Saved up energy for an overtake? The MGU-K limiter could rein you in

The Mexican Grand Prix was a test of patience for many drivers. Overtaking on the start-finish straight proved problematic. Lando Norris endured a particularly frustrating Sunday, spending a long time unable to get past George Russell despite clearly being quicker. The reigning world champion believes an incorrectly set limiter is to blame.

The FIA has to tailor everything to an energy-starved power unit concept. We have been discovering the shortcomings of the new regulations since the start of the season, and there are still more to come. According to Norris, the Mexican Grand Prix exposed another problem with overtaking: the cars have no chance of exceeding a certain speed threshold. This time, however, it is not directly related to the amount of energy in the battery.

How the FIA “restricts” MGU-K deployment

A year ago, Toto Wolff entertained the idea that the new generation of cars could reach speeds of up to 400 km/h on the straights. The reality, however, looks very different. Even at an altitude of 2,200 metres above sea level, where the air is almost 25 per cent less dense, the fastest cars reached “only” 360 km/h.

This is directly linked to the MGU-K settings, which vary from circuit to circuit. In Mexico, the MGU-K supplied the driver with its full 350 kW (469 hp) only up to 290 km/h (see graph below). Beyond that speed, the electrical output was reduced, with the MGU-K switching off entirely at 345 km/h.

A different map applies in overtake mode: the driver receives the full 350 kW of MGU-K assistance up to 338 km/h. From that point, its output drops linearly until 355 km/h. This is also why almost every car’s top speed was around that mark. The fastest overall were Gasly (361 km/h), Hülkenberg (358 km/h) and Hirakawa (357 km/h).

“I mean the main thing with overtaking is you just have the limiter on,” said Lando Norris after the Mexican race. “Like you literally have a limiter that stops you from going over a speed, so it doesn’t matter if you come out two tenths behind the guy, you just hit the limiter and the same limiter as them, and then you cannot do anything, so it kind of ruins racing.”

Lewis Hamilton also highlighted this after the race, having tried in vain to overtake Max Verstappen. That was partly down to the Ferrari power unit’s lack of power, but also to the ineffective overtake mode.

Hamilton could have saved an entire battery’s worth of energy and used it in one aggressive attack on the start-finish straight, but with MGU-K assistance cutting out at 355 km/h, he had no way of overtaking Verstappen on the straight. The speed differential was also smaller because slipstreaming was less effective than at sea level.

Lando Norris believes it is a disgrace that the pinnacle of motorsport is not faster. “It’s something that they need to improve for next season. Especially when motorbikes go 370, and you don’t have a seat belt or anything, and we should easily be able to go quicker than a motorbike, you know.”

Dreams of higher top speeds meet reality

Norris believes changing the split between combustion engine and electrical power will not solve the problem. The FIA needs to adjust the power deployment map and give more thought to the difference between overtake mode and standard MGU-K deployment.

“No, I mean that’s got nothing to do with it,” he said of the revised power split. “We still achieve the same top speeds when you have Straight Mode, and in Straight Mode and with the same power next year you still achieve the same top speed, so you just need to make the limiter higher. It’s as simple as that.”

It is, however, in the FIA’s interest to keep top speeds under control. The reason is not concern about how dangerous the cars might be at 380 km/h. Its greater concern may be how quickly the batteries would drain at those speeds.

The power needed to overcome aerodynamic drag increases with the cube of speed. This means that for a car to accelerate from, say, 300 to 330 km/h, an increase of 10 per cent, it needs as much as 33.1 per cent more power available.

We could also look at that example in reverse. If the engine department miraculously manages to increase power unit output by an incredible 10 per cent (say, from 900 to 990 hp), that translates into a gain of just 3.2 per cent in outright top speed.

Put simply, energy use at high speeds is very inefficient, and Formula 1 now has to count every joule. If the FIA does not cap MGU-K deployment, problems with energy recovery and depleted batteries will be even more pronounced elsewhere on the circuit — perhaps even at tracks where this is not currently an issue.

The rule-makers have taken a wrong turn.