Zwift Hub Grinding

Received my hub today and went through the setup following the manual and eventually watched the videos as well. Feel pretty confident I’ve got the setup correct but mine is grinding on my lower (smaller) gears. My bike has an 11-34 9-speed cassette. I ordered my hub with the 9-speed which I’m pretty sure is an 11-28. The hub seems to grab the next higher gear when I’m in the smaller 4-5 gears. Once I’m in the top end of the cassette I don’t hear it grabbing / grinding as much. I’m afraid to adjust my rear derailer because I don’t want to cause a problem when I put my wheel back on.

When I opened the box a small spacer fell out and I thought they might have just missed installing it so I took the cassette off the trainer but I found a spacer already installed between the cassette and trainer.

I’ve only been cycling for a few months so I’m new to understanding the cassettes and shifting. Just wondering if this is a simple fix that I might be overlooking.

I measured my rear frame clearance and felt it was 142mm with the cards in the box (2021 Giant Content AR 3 w/ Thru Hub Shaft). When I measured using a caliper I was more in the 145mm range. I’ve tried flipping the spacer to the 148mm side but I wasn’t able to get my axle to tighten so I feel it is correct with the 142mm setup.

I’ll forward this to support if I don’t get anywhere I was just hoping to get in a few rides this weekend on the new trainer.

Hit up support directly… these trainers (Jetblack version at least) have a history of vibration issues and jetblack replace them.

Is the Hub internals grinding, or is it something with the chain/rear derailleur and cassette that’s grinding (ie. something electronic/motor-related, or something mechanical external of the trainer)? The Hub itself doesn’t know what gear you’re in obviously.

Is your chain length too long, seeing as it was seemingly sized for a 34 tooth cassette? Do you have the issue in the smaller rear cogs no matter if you’re in the large or small front chainring (assuming you have double chainring (though conceivably you might have a triple?)?

Sounds like your gears aren’t indexed correctly or your chain has worn so doesn’t like the new cassette.

Indexing gears is pretty easy and a useful skill to learn.

On my hub, the flywheel definitely grinds. And the support answers with things like “replace cassette”, although I have even sent a video on which it is very clear to hear. What a waste of time…

I don’t hear anything just spinning the Zwift Hub. Pretty confident it’s a mismatch on the cassette. To test I pulled my cassette off my wheel and put it on the hub and most of the noise cleared up. I’m going to order a second identical cassette to what is on my wheel and go with that for now.

I didn’t want to adjust the indexing for the hub only to have to redo it for my wheel every time I switch back and forth.

But this is the way, I am afraid.

Is this true if I get the same cassette on my bike and trainer? I was hoping by doing that I could avoid tweaking the index everytime.

It does not have to be ta same cessette as long as the spacers are the same. You may need a wider or narrower spacer so that the indexing stay the same

I don’t think this is correct.

The spacers are for different speed cassettes to fit the hub.

you may need to index the gears due to the alignment of the cassette on the hub of the trainer compared to the hub of your wheel. Also, when you tighten the quick release skewer if you have this tighter or looser than it previously was this can slightly affect the position of the rear mech hanger so can mean you need to tweak the indexing slightly.

I actually tried this. The spacer that’s on my wheel is 1.5mm and the one that was on the trainer is 1mm. I swapped the spacer but the grinding still occurred.

My bike has a thru-axle but I think this would still apply?


You are 100% correct. The reason for my comment is I have one wheel where I need a different spacer than my other wheels to get my indexing perfect.

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If all wheel/freehub/cassette alignments between different setups/bikes where the same, there would be no gear adjustment necessary at all…

I am having the exact same problem. The zwift cassette almost seems to wide. Maxing out all adjustments I still could not get a correct alignment.

After trying 2 different bikes adjusting limit screws, indexing. The zwift hub excessively grinds. The grinding and vibrations make the ride unbearable. I am seeing multible threads and comments with this problem. Obviously this is a new product with problems. This problem needs to be addressed by zwift quickly. If you have the same problem please comment so zwift can see. I have already started contacting zwift.

Are you shure that the cassette on the zwift hub is the right one for your bikes gearing?
I mean something like wrongfully trying to combine a 10 speed cassette with a 11 speed gearing or similar…

I wonder how many folk are using a now-worn chain with their new Zwift cassette? I’d suggest that it’s worth trying a new chain, or switching cassettes from your bike in order to eliminate that issue (as well as learning how to adjust the indexing quickly).

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Both bikes 11-28t cassette. 11 speed cassette on the zwift hub. I wish it was a simple like that.

Bike is brand new