Wheel Size/Bead Seat Diameter

What is Wheel Size/Bead Seat Diameter?

This attribute describes the diameter of a bike’s rim. Several options are provided covering the most common labeled sizes:

700c, 29”, or 28” (Germany) - 622 BSD
650b or 27.5” - 584 BSD
26” - 559 BSD

For less common rim sizes, these may be entered into the Bike Insights database using the rim’s Bead Seat Diameter (BSD). This is the measurement of the “shelf” in the rim that the tire seats into. BSD is sometimes referred to as the ISO/ETRTO rim size since it is maintained by the International Organization for Standardization (ISO) and was developed by the European Tyre and Rim Technical Organisation (ETRTO) as part of ISO 5775.

A comprehensive list of BSD sizes is available at Sheldon Brown's Tire Sizing Guide.

Why is it important?

BSD combined with Tire Width is used to calculate the approximate wheel diameter. We use this to determine fit characteristics like Standover and Tire to Pedal Spindle Distance as well as handling characteristics like Trail and Bottom Bracket Height.

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