New Fixed-Geared Unicycle Hub! Question for the mountain bike equipment experts

Sorry, the uni hub is still a concept and a little ways off yet. I need some help to get there!

The American Classic 20mm through-axle disc hub currently sounds like a dream to me:

What I need to know is: How wide is this hub?
I can’t find specs for it. I presume there are some standards for through-axle hubs in the mountain bike world? Anyone have any clues? Anyone know anything about this hub specifically? I have lots of questions.

The geared hub design I’m trying to make has been tried (unsuccessfully) before, by dangerdog: home made geared uni

If you’re wondering about my hub, the long (yet still rather poor and incomplete) explanation is here:

So thats why you wanted a broken KH hub:D

Good luck, no idea on the specs of the hub so can’t help with that.

Keep us informed:p

Hey Magnustudios I’m thrilled you are going to build a gear driven unicycle,I still plan to have another attempt myself when time is available.You have mentioned some of the requirements to resist the forces that will be encountered like beefy axle and mounting methods.I think my method may have worked if the jack shaft had been supported on both ends rather than a cantilever this may be done by a floating bearing plate,linking the main axle to the jack shaft axle end(inboard side) If you can make the idea work and had the choice of interchangeable gear cogs it would be very good.I’ve put a few of my old photos and vid on photobucket shows some desperate bracing of the unicycle frame to try and resist the torque forces.


I wanna assemble these, mostly Profile parts…

Thanks for the responses!

First, to keep the topic of the thread going, I’m looking for any information anyone can give me about the spacing of standard 20mm through-axle mountain bike front hubs. Specifically the American Classic on I linked to, but any information is good!

Hung, yep. Got finally got a broken hub on the way, excited!

John, thanks so much for those photos and the video! Very helpful. You were on my list of people to contact with questions, I might have lots more. I plan on using a cantilevered spindle for the gears as you did, but a thick one, maybe 1/2" diameter. I was thinking about the interface between pedals and cranks: it is very strong, holds up to a lot of torque, and is quite long, yet the cantilever holds up. My dream hub/frame setup would be a plate in the middle of a V-frame with multiple threaded holes for different intermediate gear sets. Change gears with just a hex key! The fact that bracing the frame as you did wasn’t enough to make it work makes me nervous. Do you know what part was bending? Now you’re thinking of supporting the jack-shaft axle at each ends: does that mean you thought it was that shaft which was bending? How did the gears go on the jack-shaft? Did the shaft rotate or was it fixed? Did you use bearings or bushings? Sorry, lots of questions!

Jeff, that’s very cool, go for it! How far have you gotten in terms of sourcing parts? I’m wondering specifically about the spindle and bearings. And hub. All of it I guess.
Spindle: can you elaborate? Do you know the outer diameter? How wide is it?
Hub bearings: I presume the inner diameter (20mm) matches the spindle? If the spindle is thicker or thinner, how do you deal with that? I’m pretty sure the ISIS interface is more than 20mm… unless you’re planning on going square-taper?
Is the disc-mount sprocket a stock part? Very cool if so!

20 mm through axle hubs are 110mm axle to the inside of the fork legs. the axles outside width is determined by the axle that comes with the fork. don’t know if there is a common flange to flange distance.

The profile is coin, but they make an axle and bearings for unicycle hubs, if you don’t put the keyed unicycle hub body onto the axle, then you can put a profile through axle front hub onto the axle. I found a titanium and steel manufacturer of cogs that attach to a 44mm BCD 6 bolt rotor mount. Profile sells cogs in the low 20T count, and cranks as small as 145mm. the only fabrication is the jockey wheel setup and attachment to the frame.

Chain driven uni-gears

What if the chain was longer so that you could put the smaller gear(s) at the top of the frame fork. Allowing a primary chain on one side and the secondary chain down the opposite side - allowing for less twisting and a better balanced unicycle. You could probably do without the additional bracing then as well.

Just thinking…

I do need to read more about unicycle hubs and frames, and I guess I can just measure for myself when my broken KH hub gets here, and you’d probably know this but…

This page: says “This bearing, consisting of two 22x34mm OD ISIS bearings pressed into a 40 mm insert, allows older frames with 40 mm housings to fit Moment hubs as long as they have 100 mm bearing spacing.”
I’ve been assuming that’s standard for unicycle frames, 100 mm on the inside of the bearings. If your profile hub needs 110 mm, might that present a frame issue?

Thanks for the info! Need to look into this profile axle more.

Also, anyone care to clarify the axle/spindle word distinction for me? I know I read it once, but I can’t remember when to use which.

If the jockey wheels are above the tire then the chain may strike the tire. the nice thing is that the spokes move away from the uni frame as you go up and you can fit more on the inside leg. the longer the length of the chain the more lateral movement is tolerated in the chain line, so you can put both jockey wheels inside the frame, away from the person’s leg. as far as the bracing goes, it’s not for strength, but as a chain tensioner. I don’t think torque will effect the chain mechanism as much as it does the meshing gears.

I’d like to see a linkage between the meshing gears with a spring in the middle to suspend the hub!

The problem with my design was the gears want to separate under torque unlike a chain and sprocket which try to compress together.So the parallel distance between the two shafts tries to grow or tries to go out of parallel.Looking down at the two axis when applying torque one axis tries to twist forward and the other backwards,this problem I tried to overcome with the additional frame bracing which helped a lot.So with the additional frame bracing in place the focus of failure became the distance growing between the two axis.The play that caused the failure was the crank axle and bearing housing ,slight twisting in the 12mm plate between the bearing housing and the jack shaft mount,slight twisting in both the jack shaft and the jack shaft bearing holder.I would guess if my design was about twice as stiff it would have been successful.I used bearings for everything that moved and the jack shaft was 10mm dia and was welded to the gear cogs.


Nice picture of gearing on a b*ke that could be applied to Uni, taken in vintage museum in NZ, only hint it is not a uni is that tyre in background, I should photoshop it out and fool you all:)


Generally cycle measurements are center-to-center; most current hubs are 100mm bearing spacing, meaning it’s 100mm from the center of one bearing to the other. There are also 92mm hubs, 110mm, and 125mm (Super Wide).