Wednesday, January 9, 2008

Q&A: BCD of Stronglight 49D triple

Q: I recently inherited a Stronglight 49D triple crankset. The middle
chainring, 40T, is well worn and probably needs replacement. (I haven't
installed the crank yet.) I haven't been able to discover the BCD of either
the very small 5 center bolts or the larger 6 holes on the 2nd ring to see
if there are replacement rings to be purchased. Do you know if replacement
rings are available to fit this?
Thanks and Regards,

A: Hi Steve,
It's been awhile since I've seen one of those but I think what you have is
essentially a TA bolt pattern with a 50.4mm bolt circle diameter for the
chainring that attaches to the crankarm. And, I think the bolt circle
diameter for the other rings (that attach to the chainring that's attached
to the crankarm) is 86. Another measurement you can use that's easy to take
with a ruler is the bolt hole to bolt hole measurement. Just measure from
the center of one hole to the center of the next hole. Using that
measurement I think the first measurement will be 29.6mm and the one for the
chainrings that attach to the chainring will be 50.5mm.

As far as whether you can get replacement rings or not, I'm not certain, but
I think the company Specialities TA might still make rings to fit that
crankset. I found their website (they're in France) and the email to contact
them is Or, you might try contacting Peter White Cycles
as I believe he stocks TA. Peter runs a bike business in New Hampshire. His
website is

If that doesn't work, my next suggestion would be to send a message to the email list, which is a group of people who love
vintage 10-speeds. It's possible that one of them (they're all over the
world) might have a replacement chainring they'd sell you.

Hope you find what you need to keep riding that classic crankset.

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