03 - Coastdown test theory

The test is performed in accordance with European Directive 70/220/EEC – Annex III and is based upon statistical evaluation of a minimum of 4 test runs.

The test results are considered to be valid when the statistical accuracy of the average test values is ≤ 2%.

The test can be performed at any speed according to the manufacturer’s requirements, but must follow the general procedure below:
 

1. Accelerate the vehicle to a speed 10 km/h greater than the test start speed (user definable – 125 km/h in the diagram)
2. Place gearbox in neutral
3. Measure the time taken for the vehicle to decelerate from the start speed to the stop speed (user definable – 85 km/h in the diagram). This is time t1.
4. Repeat steps 1-3, but in the opposite direction. This is time t2
5. Take the average time of these two test runs (t1 + t2)/2. This is the time T
    

Repeat steps 1 to 5 until such time that the statistical accuracy of the average is not more than 2%
 

The statistical accuracy (p) is defined by:
 

Where:

= Coefficient given by the table below,

n = Number of tests

s = standard deviation 
 

	n
	4	5	6	7	8	9	10	11	12	13	14	15
t	3.2	2.8	2.6	2.5	2.4	2.3	2.2	2.2	2.2	2.2	2.2	2.2
	1.6	1.25	1.06	0.94	0.85	0.77	0.73	0.66	0.64	0.61	0.59	0.57