The Williams Formula 1 drivers reckon they could have finished higher up in Sunday's Bahrain Grand Prix had the FW36 been kinder on its rear tyres.
Valtteri Bottas and Felipe Massa have both identified a lack of rear downforce as key weakness in an otherwise solid design, and reckon the fact they were forced to make an extra pitstop compared to their main rivals derailed their bid to convert top-four qualifying pace into a podium finish.
"We were fighting with Force India [which finished third with Sergio Perez] all through the race, [but] they were much better compared to us using the rear tyres [and] they were able to do two stops, we were not able to do two stops," said Massa.
"There is a lot that we need to do to improve the car because we saw cars able to do two stops and we were not able to do two stops."
"The tyre deg, especially from the rears, was much higher than we expected and actually we were targeting a two stop strategy but we had to switch to three stops quite early and that really had us over in the end, especially with the safety car," added Bottas.
"It seems like they [the Force Indias] had much better traction out of corners.
"In the end, in the last three laps there was this train and there was Force India, there were two Red Bulls and us, but they just always pulled away exiting the corners so well that we couldn't really get close enough to overtake."
Newly-appointed head of vehicle performance, Rob Smedley, said Williams would have to look at more than just the aerodynamics of the car to make improvements.
"It's very important we don't start to look solely in one area. I think that's the wrong approach," he said.
"It's an aerodynamic formula but there are hundreds if not thousands of other minute details that we have to attack.
"Without the safety car we would have finished better than seventh. It didn't help us, but it's part and parcel of Formula 1 racing.
"With the strategy we carried out for the car we have, I'm reasonably happy."