Sometime ago, I bought a cheap bike from eBay for my daily commutes which turned out to be a single-speed bike. It works fine but I am curious as to how I am able to have a shifter that simulates gear changes.
It's obviously because of the box indicated in red in the first picture below. But after a through search I wasn't able to find a clue how that works let alone what it is.
So, what is it and more importantly how does is it work?
Also, what would happen if I just disconnect the cable going to the black box below but still keep the box attached on the bike? You know, just to enjoy a proper single-speed bike from time to time.