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406 Multibody Systems Approach to Vehicle Dynamics
Fig. 7.10 Platform motion during steering at low speed (black) in
comparison with the static platform position (grey dashed). Changes in wheel
weight are indicated; front left wheel has an increased reaction force
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Fig. 7.11 Effect of inside wheel loading in producing an excess side force due
to slip angle when the vehicle is in motion
This emphasis has the consequence of producing an effective side force
from the tyre because it is operating at a comparatively large slip angle.
Normally, side forces from both tyres work in opposition if the wheels are
effectively toed in when the Ackermann fraction is less than unity. However,
if the forces are not in balance (because of the weight imbalance between
inboard and outboard tyres) the additional side force on the inboard tyre
has the effect of reducing the steer aligning torque when the vehicle is in
motion. If the Ackermann fraction is particularly low, the vehicle will have
a ‘wind on to lock’ behaviour at car park speeds beyond certain steer angles.