An inertial force is created an object experiences an acceleration and the frame of reference accelerates along with the object. An example of this is centrifugal force. Let's say you take a left turn in a car. You will feel an inertial force pushing you to the right (because your frame of reference is accelerating). An outside observer (with a fixed frame of reference) will not notice this force, and will only see the car accelerating to the left.
When the car produces lateral and longitudinal forces, inertial forces act at the car's center of gravity in the opposite direction. This causes the weight of the car to "transfer" in the direction of that force.