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Old 02-19-12, 11:41 AM
  #9  
FBinNY 
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Join Date: Apr 2009
Location: New Rochelle, NY
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Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter

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The center to flange measurement is the least critical of the measurements.

ERD measurements affect spoke length on a 2:1 (diameter to radius) ratio, ie. +2mm ERD means +1mm spoke length

Flange diameter affect length -2:1 for a radial pattern, (-2mm dia. means +1mm spoke length), and not at all with a true tangent, ie. 4x 36h, or 3x 28h, and to varying degrees for other patterns.

Center to flange affects length on a 10:1 ratio. a 1mm difference changes the spoke length by 0.1mm

The exact ratios vary slightly within the general bands I described, but the concept holds. I offer this to spare folks the effort of agonizing over details that don't mean anything in the real world. For example a 2mm difference in CTF changes the spoke length by 0.2mm which doesn't factor when you're going to round to 1mm increments anyway.
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