Is it possible to convert a single speed rear wheel into a multi-speed rear wheel? If I buy a wheelset that was meant for a single speed bicycle, how could I convert that wheelset to a multi-speed bicycle? Note that I am not asking about converting a fixie ride into a multi speed one, I only care about the wheels. Tutorials and video links are welcome!
Conventional wire spoked wheels don't allow this. All types of conventional singlespeed hub (BMX, cassette, freewheel, track, coaster) take advantage of their one-cog-ness to have center-to-flange measurements that are either symmetrical or close to it, creating a wheel with no or almost no spoke tension disparity, which makes it stronger and more robust. (Non-flip-flop track and all disc singlespeed hubs do give some spoke tension disparity, but not much.) Such a hub offers no space to put a gear cluster.
Certain disc (as in flat and expensive) and mag wheelsets are switchable from track to multi-speed hub guts. They're not subject to the above limitations as their structure is closer to only existing in one plane. To do it you're buying the manufacturer's parts and following their procedures. Zipp 900s are a current example, allowing riders to use the same big money disc for both track and TT/tri. Aerospoke also is/was switchable, and were pretty common in their heyday, so probably represent the most popular singlespeed wheelset you can buy and then convert later to derailer use.