Red Bull joined Mercedes and Ferrari in agreeing to create "mule cars" to help Pirelli prepare for the new high downforce regulations.

Rivals teams suspected that those taking part may have gained an advantage, despite the blind nature of the testing, and Pirelli's promise to share data – a suggestion that appeared to be backed up by the big step made by Ferrari.

However, speaking in an interview for Motorsport.com's GP Gazette, Horner says that Red Bull took a wrong direction with the RB13 because the definitive 2017 tyres were not what the team anticipated after the mule car testing.

"Obviously the regulation change was reasonably significant over the winter, and I think actually running the Pirelli mule car hurt us in a few ways," said Horner.

"A few things changed late in with the tyres that we potentially were designing the car around. I think that may have perhaps influenced our development direction.

"I wouldn't say it backfired, but it definitely led us in a direction that wasn't conducive to the tyres that were ultimately nominated.

"The simple facts are that Mercedes and Ferrari did a better job of interpreting those regulations than we did over the winter. We then found ourselves on the back foot in winter testing."

Horner says development was hampered further by power unit issues that restricted testing in Barcelona.

"We didn't do anywhere near as many miles as we wanted to, because we were sat in the garage for a lot of the time with engine issues, so it was only really after Australia that we got to see a picture, and we'd got quite a bit of performance to find," he said.

"The characteristics the drivers were describing from the car, it wasn't a well balanced car. A huge amount of effort has gone into understanding the areas of weakness and addressing those. The first step to that was the upgrade we introduced in Barcelona."

Horner is confident that the team can resolve its issues, however.

"We know the areas of weakness, and it's then addressing those weaknesses," he added. "I think that's half the battle in many respects.

"We've got a very capable group of people that have demonstrated what their potential is with previous cars, and I've got no doubt that they will sort this car out.

"You obviously get into diminishing returns. But we definitely closed the gap in Barcelona, and we're going in the right direction. I believe the second half of the season for us will be far more competitive than the first."