Williams driver Valtteri Bottas says that the prime tyre could present a limitation to drivers at this weekend's Malaysian Grand Prix.
Bottas was ninth quickest during practice for the Malaysian Grand Prix at Sepang, although he squandered his best lap on options by running wide.
"We tried many things with the car today and collected a lot of data on the long runs so on the whole it has been a good day," he said.
"One challenge has been the difference in pace between the prime and the option tyre. The prime was sliding quite a lot and wearing out, so that will be something to watch out for over the weekend.
"I didn't have the best lap on my final run on the option tyres, so like most people we still have some more speed to come tomorrow. The car still needs more downforce, particularly in the high speed corners, but we have our own strengths and our top speed is looking strong which is always good in the race."
Felipe Massa added that the hot conditions in Malaysia enabled him to understand more about the tyres.
"We completed our run plan and we had no technical issues, so today was a good opportunity to learn more about the performance of the car," he said.
"It was pretty hot so we could also understand more about how the tyres are working in high temperatures. We managed to do long runs on different types of tyre which has been very useful and the car was performing solidly."