The Netherlands' hopes of a gold medal in the World Championships Mixed Relay Team Time Trial went up in smoke just moments after the trio of women rolled down the ramp. After just 22 pedal strokes - 11 full revolutions of her cranks - Annemiek van Vleuten came crashing down in a seemingly unprovoked crash.
Initial reports from commentary suggested an overlapped wheel was the cause, but different camera angles confirmed otherwise.
Having watched the footage on repeat no fewer than 30 times, even we here at Cyclingnews were initially baffled as to the cause. Van Vleuten later suggested an exploded tubeless tyre was the cause, but in all the footage we've been able to gather, the tyre remains totally intact until the crash with the kerb.
So if it wasn't the tyre that caused the crash, then what was it? We've studied the footage frame by frame and we've found the answer.
Put simply, Van Vleuten's chain dropped from the big ring to the little ring.
This happened as her left leg was at the top of its pedal stroke, so as her left leg came down, it was expecting high resistance from the big gear. The fact that the chain dropped into the little ring (rather than dropping off the rings entirely) meant that she was able to continue pedalling, but the change in resistance from the gear meant that Van Vleuten's left leg came down more quickly than expected, throwing her weight forward and to the right.
She naturally compensated by steering left but, with her weight unbalanced, she lost control of the bike - through no fault of her own, we might add.
To her left, as the road narrowed slightly, a stretch of kerb no more than a few metres long protruded from beneath the barriers. As her bike swung left, it hit this kerb before being thrown back into the road. During this impact with the kerb, the front Zipp 454 NSW wheel is snapped clean through, as shown below.
Naturally, this caused the tyre to shed from the rim, covering Van Vleuten and her Canyon Speedmax CFR time trial bike in sealant. The rear derailleur was also snapped from the bike in the aftermath.
Van Vleuten's bike is fitted with a SRAM Red eTap AXS groupset. The same, in fact, as her compatriot and teammate, Bauke Mollema, who had earlier suffered problems with his own groupset.
Her rear derailleur shift buttons are fitted to the ends of her aero time trial extensions, and there are separate shifters on the underside of each hand position on the base bar. SRAM shifters can be configured in any number of ways, so there's no knowing exactly how Van Vleuten's were configured.
It's impossible to see the size of the chainrings she was using, but footage confirms that they were standard SRAM-issue chainrings, rather than aftermarket aero rings like those used by Ethan Hayter during his chain drop issue at the weekend.
Footage of the Dutch women on the start ramp, as shown in the screen capture below, shows Van Vleuten's chain clearly on the big chainring.
As she rolls down the start ramp and stamps on the pedals, the chain remains in the big ring, as shown in the following screen capture. This is pedal stroke 18 (out of 22).
However, as you can see in the next image, with pedal stroke 22 completed, the chain is now in the little ring and her weight is thrown to the right.
A fraction of a second later, her countersteering sends her left, but at this point, the crash is inevitable.
So yes, the tyre did explode, and the wheel did break, but neither of those caused the crash. That came as a result of a chain being dropped.
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