I recently put a 1x12 on my 2013 giant trance. I have the gx rear derailleur gx with a raceface direct mount crank with a 6 mm offset chainring. When I pedal backwards in 10th 11th 12th largest cogs the chain drops down to the higher gear. I though with the 6mm offset it would improve this problem but still occurs. Has this happened to anyone who has upgraded to the 1x12 aftermarket?
1x12 chain drop
sean4414
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I recently put a 1x12 on my 2013 giant trance. I have the gx rear derailleur gx with a raceface direct mount crank with a 6 mm offset chainring. When I pedal backwards in 10th 11th 12th largest cogs the chain drops down to the higher gear. I though with the 6mm offset it would improve this problem but still occurs. Has this happened to anyone who has upgraded to the 1x12 aftermarket?
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Yes. Happens all the time. It's a characteristic of the system. I run 6mm offset on boost bikes and it happens to me. Don't pedal backward more than 1/2-3/4 of a rev when you need to phase the crank. The chain may drop off the largest cog, but it will pick right up when you start pedaling forward.
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Never happend on any of my 12x or 11x Sram drivetrains with either Sram, or Sunrace cassettes.
I suggest to overlook the adjustment of your drivetrain.
Look at the cable tension, B-screw and even chain length.
And before the chain line argument rools in.
I saw alreday lots of chain drops on brand new Shimano XTR, XT, SLX and Deore drivetrains, were the chain even when almost straight droped like 4 cogs down the cassette with just half a crank turn.
I don't know if the bike shops adjusted those drivetrains wrong.
I'm just saying I think there is more to the whole chain drops issue, than only the chain line argument.
I suggest to overlook the adjustment of your drivetrain.
Look at the cable tension, B-screw and even chain length.
And before the chain line argument rools in.
I saw alreday lots of chain drops on brand new Shimano XTR, XT, SLX and Deore drivetrains, were the chain even when almost straight droped like 4 cogs down the cassette with just half a crank turn.
I don't know if the bike shops adjusted those drivetrains wrong.
I'm just saying I think there is more to the whole chain drops issue, than only the chain line argument.
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2,773 Posts
My Chameleon will roll the chain off when I back pedal. Even on a steep punchy rocky climb thing -if I don't make it and I roll the bike backwards to turn out, chain can roll off the 50t. It didn't do it when I first got the bike, I may have tweaked the hanger since then making it every so slightly out of tune.
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1,109 Posts
It could be the cable that loses a bit of tension over time.
Try to tension it a bit and see if your chain still dropes on the 50t.
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This is a different situation.
"Chain Drop" is used in a different context than what is usually the definition.
I am currently running a 3mm offset chainring which is the suggested offset for the chainline for boost. My chain still drops as well on a GX 1x11. It is not really an issue if you don't pedal backwards. I don't notice it as an issue, but part of me wants to fix it. Lol.
However, I do think a 6mm offset chainring might be better because having the chainline closer to the big cogs may solve the issue and still maintain a good chainline. I haven't tried that yet, but I think I may try when this chainring wears out.
However, I do think a 6mm offset chainring might be better because having the chainline closer to the big cogs may solve the issue and still maintain a good chainline. I haven't tried that yet, but I think I may try when this chainring wears out.
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Yes, I have a top guide. No, it doesn't do anything for the backpedal chain drop.
What's happening on the backpedal chain drop is that chainline is just one contributor that stresses the chain laterally. Another part of the problem is chainstay length (can't change that on most bikes) which contributes to the angle of stress. Also the cassette itself is part of the issue. If you backpedal the bike REALLY slowly in the workstand, you'll see that the sideways stress will cause the chain to sit on top of a cassette tooth, and once that happens, you either have to pedal forward or the chain will fall down the cassette. It tends to happen on the same few teeth every time.
What I have done is take a file to the back side of those few teeth (slowly backpedaling to identify where it happens) to make sure that there's not a shelf at the tip of the tooth for the chain to sit on, and that instead, there's a taper that causes the chain to slide down into place.
The chainline problem is caused in large part by the fact that with 11spd and 12spd cassettes, the big cog gets dished further inboard over the hub flange. This means that the chain has to shift across more space laterally, resulting in a larger delta in chainline. Was never an issue for me on 10spd or lower cassettes.
To be clear, this is only occurring in the big cog for me. ONLY. Seems to me that a similar thing occurring in the middle of the cassette has something else going on. Maybe the freehub mechanism needs to be cleaned and lubed. I don't see how any adjustments to the derailleur can make a difference. When the problem manifests, it manifests at the TOP of the cassette (chain riding on top of cassette teeth). No derailleur adjustment is going to change that.
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I recently built a Santa Cruz Solo with a Shimano XT 1x12. But instead of using the micro spline, I used a hub with the standard HG freehub body and an after market 11-50t cassette, which overlaps the inside. When I am in the biggest cog, there is so much sideways tension, that it is rather noisy. Forget about backpedalling. So much as a quarter turn and the chain up shifts 3-4 cogs. the next cog in, this happens after a half turn. the third cog in, maybe a full turn. the 8100 crank has a 52(?) mm chainline. I noticed with the 11 speed crank the chainline is smaller (maybe 50mm), but I am not sure a couple mm at the crankset would make a huge difference. maybe slight improvement. Question. with the micro spline/XD hub bodies, does the cassette sit a bit more outbound? also, would going to a 45t largest gear help? The short chainstays of the Solo are a likely contributor, and you sorta learn just not to back pedal, but it falls off even when resetting the crank position when I have to bail on a climb. I don't need to ratchet in the 50t (frankly my hills don't really require it anyway), but it would be nice to be able to ratchet in the second cog, and even that seems dicey. My general hunch is that the xd or micro spline wouldn't help either... meaning where exactly is the cassette going to move to..but perhaps there is a flaw in the after market 12 speed HG-compatible cassettes that I haven't considered. Thanks
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