Here is the formula for calculating the area of the friction material.
3.1415927(pi)/4 x diameter squared.
Using Firechicken's T/C as an example: The OD of the friction strip is 9" and the ID of the friction strip is 7.5".
.7853982 x 81 = 63.617 OD figure.
.7853982 x 56.25 = 44.178 ID figure.
63.617 - 44.178 = 19.439 square inches of effective friction element area.
3.1415927(pi)/4 x diameter squared.
Using Firechicken's T/C as an example: The OD of the friction strip is 9" and the ID of the friction strip is 7.5".
.7853982 x 81 = 63.617 OD figure.
.7853982 x 56.25 = 44.178 ID figure.
63.617 - 44.178 = 19.439 square inches of effective friction element area.