Lance Stroll said he had no explanation for how quickly his Turkish Grand Prix unraveled, after finishing ninth despite leading the first half of the race.
Stroll, who claimed pole position on Saturday, led away and looked comfortable in the opening stages. That changed after the first stop, when he went from the full wet to intermediate tyre, as he struggled to match the pace of the chasing pack.
Despite objecting to the call, Stroll pitted for a second set of intermediates, surrendering the lead in the process, but continued to drop back through the order. The Canadian was unsure why he had been able to make the best of the tyre.
"I don't know what happened, I don't understand," Stroll said. "We had so much graining on the first set of intermediates. We decided to pit, we were losing seconds a lap.
"I just don't know where that graining came from, it just happened instantly. It grained again, massive graining, and no pace.
"We'll have to look into it, it was pretty terrible today."
He added: "It's just frustrating that you're in the lead by 10 seconds, and then all of a sudden you finish ninth. I don't understand how that happens.
"I mean I do, it's graining, but we just need to look into why it hit me so much harder than the other car.
"I'm not so sure why."
While Stroll pitted, Racing Point teammate Sergio Perez stayed out on his original set of intermediates and managed to guide the car home for second position. Perez said that call only just worked, with his tyres right on the limit when he crossed the line.
"I told my team on the radio, I think one more lap on those tyres and they would have exploded," Perez said. "The vibrations were extremely bad towards the end. But I think it also made that race, looking after them in the beginning [and] towards the end with drying conditions.
"The team did a fantastic job in terms of strategy reading the race. I think Lewis today was extremely strong, and towards the end we died, but we managed to get a good result."