Chain dropping when I pedal backwards

I recently built my bike up with a 1 x 11 and when I pedal backwards in the 2 biggest cogs the chain will drop down a couple of gears and get all snarled up. I don’t make a habit of pedaling back but obviously you need to at times if you’re getting on the bike or riding technical stuff.

I had set the BB up as instructed but have removed a couple of spacers to bring the chainline inwards a bit but I don’t want it any closer than it is right now to the stay. Could I use a spacer on the rear sprocket to bring the whole thing out further?

I read somewhere that this chain drop can happen with a new chain so should I wait a bit for things to bed in?

Ta.

Shimano? It’s a feature

Shimano shifter and derailleur, SUN 11-42 cassette.

@Mike no, it’s really not a feature. Those who don’t understand bike maintenance keep saying that, but if you follow the setup guide Shimano provide it works flawlessly. I have m8000 and M9000 and both work perfectly up to the 46t sprocket. I made this video of forwards/backwards pedalling to show you all just how smooth it is and prevent this kind of BS being spread any further!

Youtube link

@Giant, have you downloaded a copy of the m8000 rear mech setup instructions? Did you also follow the BB and chainset/chainring instructions to the letter?
What parts do you have for cassette/mech/chainset/chainring/bb/chain?

Seems to happen with some folk (Shimano AND SRAM) but improves with a bit of wear. Moving the rings over will obviously help. If you’ve a Shimano “1×11 crank” you’ll see that they’re actually 2×11. A couple of spacers and longer crank bolts will put the chainline back to where it should be.

Yep seems to happen on Shimano, like people over tightening BB’s etc. may not be a feature but something that happens

@Scotroutes the XTR 1x crank isn’t a 2x part, there’s no thread for a second ring and the cover parts are different (and £100 a set!). XT I think (hope) they did do more sensibly

Yep seems to happen on Shimano

Seriously, watch the video. It’s not a Shimano issue, it’s a poor mechanic issue!

The BB, shifter and derraileur is Shimano, the crank is raceface, chainring is on one narrow wide 30T, cassette is Sunrace 11-42.

I followed the shimano instructions but maybe I have some compatibility issues. Could it be the Raceface crank causing the problem? Having said that I’ve experimented with different spacings and I can’t get much closer to the chainstay. Maybe I can sort it by experimenting with spacers? Surely the chainline will vary a bit from bike to bike anyway?

I’ve no experience of Sunrace cassettes so won’t comment there. If you’re getting downshifts in both of the two largest sprockets then realistically 2mm won’t fix it at the chainring because otherwise the second biggest sprocket would already work.

The chainline is probably quite accurate these days, and based on various industry standards. If you have your spacers correct the line should be as intended.

Is it possible the rear axle (therefore dropouts) isn’t straight? If the axle is further forward on the right that might cause some trouble for you.

Are you certain your chain is on the right way around? (Yes, there is a right way around for most chains…)

It’s a bolt through axle so that shouldn’t be the problem. I didn’t know a chain had a right way around I will investigate! I assume I can tell by the logo on the chain? Pretty sure I got a KMC I’ll look in a minute.

lustyd – Member

Seriously, watch the video. It’s not a Shimano issue, it’s a poor mechanic issue!

I’d say it’s a case of shimano cassettes being less tolerant of setup than others.

HAve replaced shimano cassette/chain with SRAM without changing anything else on a bike andit immediately eliminted the issue.

@lustyd Did you record the video using different bikes? With different chainstay lengths?

I imagine it’s more noticable the shorter the chainstay is.

I’d say it’s a case of shimano cassettes being less tolerant of setup than others

Interesting, OP confirms that this setup has no Shimano components in a position likely to affect the packpedaling…

Did you record the video using different bikes?

I have two set up with 1×11, one XT and one XTR. Both react identically and have smooth shifting up and down, and smooth pedalling back and forth. My road bikes are also very smooth shifting, as is my 1996 XT setup with thumbies so I’d be surprised if it’s just dumb luck!

honourablegeorge it’s not a Shimano cassette unless the Sunrace is a direct copy?

I didn’t know a chain had a right way around I will investigate! I assume I can tell by the logo on the chain? Pretty sure I got a KMC I’ll look in a minute

I’ve very little experience with KMC chains, I always use the Shimano ones which certainly have sides on them. Yes the logo is what to look for, on Shimano I think it should be readable when between sprocket and chainring from memory, not upside down and not with the smooth side out. When looking closely it’s obvious that a chain is sided when that’s the case as rounded bits are in different places.

The KMC instructions don’t mention direction so may not affect them after all. Shimano definitely do though, so be aware in future 🙂

unless the Sunrace is a direct copy?

If you look closely the Shimano ramps are pretty unique from what I’ve seen so this is unlikely.

Ok thanks for your help. Seems the KMC is multi directional. Well that’s enough tinkering I’m just going to go and ride the bloody thing!

I’ve just gone from a Sram chain to a KMC chain on an XT 11 mech / shifter / crank set up with an AB ring and the chain does appear to drop more. Similar comments from a buddy. Think it might be something to do with the flexibility of the chains.

I’ve got the same issue, just changed to 1×11 shimano mech cassette and chain, sram crank and bb. Seems fine pedalling forward but jumps two cogs when back pedalling. Tried removing drive side bb spacer…no joy.

Never have an issue with SRAM, that’s with Type 2 mechs, with Shimano or SRAM cassette. Also, vital to have a narrow wide ring up front to avoid it coming off the front.

Oh and yes, KMC chain is bi-directional. I’d never use Shimano for the directional silliness and fiddly pin (not to mention the number of people who snap them on our group rides, and yet KMC are near indestructible). No chain drop with KMC for me, not until the chainring is heavily worn.

It’s a new novelty though. Always used to be… don’t back pedal! 😉

Can’t you just convert it to fixed?

I found cleaning off all the gop that comes on a new chain improved things no end. Just my 2p worth 😀

I set mine up last night so need to take it for a quick ride to see if the back pedalling is an issue or not. Yeti recommends a spacer on drive side of bb. I’ve taken it out to try and bring crank inward to overcome issue (which it hasn’t) Would you put it back on? I still
need to check chain direction.

Similar issues on a SunRace on 1*10. Also running a KMC chain and in my case SRAM mech.

Watching what’s occurring carefully at the point of derailment there is an element of chain line impact and specifically angle of entry to the chain ring as the chain is struggling to flex enough with the lack of spare room around the teeth of a n/w ring.

I think a couple of mm on the chain line could help so I’ll be trying that. I don’t think it needs to be much, just enough to compensate for the slight stiffness in the chain.

The sun race cassettes don’t seem to have the same level of machining to teeth as Shimano cassettes I’ve had. That may also make the fine entry tolerances more critical.