There are 4 gearing options for the Brompton:

1-speed: Just one gear of 5.93m (74”) - light and simple.

2-speed: A derailleur with two sprockets, for gears of 4.45m (56”) and 5.93m (74”) - almost as light.

3-speed: A Sturmey-Archer hub gear, with ratios from 3.79m (47”) to 6.76m (85”) - very reliable.

6-speed: A SRAM 3-speed hub gear and the 2-speed derailleur combined, for ratios from 3.22m (40”) to 6.87m (86”) - a wide range while still reliable.

It is also possible to move all these ratios up or down a bit, by choosing custom ratios - good if you’ve got lots of hills to cope with ;-)