Rim ERD measuring ruler
The wheelbuilding book describes in detail how to make the ERD measuring tools and the technique for taking the measurement. In the book I mentioned the availability of a custom ruler which speeds up the measuring process.
I use a custom ruler myself and I've made it available to you. The ruler is for measuring rims with an ERD in the range 400mm to 620mm using 200mm measuring spokes.
- Download and print the ruler. It's vitally important that you print the ruler at 100% so read the notes on the print and check it is correct.
- Stick the ruler onto a piece of card that is around 10mm thick (this measurement should be half the width of the rim).
- Place the rim measuring tools into the rim and position the left side tool on the left edge of the ruler (the 400 mark).
- The measurement at the right side tool is the ERD with no further calculations required.