Hey @swiftflow. It’s a known issue with the cassette. Essentially, the ramping on the cogs that help ease the chain onto the bigger cogs also make it easier for the chain to slip back down the cassette.
I spent some time on the new XT group and it’s a bigger issue on the workstand than the trail but it does happen on the trail as well and it sucks. I’m not aware of a solution.
I suspect this will be contested and positioned as a non issue until they acknowledge the issue and fix it,
Shimano is aware of this issue, but remedying it is of too great a consequence to other performance factors. To start with, they have to worry about chainrings clearing the chainstay for the bulk of bikes out there. There are already some bikes with a max chainring of 32t on the M8000 crank, so moving it in wpuld compromise that. They also need to create a chainline that works in all of the gears when pedalling forwards. Moving the chainring inbound can cause the chain to rub the adjacent cog when in the hardest gear. Finally, I’ve been riding this group for nearlt a year and it has not been a problem once on the trail. The only time I notice it is when I get on/off the bike in the granny ring, and which point I’ll hear the gears shift back up, but I won’t actually lose power transmission.
If you want to try and remedy the chain falling off when you backpedal it in the stand, you can push the ring out with some chainring spacers.
@fasttimes It seems like lots of people are trying to solve this issue by switching their chain from Shimano to Sram . Not a perfect solution, but they can back pedal 3 full revolutions before it falls off. I think I’ll give that a try.
People are actually putting on chains that perform worse when they are riding the bike just so the chain won’t fall off the big cog when they spin the cranks backwards in the bike stand? Absolutely ridiculous.