This tool measures Effective Rim Diameter – the most critical dimension when determining spoke length.

Current methods to measure rims are clumsy and imprecise. That’s why this tool exists.

Accurate, Precise, Repeatable, Fast. This will allow a perfect spoke length by determining the correct nipple seat diameter. The adjustable window can be used to add nipple height (x2), allowing a 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
• Precise to within .5mm
• Interchangeable Feelers for different applications
  • includes Standard Nipple Set only (Effective February 2024)
• Includes calibration tube

Use cases include:

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

CalipERD™