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Any help?
Where are Velocity measuring to? ERD is supposed to be to the end of the spoke when tensioned, but it sound like you're measuring to the bearing face where the nipple hits the rim. 5mm diameter difference (i.e 2.5mm radial) isn't an unreasonable difference if the DeepV has only a slightly greater wall thickness at that point than whatever rim you're measuring and Velocity's book number is to the spoke end.
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I measured the diameter and the depth of the rim
The depth of the whole rim or just the spoke bed? Sounds like you might be measuring, in effect, the internal diameter of the rim which would indeed be too small. As tester points out, the ERD should be measured to where the spokes will finish, which will be the internal diameter plus twice the thickness of the spoke bed plus (nearly) twice the height of the spoke head.
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gbj_tester
Brommers
@LewisEC
I've bought some cheap rims and hubs to have a go at wheelbuilding myself. Have measured the hubs and rims, everything looks okay other than the effective rim diameter I came up with.
I measured the diameter and the depth of the rim in about 6 spots and subtracted 2xDepth to get an ERD of 576.4mm
Velocity Deep V ERD is listed as 581mm, a difference of 5mm between two 30mm deep rims seems very big so I feel like I've made an error. Any help?