One of Williams' chief engineers, Dave Robson, explains that Robert Kubica and George Russell have exactly the same car available, and attributes Kubica's problems to tires in particular.
Robert Kubica returned to Formula One this season with great zeal and media pomp . His return seemed almost impossible after a horrific rally that left him with permanent hand injuries. A Pole who by no means finds himself in this year's Williams car feels that Williams is responsible for making his comeback not as glorious as it could be, because with a bad car he can't show everything he is capable of.
Cuba has repeatedly expressed doubts that his car is identical to that of his teammate George Russell, which Robson denies.
“We have analyzed the matter several times and I can say with certainty that the Kubica Russell has the same material available. Given the large lag that Robert has, we assume that the tire problem is where the Kubica has significantly more problems. That could explain the big difference between our racers. “