Toro Rosso team boss Franz Tost believes Formula 1 would be better off hosting winter tests in warmer climates like Bahrain.
While two of last year's pre-season tests were held in Bahrain, this year's events are all taking place in Spain with the Circuit de Barcelona-Catalunya staging the final two.
The colder conditions have made the lives of the teams difficult, and Tost feels it puts everyone on the back foot ahead of the new season.
"I have to say it's really difficult to estimate our own performance or the other teams', as track and ambient temperatures are far too low. At the races where we expect much higher ones, the tyre management will be completely different," he said.
"Personally, I don't like the tests in February here in Europe, as you don’t get the feedback on all the technical topics you need to be well prepared for the start of the season. Last year's test in Bahrain was much more useful."
Toro Rosso nevertheless had a solid week in Barcelona with Max Verstappen and Carlos Sainz Jr completing 411 laps between them.
"We now look forward to another four days of testing here in Barcelona next week, where we will also be introducing new aero parts on the car," Tost said.
"I’m pleased with how the whole team is working in the build-up to the start of the season. We now have to continue in this direction, analyse all the valuable data we’ve gathered this week and come back for the final test even stronger."