Mercedes Formula 1 technical chief James Allison says work is still ongoing to bring developments to the team's 2017 W08 car despite being on the verge of winning both championships.

Mercedes looks poised to clinch its fourth straight constructors' title this weekend in the United States Grand Prix, while Lewis Hamilton enjoys a 59-point lead over Ferrari rival Sebastian Vettel in the drivers' standings with just 100 left to play for.

The Mercedes W08 car has developed significantly through the season, overcoming Ferrari's early advantage to take 10 wins and 12 pole positions through the first 16 races.

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However, Allison stressed that the team is still working to develop the 2017 car despite already shifting much of its focus to its '18 runner.

"The truth of it is that every single team, every single year faces the dilemma of how they ramp down their efforts on the car that races and how they ramp up their efforts on the car that will race next year," Allison explained.

"Every single one of us, the teams that is, will be transferring a substantial amount of resource onto next year’s car, because they couldn’t fail but to do that.

"But there is still an amount of residual resource, more than residual, going into this one to make sure that those developments keep coming until later in the season."

Teams faced a great challenge to perfect their cars for 2017 upon the introduction of the heavily-revised technical regulations, but stability for 2018 will make the difference between success and defeat come down to refinement.

"I think I’d just say that while last year was more a blank sheet of paper and therefore you had more design choices to make, that was true for everybody," Allison said.

"We go, all of us teams, with a lot more information about how these cars behave and therefore with clearer ideas of what we would like to do for the next season.

"But that’s true for everybody, and therefore everyone will be better guided and the overall level of difficulty in making sure that you’re the quickest will remain the same.

"The new challenge of refining your current weapon will be the same for everyone."