Re: A new shift concept for the engineers....
Without a very thorough understanding of all this, I would imagine that three sprockets, the axle adapter and derailleur bracket would still cost some bucks to produce. I think the SBP kit is elegant and is tried and proven. And while it isn't cheap to buy, it also isn't cheaply made, with manufacturing of the kit coming from the good old USA. For what it does for a bike which is already geared I think it is reasonable. What starts to jack the price of going that route is with a bike which does not already have external gears. For someone like me who always ends up building a cruiser with no gears and a coaster brake, the cost of converting to an internally geared axle strong enough to withstand the forces generated by an engine is beyond my meager pocketbook. I looked in to what Barely did with his Rollfast and it is a wonderful setup, but there was nothing quick and easy nor inexpensive about it, further made difficult by his wanting a wheel with heavy duty spokes. Also, the axle could not have a coaster brake as a freewheel hub is necessary. Even if I had the funds, I don't know that I could do it as Barely's mechanical skills are much greater than mine. What I see as the beauty of this little sprocket cluster approach is that it makes gearing a cruiser a more straightforward endeavor and with a only kit to buy should make converting a coaster brake cruiser a relatively inexpensive modification... the key word being "relative". Having different kits available for different kinds of bikes is a good thing, as I see it. If I understand correctly how these sprockets mount, the hub adapter is necessary and that is now being made for only select standard axles. So it may be that you would need to have an axle appropriate for the adapter. For me that it not a great problem since I have been swapping out the original tired old wheel I find on vintage bikes for a heavy duty wheel with thick spokes, but still a single speed coaster brake as original. Heavy duty wheels is something I do anyway and Jim's sprocket adapter is also something I started using with the Elgin build last winter. There was such an improvement over the old rag joint that I'll never go back. So for me I already have the right wheel just asking for the sprocket cluster now being made.
Someday when I grow up I will probably lose interest in toys with wheels, but until then...