Williams F1 team unsure why updates are not working in 2016

The team had strong correlation between data at the factory and the track as it outdeveloped its rivals in 2014 and it felt it made consistent gains throughout last year's campaign.

That has not continued into this season and with the team producing fewer updates because of its focus on the rule changes for 2017, that has compounded its pain as it battles to hold onto fourth in the constructors' championship.

"In the last two years, we've been proud that we have brought things to the track that have performed as we anticipated," Williams technical director Pat Symonds told Autosport.

"During that time, there was only one thing we brought that it didn't do what we hoped it would do so that is a pretty good record.

"This year, we've had two quite major developments and they haven't delivered as much as we expected.

"We have made a call to switch to next year's car quite early on.

"We've introduced fewer upgrades than normal and some of those haven't performed as well as we hoped they would.

"I'll be honest and say we're not completely sure [why] yet and we're having a big investigation into it right now.

"We will get to the bottom of it, it's the nature of the way we work at Williams, and we do go into things in a lot of detail so we will sort it."

Williams has been one of a number of teams to struggle to get the tyres to work consistently this season.

Performance chief Rob Smedley has said Williams needs more expertise in that area to improve its knowledge of tyre science and Symonds echoed that view.

"As a team, I would feel more comfortable if we were more on top of tyres," he said.

"It's a difficult subject for all of us and it's an area where I feel we need to put more resource into it."