Calculating Aerodynamic Drag (CdA) And Rolling Resistance
Note: A list of CdA measured for 100’s of cars is available here.
For more technical information about how the car’s power is calculated is available here.
Setting the aerodynamic details
The aerodynamic factors and vehicle mass are required for the software to calculate the engine power. To calculate these parameters you will need to perform a "coast down" test.
Calculating CdA and rolling resistance
The method described here is suitable for use with vehicle speeds up to 100kph (60mph). Coast down calculations should be done on a flat surface on a wind free day. Testing involves timing the vehicle whilst decelerating in neutral. Time the deceleration over two speed intervals, one high speed test (about 60-100kph or 40-60mph) and one low speed test (about 15kph or 10mph). The timing can be done accurately by using the DL90/DL1/AX22 to log speed data and then plotting graphs of the speeds. Enter the details into the table below, select the units you wish to use, then press Calculate to get the CdA and the rolling resistance values.
Note: Please note that coast down calculator shown below doesn't work in the offline help (i.e. The help file distributed with the Race Technology software setup program).
An accurate value for vehicle mass is important for calculating power values. The vehicle mass is for the vehicle as tested, including driver, fuel, and any luggage.