Raoul Delmare wrote:
>
> 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 .
My chart, at http://sheldonbrown.com/
Since chainrings come in descrete specific BCDs, you don't need any
more precision than you get by holding a ruler up against the
chainring or the stack bolts and approximating where the centers are.
> 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 .
See http://sheldonbrown.com/
>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 .
Not necessary, just subtract the bolt hole diameter (usually 10 mm)
from the center-to-center dimension.
>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 .
Just subtract the bolt head diameter (usually 12 mm) from the center-to-center dimension.
Sheldon "Easier Than You Might Think" Brown
Newtonville, Massachusetts
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