My 1st Brompton was a 2012 S6L and came with a 50T chain ring/wheel.
Swapping the one piece crank/chain ring with a 44T helped me on the hills:
https://www.youtube.com/watch?v=hYo8...6zPoymgKaIoDLA
My 2nd and current B'ton is a 2013 S6L-X that came with a 44T chainwheel.
Swapping it for a 39T chainwheel helped me climb the really steep parts in my area:
https://www.youtube.com/watch?v=5AT6...IoDLA&index=11