# Brompton 3-speed hub internals



## Oren_Hershco (11 Jun 2019)

Hi,

I have a Brompton 6-speed. I really don't like the awkward gear arrangement, so I thought about "downgrading" it to 3-speed.

The question: can I just replace the BWR hub internals with BSR hub internals? Will the mechanism just slip in, so I don't need a complete new wheel? (I know, I also need a cog)

Here is the part: https://www.sjscycles.co.uk/hub-spares/sturmey-archer-aw-3-speed-nig-internal-148-mm-hsx144/


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## alicat (11 Jun 2019)

I don't understand the question. A Brompton 6-speed is just a Brompton 3-speed hub with a rear derailleur and a two-sprocket cassette. So if you don't like the awkward gear shift and just want three speed, then just undo the rear gear cable.


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## cisamcgu (11 Jun 2019)

Isn't the BWR 3 speed anyway, and it is th two rear sprockets that make the 3 into a 6 ?

AT least that is what mine looks like


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## Oren_Hershco (11 Jun 2019)

The BWR is indeed a 3-speed hub, but it has HUGE gaps between the gears. For example, when you outspin the 1st, you'll still find 2nd too hard to push. It's very unpleasent to ride this arrangement. I can live with the reduced range of the BSR hub, while enjoying normal gaps between the gears.


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## cisamcgu (11 Jun 2019)

Ah, I see - then sorry - I have no idea if you can simply swap one for the other


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## Cycleops (11 Jun 2019)

If you don't like the existing BWR hub it is possible to fit others:
https://www.bromptongeek.com/index.php/2017/09/29/which-8-speed-hub-is-best-for-my-brompton/


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## berlinonaut (11 Jun 2019)

Oren_Hershco said:


> The question: can I just replace the BWR hub internals with BSR hub internals? Will the mechanism just slip in, so I don't need a complete new wheel? (I know, I also need a cog)



No, this won't work. You can however respoke the wheel with a 3-speed BSR hub.


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## Oren_Hershco (11 Jun 2019)

Thanks, I just got the same respone from SJS cycles. 

I won't go into re-building the wheel, because 3-speed wheelsets are available for about 160f, including VAT:

https://www.sjscycles.co.uk/wheelswheelsets/sjsc-for-brompton-3-speed-super-light-wheel-set-black/


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## Kell (11 Jun 2019)

It's still cheaper to rebuild the wheel.

When my rim spilt, it was about £50 for a new rim and, obviously, rebuild of the wheel.

Certainly cheaper than a new wheelset.

As for the hub gears, I believe that a standard six speed has one more gear over the top and two underneath a standard three speed.



alicat said:


> I don't understand the question. A Brompton 6-speed is just a Brompton 3-speed hub with a rear derailleur and a two-sprocket cassette. So if you don't like the awkward gear shift and just want three speed, then just undo the rear gear cable.



6-speeds use a 3-gear hub, but it's different to 3-gear hub the 3-speed uses. The ratio of the gears are further apart to allow for two gears in each hub position. That's why it's called a BWR - Brompton Wide Ratio.


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## TheDoctor (17 Jun 2019)

I suspect that if you bought a three speed back wheel and standard chain tensioner, then Ebayed the BWR back wheel, rear mech and lever, you may well make money on the deal!


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## mitchibob (25 Jun 2019)

Depending on whether the gradients where you ride allow, turning into a two speed is way cheaper, along with better power delivery, plus is lighter to carry folded (or when doing Urban Hill Climb). There is a little more choice in what size sprockets you can have with the two speed.

Certainly, for most riding in London, I thought the two gears were enough, and it was only when I ventured out of London that I realised that I really wanted more gears. The two speed is definitely more efficient and direct, plus way lighter and cheaper. Then just save the 6 speed wheel for when you really need it, or as others have said, flog it on ebay if in good condition.


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## kais01 (26 Jun 2019)

the sa5 has similar dimensions as the bwr. maybe even internally.

regardless, if you replace the bwr with an sa5, you get 5 tighter and sequential gears for daily use, and can keep the high/low arrangement for those hilly areas only.

so "10" gears. there are kits to be had at ebay. a good bicycle mechanic can help you respoke a wheel in easily under one hour.

the sa5 has one definite advantage over hubs with more gears; it uses just one planetary gear at the time, keeping drag to a minimum. this is an issue with all >5 multihub gears where you have to crank two (sometimes even a totally forbidding three) planetary gears in series. gives a feeling of pedalling your bike in wet gravel even on tarmac.

this problem is even more aggravated with bromptons because of the higher rotational speed of the small wheels.


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## TheDoctor (26 Jun 2019)

Of course, the easiest option might be to just Ebay the Brommie you have, then buy the Brommie you want...


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## steveindenmark (30 Jun 2019)

How is the 6 speed awkward?

Once you have used it a while its simple.


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## TheDoctor (30 Jun 2019)

I can kinda see the OP's point. I have an M6R, and a while back I worked out that if I fitted a 44T chainring, I'd lose the top gear, which I never need and hardly ever use, and gain an extra lower gear, which could come in handy.
All good, right? Wrong.
It meant that my two most commonly used gears were a double-shift away from each other, and I didn't like it.
If the OP doesn't like the 6 speed system, that's a perfectly good reason to get rid, IMHO.


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## Kell (1 Jul 2019)

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.


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## rogerzilla (20 Jul 2019)

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.


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## 12boy (21 Jul 2019)

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.


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## berlinonaut (22 Jul 2019)

12boy said:


> 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.


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## 12boy (22 Jul 2019)

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.


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## berlinonaut (23 Jul 2019)

12boy said:


> 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.


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## u_i (23 Jul 2019)

12boy said:


> 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.


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## u_i (23 Jul 2019)

berlinonaut said:


> 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.


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## berlinonaut (23 Jul 2019)

u_i said:


> 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.


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## u_i (23 Jul 2019)

berlinonaut said:


> 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.


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## berlinonaut (23 Jul 2019)

u_i said:


> 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.


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## u_i (23 Jul 2019)

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.


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## berlinonaut (23 Jul 2019)

u_i said:


> 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.


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## u_i (23 Jul 2019)

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.


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## berlinonaut (23 Jul 2019)

u_i said:


> 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.


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## kais01 (29 Jul 2019)

there are many ways to rome, but if you are willing to put in some uncompromising effort a serious multigear bike for do it all street use should in my preferance have about 30 gear inches on the lowest and over 100 on the highest.

and not more than 18 percent between gears over 70, no more than 10 percent over 100.

for decent wear and efficiency no less than 12t sprocket on the rear wheel, and max one planetary gear in the driveline.

thats the wish list, and i have fullfilled it on one of my bromptons.

have fitted it with a 2x10 dura ace/shlumpf speed drive 30-120 gear inches. 12 percent max step between gears. needless to say its a highly competent blast.

with less gears you have to compromise, nothing wrong with that.

a drastic example is my 2speed brommie commuter where i have done away with all low gears and have only 71 and 95 on hand. like having only gear 4 and 5,5 on a bwr 6sp, or 2,5 and 3,5 on a 3sp. nothing for hilly areas, but the greatest fun elsewhere.

then the surprice; almost as fast as the 20sp on longer distances in reasonably flat landscapes.


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## Kell (31 Jul 2019)

kais01 said:


> then the surprice; almost as fast as the 20sp on longer distances in reasonably flat landscapes.



it shouldn't really be a surprise. If the gearing matches the terrain, then you could do it with just one.


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## kais01 (31 Jul 2019)

absolutely Kell. and the hour record is witheld with just one gear. 

but i am with this minimalistic approach really glad to have a second gear for going on and about. and with brompton and its chain tensioner/derailer its more or less built in. 

and also glad for the 2x10. it is of course the better more versatile bike. 

and is easier on the knees


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## 12boy (1 Aug 2019)

kais01 said:


> there are many ways to rome, but if you are willing to put in some uncompromising effort a serious multigear bike for do it all street use should in my preferance have about 30 gear inches on the lowest and over 100 on the highest.
> 
> and not more than 18 percent between gears over 70, no more than 10 percent over 100.
> 
> ...



How did you manage 95 gear inches on a 2 speed?


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## kais01 (3 Aug 2019)

like this

the lower gear is around what most single speeders have to barely make it up the hills, but then on this there is one more to go

climbing is also made easier by the spd pedals, regularly pull the pedals then, rather than mush my knees.


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## 12boy (3 Aug 2019)

What is that chain ring? Huge! Do you have any folding issues? I have 58/ 38 chain rings and 12/17 sprockets which with the 38 allows for some hills. No front derailleur, just the greasy finger shift, which isn't too much trouble since I don't need the lowest gears often.


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## kais01 (3 Aug 2019)

its a gebhardt.cz 69t. they can make any size up to 75t, and with any bcd. 

no problem with fold, but you have to do away with the hook at the left of the front hub, and replace with older style s1e hook that mounts on the fork. there is a small pipe brace-on there for that purpose. such a hook catches the chain and not the chainstay. i chose to make a hook myself from a piece of wire.

upper limit i believe would be about 72t. with original hub hook in place i have previously used 61t, but one or two more teeth could work.


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## the_mikey (4 Aug 2019)

Also consider changing the front chainring from a 50T to a 44T, this will also need a new chain but it brings those gear ratios down to something easier to turn, I generally dont have trouble with the standard 6S arrangement except for the very top gear, which is just hard to turn in most circumstances.

EDIT: this has already been mentioned! (I've read the whole thread now)


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## Oren_Hershco (15 Sep 2019)

Update:

Eventually I decided to purchase a 3-speed wheelset, from BrommiePlus (http://www.brommieplus.com/portal_c..._word3=&bool1=&bool2=&search_type=1&up_page=1)

It was very easy to install. I got rid of the two-speed derailleur mechanism.

Front chainring is the original Brompton, I think it's 50t; rear sprocket is 14t. The gears in the system are perfect for my almost-flat 20km commute.

I'm not going to do any hills with this bike, so these 3 gears are enough for me.

I also changed the handlebar to a lower-rise carbon one, and the seatpost to a black alloy one (both from Aliexpress)

Changing the handlebar was the roughest challenge in the process:

a. It didn't quite fit in the Brompton stem... I had to use some violence, which left some visible scars. Everything works, but I wouldn't install that bar again on a brompton.

b. A lower handlebar means you need to re-calculate all the cables lengths. And unlike normal bikes, where only "too-short" is really a problem, on a Brompton there's also "too-long" (because of the fold).

Anyway, the result is almost 1.5kg lighter than the original M6L model! The riding posture is much better now for my needs, and the simple 3-gear system is swift.

I hope I'll be able to post some photos soon.


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## Oren_Hershco (15 Sep 2019)

Photos:












Rear 3 speed hub



__ Oren_Hershco
__ 15 Sep 2019


















Seatpost



__ Oren_Hershco
__ 15 Sep 2019


















Shifter



__ Oren_Hershco
__ 15 Sep 2019


















Bike



__ Oren_Hershco
__ 15 Sep 2019


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