Fernando Alonso says that Friday's practice sessions did not reveal the optimum strategy for Sunday's Austrian Grand Prix.
The Spaniard was third quickest in second practice, behind only the dominant Mercedes duo of Lewis Hamilton and Nico Rosberg.
"In both sessions, Kimi [Raikkonen] and I were on different programmes and now we must put all the data together to choose which of the elements we tested have worked best," said Alonso.
"There were no surprises on the tyre front, the Supersoft seems quicker and will definitely be the tyre for qualifying, but for the race, it’s impossible to establish now what the strategy will be. It was always cloudy today and there were even a few drops of rain, but the next days are meant to be sunny and so tyre behaviour could change."
Raikkonen ended the session down in 11th position but played down the relevance of his lap time.
"Along with Fernando, we concentrated on different set-up tests, me on the front end and him on the rear, so as to compare the data from the second session," he said.
"In the afternoon, I had a better feeling from the car, but for various reasons, including a lack of grip, traffic and the wind, I didn’t manage to put together a good lap, or to improve in the final sector."