It took some figuring out, but I’ve got a Rohloff 14-speed hub gear conversion working happily on the Brompton 😉
The gear range with 13t rear cog and 54t front chainring – both completely standard – is 19” to 102” (1.54m to 8.11m). That’s a very wide gear range, as wide as a touring or mountain bike, with a low enough bottom gear for almost any hill – and being a sealed hub gear you can select any gear at any time with one twist of the shifter.
Don’t already have a Brompton? No problem, I can build you a complete new one – see the Rohloff Brompton Order Form.
Want to see some examples of Rohloff Bromptons I’ve built? Search the website for Rohloff Brompton.
Can this kit fit to any Brompton? Yes – the rear triangle I build will fit any Brompton made in at least the last 15 years. The kit replaces your entire gearing system, so it doesn’t matter what gears you have at the moment.
Does the bike fold as normal? Yes, with one exception – because of the wider back hub, the cranks won’t rotate all the way around when the bike is folded. The best trick is to put the cranks horizontally with the left pedal forwards, then fold as normal, this will put the pedals in the best position.
Does this make the folded size bigger? Yes, it makes it about 15mm wider – the exact amount varies a bit depending on what handlebars, shifters, brake levers and rear rack and other parts you have. The bike still fits into the original Brompton cardboard box, however.
How much weight does this add to the bike? It adds about 800g over the weight of the 3-speed Brompton.
Will the Rohloff shifter work with all handlebars? It will fit to all bars, but with the M- and H-type there isn’t much space left, so bar ends won’t work. There’s more space with the S-type and P-type.
Is the kit hard to fit? Not especially – the trickiest bit is removing your old rear triangle, the two pivot bolts can be quite solid. I do it with an impact driver, good long 4mm Allen keys usually manage, but occasionally the bolts have to be drilled out which means you need a new rear hinge kit. The rest is pretty simple – fit the new rear triangle, fit the rear wheel, mudguards and rack if you have them, fit the other parts and so the gear cables.
Can you fit the kit for me? Sure, no problem – there’s no charge for fitting if I do it here.
What’s the rear triangle made out of? It’s entirely stainless steel, brazed together. I use stainless because it’s tough – Brompton rear triangles get a lot of abuse, so a material that’s corrosion resistant is perfect.
Why don’t you use titanium? I looked into it – titanium is expensive to work with, and very difficult to repair. It would limit the designs I can make, and it can also have a limited lifespan. It didn’t seem worth it to save a few hundred grams when we’re putting a 1.6kg rear hub on the bike.
Does the rear triangle have to be painted? No – being entirely stainless steel, I can leave it as a brushed finish if you prefer.
What is the integral rear carrier? Normal Bromptons come in a couple of versions, the L-type with just mudguards or the R-type with an aluminium back rack as well. The kit I make works perfectly with these parts – you can still have just mudguards or the Brompton rear rack. However I also make a version with an integral carrier, made out of the same stainless steel as the rear triangle and permanently brazed on. It is lighter and stronger than the Brompton aluminium carrier.
Can it have a belt drive? Yes, this is possible, but with a limitation – there’s only one belt combination that works on the Brompton, 19/70, and that’s quite low geared, giving a bottom gear of about 17″ and a top gear of 88″.
What’s in the kit? The kit includes my new rear triangle in stainless steel, the Rohloff hub built into a rim, a chain tensioner, and the Rohloff rear shifter, cables and fittings. Depending on your Brompton, you might need a new chainset and/or chain, I can supply these if needed.