Formula 1 tyre graining shrinking window for quick times - Mercedes

The world championship-winning team appears to have started 2019 behind its main rival Ferrari, although a significant new aerodynamic package brought to the second week of testing at Barcelona has allowed it to make progress.

Bottas said Mercedes has suffered "quite a bit with graining" in the cooler conditions in the morning and late afternoon in testing.

While he believes other teams are encountering the same problem, he said it is "quite difficult to learn anything on the car" when that occurs.

"There's a very small window to get the tyres to work," Bottas added.

"The early morning runs, or even two hours before lunch, versus after that, when it's cooler - it can make a massive difference.

"In the very warm temperature you could do a two-stop race. If you run too early in the morning or too late in the afternoon you'd have to do four or five stops.

"That makes it difficult to read compared to others."

Bottas said Mercedes would look to complete shorter runs in the pursuit of more one-lap performance after focusing on longer stints so far.

He believes that the inconsistencies Mercedes is finding at present will be ironed out when the season begins.

"It's way too early to say," he said when asked if the W10 had "diva" qualities like previous cars.

"Track to track, we will see how it behaves in proper conditions.

"I really feel there are areas the car has made good steps forward, in slow-speed corners the car feels better than last year, but in other areas there is still work to do."

After the second day of testing, Mercedes' technical director James Allison had pinpointed graining as a particular problem.

Allison described its race run as "quite considerably quicker" than the last one it completed, but said it was "marred by front graining".

"[That is] something which we think, looking up and down the pitlane, could be a feature of the year," said Allison.

"We need to make progress on graining resistance in the next couple of days, in order to make sure we have a good way of handling it by the time the racing season begins."