Modified 3-speed hub?

My dad just found an old 3 speed hub from a bike from back when he was in college. We attempted to take it apart a little to see how the innerworkings are made and how easily they could be modified.

My Idea: If I can eliminate the coaster element of the hub, then I could build a short giraffe unicycle with a small wheel and the cranks mounted right above the wheel. If I used a small wheel, say 16" or maybe even 12", then I would have a small, portable, and extremely fast unicycle with multiple speeds. If the wheel is really small, then I am closer to the ground when riding so I wont have that “I’m about to die” feeling running through my head when I ride it.

So far, the hub doesn’t look to adaptable. It has two little coasters in it that revolve at different speeds depending on what gear the hub is in. It’s a work in progress, but I’m hoping I may be able to set aside some time to work on this project to make the most awesome little death machine ever.

Your thoughts?

my thoughts are that, that would be amazing, superb. I hope you do set out the time to do that.

Mike

Have you read Sheldon Brown’s guide to converting a normal 3 speed gearbox to a fixed 2-speed gearbox (assuming it is a sturmey archer gearbox like they used to fix to some schwinn bicycles) http://www.sheldonbrown.com/awfixed.html

Not tried this myself but looks promising

good luck

jim

It sounds like that modification results in quite a bit of backlash, which wouldn’t be so good on a unicycle. Probably worth a try though if you’ve got the kit to make one.

It is possible to make a 3 speed hub into a 2 speed fixed gear hub. Here is a link telling how.

small wheel means less tolerance for bumpy terrain, you might still be better off with a fat 20" and seat higher up. You still wouldn’t be taller than someone riding a 29er

The pedal axle (bottom bracket if it was a bike) would have to be above the top of the wheel, so with a 20" wheel, even without allowing for realistic clearances, you would be at the height of somebody riding a 40"+ wheel.

This is true. And by “realistic clearances” he means crank arms vs. fork crown. So unless you build a custom crankset (wide), you’ll be higher than you may have imagined, but still not too high. I also recommend a minimum 20" wheel so you can handle bumps.

My thoughts on the engineering part:

  1. You may find the gearing way too high. I assume even the low gear is at least 1.5:1? Probably more. It may not be fun without a low gear, and the high gear may be way too high for useful riding.

  2. In 25 years of unicycling I haven’t heard of any instances of someone converting a 3-speed hub for unicycling. This doesn’t mean it’s necessarily impossible (nothing is). What it means is that you might be the first! :slight_smile:

From reading the articles about the conversion it seems that the highest gear is a direct drive and the other one would be a 0.75:1 reduction. So you could pick the chainring and sprocket so the direct drive was as high as you could ride, and the lower gear would be a bonus. So a 20" wheel with 2:1 chainring:sprocket ratio would give virtual gears of 40" and 30". The article says you can make a three-speed fixed hub (direct drive and two reduction gears) from a four or five-speed Sturmey hub, which could be interesting - sounds like that would give a lower low gear as well (something like 0.6:1 I think). The downside seems to be that there is apparently a fair amount of backlash - enough to annoy some bicyclists so it might be enough to make a unicycle nasty to ride. It would be interesting if somebody tried it though - and it would have to be a three-speed version :sunglasses:

The Sturmey Archer 3 speed is 1.33:1, 1:1, 1:1.33 so the gear spread is not so big and the overall gearing is not too high. This could be used with standard sprockets (26,26 or 26, 28) on a small giraffe except for the freewheeling aspect. I thought you told me of someone who built such a giraffe but it was short lived. Perhaps I was mistaken.

Wow, with all the crazy people in this sport, I thought that someone else would have thought of this before me. :roll_eyes:

In response to the small wheel size not being able to handle bumps too well, I wasn’t planning on using this as a main form of transportation, just a test to see if it could be done. I’d like a smaller wheel as this would keep me closer to the ground. I have this strange urge to avoid injury, and a saftey feature seems more important than superb functionality. I could always make a frame for a 20" wheel, too.

So far the hub doesn’t look too friendly though. It’s pretty much built around the functionality of two different ratcheting parts (which allow it to coast). I’d like to keep three speeds, but I’m gonna have to come up with a clever way to do it. I’d like to come up with my own solution, though. It gives a much bigger sense of accomplishment. :slight_smile:

I have been corrected on that. What I forgot at the time is that you can mitigate any built-in gearing by adjusting the sizes of your sprockets/cogs on the outside. So no problem there.

For a test-only cycle, a 16" wheel should be fine. I don’t recommend 12", unless you build one special. Those wheels are usually built for the weight of small children. I guess the same would apply to a 16" as well.

If a design has enough backlash to annoy bicyclists, it might be pretty bad on a unicycle. Not too much to ride, but possibly too much to enjoy or be functional. My other initial concern with a 3-speed hub is its strength in resistance to hard torque in both directions. Whatever is the “stopper” for your freewheel mechanisms, it has to be beefy enough.

And please don’t forget that Sturmey Archer AWs (and many similar constructions) have a no-drive position between the gears, and can even slip out of gear depending on the condition of various internal parts… .

Regards,
j.

If you look at Lars Clausen’s website and search around for the history of his ride you may find a section where he and his father or father-in-law made an attempt to convert a 3 speed freewheel to 2 speed fixed drive for his epic voyage. They abandoned the attempt after probably running up against the limitations you are finding. This is something I read several years ago and that particular part of the site, the ride preparation, may no longer exist.

let it freewheel itll be more fun

Re: Modified 3-speed hub?

On Thu, 2 Feb 2006 17:55:42 -0600, unicyclistben wrote:

>let it freewheel itll be more fun

Ask Ken how much fun an unintentionally freewheeling geared hub is.