27.5" QX aluminum/aluminium muni frame hub options?

I am new on this forum, and I was unable to find anything on it which would answer my questions.

I am from Canada and I want to order an ISIS hub with disc mount that will fit my unicylce frame, or if that is not possible, perhaps one without a disc mount.

I have a 27.5" QU-AX aluminum QX series unicycle which has a bearing mount that is 6mm in width beyond the bearing. It does not fit my son’s mad4one unicycle wheel.

Just so I can ride it right now, I have taken an old hub from a garbage unicycle that I broke the frame riding - it is a cotterless one. Now, the bearings are only 40mm diameter, so I have had to shim that up a bit. I cut out strips from a tin can to get the old bearing to about 42mm, the size of my new unicycle frame. Not sure about how good a solution that is, as it is not exact. Hmm, that is part of why I want to get a new hub.

I don’t find manufacture’s / sellers specification’s to be exact enough that I feel comfortable ordering a hub online hoping that it will fit my frame. For instance, I don’t understand what is meant by the dimensions that one online unicycle sales company posts about the Nimbus Minu Disc 36H hub => Hub flange width (W) Disc side =31 Non Disc side 66mm.

I know I could probably simply just buy a Q-Axle hub, but an ISIS hub gives many more pedal options.

From looking around online, I have noticed that an impact hub might work, and the old mad4one tecnic hub, no longer for sale as far as I can see, might possibly work.

I am thinking I might buy a QX ISIS hub with 48 holes and lace it up to a 36H rim. The reason being that I would expect a QU-AX hub should fit a QU-AX muni. By the way, … I have built a few wheels, so I think this would work just fine … calculating spoke lengths may be a bit challenging though as I expect there may be several lengths needed.

I could potentially file the unicycle housing so that a hub like my son’s mad4one fits, but I kinda don’t want to do that to a new uni frame - I might destroy it while trying to shave off a few mm, and it might weaken something even if I was quite successful.

Anyway, I appreciate any feedback any of you have with respect to:

  1. getting more detailed specifications on hub dimensions so I don’t end up ordering something I cannot use
  2. if you know for a fact that a particular hub will fit my uni and it is possible to buy it online
  3. any advice about calculating varying spoke lengths for a mismatched hub / rim combo

Thanks for any information to help me figure out what kind of hub I could buy for my unicycle frame.


This UDC page may help.
ISIS bearings are 42mm OD and the hubs are measured center to center of the bearings.
The page also has a link to a spoke calculator.

I don’t know about the QX frame, but I bought an RGB uni and placed fhe wheel (incl.cranks obviously) in a Mad4One frame.without any issues. So maybe the QX is an older model, but the current RGB’s are compatible.

I used a nimbus steel hub in a QX frame and it’s fine

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Hi Dawson!

There are a few things to understand in order to know whether a hub and a frame are compatible:

  • the hub width: it’s generally 85, 90, 100 or 125 mm. A wider hub means a stronger wheel but it is also considered to be harder to go fast with a wider hub. Qx frames are 100 mm wide while not all Mad4One hubs are this width.
  • the bearing external diameter: it usually depends on the interface: cotterless is 40 mm while ISIS and Qaxle are 42 mm. A Qx frame fits 42 mm bearings.
  • the bearing width: it’s usually the same for all type of standard (cotterless, ISIS, Qaxle) so it does not really matter.

So, to fit a Qx frame, you need a 100 mm wide hub and bearings with a diameter of 42 mm. Your Mad4One hub may be a 85 mm so it does not fit. What’s your son unicycle (track, distance, muni ?).

Be aware that @JimT’s link is a 125mm wide hub and 32 holes so it does not meet your requirements.
One which meets your requirements may be this one (Nimbus). This second one (Nimbus) is way lighter but not as much as solid as the first one. Depending on what you want to achieve, it could break. This last one (Mad4One) would fit, too.

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not only that Maxence
bearing cap from QX frame are very large, a KH Moment hub for example is not compatible
Dawson needs a hub with flange for spokes not very wide


I didn’t know! Thanks for the info :slight_smile:

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I’m pretty sure the steel nimbus hubs (100mm bearing spacing) fit in those QX-frames, but I’d recommend sending udc an email before ordering - you are facing a known problem, so they can probably confirm (or contradict) me.

Most people file a few mm of the bearing holders and it seems to work fine - but I can understand not wanting to do it if you can avoid it.

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If you want to know, which hubs fit a particular frame, I’d suggest asking your dealer! They might know that or be able to check it themselves.

Regarding bearing shims, I like your DIY approach with strips from a tin can. Alternatively you can just buy 40mm to 42mm bearing shims from your dealer.

Building a wheel with mismatching hub and rim spoke hole count is possible. With basic trigonometry you can calculate the varying spoke lengths. Considerable diligence is needed during lacing.

In my opinion, filing down the bearing caps of the frame is a better and easier option. There’s no need for them to be that large, i.e. in the way of your hub. Just be precise when filing and it will look as if it were supposed to be like that.

Side note: Filing down bearing caps was even officially recommended – for KH frames so that the older generation Schlumpf hubs fitted.

All that said, I think the easiest option here is just getting a hub that fits.

Hi all, thanks so much everyone for taking the time to share your experience and knowledge with me. I had neglected to add in that yes indeed, this unicycle frame has a 100mm bearing width, so 125mm, or 85mm hubs would not work. Now, my son’s mad4one hub is a 100mm bearing width as well … the problem is with the dimensions of the bearing cap (didn’t know that word, thanks @bouin-bouin) are too big for my son’s hub in that the disc bolts stick out and rub on the bearing cap. When I tried it again, not only that, but the spokes also rub on the bearing cap. That was the reason for my dimensions that I had given. I mentioned that I am from Canada because some shops don’t ship to Canada … such as the UDC USA.

I think I will reach out to the dealers that do ship to Canada and see how to move forward with this.

Again, thanks all. This is my first day on this forum, you are all so helpful. I am happy my son told me about this.

Happy riding,

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As far as I remember, UDC UK ships to Canada. I think it’s because it’s cheaper to ship from UK to Canada than from the USA to Canada - due to import taxes. So you should give it a try :slight_smile:
Also, if it appears they don’t have the hub you want in stock, wait until July. They’ll be new containers arriving by this month :slight_smile:

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I’m in the US, but I’ve ordered from UDC UK before and they were very quick. I received my unicycle in 5 days and even including the shipping the price was competitive.

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@Duff @DavidTennant et. al, Ok, I finally ordered up (UDC UK) today after lots of researching and pondering how much I wanted to spend on my upgrade. My son @DavidTennant helped me make a decision to not bother with brakes, and the guy at the UDC UK shop helped me understand that this hub would work with my unicycle.

So, I ordered a Nimbus 36H hub, along with a 145mm QU-AX ISIS crank. I thought I’d also order proper shims while I was ordering so that I could more easily and less harmfully use older wheel/hubs with my new frame. Hopefully I have correctly calculated the spoke lengths, so I will put a more local order in for those.

I’m planning on using a good solid 26" rim that I have in my garage. Later when I improve in riding and I find a good 27.5" rim, I’ll upgrade once again. If I want to in the future I could always upgrade to a magura hydraulic brake system - although I understand my son is doing just fine without his brakes where he is riding now. (muni riding).

Thanks everyone for chipping in your thoughts. It has all helped.
Happy riding,