Frame and Underbody Description: Frames

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The frame structure is independent of the body. The full frame extends the entire length of the vehicle. It supports the engine, transmission and the body. The suspension supports the weight of the frame. The metal thickness of the frame varies depending on the application and could be anywhere from 3 to 6 mm thick. Frames are covered with a wax base coating for rust protection.

All frames have body mounts welded to the structure. Thick rubber insulators are positioned between the body mounts and frame of the vehicle. These insulators absorb normal road noise and vibration generated by the suspension.

The following terms are defined:

Section Modulus: A measure of the strength of a frame based on the height of the side rails, the width of the side rails, the thickness of the side rails, and the shape of the side rails. The section modulus does not account for the strength of the material used in the frame.
Yield Strength: A measure of the strength of the material from which the frame is made. The yield strength is the maximum load that can be placed on a material and still return to the original shape. The yield strength is measured in kPa (psi).
Resistance To Bending Movement (RBM): A single measure of the frame strength that accounts for the section modulus and the strength of the material used.
Web: The vertical component of a channel-type frame rail.
Datum: The plane of the underbody of the frame from which all the vertical measurements begin.
Tram Length: The measurements that are 2-dimensional. The measurements are parallel to the datum line.