Front derailleur on a Bromptopn

Discussion in 'Folding Bikes' started by Kell, 8 May 2019.

  1. Kell

    Kell Über Member

    I was having a chat the other day with one of the guys on my train that has a Birdy Folder.

    I was moaning about climbing the hill out the station and saying I might fit a smaller chainring (which I've done), and he said can't you fit a front derailleur and two chainrings?

    I did a quick search to see if I could find any details and came a cross a post by @rualexander where it mentions doing it, but doesn't say how.

    If you're reading this, do you have any more info?

    Or anyone else know if this has been done successfully?

    What I've found on my first day of my new chainring (44T) is that it's much better for climbing, but the bike now tops out at about 20mph. I'm not sure how much of a problem this will prove to be yet.

    Although it was frustrating as I was chasing down some guys on road bikes, and when we hit a downhill section, I had to give up as I couldn't spin any quicker.
  2. Tenkaykev

    Tenkaykev Well-Known Member

    Schlumpf mountain drive rings a bell

    link found!/Schlumpf-Mountain-Drive/p/45095175/category=25406218
    Last edited: 8 May 2019
    Milkfloat likes this.
  3. Dogtrousers

    Dogtrousers Kilometre nibbler

    Paging @Fab Foodie
    He uses a Brompton with a double but changes between rings manually.
    Salty seadog and raleighnut like this.
  4. One of these

    One of these (braze on version)

    And a standard Spa Cycles square taper crankset with 26,34,42 rings.

    And a front bar end shifter mounted to bars .
    Last edited: 8 May 2019
  5. ukoldschool

    ukoldschool Well-Known Member

    @Kell what size rear cogs have you got? 16/13 or 16/12? its a very cheap and easy mod to change the 13 (if you have it) for a 12 which will give you a bit more top end
  6. u_i

    u_i Active Member

    The mentioned clamp will neither work with a triple crank nor triple derailleur. I would start with a double crank and corresponding derailleur. Triple is waay harder than double.
  7. OP

    Kell Über Member

    I tried that mod (accidentally) when the LBS ordered in the wrong part. It was weird as it made fifth feel lower than fourth. It wasn’t, clearly, but they were very close.

    It just seemed to make 2 and 3, as well as 4 and 5 overly close.

    But it might be worth another try.
  8. Fab Foodie

    Fab Foodie hanging-on in quiet desperation ...

    Chap in Oxford has a derailieur on his, you need to take an angle grinder to the back end of the cage to make it work as I remember.
    I just look at my route and payload and decide which ring for the day....
  9. YukonBoy

    YukonBoy The Monch

    Inside my skull
    If you can get your climbing speed up to 24 mph you might catch the roadies.
  10. Hmm, interesting.
    Funny how I've got it working fine on my Brompton and had a successful one week tour using it a couple of months ago.
    Maybe try something out first before you state that it won't work.
  11. u_i

    u_i Active Member

    I have this clamp and several other and combinations of different derailleurs and cranksets and tried various combinations and options and can categorically state that it cannot work unless you give up on standard folding. Yes I tried that!

    P.S. There should be no problem showing photos of the operation.
    Last edited: 9 May 2019
  12. OP

    Kell Über Member


    At 16 stone and almost 50, I have a chance on the flat. But absolutely none on any incline.

    On the day in question, i thought I was gaining slightly at about 19mh on the flat. But i just couldn't get any more speed up on the slight decline. On the previous cog (and maybe with a tailwind) I could hit about about 24mph down that bit.

    On most Strava sector leaderboards, I’m almost always in the top third if it’s relatively flat. And in the bottom 10% once it gets lumpy.

    I did once upgrade to Strava premium as it looked like you could see how weight and age would affect your leaderboard scores. Unfortunately, you can do one or the other, but can't do both.

    For example, on the section I'm on about, I'm 3,098th out of 20,969 people.

    By age, that puts me up to 527th. And by weight, it's 332nd. Would be great to get a combined fat, old (and on a Brompton) score.
    Last edited: 9 May 2019
  13. ukoldschool

    ukoldschool Well-Known Member

    It wouldnt change 5th at all, but I get that it might make it feel different as it changes 4th and 6th. You would certainly give you a better top end in 6th (these are in Metres, I cant work out inches....)

    Kell and Tenkaykev like this.
  14. OP

    Kell Über Member

    Sorry, what I meant was that because 2, 4 and 6 were taller gears, it meant the ratios felt really close.

    On the 50 tooth front, 4th was my most regularly used gear - in town at least - and then I would change up to 5th when up to speed. 6th would be used, but not often. 2 and 3 I almost never used, but I always used 1 when climbing the hill near me at home.

    So although the change only affected 3 of the gears, it affected the change I made most often: i.e. 4th>5th.

    Because it reduced the ratio between these two gears, 5th felt a lot easier than I remembered prior to the change and therefore had the weird psychological effect of making it feel lower.

    What I should have said was that it made fourth feel higher than fifth.

    The result is the same, but I can see where the confusion lies.
    Last edited: 9 May 2019
  15. OP

    Kell Über Member

    I still cant decide whether the 44T is better or worse.

    It's not been a full week yet so it needs a little time for me to get adjusted.

    I took a different route last night and couldn't really settle into a gear. 4th was too low and 5th not quite low enough for in town.

    I think I'll persevere with it as I'm definitely liking the lower first gear - especially last night when I had 100kg of me, 12kg of bike, 5-6kg of my normal commuting backpack plus, because I was playing softball last night, my softball cleats, two softballs, softball glove, rain jacket, a softball bat, spare shorts and T-Shirt all in a C-bag.

    Then when time comes to swap them out again, I might look at the smaller cog on the rear.
    Last edited: 9 May 2019
    Tenkaykev likes this.
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