Practical guide

How to Measure a Bicycle Hub for Spoke Length

Measure left and right flange PCD, center-to-flange distance, OLD and spoke-hole diameter using the same references as the J-bend formula.

The J-bend spoke model needs three hub dimensions on each side: flange pitch-circle diameter, flange-center distance from the wheel centerline, and spoke-hole diameter. Measure left and right independently; cassette, brake and bearing packaging commonly make them asymmetric.

Confirm the topology first

This workflow is for a conventional two-flange hub drilled equally and alternately for J-bend spokes. Stop if the hub is straight-pull, paired-hole, 2:1/triplet, grouped-hole, crow’s-foot-specific or uses another proprietary anchor. Those designs cannot be made valid by entering an approximate flange diameter.

Measure flange pitch-circle diameter

Pitch-circle diameter (PCD) passes through the centers of the spoke holes.

1. Identify two genuinely opposite holes on one flange.
2. Measure from one hole edge to the same edge of the opposite hole. Edge-to-same-edge preserves the center-to-center distance when the holes are equal.
3. Repeat across another pair.
4. Record the left and right flange PCD separately.

Do not measure the outside metal diameter of the flange. That includes material beyond the spoke-hole centers and will change the formula.

Measure center-to-flange from OLD

OLD is the distance between the hub’s frame-contact faces—normally locknuts or end caps—not axle-tip length.

1. Measure OLD between the contact faces.
2. On the left, measure from the left contact face to the center plane of the left flange.
3. On the right, measure from the right contact face to the center plane of the right flange.
4. Calculate each side:

left center distance = OLD/2 − left face-to-flange-center

right center distance = OLD/2 − right face-to-flange-center

If the subtraction becomes negative, the reference or measurement is wrong. Do not take the absolute value to conceal that error.

Measure spoke-hole diameter

Measure the opening used by the J-bend spoke, not the flange PCD. The calculator subtracts half this diameter from the geometric center-to-center distance under its documented J-bend convention. Entering hole radius instead of diameter applies the correction incorrectly.

Offset rim sign

Hub dimensions stay tied to the wheel centerline. Rim offset moves the effective nipple plane. BrowserPowerTools defines positive offset toward the right side, so the left effective separation is |cL + o| and the right is |cR − o|. Use the on-page diagram rather than relying on drive-side shorthand.

Final checklist

• Total hub and rim hole counts match and are even.
• The topology is conventional alternating J-bend.
• PCD is through hole centers.
• Center-to-flange values are one-side measurements, not total spacing.
• OLD uses frame-contact faces.
• Rim offset direction is documented.

Preserve the checked measurements for a spoke calculation, then retain the raw result and any stock comparison separately in a printed worksheet or CSV. The spoke-length flagship remains out of the search index until its required wheelbuilder review is signed off.