If that was important, why couldn’t they allow adjusting the draft effect individually? (i.e. I can change a setting that indicates that I only want 50% of the draft effect so I have to work harder in the group). Pretty simple to divide a formula by 1/2, no?

Not really. If a rider becomes 3 times heavier, their volume increases by 3 times (assuming a constant human density). When you increase the volume of a specific 3 dimensional shape while keeping one of it’s dimensions (height) constant, the other dimensions increase by a factor of the dimension to the two thirds power. So you don’t become 3 times wider if your weight increases by a factor of three. You become 3 to the 2/3 power wider. 3^0.66 = 2. So a rider becomes 2 times wider (and 2 times thicker). Frontal area and surface area increase in the same proportion. The reason that viewing power required to maintain speed inflates the drag increase is because of the way that power varies with velocity due to the nature of drag. Power required to maintain a given speed increases with the cube of speed. As drag coefficient increases, the power required to maintain a certain steady state speed increases above and beyond the drag coefficient increase.

example 3 (rotating group riders):

example 2:

example:

For approximately steady-state testing on mostly flat ground, such as you have done here, it is possible to calculate reasonable values for CdA using the steady-state cycling speed vs. power equation with drag and rolling resistance terms. I have done that calculation and the estimated values of CdA for your lead rider cases are shown below.

height weight power Calculated CdA (ft^2)
152 50 212 2.35
198    50   254    2.88
152    75    267    2.90
198    75    306    3.39
152    150    378    3.88
198    150    437    4.62

From the drafting rider speed and power, it is possible to calculate the “effective” CdA for the drafting rider. That calculation yields a value of effective CdA of the drafting rider in the draft of about 2.37 ft^2. (You can treat riding in the draft as an effective reduction in the CdA due to the form of the draft force equation).

Since you didn’t run the height/weight combination of the drafting rider in the lead position, the free stream CdA of the drafting rider cannot be determined directly, as it was for the front position riders. However, it can be estimated reasonably well analytically. That value is about 3.31 ft^2 based on a free stream power at 40kph of about 300 watts.

The difference between the free-stream CdA (3.31 ft^2) and the effective CdA in the draft (2.37 ft^2) for your 75kg, 183cm rider is about 28 percent. Your testing shows that the draft force on the 75kg, 183cm rider is reduced by 28 percent in the draft. The power savings (225 watts drafting vs. about 300 watts free stream) is about 25%.