Source for 50.4 bcd rings
 

I have a TA cyclotourist crank that I would like to use on a bike I'm working on but I'm not in love with the existing rings as this was set up for half step gearing (52/47/32).

I haven't had much luck finding much out there. VO sells them sort of. They have a 46 outer available but their stock of inner rings is poor to non-existent. I have been tempted to buy their TA copy crank; it's beautiful and expensive and it works with a modern BB which is cool.

It looks like Hillary Stone is my best bet but that is in the UK. Hilary Stone The site for Classic and Vintage bicycles and their parts

I guess the other alternative is to put up a WTB in the C&V sale forum and see what shows up.

WTB or the for trade thread should get you something. I just traded a TA 36 for a 46 from one of our Canadian BF'er.

Boulder Bicycles
TA cyclotourist chainrings & hardware

Wow, thanks cool. I don't know how I missed that.

There is a decent flow of 50.4 rings on eBay, if you don't mind used. With patience they can be had for decent prices (<$20 @). Search for TA, Stronglight, VO, Electra, Zeus, Lambert. There were many folks making those back in the day.

Norther Cycles in Portland has both SunTour XCD and TA chainrings in stock in 50.4 BCD

I believe Jitensha Studio also has them.

I've bought them from Boulder Bicycle in Colorado and Spa Cycles, Harrowgate, England. Oddly enough the price (with shipping) and the delivery time was roughly equal. This may have changed since then.

Specialites TA is still making Cyclotouriste rings, although it does so only when there are orders. I find most of mine on eBay, but I also have bought them from Boulder Cycle.

By the way, what rings are you looking for? Those old Cyclotouriste triples shift best with the half-step. I have a 26-40-44 combination on one of my bikes, for example.

Why better with half step? The existing rings are half step, 52-47-32. I'm not in love with the gear ratios this gives me.

I understand about the ratios; this crank was designed in the era when people were using five or six speed cogsets. The half step made sense then, because it effectively gave you ten equally spaced gears (when done right!) But the shifting issue. As far as I can tell, it is because the rings do not have the ramps and formed teeth that help the front derailleurs move the chain. I have several bikes with the TA cranks, and I can attest that big jumps between the chainrings can be awkward. It's tolerable on a double (I run compact doubles on a couple of those bikes) but on a triple you can feel the front derailleur protesting.

Sure, I know it's an old crank designed to work with 5 or 6 on the back. I'm not arguing with you but I'm a little surprised that shifting is so poor with a 10 tooth jump.

Yeah, I wonder too. Maybe the rings bend a bit? I never had any issues pedaling but maybe those skinny arms let the rings move against the derailleur.

Velo Orange:

Chainrings & Hardware - Cranksets - Components

I would think it'd have more to do with front derailleur choice than rings. And for what it's worth, I'm shifting a 38/52 TA double just fine with a 70's Campy NR FD. (13-26 in the back with an NR RD.)

Cool; I'm thinking of turning mine into a compact double as well (46-30 probably). I'm impressed that the NR RD can handle that much chain (27 tooth capacity is probably near its upper limit). I'm going to run a campagnolo rally since I'll run a 13-28 on the rear.

Are you running a cup and cone BB or a modern sealed unit?

Back in the day — 1976 IIRC — I built up a touring bike with TA chainrings (on a Stronglight 49D) with 50–30t chainrings. This was with one of those Simplex Delrin front shifters that moved in and out, but not up and down. To everyone's surprise, it worked just fine.

The "secret" was using a long-arm rear derailleur that could take-up the excess chain. I used a Regina 13–29t block.

Much to my regret, I sold that crankset along with some spare rings and the stronglight extractor tool on eBay.