Proper frame alignment is critical in order to ensure normal life and function of many parts on the vehicle. If the vehicle is involved in a fire, a collision, or has been overloaded, inspect the frame alignment. If for any other reason misalignment is suspected, the alignment should be checked.

It is possible that certain conditions make the frame appear to be out of alignment when, in fact, the frame is not. Refer to Alignment Checking - Upper Body for description of these conditions.

The terms used in this section are briefly defined below:

Section Modules: A measure of the strength of a frame based on height, width, thickness, and the shape of the side rails. It 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. This is the maximum load that can be placed on a material and still have the material return to its original shape. Yield strength is measured in Kpa (psi).

Resistance to Bending Moment (RBM): A single measure of the frame strength that accounts for both section modulus and the strength of the material used.

Web: The vertical part of a channel-type frame rail.

Datum: The plane of the underbody of the frame from which all vertical measurements originate.

Tram Length: The measurements that are two dimensional and parallel to the datum line.