Robert Kubica has described his US Grand Prix as "worse than bad" as he struggled to find grip before retiring from the race.
The Pole made his one and only pit stop of the race on lap 11, switching onto the hard tyre. Kubica says the thinking behind the stop was to do something different when he had nothing to lose.
"The pace was not there and when you are last, you just try something different," he said. "We just switched to something which not really threw the coin. But when you lack the pace, you have nothing to lose."
Later on in the race, Williams pulled his car from the grand prix after it detected a hydraulic problem with his car.
However, Kubica affirmed that he was having major issues with the car prior to his retirement, as the bumpy circuit made life more difficult.
"I would say it was pretty bad, or even worse than bad," Kubica admitted. "We were just struggling with the grip. On Friday our long runs were not bad, but today it was terrible.
"It [the bumps] was a bit more difficult, with more fuel loads in the car. Especially in the opening laps, when the tyre pressures are low, you get even more of a kick.
"Turn 2 was pretty bad. I think with better cars it would not be affected so much but we were pretty affected in the first laps."
Kubica will leave Williams at the end of the 2019 campaign, with the team confirming that it will not decide on his replacement until after the conclusion of the season.
In what has been a difficult year for Kubica, the 34-year-old says he aims to bounce back stronger in Brazil, the which hosts the penultimate round of the year in less than two weeks.
"As always, just trying to do our best," he said. "We are trying to finish as best as we can in this difficult year, and just looking forward to drive in Brazil. I think it's a nice track, and hopefully we will be better there."