Bicycle Frame - Frame Geometry

The length of the tubes, and the angles at which they are attached define a frame geometry. In comparing different frame geometries, designers often compare the seat tube angle, head tube angle, (virtual) top tube length, and seat tube length. To complete the specification of a bicycle for use, the rider adjusts the relative positions of the saddle, pedals and handlebars:

• saddle height, the distance from the center of the bottom bracket to the point of reference on top of the middle of the saddle.
• reach, the distance from the saddle to the handlebar.
• drop, the vertical distance between the reference at the top of the saddle to the handlebar.
• setback, the horizontal distance between the front of the saddle and the center of the bottom bracket.
• standover height, the height of the top tube above the ground.
• toe overlap, the amount that the feet can interfere with steering the front wheel.

The geometry of the frame depends on the intended use. For instance, a road bicycle will place the handlebars in a lower and further position relative to the saddle giving a more crouched riding position; whereas a utility bicycle emphasizes comfort and has higher handlebars resulting in an upright riding position.

Frame geometry also affects handling characteristics. For more information, see the Bicycle and motorcycle geometry and the Bicycle and motorcycle dynamics articles.