Sanity check - considering 'converting' a square taper uni to ISIS

My first uni was bought off eBay in 2018, a chrome Nimbus 2 24" with a blue rim from the time they had 48 hole square taper hubs - so maybe around 2005? It’s still my go to errand and around town uni and I’m very happy with it, not least because it’s not hugely valuable to anyone else, but I think I’d be happier if it had an ISIS hub.
I know I can’t put 42mm bearings in the current frame, but I have a spare 26" Nimbus 2 frame with 42mm bearing holders - also chrome, so at a glance I might not notice the difference!
I don’t think UDC do ISIS 48 hole hubs any more, but someone is selling a uni as ‘for parts, not working’ that I think is a 20" ISIS hub Nimbus 2. It’s pretty rusty on the surface, and they say collection only, so I would need to be pretty sure I could use the hub, and then I would need to persuade them to package and send it (ie remove pedals and seatpost and chuck everything in a box without too much concern for padding!).
This is where I could do with some help, looking at the photos below -

  • Does this look like a 48h ISIS hub?
  • Would I be OK to think that I could remove surface rust and re-lace my 24" wheel with this hub instead, or does the condition from the photos look to be too far gone?
  • Also, in principle, am I right to think I could use the 26" ISIS frame to do this without unexpected problems? (there would be some redundant Magura mounts level with the tyre, but that’s just cosmetic).
    Thanks for any thoughts!

Looks to be just surface rust on that “for parts” uni, but when changing hubs you need to make sure the flange diameter is the same, along with the pitch/flange spacing, which should probably be 100mm for those two unis. If the flange diameter is different, then you will need different spokes as well. Why do you want to convert to ISIS in the first place? As a commuter uni, square taper should be more than adequate. I’ve dove some serious riding on square taper cranks both on road and off, and haven’t had any issues. They are also less fussy in my experience and are easier to swap around and service, but ISIS isn’t much harder, just requires a little more thought. Also, there’s not any issue with running a larger frame on a smaler wheel, as long as the pitch is the same, which it should be in your case. You might have to cut the seat post if the frame doesn’t allow it to pass through, but if you’re contemplating a wheel build then you ought to be able to cut a seatpost.

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My immediate thought also is: why would you prefer an ISIS hub?
Good square taper hubs are absolutely fine for riding around town. If it ain’t broke, don’t fix it, I don’t see much point in tearing apart two serviceable unicycles (the spare parts one looks like it is only a cleaning and maybe new bearings away from good).

That said, yes, that appears to be a 48h Isis hub (unless someone put spacers on a square taper hub, which would be unusual). The rust is nothing to worry about, other than potentially the bearings needing to be changed.

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I have a ‘good’ reason and a ‘bad’ reason - the good reason is that I’m slimming down to just two unicycles, but still want to learn to hop etc, so this as my smallest wheel in the future may get more rough treatment than it currently does. The ‘bad’ reason is that I want to go down from 113mm to 100mm cranks, and I have some of those for an ISIS hub but not square taper. I also have some spare 125mm ISIS cranks for if I want to do more technical stuff.
Also this seems like a fun project, and it will be fun to know I built the wheel, and I’m keeping the spirit of my original uni.

Yes, I guess I was hoping that would work, because this wasn’t a project I wanted to spend on new spokes for (I know reusing spokes isn’t the best, but with so many of them I think they haven’t taken that much strain!). I was hoping the UDC UK spoke length calculator would help me to compare the spoke needs of the two hubs, and indeed it has the ISIS 48 hole hub, however it has no less than 3 UDC cro-mo 48 hole hubs, differentiated by flange width! So now I need to decide if my original hub is Narrow, Wide or Extra Wide. I’m thinking it’s Wide:

If it is that hub, the spoke length needed is barely any different - current hub 235.08mm and ISIS hub 235.21mm, so I should be able to reuse spokes.

Sadly I can’t think of any easy equivalent to the spoke-at-a-time method of swapping rims when you lie them side by side - I think for hub swapping everything needs to be unlaced, and only then can it be re-laced with the new hub.

In case you need a plan B, Goudurix still has Qu-ax ISIS hubs with 48 holes:

It will fit the frame and is very easy to ship. I have not checked the spoke calculator though.


That makes more sense with the context.

I think completely unlacing and relacing the wheel is the only sane option for a hub swap. Technically one is supposed to try and put the spokes in the same position they were in originally (leading vs trailing, coming in vs. coming out of the flange) when reusing them. I haven’t bothered whenever I reused spokes and so far it has been fine and I’ve heard the same from others.
I’ve found 48 hole wheels to be pretty much bullet proof anyway.

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I have also reused spokes before and didn’t have any issues. You can always measure your hub and check that against the options on the spoke calculator. Or if you have calipers you can just measure exactly and input your own numbers.

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Well the project is progressing! I managed to persuade the seller of the uni I spotted as ‘Collection only - needs attention’ to box it up and send to me. So I’ve just taken delivery of a Nimbus II Blue 20" Freestyle. It’s probably well over 10 years old, rusty looking as expected and has a cracked front bumper, but other than that it looks fine, and it cost me all of £10 for the uni + £15 postage so I’m not complaining!

I bought it for parts, and will be transferring the following to my old Nimbus II Blue 24" Freestyle:

  • 48h UDC Cromo ISIS hub (replacing the cotterless one)
  • 114mm Venture cranks
  • Plastic studded Nimbus pedals
  • Old logo Impact double bolt seatpost clamp
  • possibly seatpost (prefer the black to my silver)

After doing all that I hope to rebuild the 20" wheel with the old cotterless hub, and use some shims to put it back in the frame. I have enough other parts to then put that uni back together as a perfectly good starter for someone, so it will get some more life ahead.
As for my original 24" that I’m upgrading to ISIS, what with all those ‘new’ parts from this rusty uni, and replacing the 40mm bearing frame with an old Nimbus II ISIS 26" muni frame I have lying around, I guess it will be a stretch to call it the same uni, but it will still feel like it to me!

Can’t do any more of the project for a few months probably due to being half way through a big move and downsizing (when I’m meant to be getting rid of unis, not buying new ones - but how could I pass up a 48h ISIS uni for £10??), but I’m definitely looking forward to when I get some time to work on it.

Here are some pictures of the new ‘shabby chic’ arrival - I haven’t yet admitted its existence to my wife!