AS Collie

Hi All,

I've just built up my new bike and while I was adjusting the derailleurs, I noticed a distinct vibration whenever I was in the largest ratios (50/11 and 50/12). A little reading has led me to a phenomenon called Chordal Action, which I'd never heard of before, and I was just wondering what people's thoughts on this issue was? Any help would be most welcome – I'm dying to ride this bike but I don't wanna screw anything up.

Everything is new, and the vibration goes away once I shift to the third cog. The b-screw seems well-positioned, but is it a case of extreme fine-tuning? I'm fairly handy mechanically, and I've set up countless front and rear derailleurs. This is my first 11-speed one though. Is it the large ratio, or perhaps the slimmer 11-speed chain causing this noise? Will it just go away once the bike has been bedded in?

Thanks again for any help.

wphamilton

FWIW, I've had the grinding from an new chain and cassette go away after a few hundred miles which I believe is due to slight stretching of the chain and sprocket wear. But wear would not alter chordal action in my opinion.

FBinNY 

You generally cannot feel chordal action, and in any case it would be more of a purring vibration than a grinding one.

Odds are that the problem will resolve with break in. The chain flexes through the greatest arc when bending onto and off these smallest sprockets, so any sources of friction will become more important. Chain lube does make a difference (consider the source on this), so you might consider trying another (hint!).

Seriously, I'd give it a bit of time and miles before deciding if I had a problem.

AS Collie

Really? ok. My other bikes are 9-speed, so the jump up (and the associated price tag ... ) has me a bit reluctant to rush it. The chain came lubed by Campagnolo, but I will try some white lightening or similar and see if it improves.

ps: maybe I'd call it a purring vibration on someone else's bike - but it sounds like the end of the world on my precious

ThermionicScott 

It does seem like I can feel bottom bracket roughness more in the smaller cogs -- is there a reason for this?

FBinNY 

All things equal, chain tension is higher on smaller sprockets, which is why the number one factor in chain life is sprocket size. So with higher tension you feel more of the meshing action, and likewise chain lube comes into play more.

40 years ago we all complained that 13t sprockets felt like crap, an some wouldn't use them. Then 12t came out, and 13s felt OK, now it's 11t, and we've all lowered our standards accordingly. I still hate using anything smaller than 14, because it does feel like crap, even new, and even after breaking in, but I have and use sizes down to 12t on occasion, but rarely under any high pedaling force. I'm long past the age where I can produce the kind of torque at speed to justify owning an 11t, so it's a non-issue to me.

To use an 11t, I'd be going a someplace near 30mph, which implies a gale force tailwind, or a down hill, in which case I put my head down tuck small and coast past those folks still turning pedals. It makes them crazy to get passed by someone coasting.

ThermionicScott 

I hear ya -- the only time I use the 12T cog (on the one bike that has one) is when I'm soft-pedalling down a hill or with a strong tailwind. Thanks!

FBinNY 

If it's only the one smallest sprocket, I'd have you check the trim as determined by the outer limit screw in that position. But since you say it's the two smallest sprockets, I ruled that out.

Also I hate so say anything bad about a competitor's product because it seems like sour grapes, but white lightening or similar waxes are the wrong direction if you're looking for a lube to quiet a chain. Since you're in Italy you should be able to find Campagnolo oil, or something similar or heavier yet. Apply, let it penetrate and wipe off the excess and you should see and feel some improvement.

AS Collie

You're right. I opted for a heavier oil I have here. It's deffo not the trim, as it's in the 11t and the 12t, and it's a vibration in the chain rather than a sound indicating that it would like to shift. Thanks for the input; I've oiled it and now I'm gonna go for a test ride to see if it improves on the road.

BTW, it's a shame you don't have a stockist in Italy, because your oil sounds good.

FBinNY 

I mail it all over the world, and eat it a bit on the postage so it comes out to about the same as it would be if I have dealers in the various countries. The only drawback is transit time.

Meanwhile we now have 2 dealers in Finland, and a bunch in England. I expect word will slowly drift south and eventually we'll find someone in Italy. The pattern is first a pioneering type tries it, he tells his friend, then a local club, and ultimately a dealer figures it's something he might stock.

It's the same here in the USA, dealers aren't leading, they're following after a few of their customers convince them it's something to stock.

AS Collie

PM sent.

Andrew R Stewart 

I've read that in the industral world of chain driven machines a 17T is the samllest tooth count allowed by mechanical design standards. For this very effect, chordal pulsing. Andy.

FBinNY 

Bikes violate the rules because there's little choice. We're not chasing long life or smooth, vibration-free high speed operation. Bikes operate at high torque and low speed, and much is sacrificed to the goal of low weight, and dimensional constraints, you wouldn't want a 75t chainring, would you?

But the 1st rule of mechanics applies. Whatever solves the problem and works is by definition good.