Same BCD but different hole pattern?
 

Hello!

I have Stronglight TS 52/42 116 BCD and was looking to replace 42T with 38T. I found one that says 116 BCD but the pictures show 5 hole pattern (vs 6 hole pattern on TS).

Pardon my ignorance, but a) is that possible to have different hole count for the same BCD (ie. maybe the picture is wrong) and b) if yes, am i right to assume they are not compatible ?

Thank you in advance for your help!

Well, BCD is bolt circle diameter, so theoretically you could put any number of bolt holes around the diameter. Certainly a 6 hole pattern will not fit a 5 hole pattern (360 divided by # of holes = degrees between holes), so its a no go. I don't know everything, but I've never seen a 6 hole chain ring though google seems to indicate they exist.

Thank you for your quick reply and confirmation! The spider is 3 arm but TS rings themselves are 6 hole. Pretty old by any standards.....

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manufacturer brochure page of 1976 -

​​​​​​http://velo-pages.com/main.php?g2_vi...serialNumber=2

manufacturer catalogue page of 1978 -

​​​​​​http://velo-pages.com/main.php?g2_vi...serialNumber=4

six hole Stronglight chainwheels predate the introduction of the TS model chainset by many years

they were standard on three-arm cottered steel models -

http://velo-pages.com/main.php?g2_vi...serialNumber=4

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Rotor Q often puts a bunch of holes in their rings, but unfortunately I'm not seeing 116 bcd.

:foo:

I am seeing a few 106 bcd 3 bolt rings that might be able to be modified to 116 if you were very careful with drilling. Holes might overlap a bit, but it might be OK.

https://www.hoopriderparts.com/produ...040t%20-%20nos

https://www.ebay.com/itm/154583124549


However, did you look at this set,
36/50T?
https://www.ebay.com/itm/124826612608

3-arm, 116mm BCD rings were made by many manufacturers BITD, and should be interchangeable. From Sutherland's 4th Edition:

Well, since you mention its a 3 arm spider then a 6 hole ring should fit, right (assuming same BCD).