Materials and Structure

The diagram shows typical dimensions and angles associated with a touring bicycle frame. W₁ and W₂ show the forces on the seat and the pedals due to a rider and R₁ and R₂ are the forces acting on the frame due to the reaction forces at the wheel axles. The bicycle must be in equilibrium under the action of these forces, and that requires that there are no net forces or moments acting on it.

All forces are "vertical" and force balance gives: (W₁ + W₂) = (R₁ + R₂) = 668 N.

Moments can be taken about any point, and selecting the front axle (D) gives:

From: McMahon and Graham:
"The Bicycle and the Walkman," Merion (1992)

0.63 W₂ + 0.783 W₁ = 1.064 R₂ (N.m) and solving this equation for R₂ gives: R₂ = 472.3 N. Substituting this value into the force balance equation gives R₁ = 195.7 N. All of the forces acting on the frame under static conditions are now known and may be used to evaluate forces (and hence stresses) acting on the frame tubes.