Thanks Scrod!

I am limited to a 38t chainring (I believe) if I want to stay with 130 BCD. This is for a fix gear to be set up with three chainlines, a flip-flop fix-fix hub and a custom 1/8" dingle. This is going on my old Mooney. Horizontal dropouts but just '70s Campy, not esp long. For this year's Cycle Oregon. 45 miles of gravel with 1000' plus both ups and downs on that gravel. Nw way my skinny tired (25c max) good fix gear is going. I want 35c which will fit easily on the Mooney.

Running 1/8" chain and 130 BCD means I am limited to a 38t chainring. (I think a 37t could be made a la 144 BCD 41t but I suspect they are an order of magnitude harder to find. Not bothering to chase that one.) You can quickly see that getting a good low gear for serious climbing on gravel is a challenge. 38-23 is 45". 38-24 is 43", about 4% better. Yeah, 4%, so what? At 64 yo, you take 4%. I may even use a triple crank and run a 36 or smaller on the inside and just accept that I will have to run a narrow ring climbing. (If I ran my tentatively planned 46-42-38 triple, I can use simple 10mm bolts with shoulders and old fashioned nuts instead of traditional chainring bolts and sleeved nuts. Rock solid! Riding fixed with a low gear, narrow cog and the much smaller bolts of a traditional inner ring scares me. Two things I do not want to see - a gear failure related crash; I've done enough for a lifetime and broken specialized gear because this will be the boonies. There won't be spares to be had. Climbing and descending go to the last day.

Since I cannot move the hub much and don't want to mess with chain length, I need to have a multiple chainline set-up with each pair of ring and cog adding up to roughly the same total teeth. So I am (tentatively) thinking or running a 46-42-38 X 13,17,21 with the 17 and 21 made up as a dingle. (Gear inches 96", 67" and 49") For gravel I will also bring the bigger cogs and settle for having to pull out the cog wrench mid ride. Not a big deal; I've done that the 4 COs I have ridden fixed using that wrench on the big hill days.

Yes, I know my numbers don't quite add up. Still working on this. I had been working on the assumption that I could not get a 24t and could use a 36t on 130 bCD until I drew it to scale. Good thing is I don't need the final answer until I order the rings and have the dingle made.

(This is why I ordered the Mooney with horizontal dropouts 39 years ago. It had to be able to be ridden fix gear. Never dreamed I would be doing this!)

Ben