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When pro cyclists were riding at 70-80 kph at past TdFs, I didn't wonder. Now that they are hitting 100-110 kph, I am getting curious (and also praying for them, but that's a separate issue).

Car wheel balancing

With car tyres the installers give up on the wheel being perfectly symmetrical. They glue small (lead) weights to improve balance. With cars there appears to be, incidentally, no such thing as a perfectly balanced wheel—just a wheel that will continue to give a smooth ride at faster speeds. A car wheel continues to be balanced until it reaches an acceptable or requisite tolerance. (And, possibly, a better-paid and more talented installer has the skill and the patience for better balance.)

Bike wheel truing vs. balancing

Does balancing bike wheels ever involve gluing weights? Is there such a thing as a "perfectly balanced bike wheel", or could a wheel be perfectly true when tuned by an expert mechanic, yet reveal (credit for the URL: Erlkoenig) some jitter once you spin it fast enough (on a stand, and before even loading it)? And is there anything wrong with true bike wheels that seem less true, or unbalanced, once (an amateur's) 50 kph is reached?

There are already three question marks so far. I'll add yet a fourth one. Is there a difference between truing a bike wheel and balancing it? (Feel free to answer any or all.)

Note
Today's incident at Stage 18 of TdF 2022 is unlikely to be related to the question.
Future question
Given the prestige of winning a stage at a Grand Tour, let alone the GC at a grand tour, is it conscionable of tour organizers to plan a route that enables riders to reach 100 kph on descents? What about 125, 150, ...?

Update

Renaud is pointing out that we could have a wheel that is balanced but not true. I don't know whether balancing a car wheel could fix its off-trueness, but we definitely would not want an untrue wheel on a bike, even if it's perfectly balanced. The up-down (from a wheel that's radially not true) or side-to-side (laterally not true) jitters will make it unusable, even at low speeds.

The premise then is that a bike wheel is true to begin with.

At the hands of a master wheel builder the tolerance might be 0.1 mm rather than an amateur's 0.5 to 1.0 mm, but we'll call these "more or less true". Now, can an amateur do anything to hit 50 kph without feeling wobble? Do pros do anything to go over 100 kph without the wheels starting to jitter?

Update 2

It may sometimes be futile to attempt to balance a wheel. Some rims, such as those with a sleeved-joint connection, are unbalanced by design for better strength.

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  • Ambrosio rims messed around with the concept of balancing the rim for a while. There was a weight at the valve to counterbalance the seam. There may have been other companies to do similar things. Most people find that the gyration from unbalanced wheels is pretty insignificant on bikes except in the stand. Jul 21, 2022 at 17:28
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    100 kph is about 28 m/sec. A 700x25c wheel has a circumference of about 2.1m. For a cyclist going 100 kph, those wheels are rotating about 13 times/sec, or about 800 RPM. Which really isn't very fast, especially given all the not-very-much-anyway weight of the wheel is effectively on the central plane of rotation - so there's effectively no twisting force about the rotation axis, like you'd get on a car's wheel if the rim has a heavy spot at the edge. At worst, there's a bit of a tendency to up-down wobble. Jul 21, 2022 at 19:01
  • @AndrewHenle So pros who hit 100 kph should expect to feel ~13 Hz vibration in the handlebar and the seatpost, and that's perfectly normal. They should not panic. Likewise, amateurs doing 50 kph should expect ~6-7 Hz vibrations. Oddly, at more mundane speeds the vibrations felt from the road are the ones the cyclist feels. It is at higher speeds that the road's imperfections cancel out (because the frequency is very high? because the cyclist starts to "float" over the road?), and what we would observe by spinning the wheel on a stand (as in the video linked) start to be felt.
    – Sam7919
    Jul 22, 2022 at 16:11
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    Comment to the update: given the way car wheels are manufactured, trueness for non-spoked wheels is more a matter of manufacturing tolerances (whether it's a car or bike wheel). There are no 'adjustements' on a plain block of plastic or metal.
    – Renaud
    Jul 22, 2022 at 16:14

3 Answers 3

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  • balancing a wheel: making sure there's some weight symmetry
  • trueing a wheel: making sure that the geometry of the wheel described a (near) perfect circle. This includes the radial and lateral deviations of the rim, as well as its positioning related to the center of the bike.

So an oval wheel can be balanced without being true. A balanced wheel won't jitter.

The wheel depicted in the video is probably perfectly true (because it's a new one, from a reputable brand), but has some imbalance (the valve, usually).

A untrue wheel has an impact on the ride quality, and brake quality, especially with rim brakes. Radial deviation will create vibrations/oscillations that are uncomfortable before being dangerous. When turning at speed, lateral deviations can cause traction losses, which can be dangerous (thanks Andrew for the correction). But they are often signs that there's a problem with the tension of the spokes, which is the problem that needs to be addressed timely.

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    Radial and lateral deviation will create vibrations/oscillations that are uncomfortable before being dangerous. Not always. A significant lateral deviation can cause no discomfort when riding normally, only maybe causing problems with braking. But in a hard turn, a bad lateral deviation could potentially cause a significant loss of traction and cause the wheel to start sliding. And that can be dangerous. Probably not a problem if you're not aggressively racing or riding fast, but... Jul 21, 2022 at 19:07
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    @AndrewHenle Thanks for the explanation, I corrected the answer to make sure that reading comments is not necessary to be in a non-safe situation.
    – Renaud
    Jul 21, 2022 at 20:19
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A bike wheel balancing isn't worth it. Balancing is different from truing: truing is useful, balancing is not.

The rim has a light spot: the valve hole. The tube has a heavy spot: the valve. They are in the same position and have opposite effect on balancing, but the effects do not perfectly cancel so a bike wheel is naturally unbalanced.

It's also possible that the tyre and the tube aren't perfectly balanced either, so there may be other sources of imbalance too.

Another source of imbalance is wheel reflectors, speedometer magnet and also e-bike wheel rotation sensor magnet.

Theoretically, you could attach a weight on the bike wheel to balance it, but usually that's not useful because bike wheels don't rotate fast enough and the imbalance there is, is usually so small that it doesn't harm you either.

Also if you balance a bike wheel, you probably need to re-do the balancing every time you re-mount the tyre, and how on earth would you balance a bike wheel on the road after a roadside puncture repair?

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    By habitually aligning the tire logo with the valve, you would largely remove the need for rebalancing.
    – MaplePanda
    Jul 21, 2022 at 18:12
  • Some of us make it worse by putting the wheel reflector near the valve, so that the valve hangs down when the wheel has no weight on it (e.g. on a workstand) and it's easier to attach the pump hose. It's also easier to find the valve in the dark that way. I've found the extra weight of the valve to be greater than the weight loss for the hole in the rim, so with nice bearings and no reflector, the valve will hang low on a front wheel at least
    – Chris H
    Jul 21, 2022 at 18:39
  • @ChrisH The conclusion then seems to be that there isn't much we can do to balance a bike wheel, but there might be small things we could do to improve the balance. One is to really get rid of reflectors if we haven't already, and perhaps to switch to symmetrical spoke reflectors if needed. Another is that if we are inserting a weight to measure speed (with a Reed-based sensor), we can help improve the balance (for one of the two wheels anyway) by putting it opposite the valve, assuming that the valve itself is considerably heavier than the hole it goes through.
    – Sam7919
    Jul 22, 2022 at 16:31
  • @Sam my spoke reflectors always fall off after a while, and they're quite a bit smaller than a flat one I've had the branded ones and the cheap knockoffs. I've given up on those. A reflective band on the tyre is a nice extra but no substitute for something that is more visibly rotating. A lot of reflective stuff is needed if you're doing what I do - riding country lanes year round, including right through the night and out the other side in winter. Dynamo front lights tend to be quite narrow beams, and it take a lot of battery to rely on lights alone to be visible from all angles
    – Chris H
    Jul 22, 2022 at 20:33
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    @Sam you really need 1--4 patches to avoid the effect of motion blur, big to catch lots of light and tyres are the wrong shape for that. It's also simpler to manufacture a continuous stripe. Even some of my jerseys have a little reflective fabric; unfortunately it never lasts long on stretchy things like tights - and jackets (which I only wear in the rain or sub-freezing temperatures) can be above the level of headlights. That's why wheel and pedal/shoe/ankle reflectors are good, combined with the obvious movement
    – Chris H
    Jul 23, 2022 at 8:12
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The following summarizes the multiple questions surrounding whether a bike wheel needs or could benefit from balancing.

I collected the answers below from the comments and the answers, with appropriate attributions.

Is there anything wrong with true bike wheels that seem unbalanced once 50-100 kph is reached?

"Theoretically, you could attach a weight on the bike wheel to balance it, but usually that's not useful because bike wheels don't rotate fast enough and the imbalance there is, is usually so small that it doesn't harm you either." [Credit: juhist]

Is there a difference between truing a bike wheel and balancing it?

"An oval wheel can be balanced without being true." [Credit: Renaud]

Does balancing bike wheels ever involve gluing weights?

"Ambrosio tried." [Credit: NathanKnutson]

Is there such a thing as a "perfectly balanced bike wheel"?

"A bike wheel is very light in absolute terms, and it is particularly light compared to the rider that gyration on a stand does not affect riding at higher speeds." [Credit: NathanKnutson]

What is the RPM of a wheel anyway?

"100 kph is about 28 m/sec. A 700x25c wheel has a circumference of about 2.1m. For a cyclist going 100 kph, those wheels are rotating about 13 times/sec, or about 800 RPM."

"This really isn't very fast, especially given all the not-very-much-anyway weight of the wheel is effectively on the central plane of rotation - so there's effectively no twisting force about the rotation axis, like you'd get on a car's wheel if the rim has a heavy spot at the edge. At worst, there's a bit of a tendency to up-down wobble." [Credit: Andrew Henle]

What can contribute to a wheel's imbalance?

"Another source of imbalance is wheel reflectors, speedometer magnet and also e-bike wheel rotation sensor magnet." [Credit: juhist]

"Some of us make it worse by putting the wheel reflector near the valve." [Credit: Chris H]

And now an exercise for the reader

So you've trued your wheel to perfection. Now you lift the bike on a stand and you spin the rear wheel with all the arm force you can muster. You may well exceed the 13 revolutions per second (equivalent to 100 kph). Do you see any jitter, any wobbling? Press the brakes and add a minuscule counterweight to the valve (bulky reflector, magnet for speed reader, spoke reflector, ...). Spin it again. Is it better? Congratulations! You just balanced your wheel.

Exercise #2 for the reader: It's obvious how to spin the rear wheel. To balance the front wheel, or at least to inspect whether it's balanced, you need to spin it. How can you do that? Legal disclaimer: If you injure yourself by using a power tool, you have only yourself to blame!

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    Have you tried the exercises yourself?
    – ojs
    Jul 23, 2022 at 12:18
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    Consider that when actually riding, you have well over 60kg of rider that may add some damping to the system, and the bike less wheels is 4kg and up. The wheels probably weigh 2-3kg all in by comparison. The valve stem is probably the source of the imbalance, and it’s probably 20-30g in weight? Wheel imbalance may be a small problem in the grand scheme of things.
    – Weiwen Ng
    Jul 25, 2022 at 0:37
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    This kinda goes against the way SE is designed - there are many things asked at once and not one single question, and this summary is more of a reply to a long list of related-but-separate points. Try coming up with the core question in the title, write the body trying to stay relevant and avoiding tangents, then reread the title-question to confirm it all matches. I sometimes take a day or two to write a question and review it.
    – Criggie
    Jul 26, 2022 at 8:34
  • @WeiwenNg I'm thinking of it this way. Take a gigantic timpani and play all notes but one on a huge organ. The timpani remains unfazed. Now take a minuscule tuning fork. Its frequency exactly matches that of the timpani, and striking it next to the timpani makes the membrane undulate wildly. Likewise a platoon of soldiers are together but a minuscule weight compared to the bridge they're crossing. Yet their leader demands that they not march in step.
    – Sam7919
    Jul 30, 2022 at 4:25

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