McLaren’s impressive pace on the first day of testing in Jerez in February was generated by a mistake when the car was being put together in the factory, Martin Whitmarsh has confirmed to this blog.

A suspension component was fitted incorrectly to the new car – apparently it was simply the wrong way round – and the unexpectedly low ride height that resulted happened to work well at the Spanish track. Button set the pace that day, suggesting that the MP4-28 could be the car to beat.

However once the mistake was discovered that night, it was rectified, as the car could not be run in that state long term at other venue, especially with heavy fuel loads.

Since then the team has struggled to get close to that initial performance, leading rivals and other observers to wonder just why the McLaren had been so impressive out of the box.

On Friday in Australia Jenson Button pinpointed the issue by saying: “We had a set-up we didn’t think we had. It wasn’t one we could work with.”

A little investigation has revealed that it wasn’t simply a question of a miscalculation of settings, but a part being fitted wrongly.

“It was a part fitted incorrectly which caused us to run the car unrealistically low, that happened to play to the strengths of the car,” Whitmarsh confirmed when asked by this blog. “It wouldn’t work on a bumpy circuit like this. That’s why the car at the moment is too peaky in its performance, and that’s something we’ve got to resolve. It was a set-up which on many tracks was not realistic.”

Whitmarsh also noted that McLaren’s extreme problems on Friday in Australia were related to trying to run the in a low configuration once again.