Chain jumps and runs noisily on Zwift Hub with GRX 600 1 x 11

Hi there,

I’ve been dying to try out my new Zwift Hub, but unfortunately it doesn’t run smoothly at all.

My bike is rocking a GRX 600 1 x 11 with a Shimano CS-M8000 11-42 cassette. When I first mounted the bike on the Hub, I thought the pre-installed Sunrace cassette was the trouble maker, so I mounted my bike’s cassette on the hub.

Unfortunately the problem persists. You can check out two short videos here (enjoy the awful noise!):

https : / / www . dropbox . com / s/09xk8qp6tv09y2z/PXL_20230128_084645782.TS.mp4?dl=0
https : / / www . dropbox . com / s/w91vk7xu4h6ybsb/PXL_20230128_084811316.TS.mp4?dl=0

Here’s a still from the video:

The problem is most evident when I pedal in reverse, which is what you can see above. Every revolution or so, the chain will actually get partially stuck on the next lower gear (higher sprocket on the cassette) and then jump down again. In general, there’s a terrible audible noise and the chain doesn’t seem to run smoothly on the cassette.

Obviously this doesn’t happen on my normal bike!

I’ve tried adjusting the derailleur, but to no success. Either I’m just not good at it, or that doesn’t fix the problem :slight_smile: .

Please help! I don’t want to return my Hub and get Zwifting instead!


Hi Ingo,

I saw your reply on my thread and thought I’d answer you here.

In the meantime I have bought a new chain (KMC X11) and realised that there was a silver spacer behind the preinstalled cassette. Since I also came across the Youtube video from GCN about cassette spacers, I ordered a set (1, 1.5, 2mm) off of amazon.

I tried all possible combinations of bikes/cassettes/spacers/chains but the smoothest by far for my Backroad was to use no spacer at all combined with the new chain. Even the 1mm spacer puts the cassette so far out, that i can’t adjust the derailleur far enough to the right to make it smooth.
I wonder why Zwift are installing a spacer with the pre-installed 11 speed cassette anyways, since I thought that was only necessary for <11 speed?!
For example on my 9 speed MTB I have to use at least the 1mm spacer, otherwise the casette wiggles around on the freehub.

With these two setups (11x + no spacer + new chain, 9x + 1mm spacer) both bikes are now running almost smoothly. I only get a low vibration in the frame when I put in a good amount of watts, which I heard is typical for direct drive trainers. However, the last gear on both bikes is still not running smoothly and is sounding like it is grinding / trying to shift, but at this point I simply don’t know what else to test anymore…

I personally decided to keep the Hub nonetheless since I rarely use the last gear in my rides. Still sucks though…

So all in all I would suggest you remove the spacer behind the cassette and try a new chain.

If you find another / better solution, please update me in this thread!

Kind regards

1 Like

I have GRX 2*11 and have the exact same issue. It’s been driving me mad and has made the Zwift Hub unusable for me since I can’t cope with the banging that the chain makes as it jumps back to the gear it was on. Like you, no amount of derailleur adjustment seems to make it work.
I was about to order a new Shimano 11 speed cassette to see if that works better than the supplied suntour, but perhaps it is an issue with the spacer?

Please do post again if you have found a way to resolve it!


That was actually what I going to suggest to OP as it sort of looks like the cassette is sitting too far outboard to index well. (there are limits to how far the derailleur can be adjusted)

I had same issue. Measuring supplied Suntour, it’s 1mm more lateral than my Shimano 11 speed cassette highest cog. So like you top gear isn’t slick. Rest of indexing is better now with same Shimano cassette to replace Suntour and matches my ‘real bike’ so I don’t have to faff and re-index and adjust B screw every time I swop bike to hub. Poor quality manufacturing/parts at Zwift

Thanks for the input here.

At this point I can tell you that I’ve tried the following:

  • Checked for spacer behind cassette: there is none
  • Added spacer: things get worse, no go
  • Removed spacers from cassette: no go, messes up gears
  • Changed cassette to the same of my bike: minor improvement
  • Changed chain: no improvement

Several bike component online orders later, I am getting used to the idea that I can’t go better than my current set up. At this point I put my bike on a stand and tried to listen to how it sounds when I just pedal in an indoor set up. Now, it also makes quite audible noises, and that while having no friction as it has when mounted on the trainer, so while putting in less force.

That means there are two options:

  1. I messed up my gears and the derailleur completely by now
  2. That theory many claim on the internet are true: these are noises you just don’t hear while cycling outside, so get used to it

What do you guys think, is 2. actually possible? Or should the setup run really silently?! Maybe I just have the wrong expectation from using indoor bikes at the gym.

I am in between on this, either I give it a shot and keep the 500 Euro unit, or I return it within the next few days. Kind of torn what to do.

Maybe look at this: How To Use Bike Cassette Spacers | Monday Maintenance - YouTube

Thanks Gerrie, but that doesn’t help. It only would if I would have to push my cassette more outward laterally. However, I rather have to push it inwards. Since there’s no spacer to be removed, that’s obviously not possible.


I just posted this: Guide to Direct Drive Trainer Cassette Spacing

My advice is to start with the instructions in the linked thread above - measure cassette to dropout spacing and determine if they’re different.

If the problem you’re having is the cassette is sitting too close to the drive-side dropout, AND at the same time you have no more spacers to remove, the solution is you need to add some type of spacer to the drive-side to increase cassette to drop-out distance.

While a bent derailleur hanger would lead to issues, we can eliminate that as a possibility if the bike is shifting fine while the wheel is installed.