Rocker geometry explained: apex, radius, rise angle and onset
What a rocker is
A rocker is a curve in the sole, so that the front of the shoe lifts off the ground. Describing a rocker takes more than one number: where the curve starts (the apex), how tight it is (the radius) and how steeply the toe rises (the angle).
Apex, radius, angle and onset
The apex is the position along the shoe, from heel (0 %) to toe (100 %), where the forefoot curve leaves the ground. The radius is the radius of curvature of that forefoot curve, as a percentage of shoe length: smaller is tighter. The angle is the slope of the sole near the toe tip, and the rise angle is the slope of a straight line from the apex to the toe tip, a simple summary of how steeply the forefoot rises overall.
We also keep a visible-lift onset: the position from which the sole stays more than 1.5 % of shoe length above the ground. It is a visibility threshold, so it reads later than the apex. Different websites and papers use different definitions, and the research literature reports no agreed threshold, so compare figures only from the same source.
How we estimate them
We trace the sole outline on lateral and medial product photographs and fit a circle to the forefoot. Everything is relative to shoe length, so no calibration is needed. These are estimates of the unloaded shoe, labelled AI estimated with a confidence score, and typically good to a few percentage points. A value is only published where two different photographs agree, after correcting each camera's small systematic offset.
Values on this site
- Rocker apex (%): Where the forefoot curve leaves the ground, as % of shoe length from the heel: the tangent point of a circle fitted to the forefoot sole. Earlier (smaller) means the sole starts curving sooner. Estimated from photographs of the unloaded shoe; the research literature measures apex under load, so values are not interchangeable.
- Rocker radius (%): Radius of curvature of the forefoot rocker as % of shoe length (circle fit from apex to toe). Smaller means a tighter curve. Only reported when a circle fits the sole well. Estimated from photographs.
- Rocker rise angle (deg): Angle, against the ground, of a straight line from the rocker apex to the toe tip: how steeply the forefoot rises overall. Computed from the apex and the toe-tip height of the same photograph, without curve fitting. Estimated from photographs.
- Rocker angle at toe (deg): Angle of the sole near the toe tip against the ground. Larger means the toe rises more steeply. Estimated from photographs.
- Visible rocker lift onset (%): Position along the shoe (heel = 0 %, toe = 100 %) from which the sole stays more than 1.5 % of shoe length above the ground. A visibility threshold, so it reads later than where the curve begins (see rocker apex). Estimated from photographs.
Questions
- Why don't your numbers match another site's?
- Rocker has no standard definition. Apex, onset and radius measure different things, and values from loaded versus unloaded shoes differ. Check which quantity a source reports.
See it in the data
These pages describe product measurements. They are not medical advice or a recommendation for any person or condition. More: methodology, all explainers.