Check this out, singlespeeders:

https://cgi.ebay.com/ws/eBayISAPI.dll...category=48845

A two-speed BMX freewheel. How does it work? A regular old friction deraileur/shifter? A big piece of bailing twine tied to your wrist? I'm amazed.

The way I'd work it would be to have two chainrings, set up so that there would be the same amount of chain needed (or a similar amount, enough so that the slack could be taken up w/ horiz ends) and then when you wanted another gear, you would pop the chain off of one and onto the other.

holy macoroni

but...what about the deraileur hanger?

it could be set up just so that the deraileur acted as a tensioner. I don't think two different chainrings would be used...if both "low" and "high" configurations took up the same length of chain, wouldn't that produce the same resistance (making this mod useless)?

Back around 1980, I think Suntour came out with a two speed system for BMX bikes. It used a two cog freewheel and included (IIRC) a derailer, cable and shifter. It was actually intended for BMX racing and the idea obviously never took off. This may be a update on the idea.

I'm guessing the derailer hanger is designed for the track-end style BMX dropouts. The freewheel also needs a BMX type flip flop hub with the smaller threaded side to accomodate sub-16t freewheels.

Crazy, I really cannot see to much utility to having 2 gears so close to each other, most of the time I doubt I would notice much of a difference between 15-16t especially in a freewheel setting. I am guessing it was marketed as a means of not worrying about turning the wheel (flip-flop) to change the ratio...

If they had dual track cogs that had like 15-18 or something, I think I would buy that. It might be nice to change to the easier gear just by moving the chain and adjusting the tension, if need be.

no. it is about ratio or front to back, not chain length.

I think that Bullseye came out with a shifting system as well in the mid 80's

I can see the point if it doesn't have a derailer (just loosen the wheel, move the chain over, tighten the chain and wheelnuts, as opposed to fliping the wheel over), but as a shift-on-the-fly, it seems pointless. Why only two gears, why not 8 or 9 like MTBs? Why would you want to change gear in a BMX race anyway, especially two so close together? Why all the extra weight? Stupid if you ask me.

exactly

this is designed for bmx racing, and a stupid idea at that. you need a derailer thats why there is a hanger. so unless you want a derailer and shifter on your bike then dont worry about it.