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  1. #1
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    Brompton 3 to 6 Speed Conversion

    I'm thinking of having my Brompton converted from 3 speed to 6 speed, and am wondering if anyone else has done that. How much did it cost? Did you do it yourself? How did it work out?

    I understand this conversion is pretty expensive. I've seen kits online sold in England, but none in the United States. Can you get the kit in the US, or source the parts? And how hard is it to do? I think doing the work would be beyond my wrenching skills, but I'm wondering how hard it would be.

    I got my Brompton second hand from a friend, barely used and for a great price, so I can't complain, but I would have chosen a 6 speed (and a different color). Part of me is tempted to get a whole new Brompton just the way I want it; that would be an extravagance, but a tempting one.

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    The cost difference between a 3 spd and 6 spd is less than $100 for a new bike. Contact a shop and see what they would charge to upgrade your 3 to a 6 and figure anything over $100 is $ that would make up part of the difference between what you would sell your bike for and a new one. Some people don't want to wait 2 months for a new one and would like to save some $ on a used one. Maybe you should research used prices and see what you might expect to sell yours for. It may make moving on to a new one reasonable or perhaps the cost difference would stll be more than you are willing to go. Worth looking into.

  3. #3
    coprolite fietsbob's Avatar
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    S-A S-RF5(N) would build up as a single lever 5 speed .. and a 2 lever 10 speed ,

    since it uses the 9 spline driver of the BWR hub they make for Brompton.

    I went with a Schlumpf Swiss Mountain drive Crank, it's 2 speeds are widely spaced so the 3 hub gears are used twice..


    If you want the conversion parts in the US talk to the dealer .. or import them from UK retailer SJS..

  4. #4
    Part-time epistemologist invisiblehand's Avatar
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    Quote Originally Posted by wilfried View Post
    I'm thinking of having my Brompton converted from 3 speed to 6 speed, and am wondering if anyone else has done that. How much did it cost? Did you do it yourself? How did it work out?
    Does the 6 speed conversion work with all of Brompton's three speed hubs?

  5. #5
    coprolite fietsbob's Avatar
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    Now, Its a different.. wider ratio hub BWR.. the successor to the AW3 is the BSR
    the 9 spline driver is another Shimano created standard on the BWR adoptedfrom Shimano's BMX hubs

    the 3 speed uses the 3 spline cog that S-A has almost-always used .. the Mk 3, 6 speed Brompton went to Sachs , in Germany then,

    they used the 3 spline cog type, in 3/32" thickness .. a different driver for their Torpado 3 speed .. to take 2 cogs ..
    the 15t was made as a skip tooth .. 1 in 5 was shorter.. , so the chain would shift over it.

    I use the 15t, alone, all that will fit .. on my M3L


    (edit: N/M)
    Last edited by fietsbob; 05-08-14 at 09:07 AM.

  6. #6
    PatronSaintOfDiscBrakes dynaryder's Avatar
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    Quote Originally Posted by invisiblehand View Post
    Does the 6 speed conversion work with all of Brompton's three speed hubs?
    I'll simplify fietsbob's answer;no.

    The BWR hub used for the 6 speed takes two cogs,the regular BSR hub only takes one. The BWR also has a wider(40% vs 36% IIRC) jump between gears,FYI.

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  7. #7
    coprolite fietsbob's Avatar
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    3 speed , plus, Schlumpf MD crank makes it into a wide spread 6 speed .. it will Climb mountains as if a 50,20t double

    the BWR with 13 & 16t cogs halfsteps the hub 3 ..

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    PatronSaintOfDiscBrakes dynaryder's Avatar
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    ...for only about $700.

    C'dale BBU('05 and '09)/Super Six/Hooligan8and 3,Kona Dew Deluxe,Novara Buzz/Safari,Surly Big Dummy,Marin Pt Reyes,Giant Defy 1,Schwinn DBX SuperSport/Qualifier,Brompton S6L,Dahon Speed Pro TT

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    Quote Originally Posted by DoubleDiamonDog View Post
    The cost difference between a 3 spd and 6 spd is less than $100 for a new bike " .......
    Last year, It cost me around $450 to convert a ? 2005 model to a 6 speed one. The hub gear is not compatible so Bike shop suggested I replace it with a new rear wheel/ gear.

    I suggest you resale the bike and buy a new 6 speed. I find the old 3 speed brompton doesn't have the nice ride as the new 6-speed - too slow for my liking and not good with hills in my area.

  10. #10
    coprolite fietsbob's Avatar
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    if you can spin out a 54:13 in high, you should be moving at a sufficient rate of speed ..

    Ok the BWR will take a 12.. so will the S-A S-RF5(N). which is also using a Narrow, axle, and 28 spoke.

    which has a taller internal 5th gear..

  11. #11
    Part-time epistemologist invisiblehand's Avatar
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    Well the OP might want to check that he has the right type of hub then.

  12. #12
    Senior Member smallwheeler's Avatar
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    Quote Originally Posted by dynaryder View Post
    ...The BWR hub used for the 6 speed takes two cogs...
    or 3 cogs...19t-16t-13t or 18t-15t-12t.. 9 speed brompton...

    for those of you who can't do math, that's a gearing range of over 9000 %!





  13. #13
    coprolite fietsbob's Avatar
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    or stack all that on the S-A S-RF5(N) .. , add a double or triple crank .. really Go Go Gadget !
    Last edited by fietsbob; 05-12-14 at 09:22 AM.

  14. #14
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    Thanks for the input. Word from the bike shop is that parts for the job comes to $363. That plus labor means the cost of conversion will push $600. So it looks like I'm looking at another Brompton. Or possibly another bike of some sort (A Bike Friday? A Turn?).

    Just this weekend, I took the bike out of town and did a hilly ride (a round trip so two in fact). I survived, but I had to walk a couple of short stretches, did some standing on the pedals and pulling on the handlebars, and I cursed my lack of a lower gear. On the other hand, the three speed is good enough, quite nice even, for 90%+ of the riding I do, so there isn't a lot of urgency to upgrade, which means I can dither for a long time. But the itch to get something better is becoming more persistent. The trouble is, I live in a closet of a NYC 5th floor walkup apartment, so the bike has to be a folder.
    Last edited by wilfried; 05-12-14 at 12:42 AM.

  15. #15
    coprolite fietsbob's Avatar
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    My Mountain drive crank gets me an 17" low gear with a 54 /15 BSR .. the reduction gear is as if the crank has a 21.6t granny gear
    when kicked into low range .. Yea it comes in at about $600.

    3rd to 4th double shift is Quick since both gears are internal , at any speed even stopped
    So 4th to 3rd bogged down on a hill is an easy shift..





    There is also the option of fitting a double crankset of conventional type, and use the heel of your shoe to dislodge the chain from it's Big Ring .

    that could be more affordable.. You already have the chain tensioner
    Last edited by fietsbob; 05-12-14 at 09:03 AM.

  16. #16
    coprolite fietsbob's Avatar
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    Quote Originally Posted by smallwheeler View Post
    or 3 cogs...19t-16t-13t or 18t-15t-12t.. 9 speed brompton...

    for those of you who can't do math, that's a gearing range of over 9000 %!






    Actually they (assume you found the picture , not your bike,) fitted that to what was a 2 speed hub so only gained 1 more gear.
    Lower right corner ... it's not the BWR

  17. #17
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    I don't thing a double chain ring is an option, since we're talking mostly rolling hills, short stretches of steep climb followed by downhills or flats. I'd hate to have to get off the bike to switch chain rings on top of every hill.

    Fietsbob, how did you get the third sprocket on the bike? Googling wasn't very effective. Are there instructions somewhere online?

    How hard was it to obtain and install the Mountain Drive?

  18. #18
    coprolite fietsbob's Avatar
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    Cycle Monkey in Berkeley is a US Distributor/retailler , but I expect Nyce wheels in NYC can get them .
    Mine came thru CM Wasson in California..

    there is a lot of torque developed in Low range, but the special model for Bromptons transfers that torque
    thru a lever with a Button that rests on top of the part behind the crank that carries the rear fold pivot ..

    I needed no frame modifications on my Mk4 bike .. the BB is part of the whole crank assembly
    as the shift is a shuttle pin passing thru the BB spindle center . center button is the shift from one side to the other .

    conic rings center the BB assembly in the shell .. it screws into itself not the threads in the BB..


    FWIW there is a 1.6x overdrive version, 'Speed Drive' , when fitted with a 34t chainring , in high range it acts as if you fitted a 54t chainring too.

    It does take a chamfering of the edge of the BB shell*.. there is less torque in the overdrive against the frame , so the friction
    of a gripper washer in aluminum between the frame and the crank is sufficient..

    * not for the first time , Mavic had a BB assembly requiring the bike frame edge be conic rather than flat across the face.

    Brompton already has a BB shell face that is not exactly flat, so the chamfering is not removing much metal.

    and why the fitting of the MD really didn't require, any ..

    Fietsbob, how did you get the third sprocket on the bike?
    its not my bike , I just saw the way it looks .. the Brompton 2 speed is a hub with no internal gears
    so there is a more hourglass shape to it . and a different way the driver is attached to what is a short driver freehub.

    9 spline driver style is shared by the 2 and 6 (IGH 3) but not the BSR/AW3..

    It can be done with 2 thinner spacers and Shimano Cogs .

    there are custom adapters *, by the way to bolt on what is a braze on FD where the seat tube is .
    it is placed behind the Seat tube a ways, since the seat post telescopes down behind the BB..

    * Steve Parry in UK has some ,( a brompton modifier) I got one that the Wasson Shop got made ,
    I Can resell, it .. , a Thumb shifter and a Bz on Ft Derailleur .. makes it work .
    Last edited by fietsbob; 05-12-14 at 10:36 AM.

  19. #19
    Senior Member smallwheeler's Avatar
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    Quote Originally Posted by fietsbob View Post
    Actually they (assume you found the picture , not your bike,) fitted that to what was a 2 speed hub so only gained 1 more gear.
    Lower right corner ... it's not the BWR
    good eye, fietsbob. sorry i forgot to include the link to the website in my original post.

    text from the page:

    "This Ti cassette system will turn your 2 speed into a more versatile 3 speeds and turning a 6 speed BWR driven Brompton into a 9 speed monster.

    The concept is not new (giving the Brompton extra speed), but the idea to make it effectively working for everyday DIY-er’s being able to install this at home without much of the heavy machining and customizing had to be the first.
    The system will come with 3 pieces of Ti cassette sprockets, a Ti replacement tensioner wheel’s roller and a custom made 3 speed shifter that is made out of aluminum alloy.
    There are 2 different speed group that is begin offered. They are the 19T-16T-13T set, which gives a better and easier climbing experience. Where the 18T-15T-12T set offers a faster riding experience.
    Please note that this cassette system requires certain experience with bicycle hardware installation experience. Although we try to make the installation process as easy as possible, gear tuning experience as well as some customizations are still required.
    "





    Last edited by smallwheeler; 05-12-14 at 11:44 AM.

  20. #20
    coprolite fietsbob's Avatar
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    Just normal tempered steel cogs would be fine To My Pragmatic mind .. rather than Titanium ..

    but Bike bling /weight weenieists are more willing to put the $350 out for Ti.
    Last edited by fietsbob; 05-12-14 at 02:26 PM.

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    PatronSaintOfDiscBrakes dynaryder's Avatar
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    Quote Originally Posted by wilfried View Post
    Word from the bike shop is that parts for the job comes to $363. That plus labor means the cost of conversion will push $600. So it looks like I'm looking at another Brompton.

    On the other hand, the three speed is good enough, quite nice even, for 90%+ of the riding I do
    Might want to look into a 5 speed:
    Free Shipping 16 x1 3 8" 349 Light Weight Silver 5 Speed Rear Wheel Brompton | eBay

    Parts swap is something you could do yourself,you'd just want to hit up a local co-op/bike kitchen to get the wheel properly tensioned first. You'd also still have your stock 3spd setup,which you could put on eBay/CL and sell to bring the cost down further.

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  22. #22
    coprolite fietsbob's Avatar
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    FWIW Brompton Uses a much heavier spoke on the rear, to stand up to a commuter beating , 14 gage would be the light gage they use on the front.

  23. #23
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    Quote Originally Posted by fietsbob View Post
    Just normal tempered steel cogs would be fine To My Pragmatic mind .. rather than Titanium ..

    but Bike bling /weight weenieists are more willing to put the $350 out for Ti.
    Right. And how do you replace the cogs when they're worn, and how much will that cost? And you have to have a six speed setup already.

    Quote Originally Posted by dynaryder View Post
    Might want to look into a 5 speed:
    Free Shipping 16 x1 3 8" 349 Light Weight Silver 5 Speed Rear Wheel Brompton | eBay

    Parts swap is something you could do yourself,you'd just want to hit up a local co-op/bike kitchen to get the wheel properly tensioned first. You'd also still have your stock 3spd setup,which you could put on eBay/CL and sell to bring the cost down further.
    This is intriguing. I'm not very hand with bike wrenching, but I'm learning. I do have access to a helpful friend, and a bike coop, and I know in theory how to tension and true a wheel. How hard would this be to install? It says it takes 32-349 tires. The Schwalbe Marathon I have now is 37-349 (but the Schwalbe website says 35-349? What gives?). Will it fit? I'm a little leery of this non-standard configuration, but maybe I shouldn't be. Is there a downside?

  24. #24
    Part-time epistemologist invisiblehand's Avatar
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    Quote Originally Posted by wilfried View Post
    But the itch to get something better is becoming more persistent. The trouble is, I live in a closet of a NYC 5th floor walkup apartment, so the bike has to be a folder.
    The start of bike-itis. Find a way to fit two bikes in that closet!

  25. #25
    coprolite fietsbob's Avatar
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    The 2/single speed 1 or 2 cog hub is already a weight choice, so I suppose the derailleur 3rd cog follows on that line..

    suppose next they have to create a way to use the rightLever, for the IGH detents indexing the pulley pusher.

    since the either or left shifter doesn't need a 3rd positon..


    I think the 349 'kojak' is a 32 .. and the 5 speed hub is in 28 spoke, and same hub shell diameter to use the stock Brompton rim and spoke.

    just that vendor aimed at the customer wanting the racier options.

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