I recommend using a touring/mountain/road bike with the same crank length than the Brompton (175mm) and check the development of the gear you use on the steepest incline you usually ride on your Brompton. Then see how you can achive this development on the Brompton.
On a mountain bike you normally have a development of 1.7m or lower on the lowest gear. This is not possible on the Brompton without further modifications - the limit is 1.95m with a 39T chainring with a 17T sprocket .
BTW: I use a 42T chainring that results in a development of 2.38m in combination with the 15T sprocket.
Die wollen unbedingt dick angezogene Passagiere, dann kann man zusätzlich an der Heizung sparen. Quasi das Ryanair der Schiene %#&@!