How important is it? I would think 'fat' bikes would be hard to balance; I never see wheels w/weights of any kind used for balance. Am I the only one who does this?

The rotational speeds of bicycle wheels are low enough that the imbalance would have to be rather large to be noticeable. I've heard of some riders carefully balancing their wheels using thin lead strips wrapped around the nipples next to the rims but it's pretty rare.

Out-of-round or unevenly molded tires are the most likely the source of any significant imbalance.

The only times I've read of rotational balance being an issue has been of land speed record bikes. I assume there are no spoke reflectors or other items attached to the wheels in question. The heavier the wheel/tire combo the less important balancing becomes at the level of adding wraps of lead solder to a spoke. Andy

there are videos about balancing bike wheels on youtube. So there are other obsessives out there too.

On bicycles, not at all.

Your valve stem serves as one. You can always tell your hubs are in good shape when a spinning wheel settles gradually, with the valve stem winding up in the lowest possible spot on the wheel.

Lol...balancing bike wheels.

Yeah, what's next, "Spoke Nipple Waxing"?

Yeah, and the weight of the valve stem is partially offset by the material removed to permit it's passage through the rim, and the pins at the seam if it has them.A wheel in the truing stand with no tire mounted will settle with the valve hole up,but in the real world it matters not.

But in the Tour de France it might, once in a blue moon, after a brutal 180 mile or so stage:

un even tire wear , can you feel it ?

Sometimes the valve stem settles to the bottom and sometimes not. Not only does the material removed from the rim at least partially offset the additional weight of the valve stem, but tires and even rims can be unintentionally weighted unevenly. I've had a wheel/tire (with no reflector or computer magnet) that, if positioned so the valve stem is at the bottom, will actually slowly rotate so that the valve stem ends up in the 2:00 or 3:00 position. I don't know if the wheel is unevenly weighted or the tire, but there's weight somewhere that will eventually settle to the bottom.

I know this is only partially related to the original topic, but I would say that you can tell if your hubs are in good shape when a spinning wheel settles to about the same position each time it's spun.

OK, then I stand corrected.

Strips of lead flashing sheet shaped & glued w/ contact cement, covered w/ tape.

Tennis shops sell adhesive lead strips for adjusting the swing weight of racquets.

Deep section wheels w/ valve extenders can benefit more.

Subtle, but when contemplating speed wobble on a 50 mph descent,

doesn't hurt.

Reminds me of a tech support guy I knew who, when he wrote with a felt tip pen on a burnable CD or DVD, would make extra marks below and label them "balance marks" so there was the same amount of ink on the top and bottom of the disc, and it supposedly wouldn't wobble in the disc drive while spinning at high rpms.

Spinning the crank with the bike on a repair stand will have the bike bouncing up and down, from the out of balance rear wheel. It looks bad, so this worries some riders.

I think I've felt the out of balance vibration when coasting down an extremely smooth, newly paved road. Never felt it on any normal road. It's very subtle, and has no practical effect.

Less due to the out of balance rear wheel....and more the forces you are exerting on the cranks.

Older Zipps, or at least mine, were really out of balance. I suspect because they were shooting for the lowest possible weight. The bike would bounce like crazy on a repair stand when the wheel was spun. I started to look into fixing it, but in the end didn't bother to address it; it rode fine. There were times though that I could feel that imbalance pulse when riding. It didn't affect handling or induce speed wobble or other issues. It was just noticeable as a sensation.

When I was futzing around with it, it surprised me how much weight it would actually take to get it in balance -- significantly more than a chunky wheel magnet. It would have involved putting a few of the big big fishing sinkers in a spoke hole or something, and a tubular was already glued on. Everyone said, no, doesn't matter, bike wheels rotate so much slower than car wheels.

But I feel your frustration. It was a big relief when the next set of wheels, which were similarly light, were balanced. It just makes it all feel better, especially when some big hill is sending you at 50 mph.

Not much force on the cranks after you stop turning them and the wheel is coasting.

At which point the workstand is already an inverse pendulum from the force you were applying.

I'm guessing that you have not actually done this.

If you had, you would have noticed that an out of balance wheel jumps around, while a balanced wheel does not,

with the same input from the cranks.

Well, hopefully you do wax your nipples! Or at least grease or oil them, otherwise your spokes will get all wound up, no one likes it when their spokes get wound up!

Have you noticed that if you have a friend hold your rear wheel up, you spin the cranks and get the wheel going as fast as the highest gear will allow....the bike doesn't "jump" around in his hand?

Like I said. Pendulums. They are a thing. In a stand driving a wheel hard you excite one.

With the out of balance wheel I had, it definitely would jump around. You could also just hold the wheel in your hands or put it in a truing stand and spin it, and the spinning wheel would make clear that it was a spinning thing with a center of gravity outside its axis of rotation.

I don't think so.

When I worked as a shop mechanic I installed a lot of bike computer wheel magnets. I assumed the bast place on the wheel to install the magnet would be the lightest point so I'd let the front wheel find it's balance point. Most often the lightest point was near the valve stem. If you think about it, when they make a rim, they remove material to make a hole for the valve stem and they add material where the extrusion is joined together.