Lowering the gearing on a Brompton
Re: Lowering the gearing on a Brompton
I use the 44t chainring and the standard twin sprocket set up with the SA sourced wide range hub that Brompton have used on their six speeds.
To ease the legs on 35-40 mile hilly rides I’ve added a Swytch kit. Adds a bit of weight but definitely helps on hills!
The go to sources for Brompton mods though are Steve Parry (Google is your friend) who fitted different derailleur set ups including front doubles and 7 speed rears.
Also Ben Cooper at Kinetics https://www.kinetics-online.co.uk/foldi ... hloff-kit/ who can create all sorts of gearing/braking/luggage carrying options. Spoken to him a couple of times and he’ll have a solution…..including bigger wheels on a Brompton if that’s your thing! Lots of options but some are expensive as the components aren’t cheap…Rohloff hubs for example.
The extra chainring at the front, shifted using a stick or greasy finger at the start of a climb is the cheapest way to go. You pays your money and takes your choice!
To ease the legs on 35-40 mile hilly rides I’ve added a Swytch kit. Adds a bit of weight but definitely helps on hills!
The go to sources for Brompton mods though are Steve Parry (Google is your friend) who fitted different derailleur set ups including front doubles and 7 speed rears.
Also Ben Cooper at Kinetics https://www.kinetics-online.co.uk/foldi ... hloff-kit/ who can create all sorts of gearing/braking/luggage carrying options. Spoken to him a couple of times and he’ll have a solution…..including bigger wheels on a Brompton if that’s your thing! Lots of options but some are expensive as the components aren’t cheap…Rohloff hubs for example.
The extra chainring at the front, shifted using a stick or greasy finger at the start of a climb is the cheapest way to go. You pays your money and takes your choice!
Re: Lowering the gearing on a Brompton
This looks like a sensible range of gears (no need for anything bigger than 85" for touring IMO) and adding a smaller inner chainring for particularly hilly sections would be a real plus. A 34t chainring would give a 19" bottom gear. What I don't know, which is relevant, is the capacity of the chain tensioner.Philip Benstead wrote: ↑23 May 2022, 4:12pmnirakaro wrote: ↑23 May 2022, 8:41am Thanks Philip, that's very helpful. I like to climb with very low gears, and I'm used to a bottom gear of about 18" (and even with that I'd be walking up anything that said 11.3%!). It was mentioned upthread (and I can see for myself) that a large sprocket may foul the chain tensioner; when you fitted your 18t sprocket, was that the maximum possible, or was there clearance for a bit more?
Now I am in front of my laptop I give exact figures.
My gear ratio are as follows
CR 44
13= 34.7, 54.4,85.3
18 = 25.1,39.3,61.6
I think you may be able to fit a 19 tooth just? see photo
Re: Lowering the gearing on a Brompton
" 34t chainring would give a 19" bottom gear. What I don't know, which is relevant, is the capacity of the chain tensioner."
I did no tech calcs, but no problems in practice with a 38/34.
I did no tech calcs, but no problems in practice with a 38/34.
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Re: Lowering the gearing on a Brompton
Some on here said they have they fitted a double or even a triple chainset on a brompton, do they have front derailurer, I been told they do not work can we have some photos please?
Philip Benstead | Life Member Former CTC Councillor/Trustee
Organizing events and representing cyclists' in southeast since 1988
Bikeability Instructor/Mechanic
Organizing events and representing cyclists' in southeast since 1988
Bikeability Instructor/Mechanic
Re: Lowering the gearing on a Brompton
I don't think anyone who has mentioned a double chainset has used a front mech. I haven't - "My 6 speed runs a 38/34 up front on a standard hub. Manual/greasy finger change."
However if you Google "front derailleur on a Brompton" then many examples will be revealed (including I think from past discussions on this Forum).
With the massive increase in interest in Bromptons in other countries, often with huge spend on modifications, I am sure that the full conversion has been done!
However if you Google "front derailleur on a Brompton" then many examples will be revealed (including I think from past discussions on this Forum).
With the massive increase in interest in Bromptons in other countries, often with huge spend on modifications, I am sure that the full conversion has been done!
Re: Lowering the gearing on a Brompton
The early pioneers of 'double clangers' used to use a short stick for up-changes and their heel for down-changes.
https://en.wikipedia.org/wiki/Paul_de_Vivie
https://en.wikipedia.org/wiki/Paul_de_Vivie
Re: Lowering the gearing on a Brompton
This earlier thread shows photos although the links to where the brackets come from are out of date!Philip Benstead wrote: ↑27 May 2022, 5:48am Some on here said they have they fitted a double or even a triple chainset on a brompton, do they have front derailurer, I been told they do not work can we have some photos please?
viewtopic.php?t=117916
I’m sure Google will locate something for you…Steve Parry front derailleur at a guess!
Re: Lowering the gearing on a Brompton
The Brompton chain tensioner looks to have a very limited capacity. Does this mean that the chain runs slack if it's on the smaller chainring? Is that a problem?
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Re: Lowering the gearing on a Brompton
https://youtu.be/FUVr0y_KDecPhilip Benstead wrote: ↑27 May 2022, 5:48am Some on here said they have they fitted a double or even a triple chainset on a brompton, do they have front derailurer, I been told they do not work can we have some photos please?
Re: Lowering the gearing on a Brompton
Quite opposite is true: the Brompton's tensioner may well have the highest capacity of any commercially available tensioner.
Re: Lowering the gearing on a Brompton
And one more:Philip Benstead wrote: ↑27 May 2022, 5:48am Some on here said they have they fitted a double or even a triple chainset on a brompton, do they have front derailurer, I been told they do not work can we have some photos please?
https://www.youtube.com/watch?v=KgxxOImRpHI
Re: Lowering the gearing on a Brompton
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Re: Lowering the gearing on a Brompton
You're still not clear
Re: Lowering the gearing on a Brompton
Maybe I'm being stupid here, or maybe I don't know enough about Bromptons. AIUI, some of them have a full multi-speed derailleur, others have a 3-speed hub, and a 2-sprocket derailleur (making six ratios in all), with only a few teeth difference. This version has a derailleur that looks like it will take up only a little slack, or am I mistaken?
Am I being clear now?