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ERD is the diameter where nipple threads sit, not outer rim lip. Manufacturers publish ERD for each rim model.
Spoke length comes from hub flange radius, ERD, spoke count, and cross pattern forming a triangle in the wheel plane.
L ≈ √(R² + H² + D² − 2RD cos θ) − nipple correction (standard builders formula)Rear wheels often need different lengths drive-side and non-drive because flange positions differ.
Updated: July 2026
Enter asymmetrical rim ERD and dish offset for 11-speed hub dimensions.
Use 0-cross pattern on a front hub and verify spoke tension limits with the rim maker.
Confirm ERD and cross count from an existing wheel before ordering a single spoke length.
ERD is smaller than outer rim width. Wrong value causes spokes that bottom out or miss thread engagement.
Calculate each side separately when flange offsets differ.
Order the right spokes before your wheel build. Enter hub dimensions, rim ERD, and lacing pattern to get drive-side and non-drive spoke lengths.