MPH: Revealed - the fault behind Mercedes' Belgian GP deployment chaos

Quite understandably, fans and drivers alike were left extremely confused about issues of battery deployment around the Spa-Francorchamps track last weekend. Some were more affected than others, but George Russell’s whole weekend was destroyed by it. Here, we can give the definitive explanation of what was happening out there.

It was a situation made infinitely more confusing by the combination of the nuances of deployment on this most extreme of energy-starved tracks and for Mercedes by two straightforward malfunctions, rooted deep in software errors.

Here’s what happened at the race start: both Mercs have the correct state of charge of their batteries as the lights go out. But as they exit La Source just a few seconds later, both Kimi Antonelli and Russell suddenly have lost between 30-40% of that charge. In how to distribute the electrical energy through the lap, the software algorithm can only work with what charge it has, so it will immediately have reduced the power they each had available on the charge down the hill to Eau Rouge, even though they were still deploying.

Max Verstappen, in second running alongside Antonelli, suddenly realises he may be able to overtake and so uses the overtake button to deploy more, ensuring he gets ahead into Eau Rouge. In that moment, Antonelli has to lift to make room for the Red Bull. In lifting, Antonelli inadvertently resets the system to give a less severe power restriction up the hill and down the Kemmel straight than Russell suffers. This reset allows Antonelli to deploy for longer than Russell down the Kemmel straight, but still for a shorter period than if it had been working fully. Verstappen meanwhile, having used his overtake button, also runs out of deployment early on the straight. So the battery problems on both Mercs have triggered three separate compromises for Antonelli, Verstappen and Russell.

The two Ferraris meanwhile, having not suffered any problems or been caught up in the Antonelli/Verstappen dice down the hill, are free to deploy fully and are flying along on the Kemmel, Leclerc scything by Russell and Hamilton getting down his inside, the precursor to the Hamilton/Russell clash which puts Russell out.

But why had the batteries lost so much of their charge in the opening seconds? There is a start setting which is supposed to cancel as soon as the car gets properly underway off the grid. It didn’t cancel in time, which meant the battery didn’t recharge as they braked for La Source. Once it did cancel a few seconds too late, the system was free to recharge the battery in the normal way. But in the meantime Russell’s race was over as a result.

Verstappen ran out of deployment at much the same time as Antonelli, but the Mercedes driver had the slipstream to allow him to re-pass before Les Combes. Verstappen’s compromised deployment then formed a shield preventing Antonelli from being attacked by Leclerc. With his deployment now functioning normally and with track position held, Antonelli was up and away and Russell was in the gravel. A software fault, the same in both cars, but with circumstances deciding how it was punished differently.

But the fault with the start setting was unconnected to what Russell – and McLaren’s Oscar Piastri – had suffered with in qualifying and practice. They had each ran out of deployment far earlier than their team-mates in the last flat-out Sector 3 section up to the Bus Stop, leaving them 0.5sec (Russell) and 0.2sec (Piastri) adrift of their team-mates across the line. Up until the sudden deployment cut-off, their laps were comparable to those of their respective team-mates.

This is where things get potentially complicated, particularly on an energy-starved circuit, and Spa is the most energy-starved the cars have so far encountered. Just the slightest change in input earlier in the lap can have a major impact on deployment. When the energy is spread so thinly over the lap, the battery state of charge is incredibly sensitive to what the driver is doing with brakes, throttle, entry speeds, etc. Because the algorithm can only work with what’s there and if you’ve taken more, it has to be paid for.

It will also be more sensitive to downforce, tyre grip, surface grip, wind strength and direction, and the slightest change in any of those will change how much and when the power is delivered and there will be far more variation than at energy-rich tracks where there is enough to keep the consistency.