Modified 3-speed hub?

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

Mike

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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

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Jim said:

Have you read Sheldon Brown's guide to converting a normal 3 speed
gearbox to a fixed 2-speed gearbox

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.

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

http://sheldonbrown.com/awfixed.html

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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

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thieum said:

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.

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rob.northcott said:

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! 🙂

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johnfoss said:

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.

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 😎

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johnfoss said:

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!

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.

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

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. 🙂

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johnfoss said:

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.

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.

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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.

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If you look at 'Lars Clausen's website' (http://www.onewheel.org/) 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.

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let it freewheel itll be more fun

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unicyclistben said:

let it freewheel itll be more fun

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