Riding Faster on One Wheel: Geared Unicycles

Traditionally there have been just two ways to increase your speed on a unicycle: you could get a bigger wheel, or you could pedal faster. Now there is a third option.


For more information on high-speed unicycling read Geared Unicycle Engineering Challenges and Riding Fast on One Wheel–Ignite Talk.

imageUnicycles are like fixies – there is a direct connection between the pedals and the wheel. The wheel and pedals cannot rotate independently, and being able to slow the wheel by applying back pressure to the pedals is crucial – it’s how you stay balanced.

Most unicycles have a one-to-one connection between the pedals and the wheels, and this leads to the rule mentioned above – to go faster you must pedal faster, or buy a bigger wheel. Now, however, there exist multiple designs for geared unicycles, and one of these geared designs allows for switching between two gears on the fly.

Size matters

The biggest unicycle wheels in common usage have a 36 inch diameter. With this size of unicycle a single pedal revolution will take you about 9.4 feet. More usefully, if you pedal with a cadence of 100 rpm you will go 10.7 mph. There are a few unicycles with 43 inch wheels and other large sizes but they start to become impractical. Since the pedals are mounted on the wheel’s axis a large wheel requires long legs. Large wheels also get heavier, or are made of unpleasant solid-rubber in order to keep the weight under control. A 43 inch wheel gives less than a 20% increase in speed at the same cadence, and it rarely seems worth it. A 36 inch wheel seems to be the sweet spot.

You spin me round and round

Lance Armstrong is famous for having a high cadence. Whereas most professional cyclists pedal around 90 rpm, and recreational cyclists are typically slower, he sustains rates of about 110 rpm.

However unicyclists think that Lance pedals slowly. My top speed on a 36” wheel is 17.2 mph, which requires a cadence of about 160 rpm. Better unicyclists than I have gone much higher – apparently up around 270 rpm (~29 mph on a 36” wheel).

Bicycle cranks tend to be long – typically 165 mm or 170 mm – presumably from years of research into the most efficient length. However when you have one gear and it’s not a high gear the tradeoffs are different, so high-speed unicyclists ride on much shorter cranks, to facilitate faster spinning. My maximum speed on a 36” wheel was done with 125 mm cranks, but other riders go down to about 100 mm.

Single chain drive

When you hit the limits of wheel size and pedaling fast the next logical step is to add gears.

imageThe simplest way to gear up a unicycle is to take a ‘giraffe’ unicycle – one with the pedals above the tire and a chain drive going down to the axle – and put a larger chain ring at the top than at the bottom. You can get any gear ratio you want this way. You can’t change gears on the fly – derailleurs don’t work on unicycles – but that’s okay. The unicycle shown in these pictures has a twenty inch wheel with exactly twice as many teeth on the top gear as on the bottom, making it equivalent to a forty inch wheel.

The biggest limitation is that you are sitting up fairly high. This means the entire assembly imageweighs more and the chain is long enough that it will inevitably be a bit loose. But, within reason this can work. The unicycle in the pictures is a “Penguin Giraffe” made by Abram Clark. Its small wheel is not particularly safe when it meets bumps and rocks in the road, but it can go over 15 mph. I used it once in a twenty kilometer road race against riders on more ‘normal’ racing unicycles. I didn’t win, but I wasn’t last, and I enjoyed the delicious absurdity of it.

You can see my over-produced Penguin Giraffe video on youtube.

Planetary gears

imageUsing a system of planetary gears it is possible to put a tiny transmission inside the hub of a wheel. Making such a hub work in a unicycle is complicated by the need for full back pressure. An early version by Greg Harper had a 1.5:1 gear ratio and could not be shifted.

Greg then created a hub that could be shifted with about a minute of work with tools and put it in a unicycle he called Blue Shift, pictured at right. By locking the arm (circled in red) to the hub or to the frame you could switch between 1:1 or 1.5:1. It was the beginning of the geared age.

imageThen, Florian Schlumpf commercialized a variation of this that could be shifted on the fly. With this hub you can shift up with a click of one heel, and shift down with a click of the other, while riding. In the picture to the right you can see the planetary gears, sun gear, and some tricky mechanisms to allow shifting on the fly.

In the picture below you can see the hub – big enough to contain the planetary gear system – and one of the shifting knobs, and the dual drilled cranks to allow bonus flexibility in crank length.

image

I was lucky enough to get to test drive all of these planetary gear unicycles, and I did eventually purchase a Schlumpf hub in a 29” unicycle.

Dual chain drive

PPhaze.v5.sideA final option for gearing up was developed by Pete Perron. In this system the crank shaft goes through the drive shaft but they rotate independently. Power is transferred through a set of four cogs and two chains – up from the pedals to a jackshaft, then down to the drive shaft. Unlike a geared hub, you can get virtually any gear ratio you want, and unlike a single chain design there is very little extra weight and no extra height.

Pete made two versions of this, both with 36” wheels, and I just purchased the second one, named Red Menace.

In the picture below you can see the short chains going from the cranks, up to the jackshaft, and then back down to the axle.

image

I’m enough of a math nerd to appreciate the beauty of the gear ratios that can be realized. Each chain gears up a bit, and both chains gear up by the same amount. Therefore a typical ratio is (24/20)*(24/20), or 1.44:1, which you get by having both chains going from a 24-toothed cog to a 20-toothed cog. Other obvious ratios include:

  • 1:1 (but why bother)
  • 1.21:1
  • 1.44:1
  • 1.69:1
  • 1.96:1

You can also gear it down, or do other more creative ratios.

imageMy top speed to date is using the 1.44:1 gear ratio and 170 mm cranks to get up to 20.6 mph. It’s definitely exciting when you start losing your balance on one wheel at a higher speed than you can run. So far I have had no high-speed falls (nothing over 15 mph), but pushing the limits does come with risks. It’s also cool/scary to think that with some changes to gearing I should be able to go significantly faster.

It turns out that the forces involved in a dual chain-drive unicycle are quite extreme – I wrote about those forces in Geared Unicycle Engineering Challenges, where I tell the sad story of almost breaking my dual-chain unicycle while changing gears.

Why don’t derailleurs work?

Riding a unicycle is, like walking, a constant state of near falling.The rider needs to perform tiny adjustments many times per second in order to keep the center of support directly imageunderneath the rider’s center of mass. If you start falling forwards then you need to instantly pedal faster. If you start falling backwards then you need to instantly push back on the pedals. These corrections are happening multiple times per second, usually without the rider even noticing. It’s only when the corrections almost don’t work that the unicycle perceptibly moves from the vertical and the rider’s heart rate goes up a bit.

The derailleurs which are used for gearing on bikes don’t let you apply back pressure. If you pedal backwards you freewheel, and if you stopped the axle from freewheeling then pedaling backwards would just damage the gearing system.

It is possible to ride a unicycle without being able to pedal backwards – doing a wheelie on a bike that freewheels proves this – but it is not stable, and it doesn’t work downhill. Technically it is possible to use a brake as a substitute for pedaling backwards, and anybody who thinks that that is a good idea is welcome to try it.

The challenge in unicycling is the front/back balance. The left/right balance is similar to the challenge of riding a bike with no hands – easy once you are used to it, and rarely the source of exciting falls.

Why one wheel?

About the closest thing to a rational explanation for why I unicycle is that it is an inefficient form of transportation (less efficient than a bike, but more efficient than walking or running) and is therefore great exercise. And a fun challenge. And because improving my balance skills lets me try cool toys. And because it is there. And because owning three of the coolest geared unicycles in the world (shown together below) is still much cheaper than buying fancy cars or smart-phones.

image

Speed does not equal distance

While my top speeds have been set on geared unicycles, my longest ride ever was done on an ungeared 36” unicycle. I rode the Seattle to Portland Bicycle Classic on a unicycle, covering 204 miles in two days. Some day I’ll do that again on a geared unicycle, which should make it a bit faster.

Apologies for the mixture of metric and imperial units.

For more information read Geared Unicycle Engineering Challenges and Riding Fast on One Wheel–Ignite Talk. Or look at the complete series.

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About brucedawson

I'm a programmer, working for Google, focusing on optimization and reliability. Nothing's more fun than making code run 10x faster. Unless it's eliminating large numbers of bugs. I also unicycle. And play (ice) hockey. And juggle.
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24 Responses to Riding Faster on One Wheel: Geared Unicycles

  1. Janos says:

    Hi!

    Do you know Huni-Rex unicycle? We think it’s a workable geared unicycle, with 26″ wheel, but with good parameters.

    http://www.huni-rex.com
    http://www.facebook.com/hunirex

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  3. Jim Bamford says:

    Hey bruce, interesting page, I was at a kids youth group with a couple of my kids about two months ago and was talking with another fellow there that rides unicycles a bit. We ended up discussing unicycles and how to possibly gear them. I might have a different idea for a small giraffe unicycle that might theoretically work without being too tall or heavy. If I get around to building it, ( I’m a steel fabricator by trade and eyeball engineer sometimes out of necessity at work) I’ll send you some pictures. Jim

    • brucedawson says:

      Definitely send me pictures. Although really what I want you to do is bring over a prototype so I can test drive it. I’m an accomplished test pilot of geared unicycles.

      • Nigel Loller says:

        Hi Bruce
        I followed this thread as have designed and built a 21 speed through hub drive,which at the moment freewheels and is being fitted into a full speed penny farthing type recumbent but could easily be modified not to, so that you could choose any of the ratios available,not changeable while riding.
        I think with the right rider a unicycle with a tall ratio could smash all existing world speed records
        I would build it for you
        Feel free to email me re this drive and (when it’s finished in a week or so) I can send you pics or vid
        Kind regards
        Nigel

        • vladimir visnjic says:

          Nigel, I would like to have a custom built geared wheel. Please email me if you are interested and I will send you the design. Thanks, Vlad

  4. Janos says:

    Hi Bruce,

    Would you like test Huni-Rex also :)? To find a solution – if it interesting to you, send an email: info@huni-rex.hu.

    Janos

  5. Jim Bamford says:

    Hey Bruce, its winter here in south central B.C., about a foot of snow on the ground where I live so unicycling isn’t too practical right now but I’m still thinking about my three speeder. Actually sketched something yesterday at work, they all think I’m nuts but thats okay. The huni-rex was interesting but a bit vague as to how it actually works. I’ll keep you posted.Jim

  6. Jim Bamford says:

    The wheel is rolling slowly but I think I’ve figured out my axle/drive assembly, just have to modify a hub, keep you posted. Jim

    • Jim Bamford says:

      hey bruce, just wondering can you unicycle and juggle at the same time? I can do both but not at the same time. I’m making progress on the three speed, should get to starting the frame next week hopefully, should have a twenty six inch wheel from a mountain bike so with the gearing I’m hoping to do I should have maybe a bit over 1 to one on the final drive up to better than two to one, I have my sights set on the land speed record for one wheel which I think is 26 mph on a 48 inch wheel back in the nineties I believe.Just not me doing it because I still have to go to work every day.Our snow finally started to melt here where I live in beautifull deadman valley.

      • brucedawson says:

        The fastest reported ungeared speed is now 29ish mph, and the fastest geared speed is 33.0 mph. Intimidating. See post #460 in this thread.

        http://www.unicyclist.com/forums/showthread.php?t=78667&page=31

        Darn those kids and their annoying tendency to keep pushing the limits. If I’d had Red Menace twenty years ago then it probably would have been easy to set a world record, but now…

        • brucedawson says:

          And yes I can unicycle and juggle at the same time, although I usually only do that on smaller unicycles. It’s very popular at parades, especially if you ‘drop’ a club and then pick it up while riding.

      • DIavid says:

        Years ago, when I was just getting going juggling and unicyclying, a Quebec busker came thru town with the Buskers Festival (back when it was run by crooks and rocked; before the government took over, cleaned it up, and crushed the life out of it).

        He spent half an afternoon with me, and taught me more about juggling on the uni than I’d managed in several months effort.

        First, do arm independence exercises. Ride with your arms wrapped around your chest, over your head, firmly at your sides, straight out doing arm circles, etc. Make sure that you aren’t using your arms at all for balance. Only when you can balance independent of what your arms are doing shouldb you try to juggle.

  7. jimmy says:

    wow i cant even believe this is possible, i bought my first and only uni cycle when i was 10 yrs old . and ill tell you i got on this the first time and rode it like i did all my life . i think i bought it for 10 bucks . well anyways im 46 now and havent rode a uni cycle since i was 13 , the other day i scene this kid trying to learn to ride one hanging on to a fence so i walked over to him and asked if i could try sure enough i rode like i did when i was a kid . but i just found out on hows its made about this faster high tech uni cycle and i will get one soon have to find out how much . if anybbody wants to share any other kool stories like mine email me at jimbosmith92@yahoo.com would love to hear o yeah i could also balance anything on my nose while riding a uni cycle take care

  8. Jim says:

    Bruce, I just noticed that I started all my other replies to you with “hey bruce”. So I changed it to
    just Bruce this time, anyways I’m still doing lots of coffee times and lunch times on my three speed{hopefully} went from minus 5 where I live last tuesday May1stish to 33 degrees today. Nice I like hot weather. I’ve got all the pieces built for the axle /hub assembly your pics gave me some ideas and will soon weld it all together and attach to my frame. Question is a brake a good thing, I’ve never tried one one wheeling before other than braking a little bit going downhill coasting doing a catwalk years ago. Must require a really gentle force to not faceplant I would think. I will get one of my coworkers to take some in {very slow} progress pictures and send them to you. It will probably end up being yellow. Take care Jim

    • brucedawson says:

      Watching an expert unicyclist use a brake is an amazing thing. A gentle force is the most common way to use it — to make going down long hills better — but some riders can take their feet of the pedals and use the brake to come to a very abrupt stop. I need more practice before I can safely use a brake.

  9. Jim says:

    Bruce, jim here in sunny Savona. I have a really rough looking geared unicycle sort of built. about two to one gear ratio on a 26 inch wheel. I tried riding it a couple of times, wow what a different feeling being geared up. Anyways it still needs a lot of work as the chains are way too sloppy to even begin to balance. I got an I phone for fathers day so maybe I can figure out how to send some pics tomorrow, I’m somewhat cellphone challenged so I won’t guarentee this. I still am hoping to make it shiftable but it is definatly more complcated than I origanally figured.Hoping your enjoying summer, its nice here. Jim

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  11. Frank A says:

    Thanks for posting this info :) I purchased a folding bike a couple years ago, a BikeFriday, and I love it. I bought it for the occasional commute on buses, trains, and planes; and for Burning Man ;) Last night, I was walking down the platform with my bike awaiting a train and I saw a unicyclist. I started chatting him up and he told me about geared unicycles. I think a geared unicycle might be easier for public transportation than a folding bike.

    1. Which relatively compact geared unicycles would you recommend for public transportation?
    2. Where can I get more info about geared unicycles (forums, magazines, etc.)

    Thanks :)

    • brucedawson says:

      unicycle.com sells unicycles, and unicyclist.com discusses them. Beyond that I’m not sure — my blog might contain the majority of articles posted on this topic.

      I would never suggest getting a unicycle for a practical reason (“easier for public transportation”) — do it because it’s fun, challenging, good exercise, and if it works well that’s a bonus.

  12. Dayve says:

    I want to buy a geared unicycle please can you help? I want a price list or contact details so that i can get one.

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