Lewis Hamilton has admitted that his Mercedes car has not been easy to set up this season, as he prepares for this weekend's Brazilian Grand Prix.
Hamilton lost further ground to Max Verstappen last time out in Mexico, and has won only one of the last eight races.
He now trails Verstappen by 19 points in the Drivers' Championship and insists that Red Bull have had the best car in 2021.
"I think really what we just try and focus on is getting the car in the right window, which is not easy," Hamilton told media, including RacingNews365.com. "It's not an easy car to set up.
"But I think it's very similar for everyone. [I've] just [been] sitting with the engineers, even just before now and trying to make sure we start off on the right foot.
"It's really difficult to explain it. There are too many elements to go into in terms of detail. But it's just a harder car to optimise.
"Some weekends it works, some weekends it doesn't. But to learn on the ground, with the simulations in the right place, it's just a little bit harder this year.
"We saw in Austin, for example, the Red Bulls are quite far off and then all of a sudden they switched it around. But getting the maximum potential put of the car has been harder this year."
Every race is a must-win race
Although Red Bull were particularly dominant in Mexico, Mercedes have had the strongest car at numerous events this year.
Hamilton was 32 points behind Verstappen prior to their clash at Silverstone, but managed to turn things around to retake the lead of the championship after the Russian GP at the end of September.
The British driver was asked whether this weekend's event at Interlagos, which will also host a Sprint Qualifying race on Saturday with three points up for grabs, is a must-win to hit back in the title fight.
"Every race is a must-win race," said Hamilton. "It's been a must-win race since forever, particularly since we came back from the [summer] break. But we've not really managed to be able to do so."
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