Re: [CR]Measuring BCD - - Bolt Circle Diameter

(Example: Racing:Jean Robic)

From: "Tom Martin" <tom@wilsonbike.com>
To: "Raoul Delmare" <Raoul.L.Delmare@worldnet.att.net>, "C.R. List" <classicrendezvous@bikelist.org>, "Bruce C." <BruceCumberland@comcast.net>
References: <011301c3fad4$70ae7cc0$e64efea9@oemcomputer>
Subject: Re: [CR]Measuring BCD - - Bolt Circle Diameter
Date: Tue, 24 Feb 2004 10:03:55 -0800


The original question was never answered, namely how does one measure the bolt circle diameter of a chainring? -If you have the crank, it's easy: measure from center of chainring bolt hole to the center of the crank spindle taper area, then multiply by 2. -if you don't have the crank and only the chainring, then it's a little more complicated. You gotta somehow find the center of the chainring (any of you engineer types out there have an explanation of that?). Maybe with a compass and a ruler and a pencil? measure from each chainring bolt down to the other side, and where all the lines cross is the center? 4 arm and 6 arm cranks are a lot easier than the 3 and 5 arm cranks. Once you find that, just follow the above steps/

Tom Martin Oakland Ca is cycling science in existance any longer? do they have a listserve or website?


----- Original Message -----
From: Raoul Delmare
To: "C.R. List"


<BruceCumberland@comcast.net> Sent: Tuesday, February 24, 2004 4:12 AM 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 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! :^)
>
>
>
>
> ----- Original Message -----
> From: "Steve Maas" <stevem@nonlintec.com>
> 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" <twobouvs@yahoo.ca>
> 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.