Franz Tost says Toro Rosso is still yet to fully understand why it is continuing to suffer wheel rim failures after two incidents for Daniil Kvyat forced it to withdraw both cars from second free practice for the Abu Dhabi Grand Prix.

Daniil Kvyat sat out the majority of FP1 after suffering a left-rear puncture coming onto his first full lap of the Yas Marina Circuit, only for exactly the same issue to pitch him into a high-speed spin at turn 16 at the start of FP2.

Forcing Toro Rosso to stop Carlos Sainz in the sister car took as it began investigating, Tost admits it is yet to fully understand the reasons behind the dramatic failures.

"After facing two failures on the rear rim of Daniil's car today, it was decided to avoid sending Carlos out on track again because we still haven't understood 100% where the problem is coming from. We will now work hard tonight, together with the engineers back in Faenza, and hopefully we will sort it out for tomorrow."

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