Dubinthedam

So my highest gears, 7/8, have a "Buurrry" sound/feel. I've done all the indexing, correctly! Changed derailleur wheels, chain is pretty new, etc. Hanger seems straight etc. It's not a indexing 'clicking' sound, more a 'wherring' I'm thinking maybe my chain could be shorter. But love some feedback, I'm really stumped.

alcjphil

What size are the cassette cogs in those 2 gears?

AlmostTrick

I've noticed this before. Lubing the chain quiets it down... for a while.

Dubinthedam

The cassette is 11/32, so I guess 11, 14? It's mostly when on the smallest cog, 11.

delbiker1 

I would not think you would be on the 11T cog that much to worry about a bit of whirring sound. When you are in the lowest or highest cog in the back, regardless of what chain ring you are on, that is when the most stress is put on the chain, even when spinning easily. If you are in biggest/smallest or the opposite, it will never be quiet. If your "pretty new chain" still has just the factory lubing on it, you need to clean and re-lube it. Even with a brand new chain, IME, they run smoother and quieter with good lube other than the factory applied stuff.

jadocs

What you are hearing is your chain. Think about size of each link on your chain. If it travels around a small/smaller cog it is going to be articulating more. On larger cogs it articulates much less as it travels around (that's why ceramic speed made those ridiculously expensive oversized pully wheels - it's supposed to increase drivetrain efficiency). You are never going to make it silent, it's mechanical movement. Find a lube you like and think of it as the sound of a perfectly tuned drivetrain (assuming it is perfectly tuned).

Dubinthedam

I just like having my gears as smooth as possible, but I think it is just that, the smallest/biggest cog issue, the sound of the chain. Lube helps, a new chain helps.

It's a Sora derailleur, and I have Sram 11 speed which is way smoother, but again not perfect.

Thanks for the feedback, just what I needed to hear.

P.

terrymorse 

This (I came here to write the same answer -- it's most likely chain noise).

One other thing to check for, just in case: make sure the rear derailleur's jockey wheel isn't touching the cog. That can make a "brrrrrr" sound.

If it is touching, tighten the rear derailleur's B-tension screw until it no longer touches.

caloso

Check the front derailleur cage. You may have rubbing up front.

Litespud

My otherwise smooth drivetrain does exactly the same thing (my smallest sprocket is a 12). Shifting is great and nothing is rubbing. I think this has come up before, and the phenomenon is common in chain drive systems, and there's a specific name for it (can't remember) - it's something to do with the sharpness of the chain deflection around small cogs or something setting up some vibration or something. Anyway, completely normal, AFAIK.

Dubinthedam

I think I just notice it more on my 8 speed than my 11 speed because of the bigger jump. I'm fairly good at indexing, until I watched park tools video, which takes it to a whole new level! I was hoping there might be some clever tuning tip I don't know about.

canklecat

Yeah, I get that with 11 and 12 teeth cogs. Never noticed that with my older bikes with 13T smallest cogs and the old school 52/42 chainrings. Switching to 50/39 or smaller chainrings and 11 or 12T cogs to compensate involved some compromises.

One solution is to go for a larger big chainring and sticking with the 13T cog. That slight inefficiency doesn't seem to occur with 13T smallest cogs. But the tricky bit is pushing a 53T or larger big chainring (some pros are pushing 56T or larger big rings for some time trials). And avoiding dropping the chain when shifting to the smaller chainring, especially if it's smaller than a 39T for mixed terrain.

There's a whole technical article somewhere online discussing why this occurs with bicycle chains and smaller rear cogs. I can't find the link right now. It goes into more depth about the phenomenon jadocs referred to.

MoAlpha

This, but the reason you're hearing it more on one side of the cassette is probably an (unavoidable) issue of chain angle being higher there.

Dubinthedam

My Sram NX 11 speed has 36 front, 12 on the back, chain is obviously thinner and I find the NX good stuff, so it's less 'wheerring'. So I figure the smaller chain length and and different ring sizes could explain it.
But exactly why I joined the forum, YouTube vids only tell you so much, and don't answer your questions!

smashndash

What you are talking about is called "meshing losses". Google that term for more info. From my understanding, the fewer teeth you have, the more load you have per tooth. This means that every time a tooth engages or disengages, it's a big deal. Imagine 1 out of 5 teeth vs 1 out of 20 teeth.

This is the reason why pros who use SRAM refuse to use the 10T sprocket. The meshing losses are too high. SRAM had to make custom oversized chainrings for them so they could use their AXS groups as 11 speed and ignore the 10T sprocket.

ThermionicScott 

The term "meshing losses" is new to me, but searching "chordal action" would also help explain the roughness in those small cogs.

Iride01 

It's a normal thing. The chain has to bend more as it goes around those smaller radius cogs. Some bikes it's more noticable on. Maybe the different materials the cassettes and stuff are made of make it more noticeable to some.

It is more normal for me to notice it after cleaning my cassette and chain and lubing the chain. Especially if I'm in a peaceful and smooth stretch of road with a 1% downslope putting out some power in the 52/11 combo.

But I've noticed this on bikes that only have a 14 tooth cog as the smallest.


Though your "Buurry" sound and feel might not be my buurry sound and feel. <grin>

Dubinthedam

Funny, I was slip streaming a guy yesterday on my fixed gear bike, he was a big fella, I was pretty happy with myself for keeping up, I looked down at his gears and he was on the highest gear, looked like 11t, and I was on 16t on my fixie and still a long way off spinning out.

I live in Amsterdam, we don't have any mountains, not even hills! 95% of roadracers here have the standard 10-11 speed set-up. They will sometimes have a 14-23 or 11-24 cassette, not very often, but they call this a 'polder cassette' in reference to reclaimed flat land.

Kimmo 

It's not so much that the chain is bending more around the small cogs, as it is the fact the chain is pulling on something closer to a polygon than a circle (although the former is obviously the flipside of the latter).