When an 18-wheeler overtakes your RV, it's bow-wave of air hits the left rear of the coach first, and that pushes the rear toward the shoulder. When the body rear moves right slightly before the rear axle does, it amplifies the push to the left that you feel in the front causing you to correct by steering to the right.
As the 18-wheeler bow wave moves toward the front of the coach, it pushes the front of the coach to the right, and when the body moves right slightly before the front axle does, it amplifies the steering correction you have already done causing you to have to correct to the left.
This whole thing, if you are not used to the feelings, can be quite scary. One way to overcome that is to install Vortex Generators like Air Tabs They cut down on the dead air and drag on the rear of RV and greatly reduce the bow wave of passing trucks.
I have
AIRTABS on my Class C.
They really help on a cross wind situation,no more sudden buffeting. It has stopped the sideways push when being passed or passing a large truck.
They are a vortex generator that produce a counter rotating air trail several feet behind the vehicle, This airflow alteration improves vehicle stability. As far a mileage it may helped some but the stability they provided is amazing.
