Take the rear triangle and consider the point C (the axle location of the rear wheel).

This location is in equilibrium under the forces F₁ in the seat stay, F₂ in the chain stay, and the reaction force R₂ (105.7 lbf).
These forces must be resolved in the horizontal and vertical directions, and equations can then be written for the force balance in each of these directions.

The horizontal force balance gives:
F₂ cos(11.5) = F₁ cos(58.5) or F₁ = 1.875 F₂

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

From the vertical balance:
F₂ sin (11.5) + F₁ sin(58.5) = 105.7. Substituting F₁ in terms of F₂ gives: F₂ = 58.8 lbf Substituting this value in the horizontal balance equation gives: F₁ = 110.2 lbf.

The direction of these forces show that the chain stay is in tension and the seat stay in compression