In general, on
__wet__ surfaces, the effective tire-surface friction coefficient decreases
with speed and c_{μ} (card 12:field 7) can be used to simulate the decrease.
The effective friction coefficient, used in all **SMAC** calculations, is
computed as:

μ_{effective} =
μ_{0} -
μ_{0
* }c_{μ}_{ *
}|v|

where :

μ_{0} =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 C_{μ}=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 μ_{effective} for a
μ_{0=}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 C_{μ}=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.

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