Red Bull and Max Verstappen are in Barcelona to defend the title.
Red Bull were behind world champions Mercedes and Ferrari on the practice timesheets at the Spanish Grand Prix on Friday but hopeful the gap to the Italians might at least be narrowing.
"I think it looks like we have closed the gap a little bit to Ferrari so this is a big positive," said Dutch driver Max Verstappen, who last year became Formula One's youngest winner when he triumphed in Spain aged 18.
"But it looks like Mercedes have brought a good update package as well so they're still quite far ahead," added the 19-year-old, who was fifth fastest in both of the day's sessions.
"We are still the third team but the changes are taking us in the right direction and we have found an increase in grip."
Spain, which is the fifth round of the championship, marks the start of the European season and the top teams have all brought some significant upgrades to their aerodynamic packages.
Mercedes, whose triple champion Lewis Hamilton was fastest in both of Friday's sessions, got most of the attention with a revamped front wing and other eye-catching aerodynamic additions.
Red Bull are waiting with some frustration for an update to their Renault engine, which looks some races away still, but have also made chassis alterations.
"There were times today where the car felt pretty good but at times we were still trying to find our way with the new package," said Australian Daniel Ricciardo, who was sixth fastest.
"I do see a step forward and we aren't looking too bad against Ferrari but I'm sure they will also have more to bring tomorrow.
"We didn't come here expecting to be as quick as Mercedes but we are feeling a bit of progress and now we just need to keep fine tuning everything to get a few more tenths out of the car," he added.
Mercedes lead the constructors' standings, a point ahead of Ferrari, after two wins by each of the teams.
Ferrari's Sebastian Vettel, a four times champion with Red Bull, leads Hamilton in the drivers' standings by 13 points.
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 "Red Bull, Daniel Ricciardo, Lewis Hamilton, Spain, Max Verstappen, Renault, Ferrari, Sebastian Vettel, Spanish Grand Prix, formu")
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