milktree

Start with the patient:
2017 Cannondale Synapse Carbon Disk with Ultegra everything (except the cassette, which is 105)
brakes are hydraulic
brake rotors are six-hole with a DT-Swiss adapter to center lock.

The bike appears to have very few miles on it, like maybe less than 800 miles. Tires are OEM brand/model that came with it from Cannondale.

BUT... the rear tire was damaged from a pinch-flat at some point, so it's possible the previous owner was a little reckless. (or he didn't understand why tire pressure is important)

I've only had this bike for three days so far, so I've only ridden it on a test-ride. (seller knocked some $$ off for the noise)

OK:
the symptom is that under braking, even if the wheel isn't moving, (isn't sliding against the pads) there's a very loud spoke ping/creak:

Here's a crappy video:


Some notes:
- the pinging is *LOUD*, this is not something anyone would explain away with "they all do that"
- It will do it on a stand, pressure on the ground is unnecessary. It does not make the sound when riding, only when braking
- the wheel doesn't need to be "reset", it'll ping when adding rotational force repeatedly. (i.e.: it doesn't just do it on the first time braking, it "springs back" on its own and pings/creaks again)

Things I've checked or done:
- spoke tension (as well as I can, I don't have a tension gauge)
- wheel trueness
- rotor trueness
- caliper alignment
- caliper mounting bolt torque
- put a dab of oil *EVERYWHERE* a spoke touches anything: where they cross, where they touch the nipples, where the nipples touch the rim, where the spokes touch the hub
- confirmed the head bearings are tight (enough, no slop)
- checked the pads for slipping in the caliper (they don't seem to be)

I have *not* been able to remove the rotor from the hub yet, the tool is still between The Internet and my house.

What could cause this?

FBinNY 

Are you SURE it's the spokes. I ask because it makes the sound off the ground and stationary.

If you think a moment you'll realize that the spokes are removed from the action. The only loads and possible movement has to be someplace between the brake mount on the fork, the brake, the rotor, and down through the hub to the axle, and back to the fork.

The spokes and rim are out of it.

You might test this by sliding pieces between the spokes at all the crosses. If it still pings, then it's not the spokes.

Barry2 

fify

_ForceD_

That is an interesting conundrum. But just based on the noise it’s making in the video…I can’t think of anything else that would make that “ping” sound on a bike other than the spokes. Or at least whatever is the root cause, it’s seems to be allowing it to resonate through the spokes. Do you have another set of wheels you can put on the bike and do this test to see if the bike still makes the noise, or put this set of wheels on another bike to see if the wheels still make the noise? — Dan

Iride01 

I didn't notice while watching the video if those were center lock brake rotors. If so, then check the lock ring. Mine was ever so slightly loose the other day and made some noise but not as much.

Do all the spokes seem about equally tensioned? If so, then it might be just normal noise that you'll hear when you do things with a bike that are other than riding it. But if you are unsure about the wheels, just take them off and go to a LBS. Ask them to check them out and they'll check them for true and spoke tension. Usually for not much money and it'll be worth knowing that they are in good shape.

I have sometimes had spokes creak while riding a bike. Usually when I started accelerating. Some people go to great lengths to make their wheel spokes quiet, but I'd be more happy just knowing that a wheel person said they were okay.

milktree

It's a disk brake, so all the braking forces are going through the tire -> rim -> spoke nipples -> spokes -> hub -> brake disk adapter -> brake disk -> caliper -> and then to the fork and frame.

Obviously the tires aren't going to "ping", but the spoke nipples might, or the spokes at the hub, or the spokes against each other (because of some other flex somewhere), etc.

I'm sure it's a spoke noise. It's not a "carbon fiber cracking" noise, or a "brake pad sliding in the caliper" noise, or a "loose/damaged headset" noise.

I'm not sure that the root cause is the spokes. It seems likely that something else is causing a vibration that the spokes are amplifying and showing me.

Kind of in the same way that a baseball card clipped to the fork to pluck the spokes isn't a spoke noise, but it's the spokes are making the noise.

milktree

They are center lock, with a six-bolt adapter.

The rear brake disk slips quite obviously (like, I can see it without looking hard) and it makes zero noise.

The front does not move that I can see. Maybe that's the problem, maybe it's too tight! (a bit of a joke, I'm not sure how that would cause noise)

Yes. roughly. Not perfectly equally tensioned, but pretty good.

Oh, it's loud. I noticed it on the test ride. It's not a "I couldn't hear it for the wind noise" kind of noise, it's more like "there's something wrong with the wheel or brakes" kind of noise. Definitely not normal.

I've had wheels creak, too. also under acceleration (because that's the only time the spokes are tensioned like that.) But this is much more pronounced than that. I don't like the "normal" creak, either, it indicates something is rubbing or slipping, both of which lead to wear and eventually failure.

milktree

I don't have another set of wheels, unfortunately. That would have been my first test though. The other singles have rim brakes, the tandem has disk brakes, but the rotor is *WAY* larger. (unsurprisingly, given its much heavier duties)

_ForceD_

I suppose you could put the disk brake wheels on a rim brake bike (if the caliper pads reach the rim, and it fits between the dropouts) just to do this test. I wouldn’t think that it would cause any damage to the disk brake rim just for this test. — Dan

milktree

I don't think I understand what test you're talking about.

The sound only happens when the front brake is applied, so without a caliper to put rotational force on the disk, there's nothing to test. It doesn't make noise when riding, only when the front brake is applied.

cyccommute 

I’d not be so quick to dismiss the spokes. I suspect the spokes are rubbing against each other where they cross. The spokes look they are wide blade aero spokes and the wheels are straight pull spokes. The larger area of contact between the spokes would amplify the noise and the straight pull spokes may not keep the spokes as tight together at the crossing as a J-bend spoke would.

Are the rims carbon? Even if they aren’t, the rim makes a great sound box. Carbon would probably resonate even more.

milktree

Aluminum rims, round spokes. I was wiggling the camera a lot, not great at holding it still.

What's the cure then? "put paper between the spokes" seems more like a band-aid, not like fixing the root cause.

FBinNY 

I wouldn't normally respond, but since you quoted me.....

Had you read the OP and my response, you'd have known that we were talking about pinging WHILE STATIONARY OFF THE GROUND. So I reiterate that under that condition, there is no torque and the spokes are out of it.

BTW. - that was the mystery.

_ForceD_

The spoke have to be in the equation, don’t they? If while stationary, the brakes are applied and the bike is pushed forward (as the OP did)…torque is being relayed fro the tire-ground interface, through the tire-rim-spokes-hub-disk-caliper-frame…right?

Dan

cxwrench

Please explain how you'd get disc brake wheels on a rim brake bike.

FBinNY 

Applying Ockham's razor. I'd focus my attention on the rotor hub interface. The brake deflects the rotor and it moves against the hub, or adaptor in between.

It's also possible that the rotor itself has a crack in one of the support arm and that moves when deflected. This isn't likely, but worth considering when you've eliminated all else.

FBinNY 

If Dan's conditions are met, you slide it into the dropouts just like any other wheel.

milktree

I wrote the OP. assuming "OP" means "Original Post" (or "Original Poster") Doesn't that mean, "the first post in the thread"? In other forums it does, but every forum has its own lingo and dialect. (not snarky, totally true)


Ah, I see the confusion. The "off the ground" and "stationary" bits mean, "no weight on the bike", not "zero rotational force on the wheel"

To get it to creak I have to both squeeze the brake and put a rotational force into the wheel. Axial force (like when riding with weight on the bike) doesn't make the noise. Only rotational force is necessary.

The "stationary" part means the disk isn't sliding in the caliper. That's to distinguish it from the much more common squeal you get from glazed rotors and pads.

cxwrench

The OP's bike is thru axle. A rim brake wheel is q/r. Not gonna happen.

FBinNY 

Sorry, I didn't double-check the name, and of course didn't think the OP wouldn't know where we were.

Now that we're talking about adding static torque, there's less mystery, and I'm more convinced it's movement between rotor and hub.

In any case, do the paper between spoke test to rule them out.

milktree

That sounds like an excellent application of Occam's razor.

Unfortunately, the tool to remove the rotor is in the mail, and won't get to me until Saturday, and we're leaving town for a week on Friday. I won't be able to test that hypothesis until I get back. Boo. Hiss.

Assuming it is something in the rotor-hub interface, what's the likely cause and fix? A thin coating of anti-sieze on the mating surfaces? Absolute cleaning and de-greasing?

With motorcycle and automotive brakes (which I'm most familiar with) there's no "clocking" of the rotor like there is on bicycles. Mount, torque, done. I guess the torque values are higher, or the forces are high enough that they "clock" themselves naturally.

Could it be a combination of the wrong torque and not quite clocked correctly?

It hadn't occurred to me that the rotor might be cracked. The bike is young (in number of miles ridden)

milktree

I should add an avatar. Maybe it'll be of a brake rotor!

I can do one of those today, the other will have to wait until the tool arrives!

streetsurfer

I can see your spokes vibrating at the crosses in the second video. I believe this is entirely caused by the black coating.

I believe you are hearing the spokes hang and release, hang and release, at the point they cross each other. This photo is where the same noise and vibration emanates from, but I don’t lace wheels, so I am not sure what other tensioning issues may lead to it being so obvious.

My Response Trail did this on a lesser scale and largely when cornering (also with black painted spokes) until the paint wore away where they cross. This only took a few rides with some agressive turns, which I decided to try as a remedy since they mostly “spoke up” during turns. I knew it was coming from the crosses. I can still make them squawk by hand pressing them together a little as I slide one past the other.

Chrome and raw spokes are much quieter in doing this. I am convinced it is an issue of the paint but that does not mean something else isn’t exacerbating it like nipples that are hung against improper tension at the rim interface, or a crack in the rim somewhere.

for now I’d ride it to rather spiritedly to quickly wear the paint away. I did repeated circles in a cul de sac and could hear them get quieter in one session, convincing me I was on target.

Maybe even spend ten minutes manually manipulating them. A fine grit polishing paper might be passed between them but that could wear away more paint than needed. I wouldn’t do that but instead ride it. In my experience, it will go away as the paint wears off.

Iride01 

Based on your answers to mine and other posts I highly recommend what I said in my first response.

If you want to become great at working on your own stuff that's good. But work on that slowly and don't forget you can learn a lot by watching others. Some of the shops here let you watch them work on your stuff. And they'll talk to you while they are working and tell you why's and how's.

milktree

Given how shaky my camera was, I'm surprised anyone can see anything.

But here's the gotcha:

The spokes don't touch there.

They touch at the first cross, but not at the second cross.

i.e.: they touch at the red arrows, but not at the green arrow.


spoke touch points

Sorry for the huge image, I haven't figured out how to insert a clickable thumbnail.

My next test is to slip some paper between the contact points and see if anything changes.

Interestingly, I can't make them creak by manually moving the spokes. Only under braking. This supports the hypothesis that spokes are a symptom, and not the cause; that it's actually between the rotor and hub.