How many road miles should I expect from a set of bearings? The current one is about a year old, only ~1000 mi on it. I am already getting intermittent creaking noises from the hub, it must be the bearings. Should I oil them periodically? Or grease them with lithium grease? I ride a 24" on paved roads only, never in the rain, and weigh about 175 lb.
First thing that comes to mind is that you might have over tightened them. You can do that with the crank bolt as well as with the bearing cap.
The more outside pressure it will have, the faster it will wear out.
Creaking does not sound like bearings to me.
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They are lifetime sealed bearings and in my experience opening those seals up does more harm than good. If you have a very creaky bearing and have to get through the weekend before you can get new ones, sure, open them and throw some grease in there. But not as a regular maintenance.
I’d recommend going through the list ruari linked, might not be the bearing.
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Thanks to all for the comments, all useful, especially the list of creaks and groans. As for this particular instance, I have concluded that the problem is indeed a bearing, as the creaks manifest with the cycle upside down, and the wheel spinning freely.
I have also come to a second conclusion - it is bad theory and also bad practice to use the tension on the bearing clamp bolts to do two separate tasks: adjusting the pressure to ensure unimpeded bearing rotation, and also tightening them sufficiently to keep the wheel in place. Those are two conflicting requirements. I am sure that my tightening the bolts sufficiently to keep them from coming loose also compressed the bearings and let to an early bearing failure.
The solution for me is to use aluminum washers as spacers between the clamp and the frame, so that I can tighten properly against the spacer, while not compressing the bearing in the least. This is the only way I have managed to have secure bolts, and still enough looseness in the bearing so that the wheel will spin one way and then reverse by itself under the weight of the valve stem alone.
You actually want some preload compressing the bearing. When you’re riding, your weight on the saddle pushes the frame into the bearing, and pushes the bearing cap away from the bearing. If you don’t have any preload, the bearing cap will come away from the bearing completely, and the wheel will be flopping around loose.
With the right preload, almost all of the initial pressure you applied tightening the bearing cap will disappear as the bearing cap is pushed away. The final pressure on the bearing (which is from your weight) will be about the same as the no-preload case, but the wheel will still be securely held.
I don’t know exactly what the perfect preload is - maybe a quarter of your body weight on each bearing? - but if the wheel is reversing itself from the valve weight, it’s not enough! And “finger tight” on the bolts isn’t enough, either.
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This really does seem to be a suboptimal design. I’m guessing it’s due to using bearings that were originally designed for other purposes, but from an engineering perspective I doubt it would be very difficult to increase the amount of material in the outer race of the bearing so that any compression from the bearing caps is minimized. I’d be surprised if such bearings don’t already exist. Its probably something that’s not worth the expense of sourcing new bearings or redesigning the bearing caps for though when the current design is adequate.
Wow, I’ve used, worked and designed machines using bearings. The above quote is dangerous to your bearings (Period) I would call Andy and Jim T’s suggestion the solution. Locktight is made to keep your fasteners from loosening, but not always the correct solution. I’m with JimT. in age and solution, benifit from his experience.
It’s very much the same situation as bicycle headsets, where you need some preload to keep the top bearing race from lifting off the bearing when the front end of the bike is loaded. We were arguing about this on the old rec.bicycles.tech group 25 years ago… it was a perennial subject of misunderstanding.
(And fwiw, I’m a 60 yr old with a couple of engineering degrees).
and you missed the axis of load.
Nope. Recommended would be sliding fit (no preload) for the outer bearing race in this loadcase. (Point load on the outer race). There are good reasons you don’t see bearings clamped like this in machinery, if a preload would help, that would be a common configuration. As Lobbybopster pointed out, not the same as a bike headset.
What it comes down to is: two opposing point loads on the outer race with an unloaded inner race are not the same as one point load on the outer race working against the inner race.
Why don’t unicycle frames have bearing housings designed so that the bolts can be fully tightened? Would it require lower tolerances and therefore unreasonable production costs?
Yes. To have it accurate enough, you would have to assemble the two halves of the housing together after it is welded to the frame, and then machine it. That would add up to quite a lot of extra money for something that - let’s face it, most buyers won’t care much about.
I wasn’t really talking about it as a bearing, just how the pieces fit together and stay together. It could just as easily be a solid metal disc in the middle, instead of a bearing. Under load the bottom cap will be pushed away, just like the top of the headset is pushed away.
So you need to tighten it down a little, even if it isn’t great for the bearing.
MrImpossible, I do not see the logic. Under load the bearing is pushed up, but has no place to go since it is presumably already all the way into the frame recess. There is no force whatsoever pushing the lower clamp away. Thus the pre-tension remains constant, and adds unnecessary friction to the bearing, wearing it (and me) out.
By the way, with this particular frame I find that three washers on one side of each clamp and four washers on the other side gives me a tight fit that still allows for free rotation.
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Yes. Unless you do what Andy (among JimT and many others) proposed and add a spacer between the bearing caps, so you can tighten the bearing clamps without adding pressure to the bearing… to which you replied that you want preload compressing the bearing. 
Considering how infrequently I replace bearings on my KH36 (never), and how frequently I have to re-tighten the bearing caps (also never), I remain unconvinced that there is really an issue here.
I understand that it’s not a perfect mechanical solution, and bearings are not really meant to be held in this manner, but it’s sure as heck better than lollipop housings or paying an extra £50 for housings accurately machined after a frame has been finished.
If the current two part housings were accurately machined to perfectly hold some bearings, then what happens when your bearings then happen to be slightly different tolerances because you change them for another brand/model.
Stamped bearing housings can easily destroy bearings if you clamp them up too hard, but I don’t think I’ve ever replaced bearings from machined housings that might have been done up too hard, without them also looking like they’ve been pulled from the sea. Dirt and water ingress destroys bearings far faster and more frequently.
If there’s no pressure on the bearings, they’ll slide side to side in the bearing housings. You always need some pressure pushing on the bearings to keep them in place. It’s uneven pressure that’s the problem.
For the amount of pressure that people might put on bearing caps, if that’s even all the way around then it’s not going to be managing to compress that steel cylinder by any perceptible amount. In reality that pressure is never going to be even.
What the washers/spacers above are doing is stopping the bearing housings from going past the point of deformation which will push the bearings past acceptable tolerances for roundness.
All I can say is, as soon as I put in the washers, the creaking stopped. Those bearings were screaming from the strain. And it’s not like I have a heavy hand with wrenches.
So why do some of us have problems and others not? Probably variations in the fabrication and fit of the bearing housings and caps. Anyway, now I can get back to my riding, and continue figuring out how to transition back and forth from low-inertia unis to high-inertia unis.
Ok, after reading all of these responses and dumping my own reply I went to the garage and checked out the fleet of uni’s of more than twenty hanging around out there I found a surprise or two. My original uni (a 1962 Rollfast 24") looks like a straight schwinn forged fork with round two piece bearing holders had no space between at their seem. Hmm ? took it down, road it around. Original bearings very smooth and worked great. Took it apart and as stated above, machine marks in the holder as if it was machined to size as a pair. Maybe tightend on a bar when welded to prevent distortion from the heat. The other surprise was on a old cheap “Imperial” japan import that had two set screws in each top cap to lock in the bearings after the bottom yoke was tight, to keep the bearing from moving in the holders.
I assume that this has always been a problem that has been addressed by some manufacturers at some times.