More Luna-cy - 16 speed Brompton upgrade

Quixoticgeek

Full Member
Aug 4, 2013
2,476
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Europe
After much faffing, swearing, sweating, and 3 different bottom bracket tools, I've finally completed the upgrade of my Brompton to a 16 speed configuration.

I found on my trips last year that the 33/20 1:1 bottom gear on the 16" wheel just wasn't low enough for any real hill climbing, meaning that I would spend too much time pushing her up the hills.

Because of the peculiarities of the Brompton rear frame I couldn't put a bigger gear on at the back, meaning I'd have to reduce the size of the gear at the front. Finding smaller single chainrings than 33 tooth proved next to impossible so it occurred to me (inspired by a friend), to put a dual chainring on the front with a small chainring. Long story short I ended up putting a triple crank on the front with a 28, 39 and a chain guard in the 3rd slot. Because there is no room for a derailure, changing between chainrings is a case of getting off and moving the chain manually. But it's sort of like the low range/high range on a land rover. When I know I'm about to go up a hill I can set it to low range, when I cross the border to the Netherlands, I can set it to high range...

All in all this has dropped the whole gear range by about 17% for low range, and increased it by 17% on the high range. If I've done my maths right, this gives me a tiny 1.85m bottom gear, and a nice big 8.18m top gear.

I'll post some photos when it's day light. I just took her out and cycled all the way to the top of the hill behind my flat without needing to get off and push, I'm considering that a success.

J
 

The Cumbrian

Full Member
Nov 10, 2007
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The Rainy Side of the Lakes.
Good thinking Julia, I seem to recall reading that that's how olde worlde racing bikes used to be before the invention of the derailleur. Does your bike have a rear derailleur, and has it got the range to take up the slack in the chain?

Cheers, Michael.
 

Quixoticgeek

Full Member
Aug 4, 2013
2,476
5
Europe
The Brompton has a spring loaded tension arm on the back with a pair of jockey wheels, a bit like a derailure arm, but without the ability to shift gears with it. It's needed to take up the slack when you fold it.

J
 

The Cumbrian

Full Member
Nov 10, 2007
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The Rainy Side of the Lakes.
That explains it. I think that the old racing bikes were fixies, and the double front chainrings allowed the riders to climb the passes in the mountains. Proper hardcore back in those days, they even had wine in their water bottles.

Cheers, Michael.
 

mrcharly

Bushcrafter (boy, I've got a lot to say!)
Jan 25, 2011
3,246
33
North Yorkshire, UK
The old fixies had two rings at the back, one on each side. Changing gear meant taking the rear wheel out and turning it round.

What Julia has done is a bit like the Crank brothers on their trip in africa - they did without a front derailleur to save weight and reduce complexity.
 

Tengu

Full Member
Jan 10, 2006
11,030
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Wiltshire
<shakes head sadly.>

My Uncle still isnt riding his.

I guess Im going to have to make myself terribly unpopular at Christmas when I ask for it for my present...
 

mrcharly

Bushcrafter (boy, I've got a lot to say!)
Jan 25, 2011
3,246
33
North Yorkshire, UK
Well, I dont even know how gears work...
Do you mean you don't know how derailleur gears work?

Most people don't know, including people who cycle a lot. It pretty much comes down to the chain being flexible and the whole system having a calculated amount of sloppy movement in it. The chain gets shoved sideways, bends a bit, is a bit sloppy on the cogs and catches on an adjacent cog.