Lewis Hamilton says three teams - Red Bull, McLaren and Alpine - have caught his attention in pre-season testing in Bahrain.
Perennial title favourites Mercedes have failed so far to produce much of an impression this weekend at Sakhir, although Valtteri Bottas did clock in fastest on Day 2.
But the reigning world champions endured a troubled start to their test, with a gearbox and other niggling problems undermining the team's opening day of running.
Red Bull and McLaren both saw one of the drivers top the timesheet, while Alpine which has enjoyed flawless reliability in testing hasn't been far off the front-runners' pace.
Speaking ahead of his Sunday afternoon stint with Mercedes, Hamilton says he was exited to see the "quite impressive" performance displayed by a few of his rivals.
"Without doubt it is quite impressive to see the speed of some of the other teams," said Hamilton.
"Red Bull are looking particularly strong, and it’s great to see McLaren also looking strong, also Renault [Alpine]. I’m excited as that means more fun."
Addressing Mercedes' disrupted test and its impact on the team's preparations, Hamilton reckoned it was better to have issues emerge in testing rather than on a race weekend.
"I don’t waste time worrying, that deters you from finding the solutions," he said. "So we’re just working hard and focussing on getting through the short amount of testing we have and trying to be as efficient as we can.
"I think it’s better when it doesn’t go smoothly. It’s better that it doesn’t go smooth now and goes smooth once we get into the racing scene. This is the perfect time for us to find the issues and have the problems, so I welcome that.
"I think everyone’s just keeping their heads down, no-one’s particularly fazed by it. We’re a multi-championship-winning team and we know how to pull together and keep our head down and focus on our job."
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