Grinding chain/gears

Hi, I have the Zwift Hub with 11-28 cassette. I didn’t realise that my bike has a SRAM PG1130 - 11-42t cassette. Now my chain/ gears are grinding on the Hub and making a lot of noise. Do I need to change chain cassette?


It should be fine until you go into sprockets that are bigger than your bike’s sprockets, e.g. going into the 42. Your chain will be too short for that.

If you’ve got “grinding” in the smaller sprockets (same size as your bike’s) then there’s something else wrong.

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Hi Steve, thanks for the quick reply. That’s what i was hoping. The grinding is coming from the smaller sprockets, I’ll have to have a play around.

Thanks again.

I read this the opposite way around. The bigger sprockets are on the bike not the trainer?

When in the 11t is the chain slack?

When pedalling in the 11t on the cassette push the level slightly but not enough to change gear, does the noise get better or worse? If it gets better then your gears will need indexing.

This is a problem with giving people a cassette but not letting them choose which one.


Same thought, had to read it a few times @Chris_Holton. Something else is going on as the 11-28 range is covered by the 11-42 so chain length doesnt come into it either.

@Bobby_Buckley - a few questions …is it all gears grinding, is it a 10sp or 11spd cassette, does your bike have a spacer and therefore does the trainer have the same width spacer, is the grinding coming through the frame or do you feel it more in the pedalling (ie indexing of gears)?

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Yep, you’re right, I read it the wrong way round.

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Hi all,

Yes, the Hub has the 11-28. I haven’t tried pushing slightly on the gears yet, I’ll give that a try. The chain is ok. No spacer on the bike. I feel the grinding when pedalling and it is mainly coming from the smaller sprockets. I may need to index it; I was hoping not to… Is it best to just use the barrel adjuster or adjust limit screws as well?

Thanks everyone for your help

Here is a very basic indexing guide.

If you’re struggling going from smaller sprockets to bigger ones (going in the direction of 11t to 28t) looking from the back of the trainer turn the barrel adjuster on your rear mech anti-clockwise. Just do a quarter of a turn at a time. Remember how many you do so you can always put it back if it gets worse.
If you have trouble changing from big to small turn the adjuster clockwise but still a small amount at a time.

If the middle of the cassette is fine but the two extremes are bad then you need to adjust the limit screws. There will be 2 one marked H which changes how far to the right the mech can go so adjust this if the 11t is a problem. Again a tiny bit at a time.

The other is marked L and is for the inner limit (28t). Be very careful with this, you don’t want your mech going into the spokes when back on the bike. Adjust this if you can’t get into the biggest sprocket.

Plenty of videos online showing how to do it.

It is a very useful skill to have.

Just remember what you have done so you can always put it back to how it was if things get worse.


Might be just indexing but it’s also worth noting that chains and cassettes typically wear in together. A used chain on a new cassette won’t mesh together as well as it will on a cassette of the same age, particularly on sprockets of a different size to the ones you already use, and when using a very rigid, fixed position like a trainer.


Hi Chris,
brilliant, I’ll try this and see if it helps. Just found some good youtube videos on it.

Thanks again.

Hi Dave,

I didn’t think of that, I’ve had the bike for about 6 years so that might well contribute to the grinding.


Methinks there is definitely such a thing as a chain being too long and it affecting shifting. At some point the rear derailleur would no longer provide any tension on the chain.

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Not in this case @Wannie

The chain is correct for the 11 gear on the 11-42 therefore it won’t be to long on the 11 gear on the 11-28


How do you get that conclusion? Otherwise you’re saying that no chain is too long?Given it’s an 11-42, I assume it’s a 1x up front chainring? It’s exactly in the smaller rear cogs where a too-long chain can cause problems. IOW, there’s no way that a chain that’s correctly sized for an 11-42 is also the correct size for an 11-28.

Heck, the grinding could be the chain hitting the RD’s upper jockey wheel for all we know? something along these lines from a chain that’s too long:

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because the smallest distance the chain travels is determined by the smallest sprocket on the cassette. 11t in this case. As both are the same on the bike and the trainer the chain would be either too long on both or be the correct length on both.


[edit] Nevermind, I think I got it :slight_smile: Since bike cassette has 11-28 range within the 11-42 and chain works, then would still work on 11-28 cassette where all gears cover the range. OTOH, a chain sized for the 11-28 would not work on the 11-42.

hmmm… two results from a simple chain length calculator indicates roughly should be 3.5" size difference (7 links)
4228 Length



So have tried it again. I did some adjustments with barrel adjuster The chain seems fine it’s not like the one in picture above. The grinding is on the first 2 sprockets louder on the first sprocket. The other gears don’t seem too bad now.

Yes, if a chain is set up for 11-28 it might be too short for 11-42 as the big front/big back combination is smaller but if it fits the 11-42 it will fit the 11-28 as the small/small combination is the same.

for what it is worth when i change chains i pout the chain through the small front ring, the smallest sprocket at the back, pull it until there is a little tension on the rear mech and break the chain and join it there.


If there is grinding on one part of the Cassette and not on the other part and you are shure that no other parts are rubbing or grinding, then typically your derailleur hanger might be (slightly) bent.

If it grinds just on the biggest and/or the smallest cog, then you have to adjust the limits.

Edit: Or the bike is not seated correctly on the trainer.
Try too loosen the bike off the trainer and put it back on with a little horizontal pressure on the saddle.

What happens if you take the bike off the trainer and put put the original wheel back?


EDIT: others answered

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