Hub width problems - need to find something skinnier!

I alluded to it in my thread on my amazing barn find, but lately I’ve been throwing a lot of effort at a project that really nobody sane should ever be attempting.

That’s right, I decided to soup up that crappy Chinese unicycle I bought and reviewed recently. Totally pointless? Yes. Totally something never done before? Most likely probably. Maybe. But it’s purple.

Up until now, everything had been going like clockwork. I’d been gathering upgrade parts, painting things purple, and was about ready to slap it all together.

At first I thought “upgrade to ISIS,” but then I realized that the bearings on an ISIS hub were different than on a square-tapered hub (like the Chinese unicycle currently uses). I know that there are ridiculously expensive KH adapter bearings available, but I thought, “hey, just stick to the spirit of the original and use a cotterless hub.” So I ordered the UDC CrMo square tapered hub and some 75mm cotterless Venture2s and thought that would be just peachy.

Now that I’m to the point where I should be putting things back together, I’ve run into a problem.

Here’s the old crappy hub.

Here’s the new one.

And here’s the problem.

Basically, the only hub of higher quality I can find has the hub flanges spaced too far apart (obviously making it structurally more sound) for this oddball frame.

Obviously the smart thing to do would be buy a new frame, but I really want to use this particular frame. Masochism or something. I just have this sick desire to make this particular unicycle perform better (i.e. not use the horrible hub it came with).

So what are the options here? Anybody know of any better quality hubs available with narrow flanges? Or should I just chop a chunk out of the middle of the UDC hub and reweld it? (Probably not a good idea, right? I can’t imagine that’s a structurally sound idea for a piece like this. :sunglasses: )

If all else fails, I will probably try the AtomicZombie method and hand-fabricate a new hub out of sheet metal and cold-rolled steel shaft. That’s my last option though, so if anybody has a better idea I’m all ears.

You can get narrow freestyle hubs but they only come in ISIS.

There’s a good chance you could just force the bearings in from an ISIS hub since it’s a cheaper frame made out of soft material. But it might be better to just purchase a new frame. Neither option is great. You could also try to bend the frame to a new spacing but I’ve never seen anyone attempt that on a small frame. Usually when people do that it’s on 36er frames where there’s a lot more length to bend.

Hm. You’re right about neither option being great. Instead of bending the frame I might consider cutting it and rewelding it with some kind of leg-spacers if it comes to that… although then I’ll have to repaint. Again. -_-

If I decide to stuff in the wrong bearings, I’d probably have to dremel the inside of the cups out, which would not make me feel very good on this frame. I’m looking at a pair of these maybe:

Assuming the spacing is correct on the Eclipse hub, I might have to use one of those with some of the bearings above.

Frankly, I think the “crappy” hub you have is better than the Eclipse hub, which has a tendency to disintegrate. (It’s softer metal than the Nimbus MUni hub). I’d keep the old hub and just put new cranks on it, unless you’ve found that it’s deficient in some way.

The flanges on the hub I’m trying to replace are very soft. They actually bent out of round when I was pulling a bearing, so I reshaped them and they are still not perfect. They are so soft you could probably bend them with your hands and a good amount of elbow grease. Probably not a good idea to build a wheel out of, especially after it’s already been deformed once.

I may just use it as a template for one made of sturdier material.

Typically, stamped bearing holders, which are usually made for 40mm (square taper) bearings, will accept 42mm (ISIS) bearings without adapters. The same is not true for machined bearing holders.

IIRC, the expensive adapters that you mentioned are for going the other way; putting 40mm bearings in a 42mm frame.

When selecting a hub, you have to consider the bearing spacing, as you have discovered. 100mm, center to center, is common and probably what your new CrMo hub is. If the bearing spacing is right, the flange spacing probably will be too.

As has been mentioned, you could try cold bending the frame to fit your new hub. You would probably need to repaint.

I think the reweld idea would be better than attempting to make your own. :smiley:

“Better” is subjective. I tend to lean more toward the extreme options for personal satisfaction. :sunglasses:

This is good to know - I think I was thinking in reverse when it came to those specialized KH bearings. I may grab a pair of 42mms and see how they fit in the cups, and if so I might see what else is available in terms of hubs. Even though it’s been claimed that the Eclipse hub is malleable, it is still going to be an improvement over the stock one, unless it’s made of bread dough (it isn’t, right?).

I have run 42mm bearings in two different frames with stamped holders and no problems. One was a MUni, and the other is my road 32". In fact, my road 32 has a UDC CrMo hub like yours, but i put shims on the bearings to make them 42mm because they seem to fit the holders better.

Fwiw the kh adapter bearings are for retrofitting ISIS hubs to frames with 40mm machined holders. So, you had that part right except that you don’t have machined holders.

The Eclipse isn’t malleable, it just fails at the spline. Happened to Beau in the middle of a basketball game, on a uni that was less than a year old and had never been used for anything except basketball. I’ve seen at least two other similar failures.

How about slicing the UDC hub in half with a hacksaw, grinding some off and then welding it back together?

It’s an option (except I’d probably use a zip disc instead of a hacksaw… way too much effort. :sunglasses: ). I don’t often work with 41xx so I’m leaning against it for the time being. Then again, the hub was only $30 so if I destroy it I can just write it off as a learning expense.


Oh, right. I read adapter and my mind went to shims. You’re talking about actual bearings with unusual dimensions. I defer to you.

That’s going to be extremely difficult to get back to anything approaching the original alignment.

The surfaces on each end of the shaft on which the bearings seat need to be very concentric and parallel, something which would ordinarily be accomplished by grinding them as a single piece.

In theory, if you had a lathe with a toolpost grinder and some bearings with an undersized ID you could do your best to get it close in the weld fixturing, and then take a light skimming cut and grind off each bearing surface to true things up.

But the project would be far beyond the point of absurdity. What exactly of the original bargain unicycle remains? The rim? The frame?

You’re over thinking this. It’s a cheap unicycle. Bend the frame. It looks like a 24" unicycle. The frame legs have to be over 12" long. You need to bend them out about 1/4" or so. The ratio of the fork length to the required deflection is (1/4)/12 or about 1/50 or 0.02. This is 0.02 radians or about 1 degree. Those stamped bearing holders won’t know the difference.

I’ll vote for bending, “cold setting” as it’s known. If you were to cut and reweld, it would be a different spacing afterward than what you jigged it to. Metal moves around when it’s heated to melting and then cooled and you’re pretty much guaranteed to have to reset it to the right spacing anyway. 3 or 4 mm per leg for the Nimbus hub might be more than you’d do after welding but it shouldn’t be a problem. That’s why steel is friendlier for this than aluminum.

It might even be this easy:

[Greg jumped in while I was composing my manifeso, but yeah, his math.]

This. I had a Huffy Green Machine hub (around 130mm) in a cheap 20" uni frame (100mm) without even bending the frame. When I took it to a guy to put a hole for a caliper brake he noticed it was a tight fit and asked if I wanted to bend the frame so I had him do it. The angle was noticeable but it worked fine. I rode it without problems even before it was bent.

Right here. :o I was out hunting for purple or pink rims and wasn’t really after anything special. I wanted to save painting or powercoating as a last option, and then I swung into Walmart and saw that bike.

The sales guy seemed very confused when I was buying a girl’s bike, and even more confused when I said “just grab the box of parts in the back, I just want the wheels and the tires.” :stuck_out_tongue:

Frame, seatpost, seat (with reformed foam). It begs the question: at what point does an upgraded unicycle become a one-wheeled Ship of Theseus? Regardless, as far as absurdity goes, those are the kinds of situations I seek out, and as impossible as the tasks may sound I appreciate the challenge. There is no practical reason whatsoever for me doing this - I own far better unicycles. But I agree, modifying the Nimbus hub is not a good idea, and is pretty much off the table in terms of options I’m considering. Even hand-fabbing my own hub would be a much better option.

Straightforward math and great video suggestion. Bending the frame definitely seems like a viable option and I feel pretty comfortable with that. It’s not like I have much to lose in any case. :smiley:

On Brompton bikes, some people install a wider geared hub at the rear, and that’s exactly what they do. Since the rear frame has to be widened, and it’s stiffer, people can’t do it by hand, like in that video. What they use instead is a long bolt (or a threaded bar), and a couple of nuts that they unscrew, forcing the rear forks to open up. The nuts apply much more force than what you’d achieve by hand. Just make sure the threaded bar can’t jump out when you start widening the fork.