After hemming and hawing repeatedly over the last few years, I’ve finally jumped on one of the 99 euro Huni Rex sales. (It ended up more like 350 USD after adding chain tensioners, shipping, and import fees, but I digress)
After my initial test ride today, I think I’ll already enjoy it as is… BUT I think I’d enjoy it even more with a bigger wheel. Im thinking 29", or maybe even 32".
I think it has the clearance for at least a 29". Is it “just” a matter of building one? Would I need to reuse the hub, or could I easily source a compatible one?
I’ll probably want a brake too, especially with a bigger wheel. It has from brake mounts intended for use with the stock 26" wheel. Is there a way to add a brake with a bigger wheel?
Welcome to the Huni Rex club 
I did a write-up a while back on mine.
I’m fairly confident that it can fit a 29" wheel without requiring any modifications to the frame. I was considering getting another and building a 29" Huni as well. From what I know about the hub, it’s a proprietary deal; as far as I know there aren’t any other hubs that’ll fit in a Huni Rex (though if there’s anybody that has tried a different hub and made it work… I’d really like to know 
).
The way I would do it is to unlace the current wheel and reuse the hub for the build. There is a catch to be aware of: the cogs on the hub are fastened using lockrings and a retaining compound. I highlight that because if you need to take off the cogs for a wheel build, you’ll need to reapply the compound so the cog doesn’t shift back and forth under load and chew up the splines on the hub (ask me how I know 
).
The retaining compound + catalyst is a little spendy, and to do the job right will require some patience cleaning off the old compound. But it’s entirely doable if you’ve got the time for it. I would also recommend you get the cogs off before unlacing the wheel since you’ll need some leverage to get the lock rings off (one of them is right hand threads, the other is left handed threads).
For the brake, you might be able to get long reach v-brakes to work with a 29" wheel on the upper pair of holes.
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thanks, good to know about the retaining compound issue in particular!
folks on the unicycling discord had a couple ideas for sourcing hubs -
It basically looks like a fixie “flip flop” hub, with a lock ring on both sides instead of a free wheel on one side. (though a huni rex that freewheels on one side would certainly be a … novel … ride)
someone suggested polso hubs in particular. i think i see lock ring threads on both sides here, though i wish the written specs would call it out https://www.aliexpress.us/item/3256806545979516.html?gatewayAdapt=glo2usa4itemAdapt
someone also pointed out that dual chain giraffes must use a similar hub, so we could look there too
i just realized though, i think you’d be driving one side in the opposite direction than intended, so it’d be relying on the lock ring when going forward instead of only when going backwards. This might be pretty bad for longevity…
Hi, we can ship new central hub for your Huni, so you should not have to use the existing one. Nevertheless the toothed gears are glued to the hub with industrial thread lock, so disassemble it is not easy (if possible at all).
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Thanks! I might take you up on that, but will probably do a bit more research and experimentation first.
From what you told me on Facebook, it sounds like these are track bicycle “flip flop” hubs. I think that means that in the HR one side will be running in reverse full time, relying on the lock ring much more than it would in its intended usage. Maybe this is why the adhesive is needed? Without the adhesive, are the failures consistently on the reversed side?
