Spoke Calculator

1. ERD (Effective Rim Diameter)

Nipple seat diameter inside the double-wall rim.

1. Cut 2 spokes to 200 mm. Thread a nipple until the bottom of the slot.
2. Insert them. Measure the distance D between the two ends.
3. Formula: ERD = 200 + 200 + D

2. W (Center-to-Flange Offset)

Top view. Horizontal distance between the hub's mathematical center (frame midline) and each flange.

• Identify the OLD (e.g., 142mm). The wheel center is at OLD / 2.
• Place the hub flat. Measure height (H) from the table to the middle of the flange.
• Formula: W = (OLD / 2) - H

3. d (Pitch Circle Diameter PCD)

Diameter of the imaginary circle passing through the center of all holes on the same flange.

• Measure the direct distance between the center of one hole and the center of the diametrically opposed hole.
• Tip: Measure from the outside edge of one hole to the outside edge of the diametrically opposite hole. Then subtract the diameter of one hole.

4. S (Flange Hole Diameter)

Hole measurement. Necessary because the spoke elbow rests on the hole edge, not in its center.

• Use the upper jaws (inside measuring jaws) of your caliper.
• Standard values for J-Bend spokes: usually 2.4 mm, 2.5 mm, or 2.6 mm.