Buy the Brompton Spider Complete Crankset (LH+RH) - 44T at Escapa. This is a replacement set with left and right cranks, including a chainring and chain guard, just like the one found on Brompton bikes manufactured after 2013.
A standard 3- or 6-speed Brompton comes with a 50-tooth front chainring. Switching to a 44-tooth chainring reduces the gear ratio by approximately 12%.
A standard 1- or 2-speed Brompton comes with a 54-tooth front chainring. Switching to a 44-tooth chainring will reduce the gear ratio by approximately 19%.
The bottom bracket is NOT included in the delivery. If you want to replace the old fixed chainrings and cranks, you’ll also need to replace the bottom bracket shell (the old one was ISO-standard; the new one is JIS-standard).
