George Russell conceded to being "battered and bruised" after the first day as Lewis Hamilton's stand-in at Mercedes.
Russell had already suggested the cockpit of the W11 was a tight squeeze, to such an extent he would have to drop a boot size to fit his taller frame into a space normally occupied by the seven-time champion.
Russell's reward was to finish top of the timesheet at the end of both of Friday's practice sessions of the Sakhir Grand Prix to initially prove himself a worthy replacement for Covid-hit Hamilton.
But it was not without its difficulties. He said: "I've still got a lot of work to do to get comfortable in the car, with the set-up, make some improvements, and pick it up tomorrow which is going to be a different story."
As to whether improvements could be made to the comfort, he replied: "There is. I'm pretty battered and bruised already, to be honest.
"We've already gone through what we need to change, it's not the work of a moment, changing the seat here and there. I'm working hard with the guys to improve that for Sunday. I'm sure it will be fine."
While Russell appeared to set a high bar in comparison to new team-mate Valtteri Bottas, the Finn endured a difficult Friday.
In FP1 he broke the floor of his car early on running over a kerb which led to him finishing three-tenths adrift of the Briton.
In the second session, Bottas had two qualifying simulation lap times deleted for exceeding track limits, leaving him down in 11th, with his best time set on the hard tyres.
Data, however, showed he barely gained on one of the deleted laps and would comfortably have finished ahead of Russell.
"Just because I was quicker today it doesn't mean that's where I'm going to be tomorrow," said Russell.
"[Max] Verstappen was incredibly quick in the long runs, Valtteri was quickest in P2 but had his lap deleted. He probably only gained half a tenth so I'm probably a good tenth and a half behind Valtteri on the low fuel. We'll see, we're getting better."
Russell recognises he still has plenty to work to do if he is to carry his early fine form over into qualifying and the race, beginning with his race starts.
"They're improving," added Russell. "They're not Lewis Hamilton level, to say the least, but they're getting better.
"Again, a load of practice tonight, sat in the car just trying, trying, modifying the clutch paddles to try and suit my fingers a bit more.
"There's so much I do need to get on top of, and there's such a short period of time to do that, so I think we're in for a long night."
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