Originally Posted by
79pmooney
The 50.4 BCD is the inside bolt circle on the TA where the outer ring mounts on the crank, correct? (In my TA days long ago, I never heard "BCD". My quick web scan before posting came up BCD short.) If I am right, there's a trick I used to climb Mount Washington. I wanted a 28t SS. I had a brand new Cyclotourist that was going on my soon to be built Peter Mooney. And various TA stuff from that had replaced my Lambert chainings. So, I took an old outer chainring, cut down the spider to just outside the bolt circle for the small inside chainrings. Bolted the 28 directly to the inside of the spider, no spacers. Worked like a charm.
That's that BCD means, bolt circle diameter.
I thought about that and it would work, but this is primarily an exercise in vintage bike hubris; I'm trying to do a 1-by using vintage components or at the very least vintage styling. Why? Because using modern components would be too easy and cost way less :-\ Heck I'm even deviating from 100% vintage. Suntour did do a 13-38 mega-granny freewheel to go with their Alpine rear derailleur (38t max rear cog, the largest capacity at the time and for years to come). I'm going to bump things to a cassette hub, mount the Alpine derailleur on a hanger extender, and see if I can get it to shift a 11-42t cassette. For the front I could save a lot of money if I mounted a single 34t ring on a 110BCD crank, but a 50.4 BCD crank would look better.