Daniel Ricciardo says the driveability of Renault's power unit was so bad in the early stages of 2015 that it gave him headaches from whiplash.
Red Bull and Renault's relationship broke down spectacularly at the start of the season after the French manufacturer's failure to produce a competitive or reliable engine. The fall-out saw Red Bull go full-circle to each manufacturer on the grid about a 2016 supply before returning to Renault for next season, albeit with power units which will be badged TAG Heuer.
On top of the extreme reliability problems at the start of the season Ricciardo says the driveability of the power unit was a big problem during races.
"In the first few races power was one thing, but [with] driveability I was getting a headache from my head getting whiplash," Ricciardo told the BBC. "There were a lot of splutters and whatnot going on when I got on the power. That made it nearly impossible to win this year."
Ricciardo's perseverance through 2015 has earned special praise from Red Bull team boss Christian Horner, who commended the Australian and his team-mate Daniil Kvyat for their attitude and commitment throughout the year.
"I think [Ricciardo] handled it extremely well, neither driver let their chin drop," Horner said. "The way they've worked as a pairing this year and the way they've worked for the team has been excellent, the way they've worked together. Both Daniel's have done an excellent job for the team this year."