The reasons behind Leclerc & Hamilton’s disqualifications

There was plenty to discuss after Sunday's Chinese Grand Prix as the Ferrari pair of Charles Leclerc and Lewis Hamilton, as well as Alpine's Pierre Gasly, were all disqualified.

Two of the three exclusions from the results of the Grand Prix (for Leclerc’s Ferrari and Gasly’s Alpine) were for being 1kg beneath the 800kg minimum weight limit at the end of the race once the fuel had been drained from their cars.

EXPLAINED: Why Hamilton, Leclerc and Gasly were all disqualified from the Chinese Grand Prix – and the fine margins involved

The exclusion of Hamilton’s Ferrari was for the underbody plank being 0.1mm below the minimum permitted 9mm. The plank offence was the same one Hamilton and Leclerc had fallen foul of after the 2023 United States Grand Prix.

The weight exclusions came after a one-stop race in which Leclerc’s final stint was 41 laps (73% of the full race distance) and Gasly’s was 46 laps (82%).

Hamilton, Leclerc and Gasly were all disqualified from the Chinese Grand Prix

The very high level of front tyre graining experienced by everyone on Saturday led to the general expectation of a two-stop race. Had that been the case, the final stint would have been for around 20 laps.

As it turned out the rubbering in of the track ensured that graining ceased to be a significant problem. Degradation rates were generally low and, at 24 seconds, the pit stop loss at Shanghai is relatively high. This all moved the race decisively towards an optimum one-stop.

MONDAY MORNING DEBRIEF: Why the competitive order was jumbled across the weekend in China – but Piastri shone throughout

Why is this significant? Because the weight difference between a set of tyres which has done 20 laps and one which has done over 40 can be as much as 8-10kg.

A new set of the current spec of Pirelli slicks weighs 48kg (21.4kg for the fronts, 26.6kg for the rears). Over a 20-lap stint they would typically lose up to 10% of that.

Although the relationship between stint length and weight is not linear (as it depends how hard they have been pushed, what the track characteristics are and so on), it can be that a set which has done 73-82% of the race distance could have lost as much as 8kg.

SHANGHAI, CHINA - MARCH 22: Tyres outside the Oracle Red Bull Racing garage during qualifying ahead — A new set of the current spec of Pirelli slicks weighs 48kg

Thermal degradation of the tyres was relatively low in Shanghai and the lower the degradation rate, the harder the driver can push the tyres. As a result it’s quite feasible that, untroubled by much thermal degradation, the drivers used up a lot of the tread.

With a loss of 8-10kg, which is impossible to accurately model or monitor, it is quite easy to see why a team might end the race with a car that is 1kg underweight.

But there is zero tolerance in the regulation; it’s either in or it’s out, regardless of the reasons for the transgression. Hence the exclusions.

So, why don’t teams simply incorporate the worst-case scenario of tyre wear when they are ballasting the cars up to their starting weight?

An extra 5kg will cost around 0.195s of Shanghai lap time. Multiplied by 56 laps, that’s almost 11s at the end of the race. In a field as competitive as this, teams will naturally be reluctant to be too conservative on starting weight.

SHANGHAI, CHINA - MARCH 23: Charles Leclerc of Monaco driving the (16) Scuderia Ferrari SF-25 on — Could Leclerc's long final stint have had an impact on his car being underweight?

What about Lewis Hamilton's disqualification?

Tyre wear was also a factor in Hamilton’s underbody plank offence. Just as with the weight, the teams will run the cars as close to the ground as possible as that’s where the biggest downforce is produced.

The rear-facing camera from Hamilton’s car showed how the floor was sparking extensively on the back straight even early in the race when the tyre circumferences – and therefore the ride height – would be bigger than later in the race.

But Hamilton was one of just four drivers who did a two-stop race and his final stint was for just 19 laps. This may have saved him from being underweight at the end but it offers less of an excusing explanation for the excessive plank wear.

There are feasible reasons why the Ferrari may be wearing its plank more than other cars. Visually, the Ferrari appears to be running a slightly higher rear ride height than others when the cars are stationary (i.e. it is very slightly raked).

A crucial part of the SF-25’s concept was moving the cockpit further back from the front axle than on its predecessor, to give better airflow control around the front wheel wake and into the underfloor tunnels.

To accomplish this within only a slightly longer wheelbase, the gearbox casing length was reduced by 5cm. The gearbox sits ahead of the rear axle so the deepest part of the gearbox is now closer to the rear axle than before and therefore rises and lowers more directly to the rear suspension. It will run through a bigger range of ride heights than the old car’s gearbox.

SHANGHAI, CHINA - MARCH 23: Lewis Hamilton of Great Britain driving the (44) Scuderia Ferrari SF-25 — Hamilton was one of four cars to go with a two-stop strategy in China, but he would fall foul of the rules on plank wear

The slight rake of the car seems to be part of a concept that allows it to run a relatively soft (by the super-stiff standards of these cars) rear suspension (at least in its initial travel). This will help give the car good mechanical grip and the Ferrari is invariably the fastest car into slow corners.

However, the bigger rear ride height will cost diffuser performance at low speeds when the rear of the car will be running at its highest. The Giorgio Piola drawing below shows how the Ferrari diffuser has an extra lip, unlike any other diffuser.

It is believed this is to boost diffuser performance at low speeds, an attempt at compensating for a ride height slightly higher than other cars in slow corners.

Formula 1 header templates - 2025-03-25T100708.897.png — Uniquely on the Ferrari, there is a small step at the base of the diffuser, believed to be an aid to diffuser performance at low speeds

But as the car sits down on its softer rear suspension at speed, it may be that the diffuser becomes too effective, grounding out the plank more heavily. Having the gearbox closer to the rear axle may accentuate this effect.

Hamilton made a set up change into Sunday after winning the Sprint and he reported that it destroyed the car’s balance in the Grand Prix, giving him excessive understeer.

Leclerc was notably faster despite front wing damage. Did he lower the ride height? This would tend to give a greater boost to rear load than front (increasing understeer), but may also be what caused the excessive plank wear.

Was Hamilton’s plank depth transgression just a small indicator of a tricky balancing act Ferrari is experiencing in finding the SF-25’s sweet spot?