### Examples - Tire Cornering Stiffness Calculation

When the
tire is orientated at an angle to the direction of motion, a steering force
occurs perpendicular to the plane of the tire. This force does not vary
linearly with the tire slip angle, but the relation is nearly linear for small
slip angles. The nominal cornering stiffness is equal to the side force in
pounds divided by the slip angle in radians for small angles. For larger angles
the rate of increase of perpendicular force with increasing angle falls
off as "saturation" is approached. The program handles this in a standard manner
for all tires. A Typical value for the cornering stiffness per degree of
slip angle is approximately 16-17% of the load on the tire.

Tire
cornering stiffness properties are input separately to allow the simulation of
tire damage--a damaged tire which has lost its pressure will have a
substantially lower cornering stiffness, perhaps 20 percent of that for an
undamaged tire. Under-inflated tires will have somewhat lower cornering
stiffness than those of properly inflated tires, but far greater than seriously
damaged tires.

The following example
demonstrates the calculation procedure for the tire cornering stiffness. Assume
you have a 4000 lb. vehicle with 60/40 weight distribution. Per original SMAC,
the cornering stiffness would be calculated for a neutral steer vehicle as
follows: (note that for m-smac, the inputs can be
entered as positive or negative)

For front wheels,
CSTF(1),CSTF(2) = 4000*0.60*0.50*0.165*57.29578 = -11345. Lbs/rad

For rear wheels, CSTF(3),CSTF(4) =
4000*0.40*0.50*0.165*57.29578 = -7563. Lbs/rad

The inputs in Default (EDSMAC compatible) units are
as follows:

For front wheels, CSTF(1),CSTF(2) =
4000*0.60*0.50*0.165 = 198. Lbs/deg

For rear wheels, CSTF(3),CSTF(4) =
4000*0.40*0.50*0.165 = 132. Lbs/deg

More:

DISCUSSION: Moment of
Inertia