[CR]Measuring BCD - - Bolt Circle Diameter

(Example: Framebuilding:Tubing:Falck)

From: "Raoul Delmare" <Raoul.L.Delmare@worldnet.att.net>
To: "C.R. List" <classicrendezvous@bikelist.org>, "Bruce C." <BruceCumberland@comcast.net>
Date: Tue, 24 Feb 2004 06:12:34 -0600
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/harris/new.html

( 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/gloss_bo-z.html#bcd

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 1812 - 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! :^)


----- Original Message -----
From: Steve Maas
To: classicrendezvous@bikelist.org
Sent: Monday, February 23, 2004 5:07 PM
Subject: Re: [CR]Measuring BCD -- Newbie Question


You don't need charts or anything like that. For five-hole chainrings, the bolt-circle diameter is 1.701 times the center-to-center distance between the holes. A hint for measuring the distance between the holes: instead of trying to eyeball the centers, hold the ruler tangent to both holes and measure the distance between the tangent points.

For 144 mm BCD, the holes are 85 mm apart.

For other numbers of holes, use the general formula,

BCD = d / sin(360/2n)

where d is the distance between bolt holes and n is the number of holes in the chainring.

Steve Maas Long Beach, California

PaulieFlt@aol.com wrote:
> Okay gang,
>
> I have these chainrings up on eBay and it's apparent I need to know how to
> measure BCD. Can somebody explain that to me?
>
> Many thanks!
>
> Have tape measurer, will travel,
> Paulie Davis
> Los Angeles


----- Original Message -----
From: Brian Frank
To: classicrendezvous@bikelist.org
Sent: Monday, February 23, 2004 2:46 PM
Subject: [CR]How to measure BCD


Paulie:

Check out the info & link http://www.hostelshoppe.com/tech_bolt_circle_diameter.php Saves me having to scan and email you my chart. I found it by doing a google on "how to measure BCD"

Good luck with your stuff on eBay.

Brian Frank. Toronto Canada Where it is warm enough to commute but fenders and paddles are a must.