Calculation of spoke length for a bicycle

- Take measurements of the hub and rim.
- Enter the data in the fields.
- Click "Calculate".

* Measurement of the equivalent rim diameter (Effective Rim Diameter - ERD) - it can also be called the diameter measured at the ends of the spokes. That is, ERD - it is the distance from the end of one spoke to the end of the diametrically opposite spoke in a fully tensioned wheel. In reality, it is the distance from the bottom of the slot for the screwdriver of one nipple to the same place of the diametrically opposite nipple. The equivalent diameter of the rim cannot be obtained by direct measurement without special measuring tools. It can be calculated as follows.
1. Carefully measure the external diameter of the rim ORD (from one edge (face) to the other) Make sure that the tape measure or ruler passes exactly through the center of the rim. It is better to measure through the centers of opposite spoke holes. Make at least two measurements taken at right angles to each other to check if the rim is round. If these two values differ, take another measurement in another place and average the results.
2. Insert a nipple into any hole in the rim. Measure the distance from the face of the rim to the bottom of the slot for the screwdriver in the nipple with a caliper. This will be the size HN. At this point, the spokes in a fully tensioned wheel should end.
3. Calculate the equivalent rim diameter using the formula ERD=ORD-2*HN.