karuss

Hi, I’m having trouble with my fixed gear bike (it’s a spin bike, but the mechanics are very similar).

When the chain runs over the cog, it causes a clicking sound. I think that it is caused by the chain ‘colliding’ with the top of the cog (see slow motion video).

Video 1: youtu. be/haVaFykp-qU

Video 2 (showing vibration of chain): youtu. be/hpE1M326KEE

Slow Mo video: youtu. be/-l1hSFTRvdw

The issue:

- Gets worse with increased tension, improves with decreased tension (though never completely goes away)
- Causes visible vibration in the chain
- I can reproduce the sound by hitting the cog with the chain using my fingers, up and down and side to side.

I really don’t think that it’s an alignment issue - I can manipulate the chain towards the bike, away from the bike, up, down, and rotate it both ways and none of the position changes improve the sound.

The front cog is 16T, and to crankset is 51T (both 1/8”). The chain is also 1/8”.

What I’ve tried:
- replacing the chain (same size as OEM).
- Replacing the cog (same size).
- A bajillion realignment attempts in all axes.
- Re-oiling

Honestly at a loss for what to try next. Should I try a larger diameter cog? Maybe a thinner chain? What am I missing?

Thanks for reading this epic long post.

abshipp 

That's maybe a little bit noisier than my bike is in the stand. On the road it's so quiet I can barely hear it.

Honestly, everything looks pretty normal to me, it probably seems excessively loud because you're indoors and the relative noise level of the drivetrain is higher than it would be outside.

Maybe if you sprung for some higher quality cogs and chains things would get quieter. That cog looks stamped instead of machined, but I don't know if it would really be worth the money.

karuss

Thanks for the reply -- do you think increasing from 16T to a 18T cog would help? It's a spin bike so I'm not super concerned about the gear ratio -- I can just increase the resistance using the brake pad if I want more. I think this is chordal action, which could be improved with a larger cog?

abshipp 

Possibly. If it doesn't, well fixed gear cogs are fairly inexpensive and small, and it never hurts to have some laying around

Another possible option could be to install a Gates belt drive system, but I've got no idea if your spin bike would be compatible. You have to be able to split the rear "triangle" to get the belt in. But that's a lot more money than swapping cogs.

TejanoTrackie 

Once you get to 16T, the improvements in smoothness with a larger cog are minimal. I agree with @abshipp that a higher quality machined cog is more likely to help. Also, a better quality chain may help.

karuss

Thanks for the input. Do you have any suggestions for a higher quality chain? I'm using a KMC S1 chain.

For a machined cog, I'm thinking shimano dura-ace?

TejanoTrackie 

The KMC S1 is an ok basic chain, so I don't know if paying more for a higher quality name brand would help that much. I thought maybe you were using a cheap generic Chinese chain like you might find at Walmart, since your cog appeared to be a cheap stamped steel part. As to Shimano Dura Ace, these are excellent quality at a very reasonable price, but tend to be noisier than other brands. A better choice IMO at a slightly lower price is the Soma track cog >>> https://www.retro-gression.com/colle...nt=19339747079

karuss

Thanks for the recco.

I've noticed the Dura ace has a similar profile to the stamped one that the manufacturer provided -- the teeth are on a thin 'flange', and the threaded portion protrudes from this. On the cog you mention the teeth are centered over the thread.

Is it possible that getting one of the 'thick' cogs will mess up the chainline?

Apologies if this is a stupid/rudimentary question, I haven't ridden track before.

TejanoTrackie 

There is no difference in chainline. The distance from the centerline of the cog teeth to the end of the threaded portion that faces the hub is the same. Do you know if the cog and chain are 3/32" or 1/8" wide ?

karuss

Cog and chain are 1/8".

TejanoTrackie 

That is normal. Since they are both the same width, they should work properly together. If the chainring is 3/32", it will also work.

FTB

It's not the same. Sorry to be pedantic, but Sheldon Brown has got different cog's shoulder (innermost threaded portion) to center of teeth measurements, showing that they are not always the same. This shows that some hubs advertised as 42mm chainline will give you a 43 or 41 with certain cogs. That's why phil recommend phil cogs and DA with DA etc. This has been hugely useful for me to get a perfect chainline

I realise that this is not totally relevant in this case but I thought it was an interesting source anyways

https://www.sheldonbrown.com/chainline-single.html