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Lewis Hamilton will be downgraded 10 places at Sunday’s Turkish Grand Prix after receiving a penalty for using too many engine parts.
Mercedes took a fourth part – one more than allowed – to reduce the risk of the Briton failing in the tight championship run.
But he only took one engine component – the internal combustion engine – so a complete network collapse escapes.
The aim is to lose as little ground as possible to title rival Max Verstappen.
The Red Bull driver is two points behind Hamilton in the championship after recovering from the end of the grid after his one engine penalty and finishing second behind the seven-time champions in Russia in the last race.
Hamilton led the first practice session on Friday at Istanbul Park, 0.425 seconds ahead of Verstappen, ahead of Ferrari’s Charles Leclerc in third and Valtteri Bottas’s second Mercedes in fourth.
Mercedes made the decision to change the engine for reliability and performance after Hamilton lost one of its three engines to a failure in practice at the Dutch Grand Prix last month.
The use of the fourth combustion engine gives you a little more security and also the overall performance for the championship run-in.
The team based its decision on simulations of the upcoming races and tried to weigh the negative effects of a penalty against the risk of reliability issues.
It was influenced by the fact that such a starter penalty is far less harmful than a failure in one race and thus a penalty in a subsequent race.
Mercedes said it only needed to change the internal combustion engine and not one of the other components: turbo, hybrid system, battery and electronics.
The fifth fastest Ferrari driver in the first practice session, Carlos Sainz, had already been confirmed with a complete engine change, and so was he will start from the back of the grille.
Esteban Ocons Alpine was sixth fastest ahead of McLaren’s Lando Norris, Alpha Tauris Pierre Gasly, Fernando Alonso’s second Alpine and Verstappen’s team-mate Sergio Perez.
Both Red Bull drivers complained of a lack of front grip throughout the session.
The hour-long run went smoothly and the track had gained a lot of grip compared to last year when it reappeared on their return to F1 after a 10-year hiatus and oils seeping out of the bitumen caused an extreme lack of grip.