Why Wolff and Mercedes have no way back from their Sepang upgrade

The championship leaders had their toughest qualifying of the year in Malaysia. Kimi Antonelli and George Russell were fourth and eighth, half a second adrift of Max Verstappen's polesitting Red Bull. GPblog covered the team's reaction in Antonelli admits Mercedes might be 'missing something' with Bahrain GP upgrades and in Wolff baffled by Mercedes 'going backwards' despite major Bahrain GP upgrade.

That leads to the obvious question: if the package looks slower, why not go back to the old one?

The first answer is about timing. Now the cars are in parc ferme after qualifying, there's no going back unless you want to start from the pitlane. Reverting to a better-understood spec would breach parc ferme and send the car to a pitlane start.

This means the team goes into Sunday's race with what it has. Only minor set-up tweaks are allowed under the parc ferme rules before the grand prix.

This is not a case of bolting the old floor back on, either. The package adopts a very different sidepod profile which it's understood has required the internal cooling architecture to be redesigned. For this reason it is not possible to swap between the two specifications during a race weekend.

That is also why Mercedes put the upgrade on both cars, and why it has no clean comparison to work from. Sepang's rough surface hinders efforts to understand and optimise it because there is no equivalent data set for the previous spec.

The bigger problem goes beyond Sunday. The Race reports that the old parts were reaching the end of their natural life, so under the cost cap Mercedes can't afford to revert and needs to find a way to make this work. Making fresh copies of the previous spec would take an unplanned bite out of its strict cost cap allowance.

Mercedes had already been tight on money. In August, Wolff explained the team's slower development rate bluntly: "We haven't got the money to put developments on the car," he said. Wolff has not given up on the parts. He told Sky Sports F1 that Mercedes "still believe the upgrade works", but the team will need to go through the data.

Antonelli arrived in Malaysia 302 to Russell's 236. Before Baku the gap was 81 points; it is now 66, with eight rounds to go. Since both Mercedes drivers are stuck with the same package, it will not decide the fight between them. The danger is that rivals close in. Ferrari's Lewis Hamilton trailed Antonelli by 103 points in third before this weekend.

The next test comes quickly. Antonelli has already pointed to Singapore next weekend as a better read on the package. With no way back to the old car, that read will show whether Mercedes has a setup problem it can fix or a car problem it has to live with.