SIZE for AXLE for unicycle ???

Can I use 9 mm AXLE for unicycle because I have a wheel with hole for axle of maximum of 9 mm diameter :thinking:

and can you help me also with size of bearing (outside diameter and inside diameter on regular unicycle).

I am trying to build unicycle from scratch but i have huge problem with the axle…

:frowning: :frowning:

Unicycle axle/hub

I don’t think 9mm is gonna cut it. The axle has to support cranks on the ends and your weight on those cranks. You’d twist that axle in pretty short order.

Unicycle axles are the size of Bottom Brackets, 17 to 22mm, because they basically are a bottom bracket (for attaching cranks and supporting your weight) combined with hub flanges (for attaching the wheel).

This is a bottom bracket…

… if those little ridges were flanges and it had sealed bearings pressed on (between the square taper and the flange) it would look a lot like this…

Common bearing sizes are 17x40mm for square taper uni hubs and 22x42 for ISIS. You can also buy pre-fabricated bearing mounts that fit these bearings. You just weld the bearing mounts to your frame.



can i buy this on the second picture and then just put wheel without axle, just attach spokes?

Yes. The second picture is a complete unicycle hub, it would replace the axle and hub in your wheel.

Of course when replacing the hub there are other things to consider. Spoke count, spoke length, etc. To make sure everything matches up.


why 9mm axle isn’t good? in front wheel is 8 mm axle on regular bike and it serves well…

That axle is one of two that shares the weight of you and your bike. All of that weight is basically being pushed straight against the side of the axle and it is also being spread out horizontally via the axle nuts. This force can be supported by one axle but it is usually distributed between two.

The axle in the middle of the bike is over twice as large. That one axle has to be able to support your full weight standing on the cranks. All of that force is trying to twist the ends of the axle in opposite directions. There will be even more force on that axle if you are hopping. These are the same forces that a unicycle axle must take. Put that force on a 9mm wheel axle and it will twist right off.

I’m not saying you can’t make a unicycle with a 9mm axle, but I wouldn’t expect it to last very long.