Williams' head of vehicle performance Rob Smedley has explained the thinking behind his team's strategy at the British Grand Prix, which contributed to its two cars slipping from first and second to fourth and fifth.
Felipe Massa passed both Mercedes at the start of the race before Valtteri Bottas moved up to second place following a safety car period. The two Williamses led until the first round of pit stops, at which point Lewis Hamilton stopped for new tyres a lap earlier and used the advantage of fresh rubber on a clear track to undercut both Massa and Bottas.
Smedley said Williams could not match Hamilton's strategy like-for-like as it was worried an early pit stop would mean its second set of tyres would not be able to make the end of the race.
"We didn't want to go too early, we wanted to make sure that we could make the one stop happen," Smedley said. "That was absolutely our main priority because we knew that was the fastest strategy. It's always that cat and mouse game of not having to stop too early so you run out of tyres at the end. That was the decision we were making.
"We were watching what Mercedes were going to do, knowing that they had a quicker car, I mean we saw their in-laps and they were quite stunning. Their pit stops were very, very good as well. So it was just the balance of not waiting too long, but not stopping too early so we'd run out of tyres before the end of the race."
Williams lost second place to Nico Rosberg on track and then third to Sebastian Vettel when rain hit the track late in the race. The Ferrari pitted a lap earlier for intermediate tyres, giving it the advantage in the worsening conditions, but Smedley said Vettel was in a better position due to the timing of the rain.
"We were waiting until the right time to stop. I think Lewis stopped - earlier than us - and he made a really great decision there. We were just trying to watch our sectors and in fact that middle sector - on the lap where he stopped - was getting much quicker. The rain was just hitting at the pit exit area and on the pit straight. When it did hit Sebastian Vettel had probably 15 seconds more or something to make that decision, when it clearly was going to be wet. Our cars were then just past the pit entrance and once you past the pit entry you just have to do another lap like that. That was really disappointed that we didn't quite get that."
f"We thought there'd be a chance towards the end of the race, so yeah we were always on the lookout and as the race was going on it was just quite clear that the rain was going to hit at some point. Then it's just a case of trying to get it right, you know. Also when the rain first hit, we saw cars pitting and going into intermediate tyre and that was clearly way too early. The cars that did pit at the point then had to pit again, because they'd run out of tyres when it really did start raining. It's always a case of trying to get it spot on and unfortunately with the positions where our cars were on the track, we were just a lap too late."
Smedley made no secret of the team's frustration but stood by its decisions.
"Of course there's a sense of disappointment. We've come here, you know - Williams Martini Racing - we've come here because we want to win. You know that's why we all get out of bed in the morning. There's a fair degree of pragmatism to that desire and of course we wanted to get both of our cars on the podium once we got ourselves in a really favourable position.
"We know there's no magic in it. You know once you've got the Mercedes sat behind you, and they've got a quicker car, and it'd be awfully difficult to have both our cars in front of them. So you know, we do have a fair degree of pragmatism. We do want to come here and race, and we do want to come here and win, and we do want to come here and get both cars on the podium. It hasn't happened and so therefore, we're all racers and we're all disappointed."