pengyou

It is time to retire my 7 speed Dahon. Sad, but it has served me well. One of the things I did not like about it is that the rear derailleur hung pretty close to the ground. I have seen other folding 20" 7 speeds that have a rear derailleur does not hang so low. If I find the bike of my dreams but it also has a low hanging rear d. is it something that can be easily changed? inexpensively?

BassNotBass

Derailleurs with smaller cages are available but whether you could use one depends on what your largest and smallest cogs are on the rear cluster. I've been able to use small caged derailleurs with cassettes that have 11-28 tooth cogs.

feijai

The point of short/medium/long cage size in a derailleur is how much slack it can take up. This is generally measured in terms of difference in teeth. For bikes with multiple chainrings up front, and particularly ones with big variance in size, all this matters. But the huge majority of folders have a single chainring up front, so the only difference in teeth is the rear cassette, and that's essentially always well within the range of even a very short derailleur. For example, a ginormous 11-36 rear cassette has a 26-tooth difference. But the SRAM X9 short has a conservative capacity of 30 teeth.

Frankly I don't know why folders don't always come with short cage derailleurs; it'd raise the chain further from the ground and on a folder that is always a huge plus.

fietsbob

one advantage to dual drive hubs is the low gear is 75% of the external gear, so the cog maybe a 28t,
but acts like a 35t, as it adds reduction gear like .. 7t.


Full internal gear wouldn't need a chain-tensioner at all , if you can pull the axle back in the dropout.