calculations. In a sense, the power unit ‘thinks’ ahead and calculates what it will have to do based on many parameters. I do not want to go too deeply into the technical details because I do not want to reveal aspects covered by intellectual property, but many things really happen while the car is moving.”
How super-clipping can alter a driver’s braking reference
One of the examples mentioned by Andrea Stella concerned the braking phase. When a driver approaches a braking zone after experiencing excessive power reduction, described in the source as super-clipping, the car can reach the braking point as much as 10 kilometres per hour slower than expected.
That speed difference does not only affect the time spent on the straight. It also changes the driver’s reference for the next braking zone. A driver who expects the car to arrive at a particular speed must adapt rapidly when the power unit delivers a different level of assistance.
“These situations are quite difficult to master, and that is one of the reasons why drivers often talk about the difficulty, from a driving perspective, of exploiting the power unit,” Andrea Stella explained. “It is not only about achieving maximum power, but also about managing variations in power unit behaviour that have a direct impact on driving.”
This offers important context for the challenges experienced by George Russell. The British driver has already explained how the characteristics of the Mercedes package can require a particular driving approach, even using an unusual Mona Lisa comparison to describe his Mercedes driving difficulties.
At Spa, however, Andrea Stella’s analysis suggested that the telemetry difference between George Russell and Kimi Antonelli was not solely a consequence of driving style. The deployment pattern itself may have altered how each Mercedes behaved on the straights and during the transition into the braking zones.
Modern Formula 1 power units can learn from previous laps
Electrical energy management remains one of the areas that has not yet been completely optimised with the current generation of Formula 1 power units. Their behaviour is influenced by numerous external parameters, while some functions also change according to the history of data accumulated during previous laps.
Andrea Stella explained that the power units can effectively adapt to specific usage patterns. This means that a small difference in how the system operated on one lap may affect its behaviour on the next.
“These power units are capable of learning certain ways in which they are used,” Andrea Stella said. “We could say that they ‘learn’, and this creates small but significant variations that can occur from one lap to another, also based on what they learned during the previous laps.”
This dynamic element makes the system much more difficult to predict than a conventional map that always delivers the same output at the same point on the circuit. Two drivers can begin with nominally identical settings, yet differences in driving inputs, energy recovery, braking behaviour and the system’s accumulated data can eventually produce different deployment profiles.
At a circuit such as Spa, those small variations become especially costly. A reduction in electrical assistance near Blanchimont can affect speed throughout the final part of the lap, while also changing the driver’s approach to the Bus Stop chicane.
Mercedes customer teams finally receive power unit simulation tools
Andrea Stella also revealed an important development for Mercedes customer teams. After a lengthy wait, they now have access to the simulation tools required to prepare a race weekend from a power unit perspective.
These tools allow customer teams such as McLaren to simulate energy deployment before arriving at the circuit, modify the most sensitive parameters and assess how those changes may influence power unit behaviour.
“We have reached the tenth race,” Andrea Stella emphasised, “and we finally have the tools that allow us to conduct simulations before a race weekend. You will have noticed that a large part of the discussions this weekend have focused specifically on the power units and their optimisation, and it does not concern only customer teams.”
“As I said before, it appears that differences also exist within the works teams from one driver to another.”
The timing of the development is important because McLaren had previously been forced to prepare its weekends without access to some of the simulation resources available to the power unit manufacturer. That reduced the team’s ability to study deployment behaviour and optimise the system before the cars reached the circuit.
McLaren worked with Mercedes HPP to close the simulation gap
Power unit simulation enables engineers to modify sensitive parameters and evaluate how each change will affect the system. Some of these areas are specific to the latest generation of power units, while others are established aspects of performance optimisation.
“There are some new areas,” Andrea Stella explained, “but also other more familiar ones, such as optimising the delivery, driving style, gear ratios and so on.”
Andrea Stella had repeatedly indicated from the beginning of the season that McLaren was at a disadvantage because it lacked the necessary tools. However, he stressed that the team had not entered into a public dispute with Mercedes High Performance Powertrains over the delay.
“I think I was clear from the beginning of the season in saying that we were at a slight disadvantage because we did not have these tools,” Andrea Stella said. “We never created any controversy with HPP over this issue. They were extremely busy, but it is true that not having some tools available created a few difficulties for us, simply because of timing.”
“We therefore worked together to make them available as soon as possible, and today we are certainly receiving a major benefit from them.”
The arrival of those simulation capabilities should allow McLaren to prepare its electrical deployment strategies more accurately before future race weekends. However, the evidence from Spa also shows how difficult it remains to predict the exact behaviour of a power unit that continually recalculates its requirements while the car is running.
For Oscar Piastri and George Russell, the Spa telemetry offered a revealing explanation for part of the deficit to Lando Norris and Kimi Antonelli. Their losses did not appear to result entirely from driving performance. Instead, small but meaningful differences in electrical deployment may have altered acceleration, top speed and braking references, creating a visible gap even between two cars running within the same team.
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