A riddle for you...

[TheDarkInstall]

Hi

I have an interesting problem, which I have been working through, but as yet have not found the cause and therefore the solution.

Parts involved

Rear wheel;

FarSports Carbon Clincher 38mm rim. 24h
Sapim CX Ray spokes
Tune Mag170 hub

The Problem

Simply; When pedalling, the rear wheel omits metallic sounding clicks and pops.

In detail; This occurs more when seated.

Info about me;

-I am 177cm tall, riding a 52cm Evo and weigh 68kg, so I am in no way overweight for the bike, or the wheel.

What I have done so far...

-Swapped the freebody in the Tune Mag170 hub with a brand new one. Problem remains
-Tried different lacing patterns; initially 2-Cross on drive and non-drive, and now 2-cross on drive and radial spokes-out on non-drive. Problem remains
-Increased tension of spokes slightly. Did not go mad, and did not go over the recommended maximum by the rim manufacturer. Problem remains
-Decreased tension of spokes slightly. Problem remains
-Used nipple washers. Problem remains
-Used no nipple washers. Problem remains
-Swapped cassette with a new one. Problem remains
-Used spoke prep on the spoke threads. Problem remains
-Used grease on the spoke threads. Problem remains
-Replaced nipples. Problem remains
-Tested to see if it actually is the wheel; took the wheel off the bike, put a chain whip on the cassette, sat on the wheel, and pushed down on the chain whip; recreated the exact sound, so it is definitely the wheel. Also, swapped the wheel for another one I own; no problem with the other wheel.

Theories and ideas

-I noticed that the spoke tension reduces by a noticeable amount after mounting the tyre. Could it be that the reduced tension means that when pedalling, the tension difference between unloaded and loaded spokes is large, therefore meaning that there is potentially a lot of movement in the spokes, which causes noise where they inferface with the hub or rim, or where they cross?
-The problem is more noticeable when seated, and therefore my weight is further back on the bike, over the rear wheel. Could it be that the rim is not stiff enough radially, and is deforming/compressing when I apply my weight to it, therefore reducing the spoke tension, which is then retensioned though pedalling causing the noise through movement against the interfacing parts?

If any of you have any thoughts of ideas about what this could be, I would be very grateful for suggestions, to help me get to the bottom of this. It is a living nightmare!

[efeballi]

Have you narrowed it down to the rear wheel, i.e. by borrowing another wheel from a friend?
Quick release skewers came to my mind, swap your current skewer with a Campagnolo or Shimano skewer and see if that changes anything.


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[TheDarkInstall]

Thanks for the reply.

Have you narrowed it down to the rear wheel, i.e. by borrowing another wheel from a friend?
Quick release skewers came to my mind, swap your current skewer with a Campagnolo or Shimano skewer and see if that changes anything.

-Tested to see if it actually is the wheel; took the wheel off the bike, put a chain whip on the cassette, sat on the wheel, and pushed down on the chain whip; recreated the exact sound, so it is definitely the wheel. Also, swapped the wheel for another one I own; no problem with the other wheel.

Also, yes, I have swapped skewers. Problem remains...

[Privateer]

Have you tried changing the cassette?

[TheDarkInstall]

-Swapped cassette with a new one. Problem remains

[efeballi]

Too much riding for the day, I guess...
Then I'd say it is the hub. You tried increasing the spoke tension, it should have changed the nature of the pinging at the very least. If it didn't, the problem is at the hub.


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[TheDarkInstall]

Thanks again for the response. Ha, my brain stops working after a long ride too.

I did indeed try changing the spoke tension, which changed nothing.

Since posting, I have done another experiment;

-I held the wheel at the top, and put my foot on the hub (shoes off, with only socks on so I don't scratch anything, of course!). I held the wheel hard in my hands, and pushed with my feet, to flex the wheel. This indeed flexed it, but no clicking and popping happened.
-Narrowing it down, with the wheel off the bike, I can make the popping and clicking happen by putting a chain whip on the cassette, sitting on the wheel (compressing the spokes, and therefore reducing tension) and pushing on the handle of the chain whip. When I stand up, I can make the clicking and popping happen again by pushing on the handle of the chain whip, but this only happens a few pushes, until (I suspect), the wheel returns to tension as the rim recovers shape from being sat on by me.

I don't want to definitely say it is a problem in the hub at this point, as I do not know why this would be the case; if anyone can tell me why it might be the hub, based on everything I have written so far, that would be really helpful, especially in light of the fact that it happens when weight is applied to the wheel, rather than unloaded.

[Gregorio]

Any chance it is the valve clicking against the rim? I had a rear wheel that did this. Try a piece of electrical tape around the valve where it contacts the rim or maybe put a nut on the valve to hold in place

[TheDarkInstall]

Hey,

No it is not the valve, although I have had that issue in the past, which I too sorted with a bit of electrical tape, so good call on that suggestion

I have done some more investigating...

-I took off the cassette, and put on part of an old, and trusted Dura Ace 7900 cassette. Then, I used the chainwhip to apply pressure to the freebody, in a variety of positions along the length of the freebody.

See the photo for an image of my 'rig';



The results were interesting

-The clicking continued, but not on every position of the ratchet. At certain points, I was able to apply force to the chainwhip, slightly release the tension, then apply again and the clicking a popping would start again, continuing until I had topped out the flex of the chainwhip/freebody. In other positions on the ratchet, I could not make the sound happen. When I could not make the sound happen, I then sat on the wheel again, and I was able to make the clicking and popping start.

Theories at this point

-It is definitely the wheel!
-It is not the cassette
-It might be something inside the hub, which is making a sound which is resonating up the spokes, amplifying the noise...
-It might be something related to the ratchet system, although I have done no actual investigation here, but will move onto that next.

Will bore you all with more later, as I work through the issue...

[Butcher]

How many ratchet pawls does it have? Can you remove some of the pawls and duplicate the noise? You probably need all of them for full strength, but maybe a short easy ride with one less pawl might tell you something. You might have to remove each pawl to determine which one may be the cause.

Then there are ear plugs.........

[TheDarkInstall]

How many ratchet pawls does it have? Can you remove some of the pawls and duplicate the noise? You probably need all of them for full strength, but maybe a short easy ride with one less pawl might tell you something. You might have to remove each pawl to determine which one may be the cause.

That is a bloody good idea! I will get on with that and see what I come up with. I don't need to ride it to replicate the issue, so that is not a problem.

I did, however, swap out the freebody with one from another Tune hub I have, and the issue remained, but I will go through this research to see what I come up with.

For your information, there are 3 pawls on the freebody. It is this unit...



If the investigation into the pawls doesn't reveal anything, the next step will be investigating the bearings in the hub, and also the toothed ring that the pawls engage with.

Again, if anyone has any ideas at this point, I would very grateful to know them!

[TheDarkInstall]

Interesting update...if you are interested in this kind of dull mechanical stuff

-I took the freebody apart, cleaned it, and removed one of the pawls.
-Reassembled, and tried to replicate the clicking sound. Nothing. No matter what I did, I could not get it to make a sound.
-Labelled each of the pawls with numbers 1, 2 and 3, and worked through the following combinations of presence to see if anything happened.

(Pawls present)
1+2 = no sound
2+3 = no sound
1+3 = no sound

So, with only two pawls in the freebody, in every possible configuration, there is no sound.

I then put all the pawls back in and tried to replicate the sound...

No sound.

Hmmmmm. I will take it for a ride, and see if it comes back, but I have another possible theory that this might be due to one or a number of sticking pawls, which now I have cleaned out the ratchet mechanism, no longer happens.

How very interesting.

[TheDarkInstall]

Took it out for a ride...

It was quiet for a bit, then the problem came back with a vengeance. Bugger it.

This is extremely puzzling. Do any of the real engineers on this forum have any input or ideas what this might be, given that I have tried pretty much everything I can think of.

I have tried contacting Tune about this; they completely ignored my communications. Very frustrating. Far Sports have ignored my messages about this too, despite it being their rim I am using. I don't really feel it is going to help much by getting ratty about things, but it does seem that in the cycling world, the companies are happy to sell you stuff, but seem clueless when it comes to diagnosing problems after the sale. The list of companies that have ignored questions gets longer all the time; currently it consists of; Tune, Far Sports, Shimano, Cannondale...

In all my dealings with bike companies over the decades, the only one who consistently comes through with the goods and actually knows what they are talking about is G-Sport. Everyone else seems to have read Engineering for Dummies, and is piggy-backing on the back of previous designs that work but they have no idea why...

Rant over.

So yeah, if anyone has any further ideas, please do help out, as this is getting ridiculous!

[mattr]

I've had that cracking/popping noise from a hub with that sort of arrangement before, first time was due to badly lubricated pawls. They were sticking to the engagement face of the drive ring, then slipping under load (only a fraction of a mm, but it was enough!), until they engaged completely, hence the noise. Dry pawl against dry drive ring.
Unfortunately, it damaged the drive ring and pawls, so some of the teeth were rounded/chipped. i.e. not sharply formed teeth anymore. So i "fixed" it. But it would come back after a few days, usually getting worse thanks to all the crap (metal shards) in the grease/oil. The hub was eventually scrapped, as i got fed up with it and a replacement drive ring and tools to remove/replace were really not worth it.

The second time was as the pawls weren't lining up with the drive ring (a displaced bearing was pushing stuff out of line) so the noise was the pawls being twisted, and only engaging on two corners, as opposed to both complete faces. Reseating the bearing fixed that.

Other ideas:- one is dry bearings (most cartridge bearings are delivered with minimal/insufficient lubrication for our application, they really aren't designed for bikes!), other is a crack to the mount for the pawls. I believe one manufacturer has had a recall for a similar issue. Might be worth having a REALLY close look, as the crack may be minuscule.

[TheDarkInstall]

Ah, good suggestions thanks!

I will work through all those and see if I come up with anything. Much appreciated, seriously.