Nikita Mazepin received from Haas what he asked for, namely a lighter chassis and the Russian driver claims the change has "massively" impacted his one-lap pace.
Back in June, Mazepin justified his performance deficit to teammate Mick Schumacher by a heavier chassis that was leaving him a "sitting duck".
At the time, Haas team boss Guenther Steiner confirmed that there was a weight difference between the two drivers' chassis, but the Italian insisted the disparity was minimal.
Mazepin was nevertheless supplied with a new car at Spa and insists the change has been beneficial.
"I think our one-lap pace has massively improved ever since I drive from FP1 in Belgium," said the Russian rookie.
"I think we all know what was the change in FP1 in Belgium, so it's good to know that I can trust my feelings.
"The good thing is that the pace is here now, and we have a long season ahead of us.
"So I'm sure that it's only going to get better, because the confidence that I have lost in the beginning of the year, when the car wasn't doing what it was supposed to do, now it's coming to the truth."
©Haas
Mazepin says his performance boost simply followed the laws of physics. The 22-year-old is nevertheless happy to now be on an equal par with Schumacher.
"Going into school physics, the more weight you have going with you in the corner, the more downforce you need to carry the same speed," he explained.
"Obviously, we have only so much downforce that we use in this team, and the more weight you have in the corner, the more sliding you have.
"So the less weight from the car, the more speed I can carry with being in the same position as my teammate.
"You can speak all you want, but I think I've definitely taken an all of a sudden step in a better direction. And, to me, it's very clear.
"I've been fighting for an equal position to be in for quite long, and I'm very happy to be in it.
"But as a rookie driver in Formula 1, you know, fighting with super stars, who've been here for a long time, I still need to improve in a lot of areas."
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