McLaren needed a complete chassis change to remove the fundamental problem which was hampering their car in 2018. Following a change from Honda to Renault, the team was unable to produce the results they wanted.
Apparently, an aerodynamic problem produced too much drag on the car and the lack of ability to maintain downforce in corners were the main issues on the car. McLaren's executive chairman and shareholder Sheikh Mohammed bin Essa Al Khalifa confirmed the problem was permanent unless they completely changed the chassis.
"[Nothing would have fixed it. And had we discovered that in April we would have had a b-car. But it was too late," he told motorsport.
He said they didn't discover the full extent of the problem "until after the summer break."
This morning, Zak Brown confirmed the team are "on their way to recovery." The chief executive backs this up and feels confident for the coming season.
"I don't know if we want to disclose what we discovered and why, but we've taken steps, and the development of next year's car has helped us understand what went wrong here," he added.
"So we are confident...we know why we have not been able to develop this year's car. That was a fundamental problem. And we think we have addressed it."