Cavendish followed Etixx-Quick-Step lead-out man Mark Renshaw in the sprint after 153 kilometres through Tuscany. He rose out of his saddle to move to the front, powered his cranks a few revolutions and briefly lost control when the mechanical happened. His rear wheel jumped, overlapped with Viviani's front wheel and caused a crash.
"When I tried to go, my chain dropped off from the big chainring to the right, and the momentum from the sudden loss of torque caused me to move right," Cavendish said. "There's nothing I could have done to avoid it, and it's a miracle I didn't crash. I feel sorry for Elia Viviani and the other guys involved. Hopefully it's nothing serious."
The Manx Missile coasted to 14th place, but Viviani remained on the road nusing his cuts and scrapes before valiantly getting back on his bike and wheeling across the finish line.
"[The mechanical fault] made him make that strange move, and obviously Viviani had no chance," Etixx-Quick Step's sport and development manager, Rolf Aldag said. "Cav feels really sorry for him, we feel sorry for him. We need to analyse how that happened and to make sure it doesn't happen again."
"We have to analyse it, but if you see him accelerating from the helicopter, you see his rear wheel jump, then you see his chain is off is in the front, so that's very likely what happened," Aldag added. "Either when he waited that moment to accelerate, or when he started his acceleration, the chain came off to the right [of the big chainring]."
Aldag spoke immediately on the telephone with the mechanic who took the bike to the team hotel in Pisa. He told him not to clean or re-lubricate the green Specialized bicycle because Aldag and his team want to investigate it.
"We might see some marks or a bent tooth, so then it's clear," he said. "We have to be sure that we understand what and how."
His Specialized features a FSA crankset with an integrated power metre, FSA chainrings and Shimano shifting, including the chain. When the accident happened, Aldag explained that Cavendish would not have been shifting and would have already been in his 53-tooth chainrings and his 11-tooth rear cog.
"We also had an issue with Tom Boonen in Qatar, also dropping the chain off the right side. We are not sure, so it's unfair to blame anyone, or a product, but it's clear that the chain came off," Aldag said.
"We renewed some of the products, but now it's all theory. It fell off the big ring to the outside, so you can't say he mis-shifted or something in the sprint, but it goes so quickly. We have seen it again in the bus, we will look at it again tonight, and we will have Cav try to remember how it happened."
Team Sky directeur sportif Dario Cioni confirmed that Elia Viviani has undergone X-rays to ensure there are no broken bones from the crash.
"Elia took a big bang at the end there and has lost a lot of skin," said Cioni. "It was encouraging to see him able to finish the stage though, and they are running some X-rays on him to make sure there are no broken bones."
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