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398 Multibody Systems Approach to Vehicle Dynamics
Table 7.1 Time to complete lap of a marked 200 m diameter
circle (seconds)
Test 1 Test 2 Test 3 Test 4 Test 5
Configuration A 21.38 21.71 21.57 21.61 21.50
Configuration B 21.60 21.49 21.29 21.39 21.53
Time to lap 200 m (seconds)
21.90
21.80
21.70
21.60
21.50
21.40
21.30
21.20
21.10
21.00
20.90
20.80
Fig. 7.2
A A A A A B B B B B
Repeat Repeat Repeat Repeat Repeat Repeat Repeat Repeat Repeat Repeat
1 2 3 4 5 1 2 3 4 5
Raw data from steady state test with error bars
Table 7.2
Statistical summary of test data
Mean
Population standard
deviation
Configuration A 0.866g 0.010g
Configuration B 0.874g 0.010g
Difference A B 0.008g
particularly in intermediate configurations before matters are finalized and
particularly if the tyres themselves are prototype items.
If these measurements are manipulated into lateral acceleration figures
using the simple relationship
A
y
(200 / t) 2
100
(7.1)
then treated as the results that might be obtained from a production process
and manipulated accordingly, the results in Table 7.2 emerge.
It is clear that the extrapolation to a population from only five samples is
somewhat poor practice. However, it is equally clear that the difference
between the two configurations is significantly less than the spread of the
distribution of the tests. In statistical process control, a process is regarded
as ‘capable’ if six times the standard deviation (so-called ‘6’) is less than
75% of the tolerance on the measured attribute. For the measurement processes
above, the ‘capability’ is no less than 6 0.01 4/3 0.08g – 10 times