Tire failures on the cars of Felipe Massa and Kevin Magnussen were the main story of Free Practice 1 for the Chinese Grand Prix. The session had to be red flagged twice so that marshals could clean up debris on the track.
Initial reactions were that the problems were specific to the individual incidents. Williams believed that the wheel rim had failed. And debris might have caused the puncture on Magnussen's Renault.
Pirelli tweeted: "Investigations on both failures on Williams during FP1 show no sign of puncture. Air loss connected to technical trouble."
The ambient temperature at the start of the 90-minute session was 68 degrees Fahrenheit (20 degrees Centigrade) and the track temperature was 91 degrees Fahrenheit (33 degrees Centigrade.) There was a 0 percent chance of rain.
Fernando Alonso was back in action, at least in FP1, as the doctors had cleared him to drive again. But he would have to undergo further medical checks after the session.
So the line-up for the session was: Mercedes - Lewis Hamilton and Nico Rosberg. Ferrari - Sebastian Vettel and Kimi Raikkonen. Williams Mercedes - Felipe Massa and Valtteri Bottas. Red Bull TAG Heuer - Daniel Ricciardo and Daniil Kvyat. Force India Mercedes - Nico Hulkenberg and Sergio Perez. Renault - Kevin Magnussen and Jolyon Palmer. Toro Rosso Ferrari - Max Verstappen and Carlos Sainz. Sauber Ferrari - Marcus Ericsson and Felipe Nasr. McLaren Honda - Fernando Alonso and Jenson Button. Manor Mercedes - Pascal Wehrlein and Rio Haryanto. Haas Ferrari - Romain Grosjean and Esteban Gutierrez.
Vettel and Haryanto were the first out on the 3.387-mile (5.451-km) 16-turn track.
Hamilton and Rosberg set the early (and only) times with their 1:38.802 and 1:39.012 laps.
Not much happened until Massa had his left rear tire come partially off the wheel rim and spun at Turn 6 eighteen minutes into the session.
The only other drivers to set times at this stage were Wehrlein, Ericsson and Haryanto.
The session was red flagged at the 25 mark because the marshals were cleaning up things and sweeping away gravel on the track at Turn 6 after Massa's messy spin. The green lights came on 7 minutes later.
All of a sudden the drivers were keen to get going and the track soon became very busy. But none of them were able to go faster than the Mercedes duo. Vettel got closest with a time of 1:39.291.
Forty minutes into the session the top 10 were: Hamilton, who had had a spin at Turn 11, Rosberg, Vettel, Button, Hulkenberg, Perez, Alonso, Ricciardo, Bottas and Raikkonen.
Massa had another left rear tire come loose on the rim. The session was then red flagged again 56 minutes into the session when Magnussen's left rear tire parted with the rim and scattered rubber debris on the track. As with Massa, it was the soft compound Pirelli tire that has a problem.
The session was restarted with just eight minutes remaining. Once again most of the drivers rushed out including Palmer in the other Renault but not Bottas in the Williams.
Hamilton, on the soft tires, clocked a 1:38.183, and Rosberg beat that with a 1:38.037. Vettel improved to a 1:38.665.
The session ended with no more tire dramas, but Rosberg did have to limp back to the pits because of some sort of engine problem. The top 10 were: Rosberg, Hamilton, Vettel, Ricciardo, Raikkonen, Kvyat, Sainz, Button, Hulkenberg and Verstappen.