Which is correct for measuring ERD?
04-28-20, 03:32 PM
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Which is correct for measuring ERD?
Park Tool shows the end of the spoke being lined up with the bottom of the screw driver slot on the nipple.
https://www.parktool.com/blog/calvin...e-rim-diameter
Over here it looks like the pic in the middle of the page is showing measuring from the top of the screw head.
https://leonard.io/edd/howtomeasure
https://leonard.io/edd/static/images/erd.png
"Most people prefer it near the end of the spoke nipple."
https://www.parktool.com/blog/calvin...e-rim-diameter
Over here it looks like the pic in the middle of the page is showing measuring from the top of the screw head.
https://leonard.io/edd/howtomeasure
https://leonard.io/edd/static/images/erd.png
"Most people prefer it near the end of the spoke nipple."
04-28-20, 08:53 PM
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I've followed the method and definition for ERD from the Roger Musson's, "Professional Guide to Wheel Building". Although I should add, I am not a professional nor much more than an ambitious novice. Defined by Musson, "The ERD is the rim diameter measured at the spoke ends in the finished wheel." According to that definition, I'd go with the Park Tool recommendation which is to have the finished wheel spoke end at the bottom of the slot in the spoke nipple. That way, you can still tighten the spoke a bit without it poking above the nipple or through the rim tape- important in old box rims, but maybe not so much in deep section rims.
Maybe this helps.
Maybe this helps.
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04-28-20, 09:14 PM
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ERD is not an industry agreed on dimension, or at least WRT the nipple end of a spoke. I learned it as the inside of the rim's base where the nipple head sat. As in the nipple head's flange on the outside of the nipple. Note this says nothing about the nipple head's slot (if any) or the nipple end BUT does possibly include the rim hole's eyelet thickness if any. Some rim manufactures who use eyelets on some of their rims don't account for the aprox 1mm eyelet thickness and only use the rim's spoke base as extruded and rolled.
This slight variance in "ERD" measurement points and the resulting effective spoke length calculations is why one needs to understand what the "working" definition of the claimed ERD is, by who ever is claiming a spec, and then measure for yourself to begin to gain the real ERD that your system will then return "correct" spoke lengths. This is one of the differences between a pro and an amateurs. Andy
This slight variance in "ERD" measurement points and the resulting effective spoke length calculations is why one needs to understand what the "working" definition of the claimed ERD is, by who ever is claiming a spec, and then measure for yourself to begin to gain the real ERD that your system will then return "correct" spoke lengths. This is one of the differences between a pro and an amateurs. Andy
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AndrewRStewart
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04-28-20, 09:34 PM
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ERD is not an industry agreed on dimension, or at least WRT the nipple end of a spoke. I learned it as the inside of the rim's base where the nipple head sat. As in the nipple head's flange on the outside of the nipple. Note this says nothing about the nipple head's slot (if any) or the nipple end BUT does possibly include the rim hole's eyelet thickness if any. Some rim manufactures who use eyelets on some of their rims don't account for the aprox 1mm eyelet thickness and only use the rim's spoke base as extruded and rolled.
This slight variance in "ERD" measurement points and the resulting effective spoke length calculations is why one needs to understand what the "working" definition of the claimed ERD is, by who ever is claiming a spec, and then measure for yourself to begin to gain the real ERD that your system will then return "correct" spoke lengths. This is one of the differences between a pro and an amateurs. Andy
This slight variance in "ERD" measurement points and the resulting effective spoke length calculations is why one needs to understand what the "working" definition of the claimed ERD is, by who ever is claiming a spec, and then measure for yourself to begin to gain the real ERD that your system will then return "correct" spoke lengths. This is one of the differences between a pro and an amateurs. Andy
Andy, thank you for the useful details on the ERD definitions. As an amateur, the takeaway I got from the wheel building books and very limited experience was to always measure ERD yourself (and probably for the reasons you detailed).
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