Brompton Gearing Modifications

Various gearing modifications have been attempted for the Brompton folding bicycle over the past decade to boost the ratios and have these bikes fulfill a broader function. Although the 6 speed (2x3) factory version has been successfully used for distance loaded touring, it barely squeaks by in overall gear ratios for a true "touring bike". Rohloff 14 speed hub conversions are very expensive, very heavy (about a pound heavier) and they add a great deal of width to the original folding size. A typical Rohloff conversion costs close to $3500 USD and that is not including the original cost of the Brompton bike. The Shimano 8 & 11 speed hubs also use wider drop-outs of 135mm having the same problems that the Rohloff conversions do but without the solid reliability of the German made hub. For some years now a few Brompton custom shops have been adding an additional sprocket (triple cog kit) to extend a 6-speed Brompton's gear range from 302% to 368%.  This gives 9 distinct gears and takes care of the gearing problem, however, the conversion is tricky often needing to grind metal from the frame to make room for the additional parts as well as swapping out the Brompton 6 speed chain for…

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10 Speed Brompton Upgrade

The Brompton gearing upgrade kit arrived from Taiwan this morning and I've already built it into a new wheel, complete with a Tannus "No Flat" airless tire. The kit consists of a Sturmey Archer S-RF5(W) N 5x2 10 speed freewheel, 5 speed Sturmey Archer thumb shifter, two rear sprockets (12t & 17t) and hardware bits to put it all together. The finished product is fantastic with an additional 60% boost to the overall range of 362%. This adds two more higher gears for speed and another two lower climbing gears putting this Brompton in the running for an all-round 10 speed touring bike. The thumb shifter has a positive indexing and feels solid & comfortable, unlike the original Brompton plastic 3 speed. The whole kit went together quickly with only a few snafus. The first was the fact that my donor Brompton was a 2003 Model so it had a different dust cover on the hub. I had to shave down the back of the new Sturmey Archer dust cover to make room for two sprockets. I also had a bit of trouble fitting the 17 tooth cog. A 16 tooth would have fit without modification but the 17 was…

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Brompton Electric

It is August 21, 2017 and to celebrate the completion of our newest Brompton build, I rode out to view the total eclipse of the sun. While out riding I took a few photos of the finished bike. This build has all the features of the upcoming Brompton factory electric bike plus a couple of extras I deemed necessary for loaded touring applications. It has a 500 watt Crystalyte front hub motor capable of operating on a 36V or 48V battery so the torque power & speed is increased over the factory version. The UK has restrictions on the motor wattage and top speed of their e-bikes that we in the US territories do not have to abide by so I opted to use a motor with twice the wattage.  The controller for this motor is attached to the fork yoke by a lengthened fender (mud guard) bolt and does not interfere with the bicycle fold. [caption id="attachment_3907" align="alignright" width="300"] Crystalyte Hub Motor on Brompton E-bike[/caption] There is also a pair of Tannus (airless solid foam) tires on this bike as seen in this photo.  Note the lack of a valve stem.   It is important to emphasize how stress…

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