Red Bull have driveability issues with Renault engine

Renault has made progress but not enough yet to topple dominant Mercedes admit Red Bull chiefs Christian Horner and Dr Helmut Marko, although they are confident works supplier Renault is on track with a better engine for 2015.

It has now been tested at Jerez and Barcelona, and lead driver Daniel Ricciardo revealed last week the 2016 power unit "definitely has some more ponies".

"It does have more power," team boss Horner confirmed to Auto Motor und Sport, "but it is not evenly distributed. There is still a problem with driveability."

However, his Austrian colleague Marko said some of that problem can be solved through "software changes".

"Then we will have caught up a large part of Mercedes lead," he predicted.