Red Bull's Christian Horner says the performance of its Renault engine in qualifying mode remains a weak point which the manufacturer needs to address.
The early part of the year saw the Milton Keynes-based team struggle with its RB13 chassis as a result of wind-tunnel correlation issues.
Once the latter were corrected, the car appeared to be among the best on the 2017 grid but engine reliability wreaked havoc on too many races.
As improvements finally took hold, Red Bull added two victories to its season tally, with Max Verstappen winning in Malaysia and Mexico. But overall, the team's weak spot remained its qualifying form.
"We're seeing a bit of convergence on race day but still in qualifying, with these modes and potential use of oil and so on, there is still quite a differential certainly," Horner told Motorsport.com.
"The stopwatch doesn't lie. We're now going into year five of hybrid so one would hope by season five you do start to have convergence and they [Renault] do start to understand some of the issues they have been struggling with."
On the subject of reliability, the lack of which dogged both Verstappen and Ricciardo on too many occasions, Horner noted that 2017 was the team's worst season in over a decade in terms of engine failures.
"Reliability-wise, engine reliability, it's probably been the worst year we've had since 2006," he said.
"Our engine partner is working hard to address that over the winter. They need it for their own team as well.
"Hopefully we can then put a campaign together to really challenge Ferrari and Mercedes, who will not be standing still either during the course of next year."
While results ultimately fell short of Red Bull's expectations this year, Horner praised the team's entire workforce for its efforts in bridging the performance gap with its rivals.
"The whole team at Milton Keynes has worked incredibly well to put the amount of performance on the car that we have seen during the course of the season to get us from being a second off at race one to winning races on merit and arguably, in the last third of the season, having the strongest chassis.
"On our analysis, if you look at the last four or five races, on race day, we've had arguably the best chassis. That's satisfying to see that progress."
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