The Kinetics 8-speed Brompton conversion uses a Sturmey Archer hub gear with a very wide range – the X-RF8(W) has a 325% gear range*. Compared to Brompton’s 6-speed option, it is a wider gear range with only one gear shifter – a low profile twist shifter. All 8 gears are in sequence, so it’s easier to use than the 6-speed’s twin-shifter system, and any gear can be selected while stationary. The smaller front chainset keeps the drivetrain further inside the folded package. No modification of the frame is needed.
I can fit the 8-speed to an existing Brompton for you, or I can send you a kit. The kit includes the complete back wheel, chain tensioner, gear shifter and cable, and replacement chainset. You’ll need a few spanners, and a few allen keys – fitting is not hard, and takes about 30 minutes (see the instructions here).
*I normally use a 20t rear cog and 33t front chainring, to give ratios of about 29″ to 95″ (2.3m to 7.5m).