Robert Kubica believes his pace is being impacted by variations in performance between the two Williams cars, despite having the same setup.

 The Pole finished a second down on teammate George Russell in the second Bahrain practice on Friday as the British team continued to sit at the back of the grid.

And having revealed his weekend was already setback by a lack of spares, this is just the latest reason Kubica feels his pace is falling short.

“The car characteristic with the same setup is completely different,” he claimed.

“I had some doubts after Australia, honestly I thought it was caused by floor damages, [but] the floor is in a good state here.

“Even we are using the same baseline set-up as the other car and we have different characteristics and it’s quite significant, something within the aero which is upsetting a lot the handling of the car and general grip of the car," Kubica elaborated.

“It’s definitely not helping, it’s quite big, it’s like driving a completely different car. We have to wait and see and try to find the answers.”

If confirmed, it is just another example of the problems currently plaguing Williams, who announced co-founder Patrick Head is returning as a short-term consultant in place of the absent Paddy Lowe.

However, Russell has tipped the veteran of the paddock to bring a much-needed boost to the team.

“I think it’ll be great honestly," the Briton was quoted by Crash.net. "With his presence, he’s a very strong character with a lot of personality and it’s maybe what we need at the moment,” Russell said.

“I think for all of his experience and history he has at Williams just having him around will lift everyone.”