Originally Posted by
LesterOfPuppets
Are there enough variables to account for running TT discs front and rear?
Yes, the aerodynamic characteristics of the bicycle and rider are included in the K_2 constant which depends on the coefficient of drag of the bike/rider and the effective frontal area.
To Shimagnolo's comment on the last V_g:
The formula given is correct. The drag force due to air resistance is proportional to the wind speed squared - hence the (V_a)^2. But the power needed to move at a given speed is: P = V x F, so you multiply the drag force by the ground speed of the bike.