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!

The perfect spoke length is found by determining the correct nipple seat diameter. 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 ERD measurement!

• 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 100mm but untested)
• 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™