Raoul,
It sounds like you have answered your own question here, but an easy way to calculate your BCD is to measure the center-to-center distance between the chainring bolts. (Edge-to-edge is the same thing, as long as the measurement is between points that are on the circumference of a circle passing through the centers of the bolts. This also works with the spider.) You don't have to be exact here to determine which bolt circle you have. A metric ruler or tape measure will get you close enough.
If you don't want to hunt around for that bookmark to Sheldon's chart, just enter the following formula into Google's search engine: E/(sin(pi/5)) where E is your measurement. Google will return the BCD, with the accuracy reflecting that of your measurement.
Steve Barner, Bolton, Vermont
> Date: Tue, 24 Feb 2004 06:12:34 -0600
> From: "Raoul Delmare" <Raoul.L.Delmare@worldnet.att.net>
> To: "C.R. List" <classicrendezvous@bikelist.org>,
> "Bruce C." <BruceCumberland@comcast.net>
> Subject: [CR]Measuring BCD - - Bolt Circle Diameter
>
> Hey Bruce ! Here's what you need to know , to see if Stronglight 99
> chainwheel ( chainring ) will fit that crankset you just recently bought
!
>
> I had seen the conversion charts before . I was HOPING somebody
> would post them on the C. R. List ! But a conversion FACTOR is
> something I don't recall seeing before ! THANKS !!!!!!
>
> In the past , looking at charts , the procedure was to measure the
> distance , center-to-center , or edge-to-edge , between any two bolt
> holes on your chainring ( chainwheel ) .
>
> BUT , you have to know which one your chart is looking for ,
> center-to-center , or edge-to-edge .
>
> Then just look up that number on your little chart ! Et voila !
> Instant Bolt Circle Diameter ( " B. C. D. " ) information about your
> chainrings ! Personally , I'd like to see SOMEBODY post this
> information , in a big way , SOMEWHERE ! Why not , at some public
> location , post three ( 3 ) easy-to-use conversion charts :
>
> 1.) B.C.D. derived from center-to-center distance between any two
> bolts , or bolt holes .
>
> 2.) B.C.D. derived from edge-to-edge distance between any two bolt
> HOLES - but the chainring must be OFF the crank to accurately measure
> this .
>
> 3.) B.C.D. derived from edge-to-edge distance between any two BOLT
> HEADS - but the chainring must have the bolts fitted to accurately
measure
> this .
>
> This would REALLY be a big help for those "newbie" folks , who
may
> very likely be confused or nervous about the very idea of trying to find a
> chainring of a different size for their bicycle ! Plus , it would be a
> very nice convenience for even the experienced folks who have an odd
> crankset ( or several ) ! If somebody could gather this information ,
> it would be SO VERY convenient to see it posted somewhere like say
> perhaps , Sheldon Brown's wonderful Harris Cyclery site !!!!!!
>
> http://www.sheldonbrown.com/
>
> ( Thanks Sheldon ! And those A.N.T. bicycles are very cool ! )
>
> And , by the way , Sheldon already has the center-to-center
> information on his "Bicycle Glossary" page :
>
> http://www.sheldonbrown.com/
>
> Thanks Sheldon . And thanks Steve Maas . And thanks Brian Frank .
> And thanks C. R. List . And I'll miss you folks for the next week or
two
> - traveling .
>
>
> Raoul Delmare
> Marysville Kansas U.S.A.
> ( where we know that Dolly Madison's heroic acts saved the artwork
from
> the burning White House , while the U.S.A. was losing the War Of
812 -
> Dolly Madison was a courageous hero , not a cup-cake ! )
> ( and since this will be my last post for a week or two , I'll be out
> of town , and temporarily disconnected from the list , if ya flame me ,
I
> won't be able to read it , sorry! :^)