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where specifically noted .
The vehicle characteristics which dominate the
instability modes are the following :
a . There are three wheels . Unless the vehicle is being
operated at constant speed , on level ground , in a
straight line , forces will be encountered which give rise to what I call a " tilt axis , " dictated by geometrical
considerations .
b . Of critical importance is that the line which divides stable
from unstable is abrupt , and the transition is practically
instantaneous .
c . In this geometry , the location of the center of gravity of
vehicle is critical , as is also the center of gravity of the
vehicle operator .
The following types of vehicle accidents can be anticipated as intrinsic
features of the inherent instabilities :
a . Even at standstill , with the vehicle on a side slope ,
at a modest angle , the vehicle will tilt over in
a direction forward and down hill .
b . Even on level ground , with the vehicle turning , and
even going at fairly modest forward speeds , the
vehicle will turn over in a direction forward and
toward the outside of the turn .
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