The 2008 world champion has started from pole position at both of this season's races, clinching victory at the Malaysian Grand Prix on Sunday.
The Briton told reporters: "[Reigning world champion] Sebastian [Vettel] was massively quick. He was applying pressure to Nico [Rosberg] and looking at their pace, their car is just as quick as ours through all the corners, it's just a little bit slower down the straights.
"I have no doubts at all that Renault are going to fix that and when they do, you're going to see a big race between us and the Bulls.
"They still have a fantastic car. I've looked at the GPS, they had the same speed as us through all the corners."
Red Bull have won the constructors' and drivers' titles for the last four years.