I love riding fix gear, I love riding hills. I'm in my 60s and have had chronic knee issues the past 40 years. 9 years ago I had a custom fix gear built that had a road style dropout but long enough to run any 1/8" cog I've ever heard of. (I now have from 12 to 24.) I've ridden 5 Cycle Oregons on it using a fix-fix flip-flop wheel and carrying a chainwhip.
Three years ago I set my Mooney up to ride the (canceled) Cycle Oregon with its promised 30 miles of gravel. But how to do the gears on a standard late '70s Campy horizontal dropout? Geeky engineer here. Multiple chainlines. I went with three. Made up a rather custom 110 BCD triple pushed as far in as a 38 tooth ring would allow. Had a "dingle" made using a 21 tooth cog as the core, flipping the 21 so the cog sits flush with the hub and cutting out the center of a 17 tooth and braising it to the 21 with a steel spacer. Dished a flip-flop wheel in a touch for the dingle. That kicked out the small cog a touch.
End result? I run a crankset of 46-42-38. Using a 13 tooth small cog gives me a 46-13 (96
high, 42-17 (67") level ground and a 38-21 (49") low. I can also swap out the dingle and screw on a 24 for a 43" low (very low for a fix gear on pavement) if I carry the chainwhip. All three cogs like up near perfectly with their respective chainwheel. Everything is rock solid 1/8". (A shout out for Izumi chains. $25 gets you a really good one. Lots of pin extension so driving and re-driving pins is easy and safe to do. No, not the quietest. Quiet and sweet shifting are closely related, I NEVER want to shift until I stop and pull the wrench out. EVER. So noisy Izumi chains and EurAsian cogs are up my alley. And EurAsian cogs, despite the name are made in the US.)
Yes, on both bikes, changing gears costs my a couple of minutes. Unscrewing cogs about 5. But - this is all fix gear. I ride it to get away from freewheels. Yes, fix gear internal hubs exist but I have never heard that they were up to hard riding. My Mooney has a drive train close to velodrome worthy in all three (very different) gears and the custom, with its Sugino 75 crankset, is fully velodrome worthy, just not a track bike at all.
Ben