It is not just the Honda engine that is holding McLaren back, champion drivers Fernando Alonso and Jenson Button have revealed in Melbourne.
Until now, the official line has been that while the Woking-based team has produced one of the very best cars in the field, it is Japanese engine partner Honda that is struggling the most.
"We have improved but it was not enough," Button said in Melbourne ahead of the 2016 season opener.
"Reliability is much better but there is still work needed with outright power and overall downforce."
The 'downforce' comment is an obvious reference to McLaren's chassis, and teammate Alonso agrees: "Reliability has been very strong, which is good because now we can work on the overall power between races."
But he added: "We are still far away aerodynamically in order to fight competitively."
McLaren finished ninth in 2015's standings.
