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Wondering about Brompton Philosophy

Old 01-05-16, 04:38 AM
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Wondering about Brompton Philosophy

Anyone who really knows...I'm seriously considering a 6 speed Brompton and I'm wondering about the part sprocket and part IH combination. Is there a reason that they don't simply put an all internal hub on the bike? It seems too easy to me so there must be some sort of valid explanation. Thank you.
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Old 01-05-16, 06:25 AM
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The Brompton sub frame (rear triangle) has a spacing of ~120mm which the 3 spd hubs fit in. Other IGHs tend to fit frames with 135 mm spacing although there are owners who have widened the rears of their Brommies and installed 7+ speed hubs but that compromises the bike's folded size to a small degree.

Before deciding on the 6 speed consider that it uses the BWR hub, which is entirely different than the BSR (similar to the AW) used on the 3 speeds, and replacement parts are limited for the BWR yet plentiful for the BSR. Also the jumps between gears on the 6 speed are fairly large, so much so that I personally prefer the route of adding a double chainring crank and front derailleur to my 3 speed that allows for closer gear ratios which are more usable to me.

Stock Brompton gearing:


Double chainring gearing (50/44 X 14):




Just food for thought.
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Old 01-05-16, 07:24 AM
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Originally Posted by MAK
Anyone who really knows...I'm seriously considering a 6 speed Brompton and I'm wondering about the part sprocket and part IH combination. Is there a reason that they don't simply put an all internal hub on the bike? It seems too easy to me so there must be some sort of valid explanation. Thank you.
Because the 6+ speed IGHs are…
  • wider → less compact fold
  • heavier than the derailleur + IGH solution Brompton came up with
  • more expensive.

The left-right shuffle between the two levers is a bit annoying, but until a company comes up with a 6+ IGH that solves the issues above…

Brompton Gear Calculator

Last edited by Winfried; 01-05-16 at 07:35 AM.
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Old 01-05-16, 07:42 AM
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Originally Posted by BassNotBass
The Brompton sub frame (rear triangle) has a spacing of ~120mm which the 3 spd hubs fit in. Other IGHs tend to fit frames with 135 mm spacing although there are owners who have widened the rears of their Brommies and installed 7+ speed hubs but that compromises the bike's folded size to a small degree.
FYI and FWIW: Sturmey-Archer 5- and 8-speed IGHs have been and continue to be available in 120mm OLD models.
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Old 01-05-16, 08:00 AM
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Wow, I must say I am a bit confused. I have totally relied on the Sheldon Brown gear inch calculator and it seems to yield much lower gear inches than that chart or your printout. And with 54/15 regular SA 3 speed:0.75 (Low)1.01.33 (High)[TABLE]
[TR]
[TD][/TD]
[TH="bgcolor: yellow"]54[/TH]
[/TR]
[TR]
[TH="bgcolor: yellow"]14[/TH]
[TH="bgcolor: white"]46.5[/TH]
[/TR]
[/TABLE]
[TABLE]
[TR]
[TD][/TD]
[TH="bgcolor: yellow"]54[/TH]
[/TR]
[TR]
[TH="bgcolor: yellow"]14[/TH]
[TH="bgcolor: white"]62.0[/TH]
[/TR]
[/TABLE]
[TABLE]
[TR]
[TD][/TD]
[TH="bgcolor: yellow"]54[/TH]
[/TR]
[TR]
[TH="bgcolor: yellow"]14[/TH]
[TH="bgcolor: white"]82.6[/TH]
[/TR]
[/TABLE]
[TABLE]
[TR]
[TD][/TD]
[TH="bgcolor: yellow"]54[/TH]
[/TR]
[TR]
[TH="bgcolor: yellow"]12[/TH]
[TH="bgcolor: white"]72.3[/TH]
[/TR]
[/TABLE]
I have found that I can use a 38 chain ring with no adverse effect other than the chain comes off when folding, so I now fold when on the big chainring. This gives the following ratios:0.75 (Low)1.01.33 (High)[TABLE]
[TR]
[TD][/TD]
[TH="bgcolor: yellow"]54[/TH]
[TD="align: center"]42.1 %[/TD]
[TH="bgcolor: yellow"]38[/TH]
[/TR]
[TR]
[TH="bgcolor: yellow"]14[/TH]
[TH="bgcolor: white"]46.5[/TH]
[TD][/TD]
[TH="bgcolor: white"]32.7[/TH]
[/TR]
[/TABLE]
[TABLE]
[TR]
[TD][/TD]
[TH="bgcolor: yellow"]54[/TH]
[TD="align: center"]42.1 %[/TD]
[TH="bgcolor: yellow"]38[/TH]
[/TR]
[TR]
[TH="bgcolor: yellow"]14[/TH]
[TH="bgcolor: white"]62.0[/TH]
[TD][/TD]
[TH="bgcolor: white"]43.6[/TH]
[/TR]
[/TABLE]
[TABLE]
[TR]
[TD][/TD]
[TH="bgcolor: yellow"]54[/TH]
[TD="align: center"]42.1 %[/TD]
[TH="bgcolor: yellow"]38[/TH]
[/TR]
[TR]
[TH="bgcolor: yellow"]14[/TH]
[TH="bgcolor: white"]82.6[/TH]
[TD][/TD]
[TH="bgcolor: white"]58.1[/TH]
[/TR]
[/TABLE]
Anyway I do agree with Bass not Bass this is a pretty good set up with a granny gear type low range. I use a 130 BCD sugino crank and 38 is the lowest I could find that fits, and I shift manually since I normally don't need the 38 chain ring. I just don't get why my numbers vary so much..
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Old 01-05-16, 09:22 AM
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Originally Posted by tcs
FYI and FWIW: Sturmey-Archer 5- and 8-speed IGHs have been and continue to be available in 120mm OLD models.
How are the present SA 5 and 8 speeds? I've heard/read so many horror stories about their poor reliability.

-------Added----------

The 5 speed seems to have too wide a spread of ratios for my liking but the 8 looks decent although 8th gear is a huge jump from 7th.

Last edited by BassNotBass; 01-05-16 at 09:29 AM.
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Old 01-05-16, 10:14 AM
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12boy, my Brompton came with a 50 X 13 so the GI were approx 82.4, 61.8 and 46.4 according to Sheldon's calculator which is close enough to the 3 speed standard numbers in the 'official' gearing chart that I'm sure any variances are due to slightly different interpretations of the 349 wheel's diameter with tires.

Thanks for the tip on the 130 BCD Sugino crank. I've been hunting for one that works since the 5 I have in my parts bin didn't have the correct offset. Do you have a pic of yours so that I have an image to refer to when searching for the Sugino?
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Old 01-05-16, 11:49 AM
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Originally Posted by BassNotBass
How are the present SA 5 and 8 speeds? I've heard/read so many horror stories about their poor reliability.

-------Added----------

The 5 speed seems to have too wide a spread of ratios for my liking but the 8 looks decent although 8th gear is a huge jump from 7th.
the 8 speed weighs almost twice as much as the brompton wide range hub and the smallest cog the 8 speed takes is 20t. plus, from what i've read, it has alignment issues.

i've never really understood the complaints about the brompton 6 speed system. granted, it's the only one i've ever known for the brompton. but, i actually like the way it functions and if you go with 12t and 15t cogs you will get equal spacing of approx. 25% across a 307% range. for me, this is brilliant. i've got a low gear that will handle most bridges and hills and a top gear for bombing down 2nd ave like an escaped mental patient (i am one). i find that all 6 gears are useful whereas with the 8 speed hubs i find that the close ratios (14%) sometimes feel so close as to be redundant and i find myself skipping over gears so that i'm using it like a very heavy wide range 4 speed.


for an even wider range on the BWR hub. 3 speed ti cog cluster 12/15/18.


Last edited by smallwheeler; 01-05-16 at 11:56 AM.
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Old 01-05-16, 11:54 AM
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Originally Posted by 12boy
I use a 130 BCD sugino crank and 38 is the lowest I could find that fits, and I shift manually since I normally don't need the 38 chain ring.
i like this idea (but would never do it personally)

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Old 01-05-16, 12:21 PM
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Originally Posted by smallwheeler
...
That jump between 4th and 5th is what would concern me. For the way I ride it would be ideal to have jumps from about 56 to 66 to 76 gear inches because that's where I spend most of my time. 76 g.i. gets me to a sustainable 20 mph on flatland and a good tuck position, my pointy head and substantial mass gets me above 30 mph downhill. I base this on the fact that I very rarely use anything outside of only three of the eighteen speeds available on my old 80's Nishiki Olympic training bike.

Even if I knew about that ti cog before ordering my Brompton and if it gave me the gearing I'm looking for (which it doesn't appear to be capable of), the $240 US price alone would have been a huge deterrent.

I think I'll just keep looking for a used crank and get the gearing I want for less than $100... because I'm stingy like that.

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Old 01-05-16, 12:23 PM
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Originally Posted by BassNotBass
The Brompton sub frame (rear triangle) has a spacing of ~120mm which the 3 spd hubs fit in.
It's narrower than that ... right? More like 111mm?

I suppose a cm is close enough if you're just trying to say it's freakin' narrow!
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Old 01-05-16, 12:25 PM
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Originally Posted by smallwheeler
i like this idea (but would never do it personally)
That's what I think is a great option... although I think that fitting a derailleur is a good move.
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Old 01-05-16, 12:29 PM
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Originally Posted by invisiblehand
It's narrower than that ... right? More like 111mm?
Sorry, I'm a guy and always round up when it comes to length.
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Old 01-05-16, 12:35 PM
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Originally Posted by smallwheeler
the 8 speed weighs almost twice as much as the brompton wide range hub and the smallest cog the 8 speed takes is 20t. plus, from what i've read, it has alignment issues.

i've never really understood the complaints about the brompton 6 speed system. granted, it's the only one i've ever known for the brompton. but, i actually like the way it functions and if you go with 12t and 15t cogs you will get equal spacing of approx. 25% across a 307% range. for me, this is brilliant. i've got a low gear that will handle most bridges and hills and a top gear for bombing down 2nd ave like an escaped mental patient (i am one). i find that all 6 gears are useful whereas with the 8 speed hubs i find that the close ratios (14%) sometimes feel so close as to be redundant and i find myself skipping over gears so that i'm using it like a very heavy wide range 4 speed.
I'm not a fan of the SA 8 speed hub. It's OK. But clunky enough that I'd deal with the unusual shifting pattern of a Brompton 6 speed.

Jur mentioned an SA 5 in a Brompton. I've heard of it being done but don't recall anything about performance.

A single shifter across say an 8-speed IGH is simpler. Sort of like the movement towards single chainrings with super wide cassettes in the rear.
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Old 01-05-16, 12:39 PM
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For anyone interested in retrofitting a multispeed hub to a brommie, there are two UK shops I know of:

Kinetics ? Recumbents, Folding Bikes, Custom Bicycles | Brompton

About Tiller Cycles

...although the fellow from Tiller Cycles has scaled back quite a bit. If memory serves, he was operating a business from a houseboat and got all kinds of flak from the authorities for doing so.
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Old 01-05-16, 01:52 PM
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Replacing the single chainring with a double chainring is a no-brainer:
Double plateau

Adding a derailleur is more involved, but has been done:
Dérailleur pour un pédalier à double plateau

Pictures and Google Translate are your friends.
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Old 01-05-16, 03:01 PM
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The 5sp hub was an almost drop-in job. It's been a while but as I remember the only thing was that the dust cap didn't fit. I will need to check my wife's Brompton, she has one, I took mine off after I broke a spoke while running a solid tyre.
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Old 01-05-16, 04:15 PM
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The 5 speed Sturmey-Archer hub is strangely spaced, and a nuisance to use. I didn't like it,...but my oldest son LUVS it - because I gave it to him (Schiwnn 411 IG5)!!! LOL!!!
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Old 01-05-16, 05:26 PM
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after careful consideration of all the points of view and information shared in this thread, i just ordered a single speed wheel.

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Old 01-05-16, 05:39 PM
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I think you'll enjoy the rubber band drive.
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Old 01-05-16, 06:23 PM
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I will try to get a picture soon. BTW, being a contrary person, I put my 38 T on the outside and the 54 on the inside. It is a very cheap way to make a two speed and while maybe not as light as a 2 speed hub it is light. I replaced the original BB with a 119 JIS and my chain line seems pretty good. As a matter of fact, tonight with an uphill ride and a 28 mph headwind that 38 was appreciated.
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Old 01-05-16, 07:32 PM
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All I know is that I have a six-speed Brompton and I can NEVER find a gear that works well. It's either too low of a gear, or too high. It feels like I'd have to go the speed of light to use some of the gears, and as slow as molasses to use others. I have to figure out a way to change this.
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Old 01-05-16, 07:47 PM
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5 speed SA is great IMHO. I`ve got an older 5 speed bike (w two cabels) and did not like it since It was a lot of fiddeling to adjust plus the outer chain was exposed when folding so had to remove it when traveling with the bike. My bike did not have the brace on for the rear der so the new 5 speed was an easy and cheap solution to get more than three gears. It is almost same weight as a three speed. Wery happy with it.
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Old 01-05-16, 07:49 PM
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Originally Posted by tds101
The 5 speed Sturmey-Archer hub is strangely spaced, and a nuisance to use. I didn't like it,...but my oldest son LUVS it - because I gave it to him (Schiwnn 411 IG5)!!! LOL!!!
Not sure where you got that from... I got the W (2009-) version, the gears are reasonably evenly spaced, and is not a nuisance to use at all. Mine came with a simple barend style thumb control lever, very simple to use. The only small criticism I have is that the lowest gear does not feel smooth, there is a small amount of brrrrr feeling as the little gears mesh. The other gears are not like that. Mine has the Brompton spline, so the bikes are 10-speed.

I have found that works very well indeed, mostly the standard Brompton shifter is used to switch between 2 gears, when tackling steep uphills, the additional 5-speed lower gears are used, or when going fast downhill, the highest 5-speed gear is used. For most normal riding, the 2 extreme gears are never selected. My wife has not ever mentioned that she finds the combined gear selection complex.

Perhaps yours is an older version?
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Old 01-05-16, 08:48 PM
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Originally Posted by jur
Not sure where you got that from... I got the W (2009-) version, the gears are reasonably evenly spaced, and is not a nuisance to use at all. Mine came with a simple barend style thumb control lever, very simple to use. The only small criticism I have is that the lowest gear does not feel smooth, there is a small amount of brrrrr feeling as the little gears mesh. The other gears are not like that. Mine has the Brompton spline, so the bikes are 10-speed.

I have found that works very well indeed, mostly the standard Brompton shifter is used to switch between 2 gears, when tackling steep uphills, the additional 5-speed lower gears are used, or when going fast downhill, the highest 5-speed gear is used. For most normal riding, the 2 extreme gears are never selected. My wife has not ever mentioned that she finds the combined gear selection complex.

Perhaps yours is an older version?
The problem with the 5 speed on this bike is the first 3 gears are nicely spaced, and the last 2 feel almost identical. And they're just not correctly divided. There's other users of this bike/hub who agree. The 5 speed is the one to avoid. The 8 speed is good though, as I'm deciding if I should use it on my Dahon Speed P8 INSTEAD of the Shimano Nexus hub. The Sturmey-Archer is said to be quite reliable. The Nexus,...seems to depend on the user.
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