Got a wheel wobble

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Re: Got a wheel wobble

Postby ironhanglider » Sat Nov 17, 2012 10:32 pm

il padrone wrote:...
The way I understand it, stress is built up in steel spokes (or any steel component) when they are bent but not permanently set. They are thus under continual stress as the steel wants to move back into the prior position. This stress contributes to eventual failure. Spokes laced up are crossed over other spokes and this creates a slight bend.

Stress-relieving involves turning this bend into a cold-set (permanent bend) in the spoke. Sheldon Brown describes this well and advocates using an old crank end to flex the spokes at the cross and set the bend in them

This all may be less relevant for a radial-spoked wheel as there are no spoke crossings. The only reason to 'de-stress' the wheel is really to ease the spokes into a good seating as you describe.


See the wheel failure thread as well. :D Stress relief is mostly about setting the shape of the spoke elbows, the crossings impart such a slight bend that it is unlikely that there is anything close to yield strength at that point. This is bourne out by the fact that spokes rarely if ever break at a crossing point. The Sheldon method is mostly a convenient way of stressing the elbows, with a marginal benefit of setting the shape at the crossing point. The Jobst method works just as well for radial spokes. It may even be more important to stress relieve radial spokes, since they de-tension more at the bottom of the wheel. It may not be so noticeable because most radial spoking is done on fronts, which break spokes less frequently anyway. It might be interesting to confirm if there are proportionally more radial spoke failures to crossed spoke failures in similar circumstances though.

Cheers,

Cameron
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by BNA » Sun Nov 18, 2012 1:55 pm

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Re: Got a wheel wobble

Postby Reman » Sun Nov 18, 2012 1:55 pm

+1 to IP and Cameron (again).

As Musson points out, it is also important to continually stress relieve during wheel building for two reasons. One is to set the "paths" of the spokes from the hub flange, this bends them past where they need to go and when let go return to what should be closer to the final path. Two, once one is done it allows a higher and more even tension to be created.

High (proper) and even tension stops spokes unwinding and breaking.

Spokes twisting during tensioning and truing means the spokes and nipples weren't properly lubricated in the first place.
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Re: Got a wheel wobble

Postby swon38 » Sat Dec 01, 2012 5:28 pm

I've had a road bike for 5 weeks now (new to it all), just last week I took it to get a cable issue sorted and was told my rear wheel had a wobble in it. I had no idea, but it was trued, and all was good.

I ride on bike tracks, and I occassionally come across the odd tree root that has caused a bump in the path, or a small gutter jump where the bike track joins the road. Apart from that I can't think of any other issues (I obviously try to avoid clearly visible potholes and the like).

At the moment my front wheel is rubbing against the brake pad in one particular place, which is clearly not good and a sure sign of a bent wheel. I can flick a switch on my front brake caliper to widen the calipers, and this allows the bent wheel to go through without rubbing. I can still apply my brakes, but theoretically I suppose brake trigger length will increase.

I'm wondering how common an issue this is, and whether road bike wheels are really this fragile. Obviously I need to get the front trued again, but it's just such a hassle going back to my mech, especially if I have to do it once a month, etc.

FYI, the bike is a Cannondale CAAD8 with stock wheels (Alex rims rc24).
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Re: Got a wheel wobble

Postby usernameforme » Sat Dec 01, 2012 5:43 pm

Hey swon38;

swon38 wrote:I'm wondering how common an issue this is, and whether road bike wheels are really this fragile.

This question is really subjective. It largely depends on how much you weigh and how well the wheels are built. I'm 57kg and I've never had to true my wheels. If the wheels aren't built properly built or they aren't strong enough (ie 16/20 count on a 383g rim with ti spokes and poor hub spacings) then they won't hold you up either. Since they seem to be going out of true quite quickly it could be any/all of those factors.
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Re: Got a wheel wobble

Postby swon38 » Sat Dec 01, 2012 6:18 pm

I'm 75kg, so not too heavy.

I'm also wondering if there is a limit on how many times you can true a wheel. Does it get weaker the more you true it?
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Re: Got a wheel wobble

Postby antipodean » Sat Dec 01, 2012 7:46 pm

usernameforme wrote:I'm 57kg


You quoted you weight as 60kg not so long ago now 57 are you ill?
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Re: Got a wheel wobble

Postby usernameforme » Sat Dec 01, 2012 8:12 pm

Not sure about that antipodean; usually 54-57kg depending on how slack I get :lol:

swon38 wrote:I'm also wondering if there is a limit on how many times you can true a wheel. Does it get weaker the more you true it?


No, but a 'good' wheel shouldn't require truing, and when it does you can't remember the last time you did it :wink:

Could you post details of the wheels? like what the hubs are, how many spokes they have? I assume they have 32x spokes and have Cannondale brand hubs? If this is the case, it should hold up your 75kg no issues, but spokes having uneven tension or there spoke wind-up are the two things that come to mind given the nature of your issues.
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Re: Got a wheel wobble

Postby swon38 » Sun Dec 02, 2012 8:10 am

They have 28 spokes, hubs are "forumula" branded and look like so:

Image
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Re: Got a wheel wobble

Postby usernameforme » Sun Dec 02, 2012 10:50 am

Would think a build like that would be sufficient to hold your weight. Try grabbing two pairs of spokes and squeezing them together, don't squeeze to break the spoke, just hard enough to move them. If one spoke is REALLY loose you should be able to feel it. Another way to do this by 'plucking' the spokes and listen to them resonate. Either way is fine. Also, did you hear any 'pinging' when you were riding? 'pining' noises from the spokes can be an indication of spoke wind up. The wound up spokes will unwind themselves, causing your wheel to go out of true. If this was the case, your wheels should have stayed in true, unless the LBS wound them up more... Are your spokes bladed or round?
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Re: Got a wheel wobble

Postby foo on patrol » Sun Dec 02, 2012 11:19 am

swon38 wrote:I'm 75kg, so not too heavy.

I'm also wondering if there is a limit on how many times you can true a wheel. Does it get weaker the more you true it?


Unless the rim has suffered some sort of direct impact that would alter its integrity, then no but spokes would be another thing all together, they stretch over time. :wink:

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Re: Got a wheel wobble

Postby swon38 » Sun Dec 02, 2012 11:35 am

usernameforme wrote:Would think a build like that would be sufficient to hold your weight. Try grabbing two pairs of spokes and squeezing them together, don't squeeze to break the spoke, just hard enough to move them. If one spoke is REALLY loose you should be able to feel it. Another way to do this by 'plucking' the spokes and listen to them resonate. Either way is fine. Also, did you hear any 'pinging' when you were riding? 'pining' noises from the spokes can be an indication of spoke wind up. The wound up spokes will unwind themselves, causing your wheel to go out of true. If this was the case, your wheels should have stayed in true, unless the LBS wound them up more... Are your spokes bladed or round?


I had a quick play around, when plucking the spokes I don't really notice anything too different. I don't want to mess around with the spokes too much, as my mech said if you don't know what you are doing it'll probably make things worse.

Now that you say it, I kind of recall a ping noise as I took a detour off the track. I was carrying a little too much speed, and the height difference between the track and the grass/dirt on the side of it was probably 2-3cm.

The front wheel has never been trued since I've had it. The spokes are bladed but round at the rim and hub ends.

Since I'm new to it, I guess I'm seeking clarification:
Wheel wobble due to spokes can be rectified easily by playing with the spoke nipples etc.
Wheel wobble due to rim damage = game over & need to buy new wheels
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Re: Got a wheel wobble

Postby usernameforme » Sun Dec 02, 2012 2:33 pm

swon38 wrote:if you don't know what you are doing it'll probably make things worse.


Yes, but if you want to learn its not that difficult. If you didn't notice anything DRASTICALLY different between spokes, then it would suggest that none of the spokes have tensions that are too low or too high. so your problem is likely elsewhere. I personally find it very hard to tell by sound, but if each sound is different then the tension is not uniform, which could be causing your problem.

swon38 wrote:The spokes are bladed but round at the rim and hub ends.


I highly doubt a wheel built with bladed spokes will have SWU, you should be able to see a twist in the spoke

swon38 wrote:Wheel wobble due to spokes can be rectified easily by playing with the spoke nipples etc.
Wheel wobble due to rim damage = game over & need to buy new wheels

Yes, but a wheel "wobble" will always be caused by the spoke tensions. Check your rims for cracks, if there are no cracks then the rim is fine. Your problem is most likely down to an out of true wheel. This should be easily be fixed with a 5 minute true

If your rim is obviously "bent" like so then it will need a new rim, but you still may be able to fix it:
Image
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Re: Got a wheel wobble

Postby swon38 » Sun Dec 02, 2012 4:18 pm

Cheers all, I'll have to get it trued during the week then.
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