(above) I retrofit my Dahon Speed for 50/34 front with added derailleur, replaced the (terrible) dahon compact rear derailleur with a medium (GS) cage one installed in "normal" location to handle the wider range, and with original 11-30 7-speed cassette it gives me 21-85 gear inches on 20x1.75 tires. I don't need any higher, might need a touch lower (I can do 34 low cog) if I heavy tour in serious mountains, but the 34-30 is enough for the hills here. Transformed the bike from a "folder" to a fully capable bike, that can handle full grocery-run pannier loads. It's my daily now.