Formula 1 heavyweight McLaren is expecting a sluggish start to its 2013 campaign as it struggles to come to terms with its bold MP4-28 design.

The team elected to make major changes to its package ahead of the new year after again failing to deliver either world championship title last season.

The new car endured an up-and-down winter testing program, with flashes of speed peppered by comments from drivers Jenson Button and Sergio Perez that the squad was struggling to understand how to extract consistent performance.

The duo ended Friday practice in Melbourne just 11th and 13th on the time sheets respectively.

“I’d say it was one of the hardest days I can recall,” said team principal Martin Whitmarsh of the opening day in Melbourne.

“I think we were lacking a bit of overall grip, consistency, (we had) a bit of understeer, poor ride… a very, very difficult day.

“We didn’t go forward either during the course of the day, which was a bit of a concern. It was a disappointing and tough day for the team.”

The MP4-28 was described as an evolution of the previous car at its launch in late January, but several changes, such as the move to a more aerodynamically efficient pull-rod suspension system similar to that seen on the 2012 Ferrari, are clearly bold steps.

“We took the view that there’s a natural asymptotic profile to developments and we felt that if we wanted to have the ability to develop the car between now and the end of this season we needed to make some changes,” explained Whitmarsh.

“Inevitably there’s a degree of risk in that, and that was a judgement that we made.

“We still believe that we have a platform that we can develop. It’s a platform that we don’t know as well as the one that we’ve left and, if we took last year’s car and just concentrated on that, would we be quicker today? I think we would. But would it have the development potential during the year?

“We’ll see later whether we were right or wrong, but it was our judgement that we needed to make some changes, which is what we did.”

Like Whitmarsh, Button and Perez were both downbeat about their chances this weekend after practice.

“The way things have gone today, I think points would be very positive,” said Button, who has won three of the last four Australian Grands Prix.

“We’re obviously not quick. The feeling is not good with the car, so we’ve got a lot of homework.”

McLaren’s dismal on track form follows a difficult European winter for the squad that saw the defection of star driver Lewis Hamilton followed by that of another team stalwart, technical director Paddy Lowe.

Lowe will join Hamilton at Mercedes in 2014 after sitting out this year’s campaign on ‘gardening leave’.

McLaren’s own plans for 2014 are somewhat less clear, with long-time title sponsor Vodafone this week announcing its impending departure.

A switch from Mercedes to Honda engines is also being rumoured, although that appears unlikely to happen until 2015 at the earliest.