Brompton 3-speed hub internals

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Kell

Veteran
I also went from the standard 50T to a 44T for the hill near me and because 4/5 were my two most commonly used gears - which, as you say, means a double shift between the two.

Now I've found that it means I use 4/5/6 most often as the new ratios don't suit my preferred cadence. So I'm up and down them more than ever.

The problem I have with just 6 gears is that I find I'm never in quite the right gear for the speed I'm travelling. I think moving to a three speed would be even worse.
 

rogerzilla

Legendary Member
If the hubs use the standard A-series shell (not significantly changed since 1936 or so) the internals can be swapped. I have AM internals in AM, AW and SRF3 shells. The left hand ball cup was screwed in on older hubs and the coarseness of the ratchet varies but none of this makes much difference.
 

12boy

Guru
Location
Casper WY USA
The BSR and BSW are about the same weight. Unfortunately it isn't easy to put 2 sprockets on a BSR. I've tried and there is contact between the chain and the 2 speed chain pusher. So your choices are 2 speed, BSR, 2 speed plus BSW. The 2 speed wheel and shifter are only a little heavier than a single speed. I set up my 2 speed with 12 and 17 sprockets and a 58 tooth chainring, giving me 77 and 54 gear inches respectively. I added a second chain ring with 38 teeth which yields 51 and 36 gear inches. There is a greasy finger shift involved, but in my area there isn't often a need for those lower gears. This whole set up is much lighter than the BSR and provides a wider range. The downside, obviously is the need to stop and shift and that folding the bike on the 38 tooth chain ring throws the chain off the tensioner. You get a good range with 2 chain rings and the BSR, but in your case you would need to buy the BSR wheel and another chain ring. Prior to buying the Brompton I was riding fixed and single speed 700c bikes a lot so one speed bikes are comfortable for me. Having 2 speeds or 3 was kind of luxurious in a way and I found the 2 speed chain pusher pretty nice. If I had to do it all over again I would have gotten the Ti bits and a six speed. Has been fun tinkering with what I do have, a regular Brompton and 2 wheels, a 2 speed and a BSR.
 

berlinonaut

Veteran
Location
Berlin Germany
The BSR and BSW are about the same weight. Unfortunately it isn't easy to put 2 sprockets on a BSR. I've tried and there is contact between the chain and the 2 speed chain pusher.

How did you do it? I'd assume that one could modify a BSR3 using parts from the BWR in very much the same way as the SRF5w in it's 10-speed variant and I would assume this would be a fit on the Brompton. The outcome would be more or less what the SRAM-6-speed used to offer in terms of gear-steps and spread, so for most people this mod would not be worth the effort as the gear range is limited and if you really want it it is probably easier to buy an old SRAM rear wheel cheaply. The SRF5w could however be a interesting alternative that uses just one shifter instead of two.
 

12boy

Guru
Location
Casper WY USA
Poking around a bike coop which sells used parts I found a dished 3 lobe 18 tooth sprocket that was dished to the hub instead of out. It was just about the same thickness as the plastic dish that sits inside the sprocket. Got the ring clip on ok but it made a clicking noise when pedaled which seemed to be caused by the chain hitting the chain pusher mechanism on top. When I have a bit more time it will be examined more closely. BTW, the standard 6-7-8 speed chain seemed to fit on the sprockets just fine but it's width may be part of my problem.
 

berlinonaut

Veteran
Location
Berlin Germany
Poking around a bike coop which sells used parts I found a dished 3 lobe 18 tooth sprocket that was dished to the hub instead of out. It was just about the same thickness as the plastic dish that sits inside the sprocket. Got the ring clip on ok but it made a clicking noise when pedaled which seemed to be caused by the chain hitting the chain pusher mechanism on top. When I have a bit more time it will be examined more closely. BTW, the standard 6-7-8 speed chain seemed to fit on the sprockets just fine but it's width may be part of my problem.

Ok, so you did not modify the hub but just tried to put 2 sprockets onto it? No wonder that this did not work. Using the driver and some smaller bits of the BWR hub (they are available i.e. at SJS) to modify the hub to two sprockets should work flawlessly, though - as outlined above - I have my doubts about the usefulness, especially when looking at the existing alternatives.
 

u_i

Über Member
Location
Michigan
Unfortunately it isn't easy to put 2 sprockets on a BSR. I've tried and there is contact between the chain and the 2 speed chain pusher.

Do you mean pusher or tensioner arm? In both cases there is some wiggle room for adjustments.
 

u_i

Über Member
Location
Michigan
The outcome would be more or less what the SRAM-6-speed used to offer in terms of gear-steps and spread, so for most people this mod would not be worth the effort as the gear range is limited and if you really want it it is probably easier to buy an old SRAM rear wheel cheaply. The SRF5w could however be a interesting alternative that uses just one shifter instead of two.

Closely spaced gears from the rear might be useful if one wanted to combine them with a front derailleur that would be taking care of the range. When using a front derailleur I find the range of BWR a bit of a handicap rather than value.
 

berlinonaut

Veteran
Location
Berlin Germany
Closely spaced gears from the rear might be useful if one wanted to combine them with a front derailleur that would be taking care of the range. When using a front derailleur I find the range of BWR a bit of a handicap rather than value.

I'd say the opposite is the case. If you combine a BWR with stock 13/16-44 with a second chainwheel with 39t you'll end up with a wider gear range and nice, small gear steps. If you would do the same with a stock BSR in the setup the former SRAM 6-speed had (13/15-50) combined with a 39 you end up with some pretty useless 4% gear steps. If you go i.e. for 13/16 instead of 13/15 or for a 44t chainwheel instead of 50 it get's even worse. Play around yourself:
http://ritzelrechner.de/?GR=BBWR&KB...lopment&GR2=SAAW&KB2=39,50&RZ2=13,15&UF2=1330

Where the former SRAM 6-speed (and a potential BSR-based 6-speed) shines is in combination with a Schlumpf Mountain drive. (Look here: http://xldev.co.uk/bgc.html) This offers a huge range as well as nice gear steps for the price of money and weight - possibly that's why this combo was relatively popular with touring people before the BWR got invented in 2009. But this is not achievable with a second chain wheel.
 

u_i

Über Member
Location
Michigan
I'd say the opposite is the case.

Well I cannot find a good calculator for this, so will discuss it coarsely. I consider the situation of a triple derailleur in the front with 50/20 =2.5 ring size ratio. To have no gear overlap due to the gears in rear, their highest to lowest gear ratio should no exceed sqrt(2.5)=1.58. BSR gives 1.33/.75=1.77, i.e. some overlap, and BWR gives 1.57/.64=2.45 way too much overlap. 2 or 3 sprockets add to the gear ratio for the rear, increasing overlap, which is good when there is little and bad if it is already too much. When you have a lot of span from the front, it is better to have it narrow in the rear. I suspect that you might have something like that in mind in the context of Schlumpf - I have trouble activating the linked calculator so cannot quite see it.
 

berlinonaut

Veteran
Location
Berlin Germany
I consider the situation of a triple derailleur in the front with 50/20 =2.5 ring size ratio.

That is exactly what the Schlumpf Mountain Drive offers: 1:2,5... Just w/o the hassle of chain slack and finding a Brompton compatible front derailleur that is capable of 30t difference. So regarding the possible goal and gain we seem to be in same boat, just the track to get there differs.
 

u_i

Über Member
Location
Michigan
My front derailleur side is complete, but I could use a smaller rear gear spacing, hence the ruminations. As to Schlumpf, I have some preference for 3 major gear stops rather than 2. Also I had some reservations regarding weight and price - the cheaper licensed drive seems to be limited to a lower ratio. Incidentally I saw on Bromptonauten a discussion of some problems with Schlumpf Drive during a world tour. However, the combination of my knowledge of German and Google Translate was insufficient for getting the details.
 

berlinonaut

Veteran
Location
Berlin Germany
Incidentally I saw on Bromptonauten a discussion of some problems with Schlumpf Drive during a world tour. However, the combination of my knowledge of German and Google Translate was insufficient for getting the details.

Jupp, those guys went out of luck and smashed the chainwheel and it's spider and finally the threads on the Mountain drive. The first case that I've ever heard of. Root cause seems to have been that the drive was installed wrongly by the workshop, with a massively wrong chainline which led to huge forces pulling chainwheel and spider sideways. There was kind of a warning noise before the incident, but the rider ignored it and smashed the drive while mashing heavily on a steep ascent due to the forces that were improperly led onto the chainwheel through the wrong installation.
Seems to be one of a kind, caused by an incompetent mechanic, not a quality or construction flaw of the md.
 

u_i

Über Member
Location
Michigan
Well doing a quick calculation, BSR with 2 sprockets gives no better average gear spacing than BWR with 3, to be worth fighting for. With 2 sprockets, the BSR span of 1.77 is divided into 4 jumps or 1.773^(1/4)=1.154 or 15% increments. With 3 sprockets, the BWR span of 2.45 is divided into 6 jumps or 2.453^(1/6)=1.161 or 16% increments.

OK, I am the going to concentrate now on making sure that my drivetrain works in a reliable long-term predictable manner. There are some small tweaks there that can improve the shifting for an increased cog number and interestingly some small parts towards that goal can be found on the bikegang site - these guys appear to use their bikes and think! In the case of many other designers and aftermarket manufacturers I often get an impression that they only admire but hardly use the bikes in real life.
 

berlinonaut

Veteran
Location
Berlin Germany
Well doing a quick calculation, BSR with 2 sprockets gives no better average gear spacing than BWR with 3, to be worth fighting for. With 2 sprockets, the BSR span of 1.77 is divided into 4 jumps or 1.773^(1/4)=1.154 or 15% increments. With 3 sprockets, the BWR span of 2.45 is divided into 6 jumps or 2.453^(1/6)=1.161 or 16% increments.

There's a reason why personally I am running a BWR converted to 9-speed on my touring Bromton. :tongue:
 
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