I just heard of this via ‘Velovision’ Magazine’s website:

The Huni-Rex unicycle from hungary.

It is a 26 inch uni with chain transmission (fix, one gear).
The sprockets are 24/16, a ratio of 3:2. That means the “virtual rim” that the transmission creates must be 39 inches in diameter. Correct me if I was thinking too simple.

The crank bearings are below the hub, making it especially interesting for those who are too short for a 36er, but would have the strength to propel a uni to high speed.

I hope this did not turn up before here, at least the search found no matches for “huni-rex” and “bi-drive”.

Interesting. Looks to have rather a large Q though.
I don’t reckon it would help people too short to ride a 36er - with the cranks below the axle it would need legs just as long as for a 36er, if not longer (there’s 5" difference in diameter between a 26" and 36" wheel, so if the cranks are 5" or more below the axle, all “short person” advantage is lost). Of course, you could use a smaller wheel and gear it up even more.


It probably would have been better if they used either 25/16 or 24/17 instead of 24/16 gear ratio to have a lot more wear spots.

I wonder what the slop is like in the drive-train.

…you’d have to worry about pedal strikes even more. Gaah!

Not exactly a new design, but it’s good to see a jackshaft quasi-commercialized.

39" effective wheel size I think will limit the interest; hard to see a big advantage over a Coker. But it’s a step in the right direction.

How about this as a concept; take a 700c/29er wheel, use a jackshaft to gear it up to 90" effective wheel diameter, and then have a planetary hub which gears it down from there. It’s easier to use planetary gearing to gear down than gear up; you could probably have multiple gears. 1:1, 1:2, 1:3 ratios would provide three good options (though the distance between them is still too big).

You’re right there, of course. I wasn’t thinking carefully.
It also came to me that I was mistaken with that phrase when I had just shut the computer down and I had to leave…

You could also use this basic design to put the pedals more to the front and create a crank-forward riding position, probably more comfortable.
No idea wether you could balance that though…

For me an advantage is being on a smaller wheel. I like to ride the Coker, but I feel safer on a smaller wheel. Ever since my crash, I’m more apprehensive on the big wheel. I wish I would just get over it.

I’m pretty sure you’ll feel less safe on a geared unicycle of any size than on a Coker. I know I do.

I am inclined to think that this is a very individual mental problem - and that your experience on normal unis does not help you there, to the contrary.

i’m sure I will. I will be finding out soon. I’m just happier closer to the ground.

Can’t see the price anywhere and an unable to to ‘sign up’

Cool thought, one hadn’t occurred to me. Has everyone ever calculated numbers on planetary drive efficiencies? Seems like having three gearing steps (chain on each side and the planetary) might have some impact, but I guess the planetary in 1:1 would have very little effect (since it’s just locking axel to shell. That’s good, because that would be the high hear.

I’m less interested in shifting (at least for now) but my current long-term project is a single-speed uni geared up. 90" sounds huge though, I’ve been mostly throwing around numbers around 70". the TGR at 90" with 175mm cranks would be equivalent to 70mm cranks on a 36, or 78 on a 36 with 195mm cranks. Maybe those are good numbers for the high-hear on a multi-geared machine, but that’s a pretty small mechanical advantage at potentially very high speeds.

The Huni-Rex looks pretty cool, but as was mentioned, looks like it has a pretty big q-factor. Hard to get a sense from the video, but seems to me like having lower cranks would make riding harder. I am very intrigued though about the possibility of offsetting the cranks in front or behind. Aero aero aero.

I think 90" equivalent or higher is necessary for pure speed; time trials, hour record, 24-hour record, etc. No serious bicyclist would consider a flat/rolling time trial (or even a long ride) with a max 70" effective wheel diameter.

But 90" is too high for general unicycling, so you need it to be shiftable (except for special cases like an hour record attempt). Yes, you don’t have much mechanical advantage on a 90" effective wheel; you only use that when you don’t need much mechanical advantage.

As the CG (center of the cranks) is lower than the center of the wheel, if someone put all the weight on his foot (instead of the seat), he can be automatically balanced as a tumbler. Everyone who can ride a bicycle can ride it very easily!

Is that why BC wheels are so easy to ride?

If you put your weight on your feet it doesn’t mean your feet become the centre of gravity. It would only be self-righting (“weeble-like”) if you wore huge lead boots that were heavier than the parts of your body that are above the axle.


The first thing I’d try with that would be riding SIF:p I already had an ideal like that, but I forgot it as soon as I had it, I wouldn’t have tried to built it too anyway. It looks cool to ride though.

Great to see another approach to the geared unicycle.It is not a big step in gearing configuration to other various attempts but is very different in having no crank through axle instead relying on stub axles for the cranks.Given the massive torque typically applied through the cranks there must be a compromise between rigidity and weight.It would not be a great leap to turn the drive line horizontal and mount a swing arm pivoting from the stub axles to create the fully suspended unicycle some have dreamed of,it may not be the answer but with every new idea we creep a little closer.


It would be interesting to ride one to see how it feels pedaling ‘below’ the centre of the wheel, but with that design the distance between your feet looks massively wide, can’t see that being a good thing. The frame width too… not sure what body shape is going to enjoy that. The lack of clearance pedal-ground at geared speed… hmm… don’t lean through the corners too much I guess.

Agnes from has been in contact with the manufacturers of the Huni-Rex and she informed me that there are plans to produce an ISIS version soon and also a 29" version.

She also said that the amount of slop in the drive system is very small, in fact undetectable when riding. Nice!