# Coastdown Programme

This programmme calculates the coefficient of drag and coefficient of rolling resistance using data gathered from coastdown testing. This data is very useful for the calculation of vehicle performance parameters such as acceleration, top speed etc.

## Calculate CDA

In order to obtain the CDA for a vehicle, ideally the coastdown testing should take place at a relatively high velocity such that aerodynamic drag is of higher magnitude compared to the rolling resistance drag.

For this example, the vehicle has a mass of 1400 kg and a CRR of 0.010. Coastdowns are carried out between speed points of 120 and 80 km/hr. The average time taken is 33 seconds. This results in a calculated CDA of 0.721 as shown in diagram below. Top

## Calculate CRR

In order to obtain the CRR for a vehicle, ideally the coastdown testing should take place at a relatively low velocity such that aerodynamic drag is of lower magnitude compared to the rolling resistance drag.

For this example, the vehicle has a mass of 1400 kg and a CDA of 0.712. Coastdowns are carried out between speed points of 40 and 15 km/hr. The average time taken is 59 seconds. This results in a calculated CRR of 0.0101 as shown in diagram below. Top