Help with drivetrain vibration

[nmrt]

I just built up a new to me Seven Odonata (Carbon-ti). It has brand new DA chain, cassette, FD, and RD. But the crankset is Easton EA90 carbon cranks with Easton chainrings.

The ride is just superb as I took it for a 60 mile ride today with about 6200 ft of climbing. However upon descending at 35-40 mph and when I am in the highest gear (50 front and 11 back), there is a grinding that I feel while pedaling. This grinding produces a vibration in the crankset which then transfers to the soles of my shoes. It is so bad that i do not feel like pedaling in this gear. The vibration is also present in the next gear down.

Anyone know what is going on? I took it to a bike shop and the lad said it is normal. I do not think it is normal. I have other bikes where this does not happen. I would trust the paceline brain bank than a mechanic who just does not want to diagnose something that might require some detective skills.

Thanks in advance!

[ultraman6970]

Chain too long?

[Cicli]

Check the inside of the dropout on the drive side. I had one once that allowed the chain to just hit the dropout in the 11 cog and caused a weird noise/feeling.

[David Kirk]

New chain on used chain rings? If so that's my bet.

dave

[weisan]

is it just during descending that hill?

What about when you are riding on the flats and dropping to that gear? Have you tried that?

[nmrt]

Yes, whenever I am in that gear either descending or in the flats, the vibration appears. But if I stop pedaling, it goes away.

[nmrt]

The chain is brand spanking new and so are the chainrings. But I just checked -- the cassette was used on one ride of 60 miles. Is this enough to cause these symptoms. If yes, what do I do? Buy a new cassette? Then it will be new cassette, used (60 miles used) chain. So, brand new chain and a brand new cassette? That is a bit excessive, no? :confused:

New chain on used chain rings? If so that's my bet.

dave

[pbarry]

Check the inside of the dropout on the drive side. I had one once that allowed the chain to just hit the dropout in the 11 cog and caused a weird noise/feeling.

Check the above. You should be able to feel the vibration on the work stand, maybe while using the rear brake to get some tension. Also, if the FD limit screw the isn't adjusted well, the chain may be rubbing on the FD cage in the top two gears.

[nmrt]

Will do.
Thanks for the tip.

Check the inside of the dropout on the drive side. I had one once that allowed the chain to just hit the dropout in the 11 cog and caused a weird noise/feeling.

[dddd]

Check the above. You should be able to feel the vibration on the work stand, maybe while using the rear brake to get some tension. Also, if the FD limit screw the isn't adjusted well, the chain may be rubbing on the FD cage in the top two gears.


Yes, the Hi-limit screw, and also the FD cable tension is critical here.

I've had bikes where the chain entered the rear derailer cage at a bad angle in certain gears, due to either bent derailer, bent dropout or frame out of line.
Usually this affected the bigger end of the cassette, but the chain could be feeding onto the lower pulley at a bad angle at either end of the cassette depending on what/how/where something is bent.

[David Kirk]

The chain is brand spanking new and so are the chainrings. But I just checked -- the cassette was used on one ride of 60 miles. Is this enough to cause these symptoms. If yes, what do I do? Buy a new cassette? Then it will be new cassette, used (60 miles used) chain. So, brand new chain and a brand new cassette? That is a bit excessive, no? :confused:

That little mileage on the cassette should not cause any issues.

If the vibration occurs only when you are in the smallest cog in the rear I'd suspect the chain rubbing the dropout. If it happens in both the 11 and 12 then that's not going to be it.

I believe you are feeling the chain not meshing perfectly with either the cassette or the chain rings.....and since both the cassette and the chain are DA I'm betting on the c-rings up front.

Do you have a workstand you can put the bike in? If so put it in the stand and put it in the biggest gear and then stop the rear wheel. Now turn the crank hard and see if you can feel the vibration in your hand as the rear wheel spins up. I'll bet you will feel it. If you are careful you can drag the rear brake just the right amount to give it enough load in the stand so that pedaling it hard will make it happen for as long as you have the chain tension high and are pedaling hard. As each tooth of the c-ring slips into the chain it can, depending on the tooth profile, hang up ever-so-slightly and cause the chain to grind its way down onto the c-ring. In the work stand you should even be able to see it. This grinding occurs with each tooth as it engages the chain so the faster you go the more it vibrates.

Assuming you can get it to happen in the stand try lubing the chain generously and try it again. If it's gone or lessened it's the tooth profile or sharp edges in the teeth left over from machining and it will most likely go away with some use.

dave

[Hilltopperny]

It sounds like it could be the fd rubbing in the two outer most gears. A cassette with only one 60 mile ride is fine with a new chain and rings. If not what cicli said may be the culprit.

Sent from my SM-G900V using Tapatalk

[Tony]

You may what to check your rear der., the chain running between the two pulleys is done correctly and not rubbing on the cage.

[nmrt]

Dave, you are correct. The chain is not rubbing in the dropout. I checked. Also, the vibration in happening in both the 11 and 12T.

Anyway, I just did what you asked. I could easily feel the vibration in my hand while I turned on the cranks at 50-11 while the bike was in the stand. Since it is a new chain it has a lot of that chain wax (?). I removed all of that will a degreaser and put a lot a of rock N roll chain lube. The vibration was still felt in my hand. I am unsure if it decreased. I will take it for a ride tomorrow. Am too wiped out today to grind a 50-11 combination. :-)

But I am hoping that this is something, as you said, that will go away in time.
Oh, another thing, this DA9100 RD has Kogel ceramic pulleys. Do you think this also could be an issue? I could very easily change it and see what happens.

That little mileage on the cassette should not cause any issues.

If the vibration occurs only when you are in the smallest cog in the rear I'd suspect the chain rubbing the dropout. If it happens in both the 11 and 12 then that's not going to be it.

I believe you are feeling the chain not meshing perfectly with either the cassette or the chain rings.....and since both the cassette and the chain are DA I'm betting on the c-rings up front.

Do you have a workstand you can put the bike in? If so put it in the stand and put it in the biggest gear and then stop the rear wheel. Now turn the crank hard and see if you can feel the vibration in your hand as the rear wheel spins up. I'll bet you will feel it. If you are careful you can drag the rear brake just the right amount to give it enough load in the stand so that pedaling it hard will make it happen for as long as you have the chain tension high and are pedaling hard. As each tooth of the c-ring slips into the chain it can, depending on the tooth profile, hang up ever-so-slightly and cause the chain to grind its way down onto the c-ring. In the work stand you should even be able to see it. This grinding occurs with each tooth as it engages the chain so the faster you go the more it vibrates.

Assuming you can get it to happen in the stand try lubing the chain generously and try it again. If it's gone or lessened it's the tooth profile or sharp edges in the teeth left over from machining and it will most likely go away with some use.

dave

[muz]

11t never feels smooth on my bikes, I think that's just the nature of the beast. 12t feels smoother, after that no issues.

[Louis]

How close is the upper r-der pulley to the cassette cogs? Too close? (however, that won't sound like grinding, more like thump, thump, thump, thump)

[BdaGhisallo]

On just about every bike I have had in the last ten years I have felt a vibration on the workstand when in the 53x12. There's something about that smallest cog that sets up a vibration. There's no dropout contact or FD rubbing. I read something somewhere about it, perhaps, setting up some kind of resonant frequency.

It doesn't bother me in practice since I am never in the 12 when on the road - don't have the terrain to enable someone with my power output to use it, but I have always found it curious.

[oldpotatoe]

Dave, you are correct. The chain is not rubbing in the dropout. I checked. Also, the vibration in happening in both the 11 and 12T.

Anyway, I just did what you asked. I could easily feel the vibration in my hand while I turned on the cranks at 50-11 while the bike was in the stand. Since it is a new chain it has a lot of that chain wax (?). I removed all of that will a degreaser and put a lot a of rock N roll chain lube. The vibration was still felt in my hand. I am unsure if it decreased. I will take it for a ride tomorrow. Am too wiped out today to grind a 50-11 combination. :-)

But I am hoping that this is something, as you said, that will go away in time.
Oh, another thing, this DA9100 RD has Kogel ceramic pulleys. Do you think this also could be an issue? I could very easily change it and see what happens.

I would change the pulleys to OE ones and make sure the chain is installed correctly...name on chain outboard.

[cmg]

did you check the front derailleur as suggested? might be chain ring rub in this position. check rear derailleur upper cog position, may be to close to cassette. Also look at chain position between 11, 12 and 13 tooth cogs and check for bent teeth. take the chain off the chain rings and spin the crank. I discovered loose chain ring bolts when I did this

[Mark McM]

On just about every bike I have had in the last ten years I have felt a vibration on the workstand when in the 53x12. There's something about that smallest cog that sets up a vibration. There's no dropout contact or FD rubbing. I read something somewhere about it, perhaps, setting up some kind of resonant frequency.

I think you are referring to a phenomenon known as Chordal Action:

http://chain-guide.com/basics/2-2-1-chordal-action.html

Essentially, chainrings and sprockets are not actually round, but are polygons (one side per tooth or chain link). As these polygons rotate, their effective radii increase and decrease, resulting in fluctuations in drivetrain speed. For a large number of teeth, the variation in radius and resulting speed fluctuations are relatively small. But as the number of teeth decreases, the number of sides to the polygon decreases, resulting in larger radius changes and larger speed fluctuations. This can be felt as vibrations in the drivetrain.

[zennmotion]

I would change the pulleys to OE ones and make sure the chain is installed correctly...name on chain outboard.

I experienced this with my first Shimano 11 speed build. Then I RTFM.

[nmrt]

Thanks for the tip. The chain is installed properly. I will change the pulleys to OE in the pm today. Crossing my fingers that this does the trick.

I would change the pulleys to OE ones and make sure the chain is installed correctly...name on chain outboard.