Bike Forums - View Single Post - Wheelbuilders: I have questions about 650b HED Belgium Plus rims
Old 03-03-18, 11:41 AM
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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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Your question about the ERD discrepancy is evidence of the problem with ERD as a spec. Keep in mind, that the ERD isn't an actual measurement, but the desired diameter of the theoretical circle at the ends of the spokes. As a practical matter, it's measured to the tops of nipples in the rim, less a small margin to account for the spokes ending shy of the top.

IMO that makes ERD a fail as a spec since it relies on various assumptions, namely the thickness of the nipple heads, and the amount of allowance for ending shy. Because of that it's not only possible, but highly likely that two people measuring ERD will come up with different measurements.

For my part, I wish that rim companies would go back to providing the actual rim diameter, measured at the nipple seat. Then we'd all know where we stood, and could add our own allowances for spoke engagement into the nipple head, without playing the Newlywed Game and trying to guess what the rim maker had in mind.

As for the right/left lacing direction, I don't believe it's because of different angles drilled, since the difference is too small to make a difference. As a basis of comparison, consider that the difference is right/left angle is less than the difference in the forward/back angle you see in crossed patterns. I suspect that the rim may have a right/left offset or asymmetry in spoke vs. tire placement, like the one shown here.
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Last edited by FBinNY; 03-03-18 at 11:48 AM.
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