WikiPedalia is not endorsed or affiliated with the Wikimedia Foundation.
Extension
The length of the part of the stem that runs forward from the shaft to the handlebar clamp. Stems are available with different length extensions to allow the bicycle to be adapted to fit the rider. See also my article on Frame Sizing.
Extension (or "reach") is commonly measured from the centerline of the shaft to the center of the handlebar. Unfortunately, common industry practice is to measure this along the direction of the part that points forward. Since different styles of stems have different shapes, two stems with the same extension measurement may not have the same actual distance between the centerline of the handlebars and the steering axis.
Occasionally the term "extension" is used as a synonym for a handlebar stem, particularly one with a long extension.
