Theory of OperationIn heavy load conditions, the normal acceleration rate of the truck is limited due to the amount of Torque / Inertia needed to move the truck and get it up to speed. As you can see in the diagram, the red heavy loaded line is already operating below the VAM values in normal operation. When a truck is lightly loaded (is in a bobtail condition or in diminishing load applications) the vehicle can accelerate and continue to accelerate at a much quicker rate. This excessive acceleration can lead to an increase in the fuel consumed, and an increase in driveline and tire wear. Enabling VAM and utilizing the default values trucks in lightly loaded conditions will have a limited acceleration curve that follows the black 'VAM' line in the diagram. This line mimics the typical acceleration of a heavy loaded vehicle.