abdon 

The smallest ring I have seen that fits a 50.4 BCD is 33t, and that is sort of a fluke; it is the ring that mounts on the opposite side of a tandem. The next step I have seen on 50.4 BCD is 48t.

Is there something smaller than 48t but larger than 33t? I would love to find a 36t or 38t but I'm not even sure they exist.

nlerner

Specialites T.A. - pro 5 vis chainwheels

obrentharris 

Scroll almost to the bottom of This Page where it says "Pro 5 vis aka cyclotourist" and you will find that Peter White Cycles sells a 40 tooth. This is the smallest size they list.
Brent

abdon 

Can't see the first link (work computer, probably firewalled) but the second shows 40t as the smallest. I'm still hoping to find one a tad smaller. Having said that Peter White sounds like the person to ask about it so I'll send him an email.

nlerner

Velo Duo in the UK will sell you a brand new outer ring, but smallest is 40t: https://www.veloduo.co.uk/collection...nt=34104480583

abdon 

Funny enough shortly after posting I saw that not 3 posts down there is a person selling custom 50.4 BCD rings...

His smallest is 34t, I PM him to see if he could CNC a 36t or 38t one for me. I would probably buy both sizes

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.

abdon 

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.

nlerner

A vintage alternative is a Stronglight 99 or other 86 bcd crankarm, letting you run a ring as small as 28t.

abdon 

I'm aiming for 36~38t, for which a standard 110BCD would work, which I even own already; I would just need to flip the middle ring to the outer spot. I would like the 50.4 BCD crank for the highly technical reason that I think it would look better 😕