Get your spoke lengths exactly right with CalipERD™!

This tool provides a new way to measure Effective Rim Diameter – the most critical dimension when calculating spokes.

Current methods to measure rims are clumsy and imprecise. With CalipERD™ you get results that are Fast, Accurate, & Precise!

With this tool, you know with certainty what you’re measuring and how it compares to published values.

Use the adjustable window to allow one-shot exact measurement of ERD!

• Adjustable calibration window
• Measures nearly any rim!
  • up to 750mm reliably (fits 32″ and 36″ rims)
    • 125mm minimum (~ 12″)
  • 53mm throat/swing/reach distance – fits most fatbike rims
  • 100mm feeler depth – fits 80mm deep aero rims (theoretically works on 100mm rims, cannot test them all)
• Precise to within .5mm
• Interchangeable Feelers for different applications
  • includes Standard Nipple and Internal Nipple Feeler Sets (v1.1, April 2025)
• Includes calibration tool

Use cases include:

• Checking factory specifications
• Obtaining Data-driven roundness of a rim
• Verifying stated dimensions of Manufacturer
  • (are they suggesting an actual ERD? Based on which nipple?? Do they mean Nipple Seat Diameter? Using their own washers???)

CalipERD™ Instruction Manual v1.1

CalipERD™