It’s sad to see an otherwise exciting stage have an incident like this, especially when it’s a rider like Jens Voigt, who could drastically affect the overall GC outcome (and is just plain awesome—speedy recovery, Jens!). Still, crashes are a part of the sport, and picking apart how they occur can help you learn their causes and avoid them in the future.
(Editor’s note: his hand probably just slipped. Watch his left hand as he first his the bump.)
As far as I can tell, the crash was caused by a bouncing chain getting caught up, probably after being bounced inside the small chainring with the front derailluer set in the “high” position. I think everyone’s first thought seeing the crash was something in the front end—broken rim, fork, tire blowout, loose wheel, etc.
But after re-watching his post-impact slide a few dozen times, and looking at this photo, everything up front appears to be intact. The spot shadow above reveals that Jens’ rear wheel definitely gets airborne when he hits a lump in the pavement, and the saddle definitely gives him a good kick in the butt, but at that speed, there’s a lot of angular momentum keeping you upright and in-line; you can see the other riders handle it fine.
It could be that Jens’ front tire slips—it is right on the painted stripe when he begins his crash—but on sun-baked pavement I find that very unlikely, even given the miserable performance of SaxoBank’s rubber at this years’ Tour. Instead, I think he went to pedal, got an entirely unexpected response from the drivetrain, and as a result, lost his balance and fell.
While the though the direction and length of shadow makes it impossible to rule out that he pedaled with his wheel still in the air, I’m inclined to say that his legs don’t move until the wheel is back on the road based on jolt in the chain that appears to coincide with tire contact. Furthermore, I think that jolt leaves the chain in a different position than a few milliseconds previous.
For me, what seals is the position of his legs and static position of the rear derailleur: after a sunden jerk forward—as if there were no resistance from the chain—his legs stop, and his derailleur remains static when it should still be bouncing around from the impact of the road lump.
I suppose it’s possible the the rear wheel was jarred loose, but I don’t think that would have caused the derailleur to be pinned in such a fashion—there’d be no tension on the chain anywhere but the top section, between the chainring (source of power) and the cogs (location of jam).
The angle at which the derailleur suddenly stops—sharp enough that the chain probably isn’t on the big ring, given the its position in the cogs—also suggests the chain has been at least partially dislodged.