What is rims ERD? How is ERD measured?

What is rims ERD?

ERD (Effective Rim Diameter) is important data for calculating the length of the spoke. ERD refers to the maximum distance of the spoke from one end of the rim to the other end. Next, we discuss how to calculate ERD.

As shown in the picture below, ERD=nipple length*2 + the length between 2 opposite nipple seats of spoke holes. So the length of the nipple will affect the ERD, with different nipples, the ERD value will be different, so we recommend that you measure the ERD before building the wheel.

How to measure ERD?

First, you need to insert the two spokes into the opposite holes, then screw the nipple onto the spokes.

Then measure the length between 2 opposite nipple seats of spoke holes (A). The measurements were averaged at multiple locations of the rim.

Finally, measure the length of the nipple (B). Finally came to the conclusion ERD=A+2B.