Working 10hrs a week lately, I have had a lot of time to sit at home and stare at my bikes. I continually pose the question... how can I make them weirder?
I started on the old Schwinn Criss Cross today. It was set up as a 1x9, but the gears annoyed me. Still, I couldn't stand the thought of spinning a 2:1 around town, or mashing a slightly bigger gear in a cross race.
This spawned an idea, loosely based on the Surly Dingle Cog concept. What if I took a 15t and a 17t cog, spaced them about 2.5mm apart, ran an 8spd chain and a 34t ring...?
Now keep in mind the bike has vertical drops, so this means I need a tensioner. I think in this case its actually beneficial. I used an old Suntour ARX rear derailleur, mid cage, and wrapped the chain around the rear cog, and then down and through the *lower* pulley, effectively bypassing the upper pulley all together. This gives me a ton of downward tension on the chain, and allows me to leave enough extra chain so I can switch between the 15t and 17t without having to monkey with chain tension. To visualize it--the bottom pulley is actually pulled up so it is nearly touching the rear cog with the 17t cog, and has about 8-9mm of clearance with the 15t. Great tension in either cog.
Now, I adjusted the derailleur so it would rest below the 15t (outer) cog. I then set the derailleur limits just as I would on a full cassette, adjust the travel so the low limit was right below the 17t (inner) cog. This allows me to change gears by simply pulling the chain off one gear and plopping it on the other. The play I left in the derailleur allows it to make up for the "bad" chainline a bit. Rather than jumping off the cog, the derailleur moves with the chain.
The chainring sits almost in the middle of the two, so the chainline is only off about 1mm in either gear. So far, works great. Seems like a really good option for anyone with a vertical dropout conversion. The derailleur holds tension much better than a Singulator, and is much easier to adjust. The springs and pivots give a little room for error as well, vs. the static Singulator. Can you tell I've never liked Singulators?
Anyways, hope to have pictures up soon. Meanwhile, I'm going riding in the snow!