Riv-Lantis

I just got my new road bike with full DA. I have noticed a rough feeling in the cranks when pedaling at very specific power levels. When I'm just cruising along at low power, the cranks are smooth as silk, and when I'm hammering they seem smooth. But when I pedal at an intermediate effort there seems to be a rough feel to the pedaling, kind of like I'm riding on very small rumble strips. I can feel it/ hear it every time I put power down after each foot comes over top dead center in my pedal stroke.

I can't figure out what could be causing this. It's not any derailer adjustment, and I don't think it's in the rear wheel/hub/cassette.

Any help or suggestions for me to troubleshoot this on my own without a trip to a shop?

TallRider

Pretty weird, I can't think of anything in the structure of the bearings that would cause this. Are you confident that it's not just your biomechanics of the pedal stroke at that effort level?

Riv-Lantis

I'm pretty sure. I've got 3 other bikes, one with over 35k miles on it, and I've never noticed this on any of them.

I'm stumped. I guess I'll have to cave in and take it to the shop.

San Rensho 

Rule out a chain/cassette problem. Put another rear wheel or cassette on and see what happens.

Check the BB for play by gripping the cranks and moving back and forth (not around), if thats ok, take the cranks off and turn the spindle by hand to see if it feels ok.

HillRider

What series DA is your crank and bottom bracket, the older Octalink 9-speed or the newer 10-speed external bearing type?

The DA Octalink bb was a maintainance hassle as it was built for lightness and absolutely minimal resistance at the expense of longevity. Most riders, including a lot of Pros, substituted the Ultegra Octalink for it.

The new external bearing bb is very alignment sensitive and the bb shell must be square and parallel for it to work properly as it indexes on the shell faces.

Riv-Lantis

It's the new 10 speed external bearing crank.

The frame is a brand new IF Crown Jewel that was faced prior to putting the BB in it. The crank arms seem tight, with zero play when I try to move them back and forth perpendicular to the frame.

Maybe it's the chain????

HillRider

Well, there go my pet theories.

TallRider

If I had the money for that kind of bike (I guess I do if I allocate it away from lots of other things - and most of us could probably say that) then I wouldn't be trying to do-it-myself. It makes your namesake bike (I don't know if you have a Rivendell Atlantis) look cheap.

Seriously, even if I were going to have other people work on my bike, I'd still want to know what was going on and would probably ask on these forums.
But sadly I have no idea what's the problem on your bike. Tell us if you figure it out.

OneTinSloth

it's probably not a bearing issue. if it was, you'd be detecting it ALL THE TIME, especially when hammering.

first thing i would do though, is put the bike up on a trainer, or rollers and try to re-create the vibration while someone else watches. it's a controlled environment, where you can repeat the symptom over and over and having someone else there can go a long way toward pin-pointing where the vibration is coming from.

check your cleats, and monitor your pedal stroke very closely. make sure the bolts are all greased and tight first, then try to determine if they're sliding back and forth a bit while you're clipped in. the cleats sliding like that might cause enough of a vibration that you'd feel it through the soles of your feet. you might actually be able to hear it as a kind of low rumble, but it probably won't be constant; it will only be at the beginning of your power stroke. it sounds like this is happening at a time when you're seated, but putting down a little extra power, probably concentrating a little more on your pedal stroke and possibly doing more pushing over top dead center and pulling through bottom dead center than you are pushing down and pulling up. applying power evenly through the stroke is super efficient, but pushing through the top and pulling through the bottom can create a forward and backward force on the pedal and if your cleats are worn, not fully secured to the shoe, or hell, even if they were bolted into the pedal you'd still get a little bit of play which could cause a similar feeling to what you're experiencing.

also, if the bike is brand new with all brand new parts, the chain, cassette and chain rings may need a few dozen miles to mesh together, this is unlikely, as i've never heard anyone mention this specific issue before, but it's certainly possible. if the parts aren't all brand new, i would check the chain for wear and replace it as necessary.

check to make sure your hubs are adjusted properly. if they're too tight or too loose, it could also cause this rumble.

make sure you're not cross-chaining. putting extra stress on the drive train by cross-chaining, particularly big/big combinations can cause a vibration. it's not likely that this is the source of your particular vibration, given your description of the circumstances under which it occurs, but it's good advice nonetheless.

when you've eliminated all of the really simple possible causes, then take it to the shop. and don't feel like you're "caving in" it's a mechanic's job to work with you to solve the issues you're having (unless of course, the issues are all in your head).

if, by a snowball's chance in hell, you happen to live in the SF bay area PM me and i'll get you a list of shops with very good mechanics in the area if you don't have one already.

Bobby Lex

The tried-and-true method for checking bb problems is to remove the chain (if you don't have a quik-link, just take it off the chainring and rest it on the bb shell), then spin the cranks. If they spin smoothly with no play in the crank arms, your problem lies elsewhere.

(And from your description of the problem it sounds to me like it is not your bb.)

Bob

Nessism

I've noticed noise on new drivetrain parts before while they were breaking in. Give things a few hundered miles to mate together. Of course, this assumes all the parts are new.

operator

It could also be because your crosschaining.

Riv-Lantis

Thanks for all the replies and help.

After some further investigation, here's what I've found:
Like alot of you have said, it doesn't seem to be the BB. The cranks spin like tops, there's no drag anywhere when either pedaling backwards or with the chain off and the bike on the trainer.

The harmonics of the vibration seem to be the exact same as they are when the chain rubs the front der. when it needs trimmin. That's NOT what is making the noise on my bike, but the rythm of the vibration is the same. So this leads me to believe that it's chain related, not bearing related.

It only seems to happen in the small ring (39t). I did a solid effort in the big ring last evening and the problem wasn't there on a 24mph+ burst for over 5 minutes.

It's definately not a noisy drivetrain from cross chaining.

So my conclusion for now is that it's just a meshing issue with the small ring and the chain???? They're all brand new components, so I'll give them a couple of hundred miles to get to know each other and see if the problem goes away.

BikeWise1

If you put your bike on a stand in the gear in which you notice the vibration and watch the chain carefully as it comes forward over the top of the rear cog, you will see it going up and down slightly. This motion can coincide with the resonant frequency of the tensioned part of the chain and manifest itself as a rumble or rippling feeling in the cranks at certain crank speeds and chain tensions. Wearing in seems to help a little-I don't really know why.

Riv-Lantis

That's exaclty what I have been thinking it is. The reason that it only happens at certain power levels is that the chain only vibrates at the right frequency when the tension is just right for the condition to happen.

I'm hoping that a few hundred miles will settle it out on it's own.