At just past the 6:30 minute mark of this video from Bariani Road race, there is a guy on the left hand side that the rider taking the video points out. His chain is clearly just hanging without tension and yet he is pedaling and keeping up with the group. Any reasonable explanation for this? I’m not trying to say he was cheating, I just don’t understand what is happening.
This looks to be one of those uber-expensive AbsoluteBlack hollow cages.
Check out this assembled pic from their site, and notice how there is only a very small chain retention tab at the bottom rear in the pic:
I am going to propose that the rider hit a bump in the road, that disturbed the chain in a way that it hopped off the lower part of the pulley wheel while pedaling, jammed into that retention tab (red X) and quickly broke it off.
The pic of the bike at the top shows the derailleur in full collapsed position (blue circle with like to top pulley) which would happen if the chain slipped entirely off. The chain slack is dangling (orange in my pic), riding up onto the upper pulley, and around the cassette.
This may be an extreme case, but is an example of how the minimal cage design here differs from the typical one from Shimano & SRAM, that has far more coverage and enclosure to keep this from ever happening.
To hit this question specifically, you can see in several moments the top side of the chain is in place and under tension, which is directly connected to his pedaling and forward motion. There is not motor or other propulsion happing here if that is implied or at least questioned in relation to what seems like a chain not functioning.
The chain is present, and surely drooping off the bottom, but it is still flowing around the system and under tension. It’s very possible for this to happen and I have done a range of tests in the stand over the years with RD’s and tensioners to know that super slack can still work to rotate the rear wheel from pedaling.
I suspect that at some point, he may have tried a shift on the rear, hit a bump or had another disturbance that lead to a larger jump as the chain followed over the top pulley and onto the cassette, that lead to some major alignment issue and the chain stopping in one way or another after that point where it was working amid the failure.
Thanks for that explanation. I had never seen something like this and the way you describe it makes perfect sense,
Have you seen the video of Hambini (take what you will from his persona) tearing a part the Absolute Black pulley?
No, I haven’t watched it.