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Hi, Im designing the brake system for a Formula SAE student project with the help of the volume Brake Design and safety (3rd ed) and I have a question about one equation. The equation (5-2) at page 126 computing the braking force on one axle is the following:
2*(Pl-P0)*Awc*nc*BF*(r/R)

My question is do the term Awc take in account the total wheel cylinder area or the pistons of one side of the caliper (assuming its a brake disc)? For example, will Awc for a 4 pistons (2 each sides) fixed caliper with pistons of 1.25in diameter will be : (4)*pi*(1.25^2)/4 or (2)*pi*(1.25^2)/4 ?