Only 15 minutes to the end of the morning session in Shanghai, Buemi saw how both the front wheels of his STR5 flew off simultaneously when trying to brake for the right approach on Turn 14. Coming after a high-speed straight line such as the one in Shanghai, the car curiously did not hit the barrier once it ran out of wheels, but was stalled into the gravel, preventing the race stewards to red-flag the session for even a few seconds.
Shortly after the incident, Buemi's teammate Jaime Alguersuari was not allowed by his team to leave the pits for the last few seconds of P1, until further clarifications on what caused the Swiss driver's problem were brought. After some thorough investigations, it appears the crash was caused by a front right upright failure on Buemi's car.
When the racer tried to slow down and the front right upright failed, all the load pushed in front of the car was transferred to the left upright, who couldn't take it and failed too. Consequently, both wheels flew off the car.
What's even more intriguing is that the new upright for China was actually a new design put in place by Toro Rosso (see what lack of testing can do to F1?). Additionally, the wheel tethers were attached to the broken uprights, which is what caused the wheels to flew away from the car and over the spectator fences.
Further investigations on what caused the right upright to fail are still under way. According to Autosport, the team will go back to their usual upright design for the rest of the Chinese weekend.