Wheel balancing?

Everything about building wheels, glueing tubs, etc.
addictR1
Posts: 1754
Joined: Sun Jun 10, 2012 1:11 am

by addictR1

So how would you do it for tubular wheels?


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mattr
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Location: The Grim North.

by mattr

Use some of those axxios stickers?

by Weenie


ichobi
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Joined: Thu Jan 19, 2012 11:30 pm

by ichobi

addictR1 wrote:So how would you do it for tubular wheels?


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A simple lead tape stuck on inner rim would do just fine, if not unsightly.

Butcher
Shop Owner
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Joined: Sun Jan 03, 2010 4:58 am

by Butcher

I'm not saying that a balanced wheel will fix anything, I just no not see any harm in balancing any rotating object. My field of expertise is the automotive industry and everything that rotates gets balanced. From driveshafts, to wheels, hubs, etc. Heck they make engines with balance shafts that will compensate for the abnormal balance of the engine.

Why is it that a bike component should not be balanced? So harmony is the wrong word, but I do not know any other that would apply.

This forum has a bunch of bike nuts that think that saving a few grams here and there will make things better. We all know, a few grams will not make us faster, but we all feel it will. That is how I feel about balancing a wheel. Maybe it does not make it better, but it surely will not hurt.

akaspin
Posts: 68
Joined: Mon Apr 09, 2018 4:36 pm

by akaspin

Doing this for all my wheels. To be honest I don't test watt saving. But the biggest benefit is removing pulsing for rim brakes and better modulation.

youngs_modulus
Posts: 575
Joined: Wed Sep 20, 2006 1:03 am
Location: Portland, OR USA

by youngs_modulus

Butcher wrote:
Tue Mar 19, 2019 3:52 pm
I'm not saying that a balanced wheel will fix anything, I just no not see any harm in balancing any rotating object.
<snip>
Why is it that a bike component should not be balanced? So harmony is the wrong word, but I do not know any other that would apply.
I’m sorry; I didn’t mean to pick on you, especially for something as trivial as word choice. We totally agree—there’s no harm in balancing wheels. There’s just not a lot of benefit, either.

I’ve been thinking about this and my speed-wobble-with-a-disc-wheel example from a few posts ago. While I still think balancing bike wheels is kind of silly most of the time, it’s a reasonable thing to try if you’re attempting to cure a speed wobble. Unbalanced wheels don’t cause speed wobble—it’s a complicated and poorly-understood phenomenon with multiple proximate causes. But in a subset of cases, balancing wheels can raise the onset speed of a particular bike’s speed wobble, which can seem a lot like solving the problem.

So while bike wheel balancing is mostly woo, in rare cases it can be worth doing.
Butcher wrote:
Tue Mar 19, 2019 3:52 pm
This forum has a bunch of bike nuts that think that saving a few grams here and there will make things better. We all know, a few grams will not make us faster, but we all feel it will. That is how I feel about balancing a wheel. Maybe it does not make it better, but it surely will not hurt.
This is a totally fair point.

youngs_modulus
Posts: 575
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Location: Portland, OR USA

by youngs_modulus

I just mentioned that there’s a lot of woo around bicycle wheel balancing, and this post illustrates that point very well.
akaspin wrote:
Tue Mar 19, 2019 4:16 pm
Doing this for all my wheels. To be honest I don't test watt saving. But the biggest benefit is removing pulsing for rim brakes and better modulation.

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TonyM
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Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

I never did it so far - but that is for sure a project whenever I have time.

mattr
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Location: The Grim North.

by mattr

youngs_modulus wrote:
Tue Mar 19, 2019 4:34 pm
I just mentioned that there’s a lot of woo around bicycle wheel balancing, and this post illustrates that point very well.
The whole industry is rammed full of woo. Unfortunately.

joshatsilca
Posts: 20
Joined: Thu Feb 21, 2019 4:52 pm

by joshatsilca

youngs_modulus wrote:
Tue Mar 19, 2019 5:14 am
I didn't address speed wobble in my earlier post. Due to the analogy with car wheels, some people may think that speed wobble is a resonant phenomenon. It isn't. I admit I assumed that it was until I read this letter to Velonews' Lennard Zinn.

It's not resonance; it's a Hopf bifurcation, which is more like the flutter your rain jacket develops above certain speeds. The difference is subtle and hard to explain without getting hopelessly technical. Here's a concrete example of a Hopf bifurcation: speaking. The vibration of your vocal chords isn't due to resonance...it starts because of a Hopf bifurcation. That's why you don't have to alter your breath rhythmically (creating a forcing frequency) in order to speak. As long as air is flowing over your vocal chords at a sufficient velocity, they'll vibrate. Bikes and rain jackets are like that too--they don't require a forcing frequency in order to flutter/wobble.

Perfectly balanced wheels would provide no forcing frequency, and wobble would happen anyway. So no, speed wobble isn't a result of unbalanced wheels. That said, grossly unbalanced wheels might allow a Hopf bifurcation to occur at a lower speed than it otherwise would. When I was a junior, I borrowed a disc wheel for the district TT championship. At about 38 MPH and with the disc installed, my Ciöcc would wobble violently. With my regular rear wheel installed, it wouldn't. Unbalanced wheels don't cause speed wobble due to a forcing frequency, but it may be that the onset of bifurcation happens at a lower speed with an unbalanced wheel than it does with a balanced wheel. This is similar to a rain jacket made from a stiffer material fluttering at higher speeds than a jacket made of a more supple material.

I admit that sounds a lot like "unbalanced wheels can cause speed wobble," but it's not quite the same. Maybe Poertner was thinking of Hopf bifurcations when he mentioned "improved handling" in his ad copy for wheel weights. Fair enough. But the vagueness of "improved handling" seems (at least to me) contrary to the spirit of the substantial work that Poertner has done in making rolling resistance and drag data available to consumers in general.
I've written pretty extensively on this over at Slowtwitch but I'll chime in here since there seems to be a lot of confusion about what has been said.

So for wheel balance, our kit is a way to replace unaero spoke magnets and for perceptive riders to eliminate imbalance. The handling benefits are simply that you eliminate the pulsing that can be felt at high speeds which are often confused with the onset of a speed wobble. We do not and have never claimed that balance can eliminate speed wobble because it cannot, other than through the changing of the system mass as the overall mass of the system has proven to be the largest driver in onset speed for a wobble.

As to your pro team references, Mark Cavendish has exquisitely balanced wheels, something I personally did for him for a number of years when we worked together, so did Cancellara, Tony Martin, Kristen Armstrong, Peter Sagan and others. Every one of these riders found the imbalance of a 100mm valve stem on an 82mm wheel to be notable and we worked to fix that, ultimately balancing all of their wheels. As imbalance becomes more notable on lighter systems, so tends to be something more of an issue for tubular riders than clincher riders. It is no coincidence that the largest Lightweight dealer in the world is also the largest seller of Speedbalance kits. Any efficiency gains associated with balance are so small as to be imperceptible to the athlete, but there is most likely something there and you will find that a balanced wheel will spin for longer than an unbalanced one with identical energy input.. we are talking fractions of a watt and while this is the most marginal of marginal gains, it most certainly isn't a loss. While no wheel company will allow their wheels to be raced with a Speedbalance on it, we ship thousands of our tungsten slugs to nearly a dozen teams each year so they can be glued into the inside of wheels, so you don't see it, but it is happening.

The discussion about impedance and rolling resistance is a completely separate and unrelated discussion and something unrelated to wheel balancing. Our stealing of the word impedance from electrical engineering was done to try and name the thing we were seeing when rolling losses became more dominated by vibration of the system than they were by deflection of the tire casing. I completely understand people having some issue with our use of the word 'impedance' and it's something Tom and I debated for a while before using is officially even pulling Robert Chung, Doug Milliken and a few others into the fray before everybody agreed that we didn't have a better word for it and that it does sort of fit..
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youngs_modulus
Posts: 575
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Location: Portland, OR USA

by youngs_modulus

Thanks for responding! I admit that I only look at Slowtwitch intermittently, partly because I haven’t bothered to create an account there. I don’t mean to make you repeat yourself.

Thanks for the info on Cavendish’s wheels and all the rest. I’m curious about all those pros who could feel wheel imbalances: was the sensation constant? Or did the feeling come and go? I’d be pretty dubious of anyone who claimed to feel a constant or strictly speed-dependent oscillation due to wheel imbalance, mostly because as two unbalanced wheels slowly go in and out of phase with each other, the magnitude of the oscillations should increase when the phase angle is small and decrease (to almost nothing in most cases) when the phase angle is around 180 degrees. (Of course, one balanced wheel and one unbalanced wheel wouldn’t show this effect). Was there a beat frequency according to most riders?

I concede that one reason I’m so skeptical of wheel balancing is that I’ve never perceived any effects I could attribute to an unbalanced wheel. On the other hand, that’s a sample size of one, and that one hasn’t ridden rims deeper than 45mm. I’m about to go for a ride, so I’m going to tape a random piece of tungsten to my front rim and see what happens. Maybe I just haven’t ridden a sufficiently un-balanced wheel.

I’ll take your word for it that a balanced wheel spins measurably longer than an unbalanced wheel...but where is that lost energy going? If you don’t know for sure, do you have a theory?

I re-read the post in which I discussed your use of the term “impedance losses.” Your observation that rolling resistance “impedance” and wheel balance “impedance” are unrelated precisely underscores my objection: it’s a vague and slippery term, easily confused with other closely-related concepts.

“Mechanical impedance” is typically defined as the set of dynamic relationships between force vectors and velocity vectors for a given structure. Put simply, it’s a measure of how much a structure moves in response to vibration. In that sense, felt vibrations due to un-balanced wheels is a pretty straightforward example of mechanical impedance.

As Tom Anhalt’s work shows, a bike on a bumpy road has high “impedance losses” if its tire pressure is too high, but low impedance losses if the tire pressure is below a certain threshold. In other words, when the bike/rider system is a high-impedance structure, the losses are low, but when it’s a low-impedance structure, the losses are high. IMHO, it’s unnecessarily confusing to assert that when you don’t have much impedance, you lose a lot of energy to impedance. Meanwhile, your impedance losses are low when the system has high impedance.

You’re right that these are two different uses of the word “impedance,” so there’s not really a contradiction there. But it’s unnecessarily confusing, n’est pas?

I can’t help thinking of your discussion group as the Monsters of Rock but for bike geekery. I was familiar with Doug Milliken because his book, Race Car Vehicle Dynamics, was one of the texts I read in grad school for my vehicle dynamics class. I didn’t realize he worked with bicycles, although hey—bicycles are certainly vehicles! At any rate, I know the concept of mechanical impedance I described above is not at all new to any of your group.

I follow that you’re using the term to distinguish between conventional rolling resistance losses and vibrational losses, but why not just call them vibrational losses or chatter losses?

I mean, lots of situations exhibit step changes (or quasi-step-changes) in drag due to speed: a planing boat can have less drag just after planing than it did just before planing; hydrofoils are an even more extreme example of this. Drag can increase sharply as an aircraft transitions from subsonic to supersonic speeds. I guess you could describe these as changes to impedance, but I haven’t heard the term used that way very often.

A term like “hysteretic/vibrational transition” would be accurate and descriptive, although I concede it doesn’t roll off the tongue. I’m partial to “chatter losses,” I think.

One final note: I used the phrase “snake oil” to describe wheel weights upthread. I didn’t mean to imply that Silca is being intentionally deceptive or promising impossible benefits. I still find the claim of “better handling” to be a little vague, but it’s well within the norms of the bike industry. But if out-of-balance wheels really do produce a perceptible vibration, why not pitch consumers on aluminum-valved tubes for wheels that are heavy at the valve stem? That’s not a “gotcha” question...I’m really curious.

MikeD
Posts: 223
Joined: Thu Dec 11, 2014 9:55 pm

by MikeD

Jobst Brandt once wrote that balancing bicycle wheels with high pressure tires is unnecessary because the tire is so stiff that an imbalance won't cause a bounce. However, for wide, low pressure tires I would think it could. Then, what if you run tubeless tires or tubes with sealant?

chiumomo
Posts: 100
Joined: Tue May 29, 2012 1:38 pm

by chiumomo

I would like to share a video about balancing bike wheel
https://www.youtube.com/watch?v=RIi0BVj4_EY


Imbalance wheel can have noticeable impact on handling, it's much "calmer" after adding the ballast.

Here is a Centrifugal force calculator
https://keisan.casio.jp/exec/system/1245903825

5g of imbalane at 50km/h it's like 290g

Butcher
Shop Owner
Posts: 931
Joined: Sun Jan 03, 2010 4:58 am

by Butcher

I do not know why there are not many aluminum stem tubes out there. Maybe a possiblity of corosion? I believe Zipp had some latex tubes with aluminum stems but when I went to buy them a few years later, I found none. I also understand that a tube will not last that long that corosion would be an issue.

It may be possible that balance is not a normal concern because we rarely travel at those speeds. Pros certainly could on a daily basis.

The youtube link above is interesting. Although a bike may be able to dampen the vibration, I do not understand how people cannot acknowledge that the vibation does exists.

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TonyM
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by TonyM

On a fast downhill we achieve such speeds...



by Weenie


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