Re: [yak] Digest for yak@bikefriday.com - 2 updates in 1 topic

[Judith Humbert]

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

On Thu, Jan 23, 2025, 2:57 PM <y...@bikefriday.com> wrote:

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Digest for y...@bikefriday.com - 1 update in 1 topic

Judith Humbert <planetp...@gmail.com>: Jan 22 08:04PM +1300 Cool bike. Would you have a list of components for the drivetrain + the year the bike was built by BF? Looking to convert my SRAM DualDrive setup to a regular one. Thanks.

John Thurston <y...@thurstons.us>: Jan 22 10:07AM -0900 When you say 'regular one', do you mean 'with multiple front chain rings and front derailleur" ?   If so, the technical questions to ask are:   1. Do you have a derailleur hanger brazed on above the crank? 2. How wide a gear range are you hoping to achieve?   The philosophical question to ask is:   * What are you trying to change?   Is the DualDrive too heavy? too strange? broken? restrictive?     -- John Thurston Juneau, Alaska   On 1/21/2025 10:04 PM, Judith Humbert wrote:

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[John Thurston]

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. 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

[Geof Gee]

@Judith ... Before you proceed any further, since you wrote "likely", go look to see if your bike has a front derailer hanger.  Your options are quite different.  

Memory says that front derailer hangers were included on some SRAM Dual Drive builds despite not needing them. Although some build did come sans a front derailer hanger too.  

If you do have a front derailer hanger, then you have tons of options.  Very wide cassettes are plentiful today such that with a double you can get a very wide range without worrying about the derailleur's ground clearance in the back.  

If you lack a front derailer hanger, then you are looking at single chainring option with super wide cassettes. Memory says that folks have done builds with 40 and 42 tooth cogs in the rear. Can't say if I've seen anyone get a 50t cog on the rear without ground strike.

Anyway, Bike Fridays are steel bikes. You might ask if there is a local bike builder willing to add a derailer hanger. Memory says that is a pretty straightforward job that might be cheaper than getting a premium single chainring build that typically have 9t or 10t as the smallest cog.  

-G

Arlington, VA   

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[Josh Brown]

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.

Using a clamp on FD, I'd reckon a wide range double would be easier to achieve good shifting?

J

[robert clark]

Had no derailleur hanger on my Brompton,  I found an  internally geared 2 speed crank.

2.5:1 reduction gear   50t has a '20t' by having pedals turn faster than than the chainring...

Efneo GtRo  is a 3 speed internally geared crank... 

 a physical 28t + 2 overdrive ratios create a 40 & 50 

 bigger than 28t the higher 2 proportionally higher..

[John S. Allen]

Here is how I handled the wide range/chainwheel size issue on my 2007 NWT -- similarly to how John Thurston did when he had DualDrive.

First of all, my NWT came with the earlier Sachs 3 x 7 hub. It is made to take only a 7-speed cassette, but the 3 x 7 is more reliable than the DualDrive, and particularly because it shifts with a pullchain rather than the troublesome plastic Clickbox of the DualDrive. (Neither hub is made any more, but I have a spare 3 x 7 in case I have to replace the internals, and they are still available on eBay.). I can't comment on the reliability of the Sturmey-Archer hybrid-gearing hub, never having had one.

With any of these hubs, it works well to use a cassette whose top and bottom pairs of sprockets have half the step width of the hub. Then shifting the hub to top or bottom gear gives two more steps at either end of the range. Small steps in the middle of the range are also desirable. Many 7 and 8--speed cassettes have a 17-20 tooth jump, right in the middle of the range, which drives me nuts. The 7-speed Shimano M cassette, 13-15-17-19-21-24-28, is good. I got fancier and left off the 11-tooth sprocket of the 11-13-15-17-19-21-24-28 Shimano HG-50. The slightly narrower 8-speed spacing let me add a 33-tooth dished sprocket which Tom Ritchey used to make -- details at https://sheldonbrown.com/k7.html#897. With a 46T chainwheel, this gives a gear range from 19 to 90 gear inches. It is also possible to use 8 of the 9 sprockets of a 9-speed cassette on a 7-speed body.

The right crank supplied on my bike had fittings for an inner chainwheel so I added a 28T, taking the bottom of the range down to 12 gear inches. This gets me up the longest, steepest grades, spinning at 3 mph. near the limit of where I can maintain balance.My NWT has no bracket for a front derailleur. The bottom gear with the 46T chainwheel is already so low that I rarely need it and shift manually using a stick or a screwdriver on the bottom run of chain, turning the crank backwards.

As I use only the inner one or two sprockets with the small chainwheel, I get by with a derailleur that has a mid-length chain cage and is well clear of the ground. 

An ordinary front derailleur is an odd match to a BF because of the different angle of the chain from the chainwheels to the lower rear hub.Gary Keese, did you do anything special to make yours work?  One possible option which I have not tried is a Type E front derailleur, which attaches to the bottom bracket rather than the seat tube. But it moves the chainwheels outward by a couple of millimeters, leading to other possible compilations.

On 1/23/2025 12:52 PM, John Thurston wrote:

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. 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

-- 
John S. Allen

CyclingSavvy Instructor
League Cycling instructor
Author, Bicycling Street Smarts
Technical Writer and Editor, sheldonbrown.com

[robert clark]

have been happy with the  1 by 14 of the Rohloff hub    in a 20" 

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[robert clark]

16t cog* 53t chainring  even with a 16" wheel 13t cog common 53t chainring is an excellent ratio range,, 

as calculated on the gears part of Sheldon's site John Allen keeps updating...

*default cog  that typically came on the hub, 

 though Bike Friday for the original customer that, i'm told did not like the color , 

has a 15t..   I got a shop-worn  refusenik bike.. from the company..

As my rain bike (disc braked) The linear sequence rotating the shift grip   is the ideal

 while wearing a cycle rain cape draping over the handlebars... 

Rain forecast to return to Pac NW coast  Friday,  so it will be a bit warmer..

[Mahesh]

For the existing pocket llama with 3x8, is it possible to upgrade it to a larger cogset (3x9 with better derailleur like shimano XT or the likes)?
My LBS told me that it is not possible due to the hub cog space.
So a new hub maybe?

[John Thurston]

If you have an 8-speed Shimano-compatible freehub on your wheel, then you can natively fit cassettes for:

• Shimano 9-speed
• Shimano 10-speed
• Some Shimano 11-speed

 The derailleur you need will be dictated by the shift levers you have, the number cogs in the cassette, the size of the large and small cogs, and the total amount of chain it needs to be able to absorb. The derailleur choice will be limited by the ground clearance of the cage.

It is a dance of variables. Use too large a cog, or too long a cage (to absorb a lot of chain) and you can place the lower end of the cage with striking distance of the road. Too short a cage, and you will risk slack-chain, or a broken derailleur when you try to shift into a large/large combination.

Those cassettes above *will* fit on your wheel . . but can you then perform the dance and find the chain-length and derailleur combination which will let you shift across it?

I have re-geared my Llama several times. Each has required much staring at the bike, studying the product specifications, and purchasing products to trial-fit.

-- 
John Thurston
Juneau, Alaska

[robert clark]

adding more in the middle ?   over all ratio range ...  small & big cog un changed?  

To view this discussion visit https://groups.google.com/a/bikefriday.com/d/msgid/yak/4baca5be-dd24-454a-afb6-112698da8a2a%40thurstons.us.

[Geof Gee]

On Thu, Jan 23, 2025 at 12:53 PM John Thurston <y...@thurstons.us> wrote:

 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%

Regarding the 1x11 gearing ... to get a wider range without even larger cogs in the rear is why there are cassettes with 9 and 10 teeth.  You pay through the nose for them and you need to build another wheel with the XD body; but you get the convenience of > 400% wide gearing on a single chainring.  

[robert clark]

Rohloff advantage just 1 cog  to replace * chain tensioner cage is  short ..  

1st an 0.279:1 reduction  11th 1:1 14th 1: 1.467... 

* Priced the replacement 10-40 cassette? 

  & how close to the dirt the long cage derailleur bottom, chain slack take up pulley, has to be?

the 3 speed + cassette hubs now a Sturmey archer product  can take 10 cog cassettes 

in 3rd the 12t acts like a 9t , ratio wise

[John Thurston]

I have done this on another small-wheeler (not a Friday, so probably off-topic here) using a cassette/hub/freehub which is xDR-compatible. From my perspective, everything about this solution was expensive, but it worked well for the bike in question and I was able to allocate the required money to the project.

If you choose to go down this path, study the available cassettes carefully. Many of them have massive large-cogs, to provide hill-climbing gears for big-wheel bikes. We don't need those on our small-wheel bikes, and the huge cogs will tend to force the derailleur closer to road. So shop carefully, and use that gear-calculator.

3T used to make an awesome 360% cassette. It is discontinued, but if you find a good example on flea-bay, and you are willing to build an xDR wheel, consider grabbing it. It was 9-10-11-12-13-15-17-19-22-26-32, so didn't require a long-cage derailleur. With a 46t chainring, it would deliver 28->99 gear-inches, or drop to a 44t for 26->95 gear-inches.

-- 
John Thurston
Juneau, Alaska

[robert clark]

Maybe an option opted from the MTB world ...  a front derailleur mount, held on 

 by the outside flange of the  BB fixed cup, or the cartridge BB  that shimano made so common.. 

There is another sector  where the frame does not have a seat tube in the typical angle ..

Brompton another ..  it has a seat tube but is not angled from the BB axis 

instead it passed the seatpost past , behind the BB shell ,

so fitting a front derailleur takes a different sort of adaptation.....

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[Dirk Bolle]

I’d just go with a wide 8-9 speed (no front  derellieur) drivetrain. Dual drive is a heavy pita, IMO. Not a setup for a regular user, or one without a LBS that’s not familiar. A Shimano 11speed Aldine is an option. But, again, a specialized item. 

Sent from my iPhone

On Jan 30, 2025, at 1:38 PM, robert clark <ro3ert...@gmail.com> wrote:



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