In general, on wet surfaces, the effective tire-surface friction coefficient decreases with speed and cμ (card 12:field 7) can be used to simulate the decrease. The effective friction coefficient, used in all SMAC calculations, is computed as:
μeffective = μ0 - μ0 * cμ * |v|
μ0 =the nominal coefficient of friction, and |v| =the absolute value of the tire speed in inches/sec.
Some manuals for other versions of SMAC have recommended the use of a value of Cμ=0.0003 sec/in. This value should not be used for dry pavement. The use of this value for dry pavement results in the following μeffective for a μ0=0.70:
Speed in MPH XMU Speed in MPH XMU
20 0.63 60 0.48
For dry pavement applications a reduction in the effective friction coefficient is normally not as apparent as in wet road applications.
Therefore, for dry pavement, normally you should set Cμ=0.0.
NOTE: An additional option of different CMU form Vehicle 1 and Vehicle 2 has been added. Simply set CMU2 = some value other than 0.0 and it will set CMU2 for ONLY Vehicle 2. CMU will then be used ONLY for Vehicle 1.