Sergio Perez in Force India set the new top speed record in 2018 F1 Championship at the Canadian GP, which was as much as 10 km/h faster than the second fastest driver.
Since 2017, the F1 cars have been slower in the straight line due to a huge downforce increase of around 20%, which inevitably carries more aerodynamic drag which is also increased by 25% wider tyres, also introduced in 2017.
So far, the 2018 F1 top speed was 344.4 km/h set by Daniel Ricciardo in Red Bull RB14 in the race in Baku (Ricciardo was also the fastest in qualifying with 341.8 km/h).
Perez in Force India VJM11 achieved 349.7 km/h on the back straight of Circuit Gilles Villeneuve, 10.4 km/h faster than his team mate Ocon.
Given that Perez was only 1.1 km/h faster than the Ocon in qualifying, the huge difference in the race top speed could only be attributed to the big slipstream effect that Perez had caught behind some driver, while Ocon had less chance to do it in his much less eventful race.