Originally Posted by
shipwreck
Thats absolutely what I figured about smaller wheels... An idea I have is to replace the crank with a 54/48 half step, and shift the front manualy as needed, making sure that the rear meck can handle it. If it does not work, then it can always go back to stock or try something else. Some of the low gear ratios have me thinking about this, sort of a cart before the horse thing
Typically you won't see the best gearing on a folder (standard 586% range on a mountain bike (22/32/42->11/34 casette), but that's also mitigated because many folders aren't gear to let you go as fast.
You can choose the gearing as low as you want, you just cut your top end. If you want to spin at 4 mph, your top end is at 12mph. I think most folders have around a 300% gear range, whether that's obtained with an internal gear hub, or a more limited cassette/double chainring. A 34tooth cog in the rear on a 16" wheel is too big, it's almost too big on a 20" wheel, leaving about 1-2" (if I remember) between the derailleur and the ground under normal range tensioning.
I think what you've seen is from folders that are normally spec'ed to let you pedal at 90rpms around 15mph, which gives you a low end (typical 300% range) at 5mph or more. Bromptons have a gear range around 186%, which would drop that to 8mph. Some hills could make that a challenge for the gearing, as normally your not outfit as well for hills as you would be on a road bike, and there are some other inefficiencies that don't make it as easy to equate the speed difference - meaning if you don't struggle at 8mph up a certain hill on a road bike, that doesn't mean the same would be true on a folder.
You can always drop your front ring to be lower, you'll just lose top end.