Valtteri Bottas says Mercedes' inability to challenge Ferrari for pole position in China was surprising.
Bottas qualified a distant third in qualifying, 0.530s off Sebastian Vettel's pole position time. Mercedes has struggled for pace and grip on the ultra-soft tyre throughout the weekend in China, while Ferrari has traditionally excelled on that compound.
The Finn believes Ferrari's advantage in Shanghai came in the long corners, particularly in sector one. With both teams now appearing to be evenly matched in terms of engine power and straight-line speed, Bottas admits Mercedes has work to do in terms of improving its understanding of the Pirelli tyres and general improvements to its chassis and aerodynamic performance.
"We are surprised by the gap,'' Bottas said. "We thought going into today we could fight for pole position but that was definitely out of reach, there was nothing in the lap that we could gain that much, in terms of getting the tyres ready, but not by half a second.
"I think they have a really strong car, as can see in very long corners, like Turns One and Two they gain quite a bit on us, and now there is no speed difference on the straights and with the gains they are making on the corners, we have definitely work to do.''
Like Ferrari, Mercedes has opted to start Sunday's race on the more durable soft tyre. Traditionally, the German manufacturer has performed better on the harder compounds but with temperatures expected to be considerably warmer tomorrow, Bottas is unsure how this will impact Mercedes' chances.
"I think we saw in the race [in Bahrain] before that we are, in general, a bit better with the harder compounds. We're still working hard to get better with the softer compounds and Ferrari has done a better job on that.
"Tomorrow will be quite different from today, it will definitively be warmer, at least the air temperatures but the track temperatures will be a question mark. We don't think we are less competitive with the cold weather, we struggled a bit more with the heat in Bahrain, so for sure we need to understand it a bit better and need to make the car better.''
Formula 1 Heineken Chinese Grand Prix U.S. coverage presented by Mothers Polish (All times Eastern)
Qualifying - Saturday, April 14 1:55 AM - ESPN2
On the Grid - Sunday, April 15 - 1:30AM - ESPN2
Race - Sunday, April 15 - 2:05AM - ESPN2
Encore - Sunday April 15 - 1:00PM - ESPNEWS
Encore - Sunday, April 15 - 09:00PM - ESPN2