Nico Rosberg's frustration after the Spanish Grand Prix was understandable. He might not get another chance to extend his lead in the championship to 50 points over teammate Lewis Hamilton this year and he is even less likely to get another shot at winning eight consecutive races in his career. Both those scenarios looked eminently possible as he exited Turn 2 in the lead, but a mistake just 30 seconds earlier as he lined up on the grid proved to be the catalyst for the massive accident that put both Mercedes cars out of the race at Turn 4.
That's not to say Rosberg is to blame for the accident, the stewards' assessment that it was a racing incident seems to be the most sensible view of the coming together, but Rosberg will know it could have been avoided with one flick of a switch on the starting grid.
"Nico was in the wrong setting and that's why he lost power coming out of Turn 3," Mercedes team principal Toto Wolff confirmed after the race. "He did not have as much [electrical] energy as Lewis had. That explains why everything went so quickly because there was such a discrepancy in speed. They needed to make a decision in a split second and they ended up hitting each other."
The setting in question is controlled by the rotary dial on the bottom left of the Mercedes steering wheel. It is labelled "STRAT" which is shorthand for "strategy mode" and is used to select different energy settings such as the fuel flow and, crucially, the Energy Recovery System's (ERS) deployment. On the formation lap, for example, the STRAT mode will be set so that the ERS fully charges the battery in preparation for the opening lap and maximum deployment of electrical energy to the rear wheels. It seems Rosberg did not switch his STRAT rotary to race mode before the start and as a result he was still in another setting, most likely the one designed for the formation lap as he pulled away.
Under new restrictions on team radio this year, drivers are not reminded of the settings they need to be in during the formation lap. Instead it becomes a memory test to make sure all the switches are in the right place before the lights go out. In the pressure of the moment it seems the change of STRAT mode was either overlooked or incorrect.
The oversight did not affect Rosberg's initial pace at the start, however, and he passed Hamilton around the outside in Turn 1. That's because Rosberg had correctly put his car in launch mode as he lined on the grid. Rosberg's launch button is located on the top left rear of his steering wheel and as he engages it two lights become illuminated to the left of the main display screen. The launch mode overrides all the other settings on the wheel to ensure the car is perfectly primed for the run down to Turn 1, so Rosberg's STRAT mode error was initially covered up.
But as his left index finger switched the car out of launch mode midway through Barcelona's high-speed Turn 3, the error on the STRAT mode rotary became apparent and his car reacted as though it was back on the formation lap. In the post-race interviews, Hamilton let slip that Rosberg's incorrect setting effectively stripped the power unit of 180bhp as the ERS started to work in reverse, harvesting energy from the rear wheels rather than deploying power to them as is desired on the opening lap.
To warn following drivers that a car is harvesting and will therefore start to slow, the red rain light at the rear starts flashing. For Hamilton that was the signal that something was wrong for Rosberg, and through the exit of the long sweeping Turn 3 he closed in and prepared to make his move. Rosberg realised his error within a matter of seconds and before the exit of the corner changed his STRAT rotary to the correct setting and hit the overtake button at the top left of his wheel to try to fend off Hamilton. But the damage to his corner exit speed had already been done, allowing Hamilton to attempt a move on the inside as he closed in at a speed 17km/h faster.
"I had a great start and was really excited about the first corner move and getting the lead and then I was sure it was my race to win," Rosberg later explained. "Coming out of Turn 3 I noticed I was down on engine power -- which now I know was because I was in an incorrect engine mode -- I saw Lewis closing in and as soon as I could, I closed the door, I went to the inside.
"It was a clear and strong move to make sure he understood there was not going to be any space there and I was very surprised he went for it anyway. But that's it and then we're in the sand trap. I wasn't surprised because I didn't see him, I was surprised he still went for the inside gap."
Rosberg's blocking move looked aggressive, but it must be remembered that by that time the STRAT mode error midway through Turn 3 meant he was travelling significantly slower than Hamilton as he made a split-second decision to close the door. By the same token, Hamilton's closing speed meant it was very difficult for him to avoid the accident as he was squeezed on the inside. Everyone will have an opinion on the collision, but had Rosberg been in the right STRAT mode from the start it would not have happened.