Christian Horner thinks Red Bull's participation in last year's Pirelli tyre tests has had a detrimental effect on its 2017 car because the tyres developed differently than expected.
Red Bull, Mercedes and Ferrari provided "mule cars" to F1 tyre manufacturer Pirelli last year so it could extensively test the wider tyres introduced as part of the 2017 rule change. Tyre testing was blind, with Pirelli sharing data among the teams equally, though many have suggested Ferrari's big step forward this year shows there was an advantage in taking part in the test programme.
However, Red Bull has failed to live up to pre-2017 expectations and finds itself a distant third in the pecking order, something team boss Horner says can be traced back to those mule car tests.
"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," Horner told GP Gazette. "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."
Despite Daniel Ricciardo finishing nearly a lap down on Lewis Hamilton and Sebastian Vettel in Barcelona, Horner is convinced Red Bull cut the gap to the front with the upgrade it brought to the Spanish Grand Prix.
"We know the areas of weakness, and it's then addressing those weaknesses. 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."