Kamui Kobayashi believes Sauber lost pace as the temperature rose on Canadian Grand Prix qualifying day, having narrowly missed out on a top-10 place on the Montreal grid.
The Japanese driver had been in the top 10 in both Friday sessions, but could only manage 11th in qualifying, lapping just 0.008sec shy of a Q3 spot.
"I think on Friday in free practice, when it was cooler, we looked more competitive than today," said Kobayashi. "The car's balance was good yesterday and we didn't change it. Also my fastest lap was fine, and there were no mistakes.
"I think this was pretty much what I could achieve today. Apparently the others improved in comparison to us."
Kobayashi's team-mate Sergio Perez was back in 15th, and blamed himself for flat-spotting his tires.
"Having qualified only 15th is a big disappointment for me, as certainly a place in the top 10 would have been possible," said Perez. "Unfortunately, on the first lap of my last run with new super-soft tires, I flat-spotted them when braking into Turn 8. The car was then vibrating a lot, which meant I could hardly see the braking points.
"It is obviously a difficult position to start from, but it is still my target to score points tomorrow."