Get your spoke lengths exactly right with CalipERD! This tool measures Effective Rim Diameter – the most critical dimension when determining spoke length.

Current methods to measure rims are clumsy and imprecise. With this tool you can get results that are Accurate, Precise, Repeatable, & Fast.

This provides the perfect spoke length by determining the correct nipple seat diameter.

Use as a strict measuring tool or enjoy the adjustable window to allow one-shot exact ERD measurement!

• Provides direct measurement of a rim
• 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™