Bromption 6 speed gear mods?

Discussion in 'Folding Bikes' started by ukoldschool, 14 Sep 2018.

  1. ukoldschool

    ukoldschool Active Member

    Hi all,

    Have been riding my brompton on the commute now for a month or so, and now that I've finally sorted my seat position to give me full leg extension, I'm left wondering if there are any mods I can do to make my gears a bit more useable? On my commute I generally dont ever use 1st and rarely use 6th. I set off in 3rd and use 4th most of the time, only using 2nd for a hill (and using 6th for a short burst on the way down the other side).

    Please forgive my brain as it cannot seem to fathom gear inches and I still cant work out if a 'low' gear is 1st or 6th and talk of that nature :laugh::laugh:, but is there anything I can do to give me a slightly better range (as I dont really use the 1st gear) by changing the front sprocket or similar?

    Thanks!
     
  2. Kell

    Kell Senior Member

    There are recognised methods that will change the gearing which all essentially involve either changing the front chain ring or the rear sprockets.

    You don't say which version of the 6-speed you have - standard (50 tooth), -12% (44 tooth) or +8% (54 tooth).

    But if you're on the standard chainring, going either way will solve one problem and give you another. i.e. If you get a smaller chainring, then you may find 6th more usable, but then you'll end up (possibly) with 1 and 2 being of no use. And if you get a bigger chainring then 1st may be more usable, but 5th and 6th might then be too high.

    While you say you don't understand gear inches, this table is a useful comparison. i.e. - you can look at which version you have now and see the figures for your gearing and work out how this would compare if you were to swap them out.

    23509505_10154843934676021_3444676570194450348_o.jpg

    It is also possible to swap the rear sprockets. The standard 6-speed parts are 16T/13T but it's possible to fit a 2-speed set which is 16T/12T. But this will only succeed in giving you higher gears in 2nd, 4th and 6th. I did this once and all I found was that it made 4th gear and 5th gear quite close.

    However, it might be an option if you were to reduce the chainring size and also reduce the smallest chainring so that 6th is still usable.

    (Does that make ANY sense?)
     
    tds101, the_mikey and ukoldschool like this.
  3. Kell

    Kell Senior Member

    PS - if you really want to spend some money, you can think about a conversion to a Shimano Alfine hub or even a Rohloff - but then you're talking massive amounts of money.

    The above is achievable with a £25 chainring.
     
    ukoldschool likes this.
  4. OP
    OP
    ukoldschool

    ukoldschool Active Member

    Hi Kell,

    Thank you for the reply. Mine is a standard 50 tooth so as you say no easy fix for both 'ends' of my issue :smile:

    I wonder if there is a way to try and replicate the box you have shown with the following scenarios by way of a comparison (probably need somebody with a brain, which is where I bow out :smile: :smile:)

    Front hub 44t, rear hub 16t/12t
    &
    Front hub 54t, rear hub 16t/12t?
     
    Lonestar likes this.
  5. 12boy

    12boy Senior Member

    Location:
    Casper WY USA
    Here is a slightly different approach....try Sheldon Browns gear inch calculator and specify gear inches instead of gain ratios. Use whatever you have been riding previously ( a 700c bike?) And jot down or printout the gear inches you get. Then use the calculator to derive the various ratios you would get with your Brompton. I would think there is a little difference between 700c bikes and 16 inchers in that its easier to ride with 88 gear inches on level ground on my 700 c Holdsworth than the Brompton, but you will have a pretty good idea from this what a given gear inch is like. By relating gear inches to what you are already used to you figure out what works best for your locale and style.
     
  6. raleighnut

    raleighnut Guru

    Location:
    On 3 Wheels
    I rarely use the extreme gears on any of my bikes, it's nice to have them though.
     
    simon.r likes this.
  7. simon.r

    simon.r Person

    Location:
    Nottingham
    Agreed.

    I’m exactly the same. The vast majority of my Brompton riding is done in gears 3,4 or 5. Occasionally I’ll use gear 2, even less often gear 1 or 6.

    But isn’t that the point of having a wide spread of gears? That the extremes are there when you need them.
     
    stoatsngroats and raleighnut like this.
  8. Kell

    Kell Senior Member

    Going from the Sheldon Brown Calculator I *THINK* you'd get the following: for 44 tooth/12/16.

    1st - 28.2, 2nd - 37.6, 3rd - 44.2, 4th - 58.9, 5th - 69.3, 6th - 92.4

    Although, that can't be right as there should be no difference between the -12% option in the table above for gears 1,3 and 5 so I obviously put in an incorrect figure somewhere.

    Try it for yourself:

    https://www.sheldonbrown.com/gear-calc.html

    For me, weirdly, I use 1, 4, 5 and 6. 4th for setting off, 5th for most riding, 6th from about 17mph and up (and for downhills). Plus, I live in High Wycombe and have a 12% gradient hill straight out of the station on my way home. 2 and 3 rarely get used.
     
    ukoldschool likes this.
  9. OP
    OP
    ukoldschool

    ukoldschool Active Member

    Yeah... that isnt really going to help but just in case its 44/17 thanks :laugh::laugh::laugh:

    3110204305_eb6133fe4a_o.jpg
     
  10. OP
    OP
    ukoldschool

    ukoldschool Active Member

    Thank you. I know that hill well as I used to work at the hospital, you clearly have a better developed set of legs than I do ;)
     
  11. Joe Brom

    Joe Brom Regular

    Most people who make a change do it to get a gear they're missing. You're using 5 of 6 with one low one left as a bailout..that sounds ideal to me.
     
  12. Mrklaw

    Mrklaw Active Member

    if you set off in 3rd and cruise in 4th, what will you achieve by fiddling with it? You already aren't using 1-2 or 5-6 much so just ignore them. I'm mostly using 3&4 like you, and I like how it means I only need the left hand to change gears - no double shifting. Occasionally on a steep hill I'll change down to 2nd but thats rare and only for a short time. 5th I could use but in London I'm at a traffic light by the time I can think about it, and at the home side of the journey I'm not yet comfortable enough at that kind of speed - maybe later.
     
    ukoldschool likes this.
  13. OP
    OP
    ukoldschool

    ukoldschool Active Member

    fair points :smile:

    I guess some of it is a bit of an obsession with 'fiddling about' (not in an evil uncle Ernie way...)
     
  14. Mrklaw

    Mrklaw Active Member

    oh it seriously is. If you so much as mention you're thinking of buying a Brompton there will be gear inch charts posted within seconds :P
     
    ukoldschool and simon.r like this.
  15. TheDoctor

    TheDoctor Exterminate Christmas! Moderator

    Location:
    Stevenage
    If top is too high, and bottom is too low, then there's actually nothing you can do.
    For what it's worth, mostly I just use 3rd and 4th on mine. I needed all six when I toured Provence.
     
    ukoldschool and raleighnut like this.
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