I am fortunate enough to live in a city where any given day there are 15-20 used bromptons for sale.
I’m currently planning to buy a 6 Speed C-Line (Year Range: 2017-2022) in the 950-1200 Euro range and then add a [dual chain ring](https://www.fantastic4toys.com/products/h-h-bcd130-54-33t-unibody-cnc-duo-chainring-for-brompton-bicycle) to increase the gear range to 493% and make the lowest gear close to 20 gear inches which is great for the hills in my area.
Today I noticed there are older Used Bromptons for sale for 500-650 Euros. I realized MAYBE I could just buy one of those and add a schlumpf drive for about 750 Euros and the price comes out to be about the same. But I’m guessing it’s not as simple as the dual chain ring solution nor as cheap. So what is the total cost of installing a schlumpf drive? Are there extra parts I must buy aside from the drive? Can a schlumpf speed drive or schlumpf mountain drive be installed relatively simply on any Brompton 3 Speed or 6 Speed? Can it only be a 6 Speed? Are they the same difficulty to install on Bromptons made before 2017? Please enlighten me 🙂
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by StewzilianPortuguese
2 Comments
as far as specific tools for the schlumpf go you need the socket tool (included in [SG-820010](http://www.schlumpfdrive.com/index.php/werkzeugwartung.html)) and the 45° cutter for the BB shell (SG-800300).
the bb shell needs to be chamfered at a 45° angle to install the schlumpf. converting back to normal bottom brackets gets fairly difficult at that point. the only options are [threadless bottom brackets](https://www.sjscycles.co.uk/bottom-brackets/110-yst-threadless-68-mm-sealed-bearing-bottom-bracket-for-frames-with-damaged-threads/?geoc=DE).
you’d want to choose a (high) speed drive with a small chainring instead of a mountain drive with a big chainring. reasons for this are weight and better frame clearance with a smaller chainring.
if you were considering a mountain drive with a small chainring for extremely low gears, be aware that internal gear hubs aren’t built to survive infinite torque.
as long as the chainring clears the frame it doesn’t matter if the bike is a 2,3,4,6 or 12 speed
Schlumpf made a speed drive kit specifically for the Brompton with special locking rings but as far as I know it’s been out of production for a while. Fellow Redditers that know better please correct me.
The normal Schlumpf drives can be made to work but you have to chamfer (recut the threads) the bottom bracket holes on the brompton frame which should be a bike shop process as you need the chamfering tool and experience to run the tool correctly.
However hope is not lost. There actually 2 possible options for a forward bottom bracket planetary gear:
The first, there is a licensed copy of the Schlumpf speed drive for the Brompton by the Taiwanese company ATS. An added bonus; the copy is cheaper than the original Schlumpf kit. Here’s a vendor who has it in stock. So even with international shipping it should still be cost effective.
https://bikegang.ecwid.com/Brompton-New-Non-Chamfer-BB-Shell-Speed-drive-Gearing-System-ATS-p51233512
The 2nd option is GTRO by Efneo which is a 3 speed planetary for the bottom bracket. They have a Brompton kit. Check with them for when they will have in stock. Some stores carried so you may find stock there.
https://www.efneo.com/shop/gtro-for-folding/
Good luck