Lewis Hamilton says Mercedes still have not pushed their 2016 car to the limit ahead of the final day of pre-season testing.
Rivals Ferrari have clocked the three fastest times in testing at Barcelona with the Italian team having sampled all five of Pirelli's slick tyre compounds.
By contrast, Mercedes have just run on the medium and soft compounds. Although they have set the quickest time of any team on the medium tyres, Ferrari's Kimi Raikkonen lapped marginally faster on the yellow-striped softs on Day Three.
Hamilton's afternoon in the car on Thursday saw the Briton again concentrate on heavier-fuel long runs and, asked if was yet feeling comfortable in the W07, the world champion replied: "I feel good in the car.
"We've not really pushed it to the limit yet in terms of qualifying laps. We had a couple of fast laps yesterday, but in terms of really putting the car on the knife edge and homing in on set-up and everything, I don't really know.
"But so far I feel relatively comfortable in the car."
Both Hamilton and team-mate Nico Rosberg completed qualifying-style simulations on Wednesday and Tuesday respectively on the soft tyre - short stints which delivered Mercedes' best laps of testing so far.
However, Hamilton hinted the car still had not completely been in qualy-trim, adding that Mercedes' winter long-running had prepared him well for the record 21-race season.
"I've done three or four laps in a lower attacking mode in terms of fuel and I've just done loads of mileage on race runs," he said. "So I'm super ready for the race - no problem - in terms of doing the distance, managing the tyres, fuel, systems and all that kind of stuff.
"Now it's really just trying to understand the car on a knife edge, so I'm hoping tomorrow we'll do a bit of that."
And although Hamilton has made no secret of the fact he finds many aspects of winter testing "boring", he reiterated that Mercedes were preparing in the best way possible for their title defence.
"We have to describe it as we're trying to build a pyramid - and you can't start by building the top part," said Hamilton.
"You have to build the base and the long runs are really building the base, the stability and the endurance of this car. Then we can start putting the pieces on to the top as the bigger the base the higher the top can be.
"For sure, I don't want to do this long running because it's boring, just going round and round doing the same times. A race is much more exciting because it's a challenge.
"When you're out there on your own, you don't know what the target needs to be… So that's why I can't wait for the race, I'm excited about that."
And with just one half day left in the car on Friday morning before the season begins in Melbourne on March 18, Hamilton added: "My engineers are working very diligently to help me understand the tools which we have to set the car up so that we utilise it.
"They have done a fantastic job for the last three years so I have every confidence in them and myself that we will get there."
The first race of the 2016 F1 season, the Australian GP, is exclusively live on Sky Sports F1. The race in Melbourne starts at 5am on Sunday March 20.