Renault has admitted that its new exhaust design is pushing the limits of what's currently allowed in the sport.
"It's no secret there is some benefit from the exhaust flows around the rear wing," the team's technical director Bob Bell told Autosport.
"We've chosen to push our exhaust up as high as you legally can to try to maximise the benefit.
"It's a small gain," he acknowledged. "It's not where it was four or five years ago with blown diffusers by any means. It's nowhere near there. But it's still a useful benefit.
""Different manufacturers have different solutions to that," he added.
So far, it certainly seems to be worth the effort. The new R.S.18 has already got the thumbs up from the team's senior driver Nico Hulkenberg.
"I have more speed, grip, driveability - a little of everything," he told the Kolner Express newspaper during a break from pre-season testing at the Circuit de Barcelona-Catalunya.
"We are fine tuning what we have here and then we will be well prepared for battle," he said. "I would not call ourselves a secret favourite, but we did our homework and fixed our weaknesses."
Renault have made it clear that their 2018 objective is to finish in fourth place in the constructors championship, ahead of rivals Force India.
"We have to show that we can safely finish among the top four," Bell told Auto Motor und Sport. "Only then will the company issue the cheques to further upgrade the team."
Renault is hoping to have at least one of those upgrades - a new aero package - ready in time for the final day of testing in Spain.