Bottom bracket for using Specialites TA cranks on a modern bike
 

Hello,

I'm building a surly long haul trucker for my wife and Specialites TA cranks seem to be only decent ones I have found in 160mm lenght. I found a pair but I'm a bit confused which bottom bracket to choose to make these french parts to work on a modern frame and get the chain line as it should be. Any suggestions? We are planing to do some touring so it should be something that would last and be trouble free.

Thanks!

Yes. I like short cranks too, and there are alternatives to T/A in 160mm. That makes BB matching a lot easier.

One person who shortens cranks is Mark Stonich. I've had him shorten a couple cranks for me. Not all cranks can be shortened, fair warning.

See his website for options: BikeSmith Design and Fabrication

I think your question is what bottom bracket do you need. Obviously, a TA Specialtes bottom bracket would work. The attachment shows BB for various brands, scroll down to TA. Hope this helps.

https://www.sheldonbrown.com/bbsize.html

The OEM spindle for a TA double is the #344. If you're looking to mount the crank on a modern cartridge, you'll want something with a similar drive-side extension:

http://www.os2.dhs.org/~john/ta-spindles.jpg

Surly uses a normal threaded BB shell . There is not a problem. Pay no attention to the French vintage shape of the taper, it will work with any spindle you can find. Spindle length for proper chainline with a 135mm 11 speed hub is by trial and error.

Any modern sealed JIS bottom bracket will work, if it's the right length, if that's what you're wondering.

Length determination generally will involve trial and error, as noted above ^^^, which is why this is always something that you should consider taking to your LBS. If I had to guess I'd start with 115 for double and 118 for triple.

Phil Wood bottom brackets are expensive, but I like them because they adjustable, and I am OCD enough that I prefer my chainlines to be perfect. Also they are very well made, at least nowadays.

+1 for Phil Wood bb's, especially for touring as they are overbuilt and therefore very reliable in addition to being adjustable as mentioned above.

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...just another thing to consider on this : Depending on what you choose for your cluster gearing in the rear, you get more or less locked in to a particular chain link width (6-8 speed, 10 speed, 11 speed, etc.). Not sure how difficult it might be to get the narrower chains to fit on the chainwheel teeth of a TA crank, because I've never tried it. You should be fine if you stay with 8 or less on the back.

Nt certain what might be involved if you want to try adapting modern, narrower 10-11 speed chainrings to an old TA crank. Again, this is something I've not attempted.

Hmmm. Good question what will work with modern narrower chains. Velo Orange says their rings are good with ten speed cassettes. Found a link saying Sun XCD should be 8 or fewer, not sure if I believe that. Original TA no way past 8. My bikes I will never need to know. Once changed a 1/8” TA chainring to 3/32”, not recommended.

I have a TA crank with their current production rings (30/46) and I am using a 9sp chain. It shifts like they were made for each other.

Yeah I was going to mention that maybe the current issue chainrings will handle narrower chains. Also it should be noted that TA is still going and you can buy brand new Cyclotouriste crankarms etc. They might even have a BB. There's a website somewhere. Not sure if it is French only.

I would think that even the older chainrings would have no problem with newer, narrower chains. All chains from 5sp to 11sp are the same width on the inside (3/32", 2.38mm) and only the outside distance changes. I use a 9sp chain on all my vintage bikes and they have worked fine over a variety of different parts. The only possible place that I could see a problem would be if the chain was narrower than the chainring spacing and would get caught in between, but that hasn't happened with the older cranks that I use....Campy, Zeus and TA.

A few years ago I did some measurements out of curiosity. I measured the chainrings at the base of the tooth since they taper towards the peak and for the back I measured the thickness of the cog itself in a spot where there were no ramps.

Chainrings:
6sp - 2.07mm
8sp - 2.19mm
9/10sp (marked as such) - 2.14mm
11sp - 1.85mm

Freewheel/Cassette
6 and 7sp - 2.05mm
8sp - 1.97mm
10sp - 1.65mm
11sp - 1.65mm

I’ve used V-O 118mm cartridge BBS for TA Pro vis 5 doubles, and all seems to work fine.

118mm

Same here. I use a vintage 52 and 42T ring and a modern 26T and they work perfectly fine with my 9-speed 11-34 cassette and chain with friction shifting.

The main advantage of using some of the modern rings like VO offers is that they are pinned and ramped, which works smoother when using indexed shifting.

EDIT: Modern cranks in 50.4mm BCD

• Velo Orange Grand Cru
• SunXCD
• Luxe 50.4mm crankset

Now that you point it out, you are right I think. Internal dimensions haven't changed. Should not on principle be a problem to use modern chains on new 'narrow' chainrings. I measured my 10/11 speed modern Sugino chainrings and they are 1.92 mm. I've got some old TA rings in my stash somewhere. I'll pull them out when I have time, but I assume they'll also be in the ballpark of 2.0mm.

FWIW I did have some trouble with a modern 7 speed chain getting stuck between chainrings on my vintage Stronglight 93 cranks. Not stuck as in jammed in, but every once in a while it would not quite make the shift and kind of ride in between. So modern chainrings with their pins etc and modern chains have obviously evolved together.

AFAIK and FWIW, an actual 5/6 speed width chain is no longer made by anyone. Modern 5/6/7/8 speed chains are the same width as the old Suntour 'Ultra' and Sedisport chains. Once upon a time those were considered narrow. From memory I think that width is 7.1mm. The old full width bushed chains were more like 7.4 I think, but I don't think I have one around to measure.