Re: [yak] Digest for yak@bikefriday.com - 3 updates in 2 topics

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Gary Keese

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Jan 24, 2025, 1:24:09 AM1/24/25
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Hi Judith,
 
My first BF, a Pocket Tourist of about the same vintage (around 2008), originally had a 1 x 8 drive train.  A few years later I successfully installed a compact double crank to get a 2 x 8 drive train with the low granny gear that I (at 74 years old) need to get up hills.
 
I also installed a new bottom bracket to accommodate the double crank, and a clamp-on front derailleur.  I don't remember the cost, but it was reasonable.
 
As for your rear wheel issue, I have found 20 in 406 rear wheels (that are compatible with a cassette) at shops that specialize in recumbents, since some of those use 20 in wheels. 
 
BMX wheels are, in my experience, usually single speed and therefore not cassette compatible.
 
Good luck. 
 
Gary Keese
 
 
On 01/23/2025 5:57 PM PST y...@bikefriday.com wrote:
 
 
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Judith Humbert <planetp...@gmail.com>: Jan 23 05:09PM +1300

Hi John,
 
Thanks for your reply.
 
No my BF Pocket Llama likely doesn't have a braze on for a derailleur above
the crank. The crank only has 1 chainring so unless I wanted to be a 7-9
speed bike I'd have to change that out too.
 
Not sure about the specs for the crank and the bottom bracket. The bike was
built in 2007 and is still in very good shape. I looked into getting a
custom rear wheel made here in NZ and was quoted I think around $500+ NZD
for one. My hunch is there's an old BMX wheel around somewhere that could
work as well...or take the current rim and use that instead for a rebuild.
I've hardly ridden the bike.
 
As for the Dual Drive it's been a royal pita to maintain. I've tried
installing new parts, new oil (proper one for DD), adjusting it and it
still skips gears. I'd rather have a more traditional easier to maintain
drivetrain.
 
Gear ratio - preferably one suitable for long climbs - slow and steady.
 
Thanks,
Judith
 
 
 
 
John Thurston <y...@thurstons.us>: Jan 23 08:52AM -0900

It's unfortunate that the Dual Drive hasn't worked out for you. The
hybrid gearing is the best way to get a 'normal' gear range on a small
wheeled bike, without needing to resort to super-sized chainrings.
 
And the absence of a front derailleur hanger is going to be a challenge.
While you can probably use a clamp-on derailleur, I suspect it will be a
challenge to get it positioned correctly. The only way to see if it will
work is to try it. Fortunately, that can be done without changing your
rear wheel.
 
If you really want to pursue this, I suggest the course of action is:
 
1. Identify your required gear range
2. Determine what chainring numbers and sizes will be required
3. Choose a derailleur which can handle those rings
4. See if crank/rings/derailleur can be fitted and made to work
5. Build out the rear wheel with the required cassette and derailleur
 
Let's look at the gear range of my Llama
<http://www.ritzelrechner.de/?GR=DERS&KB=31.5,42,55.86&RZ=12,13,14,15,17,19,21,23,25,28&UF=1540&TF=90&SL=2.6&UN=MPH&DV=gearInches&GR2=DERS&KB2=50&RZ2=11,13,15,17,19,21,24,27,31,35,40&UF2=1540#>.
The top bar is the gearing I had when it was equipped with its hybrid
(e.g. Dual Drive) gearing. With a 42t chainring, my gearing was a 414%
spread between 22 and 90 gear-inches. (I'm in USA, so we usually express
our gearing is this unit. The calculator I linked to can display in
other units). With the hybrid gearing, the derailleur only needed a 17t
capacity.
 
The lower bar is the same bike with 1x11 gearing, with a 50t chainring.
That gives me 364% spread between 24 and 88 gear-inches. I'm using an
11-40t cassette, which requires a rear derailleur which can absorb 29t
of chain. I'm still able to do this with a short-cage Shimano
derailleur. But, that 40t cog on the cassette requires some extra work
to let the rear derailleur work with it.
 
If you change the cassette to a more common 11-28t, and install a
relatively common 52/42/32 triple crank, you can re-achieve the 414%
range of the original Dual Drive configuration. But now you will need a
derailleur with 40t capacity, and a triple (clamp on, bottom pull) front
derailleur which can handle the 10t shifts. And you will need to ensure
the chain clears your tire on the small ring, and isn't too far outboard
on the large ring. And you'll need to choose your derailleur and
chain-length so the cage doesn't come too close to the roadway as you
get into your lower gears.
 
As an aside . . . it isn't a _requirement_ to fit a front derailleur to
handle multiple chainrings if you don't shift often. After I chose to
switch my Llama to 1x11 gearing, I discovered I really needed a lower
gear when I'm in 'hill country'. So I added a second chainring to my
crank. I can 'shift' to the smaller ring (using the toe of my shoe) as I
enter 'hill country'. When I need the upper range back, I need to stop
and lift the chain back to the larger ring. This second chainring pushes
my overall range back out to 400%
 
--
John Thurston
Juneau, Alaska
 
 
 
On 1/22/2025 7:09 PM, Judith Humbert wrote:
robert clark <ro3ert...@gmail.com>: Jan 22 06:30PM -0800

Sram abandoned the 3 speed + cassette hubs, Sturmey-Archer continues.
Common rear hub 135 wide ... will do ... even disc type no need to fi a
disc,,
Shimano alfine & chain tensioner , & 1 cog is practical...
On Wednesday, January 22, 2025 at 11:07:33 AM UTC-8 John Thurston wrote:
 
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