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I recently got a Tacx Flux 2 Smart trainer (because lockdown) and decided to get a new cassette and chain as well, since I won't be doing any riding anytime soon and would like to keep everything nice and clean in the house.

I installed the cassette on the trainer,checked I was using the right adapters for cassette and QR, and then measured the new chain against the old one (they are the same KMC 9 speed), making sure they were exactly the same length. I then installed the chain with the supplied quick link, making sure it is routed the right way through the jockey wheels.

However, I now get a very clear droning, grinding noise and perceivable vibration when in the smaller 3 rings. The noise almost disappears when in lower gears. The shifting fine though, and I can get shift in all gears.

I have no idea what can be wrong and it feels almost like the chain has a hard time slotting into the teeth of the chain rings. Almost like the each roller slightly hits every tooth before grabbing on. If I had to describe it in an onomatopea, it would be a grindy "RRRrRrrrrrrRRrrrRrRrrrRr"

What could be the cause of this? Is it just because the chain and cassette both need to be bedded in? Is it lubrication?

** UPDATE ** I finally managed to ride the bike outside and cannot reproduce the same noise or vibration. It seems that the issue is with the bike one the trainer.

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    You might get this if your chainring is fairly worn -- 1000 miles or so. – Daniel R Hicks May 27 at 22:06
  • Can you add a closeup photo of your chainring? Does this noise happen on your other chainring/s and in high (small) gears ? – Criggie May 28 at 0:37
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    @Criggie I have attached some pics. Hopefully they are good enough. Sorry for super late response but I had notifications off and I thought no one saw this. – Granvanoeli Jul 10 at 15:47
  • That chainring is worn, I'd be replacing that, but that's just me 🤷🏻‍♂️ – Lamar Latrell Jul 10 at 22:39
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I got the same with my new COVID-Kickr, in my case it was simply the alignment of the cassette/trainer with respect to the frame/rear-derailleur/chainline.

For whatever reason the usual stops in the frame that ensured same/similar alignment when mounting the wheel just wasn't quite right for the trainer (skewer QR system here).

It's hard to notice as without the wheel you can't check the placement with respect to the front of the chainstay (or brakes in terms of 'roll' misalignment) as you would with a wheel (assuming it's correctly dished).

If you're grinding in the bottom 3 then I'd suggest your first tweak would be rotating the trainer slightly counterclockwise (looking down) with respect to the frame, this amounts to relatively more rearward in the left dropout, and/or more forward on the drive-side. If it's better then that's a win, if it's worse then go the other way.

Either way it's helpful to get someone else to ride while you investigate (wish it were so easy on an actual bike huh!)

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    Hi Lamar, thank you for your answer, I just saw it. My notifications were off and I didn't notice it until now. I have tried your solution but I am not sure I am doing it right doesn't rotating the trainer rotate the bike as well? I understand what you are saying in theory but I don't understand how to rotate the trainer without rotating the bike that's attached to it..I am using a Tacx Flux 2. – Granvanoeli Jul 10 at 15:46
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    @Granvanoeli Have you loosened the dropout first? – Lamar Latrell Jul 10 at 22:38
  • You mean open the QR, then turn the trainer and then close it? Sorry if it's a stupid question. – Granvanoeli Jul 10 at 22:41
  • @Granvanoeli, Yes, rotate the bike with respect to the trainer and see if this fixes it, it may get worse before it gets better, you may need to open/close the QR a few times, align according to your findings. – Lamar Latrell Jul 10 at 22:46
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Since the bike's in a trainer and self-supporting, I'd get my head down low on the right-hand side of the bike, and hand-pedal with my right hand while trying to identify the cause. You can pull on an exposed length of inner cable to change gears, or an assistant can help if its electronic or all-enclosed.

RRrrRRrr sounds like a rub of the chain on something, with the RRR on each downstroke and the rrr as the pedal comes underneath/over the top. So its also related to chain tension. Do please be careful of your fingers (and lockdown hair!) because there are many pinch points with the chain and wheel moving, even slowly.

You can also carefully push the derailleur around with your left hand, to see what effect you can change. I expect that a gentle push sideways will make the noise better/worse or change gear up/down.

Good luck!

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