Valtteri Bottas believes it's more important to be quicker on the straights than the corners as Mercedes decide how much rear wing they should run for the Belgian Grand Prix.
Mercedes trialled low and medium downforce rear wings with Lewis Hamilton and Bottas during Friday's running as Bottas went fastest in the opening practice session and was only 0.041 seconds slower than Max Verstappen in the afternoon.
"It didn't look too bad today with the pace in the short runs and the long runs," said Bottas. "It was pretty decent.
"[It's] always tricky to compare in detail from the practice but at least the feeling is good so that's a positive.
"We definitely seemed quite fast on the straight line, maybe less so in Sector 2, where the corners are, but for me, for the race, it's important to be quick in Sector 1 and Sector 3."
Wet weather is forecast throughout the weekend at Spa-Francorchamps with an 80 percent chance of rain for the race on Sunday.
Bottas says Mercedes will take it session-by-session as to what their weather forecast is showing, which will help them in their setup decision.
"It's going to be a key decision for what we choose [to run] for qualifying," added Bottas. "It's going to be close with Red Bull, no doubt. We just need to find some marginal gains tonight."
Video: The secrets of the Spa-Francorchamps F1 circuit
Follow Rudy van Buren as he takes you on a flying lap around Spa-Francorchamps while explaining what makes the track so exciting.