What chainring for Hub One trainer? And mountain bike?

It is recommended to use the small or middle chainring when using the “Hub One”. Is that also the case with mountain bikes where the chainrings are much smaller?"
Or is it a placement ting and not a size thing?

Hi @Thomas_Hansen6 welcome to Zwift forums!

We have an FAQ about the Hub One single-speed trainer here. This will help guide you to the difference between the single-speed Hub One trainer vs. the Hub Classic trainer which uses a multi-speed cassette.

When using Virtual Shifting with either the Hub One or the Hub Classic - we recommend you keep the chainline as straight as possible so that it runs smoother and more quietly.
For a 2x crankset - put the chain on the smaller chainring.
For a 3x crankset - put the chain on the middle chainring.

Correct - it’s not a matter of chainring size. In the first 10 - 15 seconds after your avatar spawns in a Zwift activity - The Hub will determine what physical gears are on your bike by comparing your pedal RPM to the trainer’s flywheel speed. It then sets the trainer in a virtual 12th gear, right in the middle of the 24 speed range.

What this means is that you can put a mountain bike with a small chainring, or a TT bike with a big chainring, and both bikes will start your Zwift ride in a similar-feeling virtual middle gear.


I tried both versions of this Setup. Big Chainring in front and small chainring in front. Both times with the chain perfectly straight. I don’t know exactly why, but using the big Chainring feels a lot smoother to me. 50/15 in numbers.

Thats without cog and using 105 Cassette and Play Controllers for virtual shifting.

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Chain alignment in the big ring on the front x 15 tooth rear position would be reasonably straight too.

Other factors that contribute to a smooth-running, quiet drivetrain on a cassette-equipped bike or smart trainer:

  • Properly sized chain - a chain that’s too short (very common problem actually) will strain the derailleur beyond its capacity and the chain will make a lot of noise
  • Clean chain: a well-cleaned drivetrain reduces friction and wear.
  • Properly lubricated chain - not too much, not too little. Only lube a cleaned chain, and only when it start making noise. Always wipe off excess lube so it doesn’t attract dust and grit.
  • Properly aligned derailleur hanger: a bent hanger means the derailleur will sit crooked below the cog.
  • Properly adjusted derailleur - adjusted so the jockey wheels are centered beneath the cog.
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What I meant was that despite the properly sized chain in both setups (big/small ring on front) it felt somehow different. The smoothness of resistance was different, much better on the big ring. Hard to explain.

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Possibly difference in flywheel speed?

I think it’s pretty well known that for the same effective gearing, running a Large Chainring plus Larger Cog has more drivetrain efficiency (and will wear down slower) than Small Chainring plus Smaller Cog. For the Hub One, there’s obviously no choice (out of the box) on the rear cog size, but a larger chainring should be more efficient.

I might even think that given an example setup – if your bike has a 50/34 chainring, and 11-28 cassette, the current Zwift recommendation is to run the One on the 34 chainring with the supplied 14-tooth cog. However, I wonder if you’d be better off swapping the 14T cog for a 19 or 20-tooth cog and run your setup from the 50t chainring?

I’ve posted a video review doing the same thing. I found that for the same watts at the same cadence, the larger chainring was smoother, but the chain line caused a bit of noise.

Not sure why that should be the case other than the ‘feel’ of mechanical gearing vs magnetic.

Today, I tried the same race using a combination of large 44t chainring and small 15t cog on the standard 9 speed cassette with the Zwift Click

Maybe flywheel speed greater = better?

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Just reading some articles on this and found some evidence that a lower chain speed, which would be the case with larger front chain ring, yields more friction savings for the angular momentum of the rear cog (which sounds plausible). The improved feel might come from higher chain tension, less friction, and less bend on the chain.

I´m using 50t/15t on a 11-speed cassette and the result is very good.

I believe the advice to use the smaller chainring when using the cog is because otherwise the chain maybe isn´t straight and could cause noise etc.

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Not relevant to OP but I recommend Voice Attack for those whose PC or Laptop recognises voice commands. Loads of potential.

I can second that. Started using it last week and works nicely if you use a good word choice. If there is chatter in the background it can setoff actions.
I’ve got mine set to a couple of different views and to fire the powerup.

How does the Zwift cog fit on the classic? The free hub is to big or do I have to take free hub off? Don’t know much about bikes I just ride them.

It’s pretty easy. If you ordered the upgrade kit, your Cog comes already on a Hub. You just have to loose one screw and that’s it to get the old one off. On YouTube there is a video from Zwift where it is explained how you install it. Just search for „Zwift Cog“ and it will be one of the first results. I‘m not good at such things too and it was really easy for me.

Thanks Justin. I eventually got it on but had an issue this morning with the click connecting which screeed up my ride. I had to put my cassette back on so I could ride. By then the click connected. I think I’m going to leave the cassette on incase it happens again. The cassette runs smoother anyway.

Hey Bob! There is no reason why the cassette/cog should be the problem here. Both have no technique in them. The Click connects with the zwift app and the zwift app is telling the hub that you are shifting so it changes the resistance (hope I’m not wrong with the technical part, but it definitely cant’t communicate with your cassette or your cog).

So if your click works now it should also work with the cog. But if you are happy with the cassette anyway then don’t change it. Up to you! :slight_smile:

Hi Justin,

The point I was making is if the click doesn’t connect and I have the cog on then I can’t ride because I won’t be able to shift. I was having that issue this morning so to ride I had to switch to cassette.



Now I understood. Thanks for the explanation. :man_facepalming:t3:

Hey! Did anyone tested sprinting? Some of the review suggested that it might be better on the big ring.

I‘m fine on the small ring atm - as recommended by zwift, but after a couple of sprints in the last days I‘m not sure if it feels the same. It could well be that it’s just imagination as I was tired too, but I‘d be glad to read some experiences from users who did some sprints on the cog/hub one. Thanks!