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.

  1. 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.
  2. Stick the ruler onto a piece of card that is around 10mm thick (this measurement should be half the width of the rim).
  3. Place the rim measuring tools into the rim and position the left side tool on the left edge of the ruler (the 400 mark).
  4. The measurement at the right side tool is the ERD with no further calculations required.

It is advisable to periodically check your ruler accuracy (re measure the 220mm as shown on the print) to make sure your printer paper has not shrunk or expanded due to humidity changes.