Any idea what's causing this noise?

[Deleted member 121159]

So there's a very strange occasional sound and sensation coming (I think) from the drivetrain of my bike. It's not really a problem so I haven't worried too much about it. But it'd be good to know why it's happening. Also I've changed everything in the drivetrain since I got the bike (rear wheel, cassette, chain, rear derailleur, front derailleur, cranks, chainrings, bottom bracket). The only thing I haven't changed is the pedals, so maybe it's the pedals?

Anyhow this is what happens. Very occasionally, it feels like something clicks or snaps somewhere in the drivetrain and I can feel this on the pedals. A bit like when you change gear under torque, but definitely not that. Something clicks or snaps, and at the same time the pedals slip for a fraction of a second, so very briefly there's loss of power. Currently I have new everything including chain, cassette, RD, chainring so it can't be that the chain is actually slipping. This happens randomly, or at least I haven't been able to detect any pattern so far. The bike can go for weeks without doing this, and one day it happens 3 times in a row. The clicking sound is quiet but definitely noticeable when I'm pedalling gently. Under load, the sound is much louder, there's a pinging sound like when something gets caught between the spokes and the spokes ping. It's definitely not that though.

Initially I thought it must be the freehub, something in the pawls and rachet that went wrong. Bought a new wheel, and it's the same. Luckily I've been able to just accept it rather than worry about it. This morning I just had the thought of posting this just in case I've missed something obvious.

 

[Paulus]

So there's a very strange occasional sound and sensation coming (I think) from the drivetrain of my bike. It's not really a problem so I haven't worried too much about it. But it'd be good to know why it's happening. Also I've changed everything in the drivetrain since I got the bike (rear wheel, cassette, chain, rear derailleur, front derailleur, cranks, chainrings, bottom bracket). The only thing I haven't changed is the pedals, so maybe it's the pedals?

Anyhow this is what happens. Very occasionally, it feels like something clicks or snaps somewhere in the drivetrain and I can feel this on the pedals. A bit like when you change gear under torque, but definitely not that. Something clicks or snaps, and at the same time the pedals slip for a fraction of a second, so very briefly there's loss of power. Currently I have new everything including chain, cassette, RD, chainring so it can't be that the chain is actually slipping. This happens randomly, or at least I haven't been able to detect any pattern so far. The bike can go for weeks without doing this, and one day it happens 3 times in a row. The clicking sound is quiet but definitely noticeable when I'm pedalling gently. Under load, the sound is much louder, there's a pinging sound like when something gets caught between the spokes and the spokes ping. It's definitely not that though.

Initially I thought it must be the freehub, something in the pawls and rachet that went wrong. Bought a new wheel, and it's the same. Luckily I've been able to just accept it rather than worry about it. This morning I just had the thought of posting this just in case I've missed something obvious.

Is the gear changing crisp, it could be the indexing needs a tweak.
Or, is the rear mech going over too far in bottom gear and pinging off the spokes, a potentially serious problem.
I noticed that you have changed almost everything that can be changed, so try a different set of pedals to rule those out.
Sometimes these annoying problems are difficult to pin down.

 

[Mike_P]

Others to above;
Chainring bolts fully tightened?
Length of cable beyond RD not excessive resulting in the cable catching the spokes depending on the gear selected.
Cleats, if used, bolts tight and the pedal mechanism set right and appropriately oiled / greased

 

[Ian H]

Check the simple things first - are there any tight links in the chain? (Does the 'skipping' happen less after you've lubricated the chain?).

 

[presta]

I thought it must be the freehub, something in the pawls and rachet

That's what I think, too. Your description sounds like what I get very occasionally too, and I've always made the same assumption.

There must, by chance alone, be occasions when you take up the drive just as a pawl is about to drop into a notch on the ratchet, and the tip of the pawl just catches on the edge of the ratchet slot without dropping all the way home. When you then apply the load, the pawl is liable to either pop the rest of the way into the ratchet, or jump out so that the pawl then catches on the next notch.

It's always occurred from time to time, and I've never worried about it, or had a problem.

 

[Deleted member 121159]

Very reasonable suggestions and a good reminder to check for those things regularly anyway. Unfortunately I think we can rule out the chain, cable, and chainring. I've gone over many times to check whether they are properly adjusted, tightened, etc. Tight link in the chain is not something I had thought of. But the chain is new and we'll lubed, and yet it still happens. I forgot to mention I changed the RD hanger as well and RD is definitely safely removed from spokes in all gears.

I'm leaning towards agreeing with @presta . That sounds plausible.

 

[presta]

The green line shows the locus of the pawl tip if the speed of rotation is slow, and the change of direction is late after the pawl drops, the red line shows the locus with faster rotation, and earlier direction change: