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  1. #1
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    Brompton 6 speed questions

    I've read mixed views on the dual-shifter Brompton system, some people claim it becomes entirely automatic in use whilst others say there are both mechanical and utility issues. I've heard mention of the chain tensioner jamming up and not shifting cleanly.

    For those who claim it becomes second-nature, is this always the case or are there moments when you end up making the wrong shift because somehow you thought you were in a different gear position? Do you have to consider the shift order or is it a case of flipping both shifters simultaneously? Or perhaps you have to shift up on the hub and take your pressure off the pedals, then shift down the sprocket whilst pedalling etc.? I can imagine that accounting for the shifting characteristics of hub gear and deraileur might be messy.

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    The problem with the Brompton 6 speed is that you have to alternate the shifting between the derailleur and the hub gears to go sequentially from gears 1 to 6. I realize a similar scenario exists in 20 speeds in my road bikes but the big difference is that in the Brompton, gears 1-3-5 (on the big cog) and 2-4-6 (on the small cog) are too widely spaced. In most cases on my short commute this is not a big problem as I usually end up just using 2 gears which are 3 and 4 meaning I mostly shift by changing the derailleur and leave the hub at the middle gear. However on longer rides on various terrain and speeds it can get a bit confusing.

    With a road bike this is rarely a problem as the gears are closely spaced apart whether you are using the small or the big chainring. I still prefer the 6 speeds despite the un-intuitve shifting because I may end up using the Brompton on longer rides/commutes where the extra gears can come in handy.

    EDIT: I would have preferred a 6 speed hub gear (an 8 speed hub would even be better) as opposed to a hub/derailleur combo but I understand that this would mean more weight and might be too wide (esp. hubs > 6 speeds) to fit the Brompton's frame.
    Last edited by cyclocommuter; 08-05-11 at 12:44 PM.

  3. #3
    Senior Member bhkyte's Avatar
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    Quote Originally Posted by cyclocommuter View Post

    EDIT: I would have preferred a 6 speed hub gear (an 8 speed hub would even be better) as opposed to a hub/derailleur combo but I understand that this would mean more weight and might be too wide (esp. hubs > 6 speeds) to fit the Brompton's frame.
    Yes, the Brompton rear axle spacing is about 112mm where as a dual drive, or normal drailer(5 to 9 speed) is standard 135mm. You can also consider a front mech with a Steven Perry mount, but it have simular problems to the 6 speed. How do owners find the 5 IGH speed over the 6 (IGH 3X2)?
    Dual drive Mezzo (GOLD), Dual Drive Mezzo with bullbars (black), White Brompton thingy with Dahon Androes stem and bull bars. Birdie (old sytle) 7 speed. Downtube NS8. Birdie red.

  4. #4
    coprolite fietsbob's Avatar
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    My 6 speed : a wide range AW3 + a Mountain drive crank 2 speed crankset.
    both are planetary gears, so a quick shift , whether moving or not.

    2.5 reduction gear , heel button, center cap, and trigger shift ..
    Low range crank reduction gear, high gear in the hub, is the next lower gear ,
    below low gear in the hub, direct drive in the crank.

    Still .. have a SP type FD mount in the US, I'm not going to use >> PM?
    Last edited by fietsbob; 08-11-11 at 10:35 AM.

  5. #5
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    Quote Originally Posted by cyclocommuter View Post
    The problem with the Brompton 6 speed is that you have to alternate the shifting between the derailleur and the hub gears to go sequentially from gears 1 to 6. I realize a similar scenario exists in 20 speeds in my road bikes but the big difference is that in the Brompton, gears 1-3-5 (on the big cog) and 2-4-6 (on the small cog) are too widely spaced. In most cases on my short commute this is not a big problem as I usually end up just using 2 gears which are 3 and 4 meaning I mostly shift by changing the derailleur and leave the hub at the middle gear. However on longer rides on various terrain and speeds it can get a bit confusing.
    That's pretty much what I imagined. It seems that you need a kind of systematic way to conceptualise what gear you're in and what gears are readily available from that position. I could imagine starting off from traffic lights in gear 1 and then moving straight to 3 to cruise in 3 and 4. . . that sort of thing.

    The reason why I'm interested in this is that I'm not yet happy with the performance of the X-RF5 that I installed on my Brompton. I currently have 3 instances of this hub and I know the peculiarities of it quite well. . . but I still haven't fully mastered it yet. It's strangely temperamental and not particularly efficient. I've been quite happy with in on my Dahon but I've found that combined with the Brompton chain tensioner the total inefficiency is a dissatisfying. The overall feeling is quite grindy. I've already swapped out the jockey wheels for sealed bearing types to mitigate friction in that area and I'm going to have to experiment with chain lubes a bit to try to get the best out of my chain. . . and I guess I'd better open up the hub yet again and make sure it's all greased and adjusted optimally.
    But it's struck me that the chain tensioner does decrease efficiency a fair bit and for that reason it makes sense to utilise a 3 speed IGH as the 6 speed Bromptons do.

  6. #6
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    Are the gear jumps in the wide range 6 speeds 25%? I.e. the hub is 50%, 100%, 150%?

    I think I'd prefer the old system, a 215% gear range is fine for my needs.

    Was the SRAM hub a special Brompton version or was it a typical T3, i.e. can the T3 accomodate a double sprocket?

  7. #7
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    On 2 gear levers:

    When I first got my old Brompton, it had the 5 speed speed hub with the two shifters (a similar setup as the current six-speeds, but all in one hub). I have to say, I didn't have any trouble adjusting to the shifting pattern. It became automatic after a day or so.

  8. #8
    Senior Member snafu21's Avatar
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    I solved all my Brompton problems by putting mine on Ebay. I realise this may not be preferable for some. :-)
    Last edited by snafu21; 05-24-14 at 09:45 AM.

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    Quote Originally Posted by bendembroski View Post
    When I first got my old Brompton, it had the 5 speed speed hub with the two shifters (a similar setup as the current six-speeds, but all in one hub). I have to say, I didn't have any trouble adjusting to the shifting pattern. It became automatic after a day or so.
    I guess the hub would shift more immediately than a sprocket.

  10. #10
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    Shortening the chain would straighten the path of the chain when unfolded, or so it seems. It it possible to adjust the spring tension in the tensioner?

  11. #11
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    BWR L = 0.64, H = 1.57 ... BSR/ AW3 L = 0.75, H = 1.33

    SRAM uses a 0.73, and 1.36 in the 3 speed part of their dual drive..
    might be the internals on hubs sold in Mk 3 .. 3 by 2 hubs

    {edited version of IGH math engine : http://sheldonbrown.com/gears/index.html
    Last edited by fietsbob; 08-11-11 at 10:38 AM.

  12. #12
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    I've had occasional moments when my drivetrain has been perfectly smooth and it's only lasted an hour or so and I've no idea why. Times when I've assumed it was down to chain lube it wasn't repeated on re-lubing. It's really annoying as there are so many areas to troubleshoot. . . I'll most likely strip the hub this weekend and examine it closely. I may have over-tightened the drive side cone a bit, plus there's a lot of friction with the dust cap rubbing against the hub shell. . . not sure what I can do about that.

    Looking at the chain tensioner jockey wheels, this does seem to be a source of a fair amount of friction. There's quite a bit of work being done as the chain engages/disengages with the teeth.

    I've just put on a new chain and that's not made any difference.

  13. #13
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    OK, I have the bike upside-down and I'm moving the pedals forward. If I press on the tensioner arm to create slack in the chain efficiency is improved massively (very much audibly). I'm not sure what conclusions to draw from this, I mean, obviously if you have a chain too tight on an IGH bike it'll grind. . . but in this instance tautness is created through the strength of the spring in the tensioner, i.e. there's elasticity in the system. Pressing the tensioner arm down (with bike upside-down) straightens the path of the chain a little which must also have some effect. So which would improve efficiency more: shortening the chain to move the tensioner arm to the position it's in when I depress it, or decreasing the strength of the spring in the tensioner arm to allow more elasticity in the system?

  14. #14
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    I've checked my chain tensioner (from Mark 3 model) and there's no spring adjustability, there's only one position it can sit in. I wonder if this has been changed since?

  15. #15
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    I'm going to try shortening the chain today but I doubt this'll improve things much, it may make it worse as it'll increase spring tension. I've noticed looking at images of Bromptons with different gearing configurations that the tensioner arm rests in quite different positions.

  16. #16
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    Actually the jockey wheel nearest the sprocket is kinda unnecessary, it's function is to make the chain travel enough distance when folded. It'd be preferable if it disengaged with the chain when unfolded. . . it might be possible to remove it and have something else in it's place for the chain to wrap around when folded, the type of un-toothed guide pulley wheel that some tensioners use.

  17. #17
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    Further examination highlights the fact that excessive tension makes it hard for the chain to disengage with sprocket / jockey wheel teeth as it passes them, or more exactly increases the friction between chain and wheel and force necessary to disengage them.

  18. #18
    coprolite fietsbob's Avatar
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    Actually the jockey wheel nearest the sprocket is kinda unnecessary, it's function is to make the chain travel enough distance when folded.
    [this confirmed by the company itself?, can you quote that footnote?]

    seems like you can leave it off and run a test of this theory.

    Brompton's 2 speed shifter pushes the flanges of their pulley assembly, does it not?
    by the upper pulley .. lower one just follows it sideways.


    Differing Opinion : presses the chain close enough onto the cog
    so it won't come off and/ or, skip.
    and control the chain better for shifting quicker ..

    long time ago derailleur schemes
    adopted the 2 pulley mech ..

    and shifting get a skosh sluggish on the small cogs,
    when you crank in the B screw to clear a big low gear cog

    a nylon -sealed bearing pulley may me a substitution to try
    10 tooth will probably clear my 15t cog better than an 11.

    Only have a 3 speed, I could cannibalize the Carmichael Ti pulley pair
    off my touring bike.
    though metal derailleur pulleys do make their presence heard.
    Last edited by fietsbob; 08-12-11 at 10:37 AM.

  19. #19
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    I meant with regards to the 3-speed setup.

  20. #20
    coprolite fietsbob's Avatar
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    I meant with regards to the 3-speed setup.
    EZ to unscrew and take the fixed pulley off the chain tensioner
    and give it a test , for a while , then ..

    give it a go.

  21. #21
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    Turns out there wasn't enough clearance to shorten the chain, thought there would be but nope. So instead I've added two links to see how it runs with a little less tension.

    No difference apparently.

    Guess there's not much else to do but service the hub.
    Last edited by chagzuki; 08-12-11 at 05:08 PM.

  22. #22
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    Quote Originally Posted by fietsbob View Post
    EZ to unscrew and take the fixed pulley off the chain tensioner
    and give it a test , for a while , then ..

    give it a go.
    I just did and it didn't make any clear difference in terms of friction which leads me to think it's the strength of the torsion spring that's the main factor. It also made it easy for me to disengage the tensioner and A/B the difference, as it turns out the hub gear is responsible for a lot of the friction, perhaps 65%, but the tensioner adds a significant amount on top. If I can't get better performance out of the X-RF5 I'll have to give up on that hub. I don't want to go back to an AW type though. . . I think I'd prefer an AM as it's the middle gears on the 5 speed that get most of the use. Perhaps the Brompton 6 speed system would be the best solution for me, or like Snafu perhaps the Brompton isn't going to be a keeper.

  23. #23
    coprolite fietsbob's Avatar
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    Ok so this is about something other than the BWR hub and the 13/15 cog set?

    How about a Bike Friday with a Rohloff ?

    AM, hub was not built in Bromptons , ever, was it?...
    when did they stop/restart making them?

    or the 2 speed no IG hub, and 2 chainings?

    still feel the pea? more mattresses !

  24. #24
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    According to Sheldon the AM hub is rare and I don't see any on ebay so I doubt it'd be an option.

    I think I'll have to test ride a Brompton 6 speed and see what the shifting is like myself.

    I've just modded my chain tensioner by dremeling an extra slot for the torsion spring to fit into, to reduce the spring strength. The chain feels looser, perhaps it'll be too loose. . . seems OK though.

    The X-RF5 hub baffles me, of the 3 I've owned they each feel grindy in different gears, i.e. they have distinct personalities. When I've inspected the internals I can't see any difference at all. Looking at the design it strikes me the hub ought to work way better than it seems to in practice.

  25. #25
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    Just took the hub apart and one of the cones was seriously worn, don't know how I hadn't seen that last time I was messing with it. I swapped it out for one from another hub. Problem is I don't know how to get the dustcovers off either the ball cage or the shell, they seem to be pressed in such that prising them with a flat screwdriver would deform them and a slip would damage something else. . . I need to replace the bearings and check inner surfaces for wear.

    For the time being the hub is back on the bike and I shall have a ride today to see if there's any improvement.

    Edit: yep, some improvement but the grindiness is still there. Maybe oil would be a better lubricant. . .
    Last edited by chagzuki; 08-14-11 at 12:23 PM.

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