Measuring & Using Frame Angle

The CASTER specification assumes a level frame, so it is necessary to consider frame angle in all checks and adjustments. First, measure caster in the normal manner.  Next, using a frame angle protractor, measure the frame angle at the location indicated in the illustrations below. If the frame is inclined toward the front (up in rear), add the frame angle value (without + or -) to the measured caster angle. If the frame is inclined toward the rear (down in rear), subtract the frame angle value from the measured caster angle. The resulting value is the corrected caster angle.  Compare the corrected caster value with the specification to determine what change is needed. All models should be adjusted at curb weight.

Example 1: Caster Specification:  4.5º Measured caster angle:  3.5º  (out of spec?) Frame angle:  1.0º  (up in rear) Corrected caster:  4.5º  (3.5 + 1.0) Change required: NONE	Example 2: Caster Specification:  3.5º Measured caster angle:  3.5º  (in spec?) Frame angle:  -1.0º  (down in rear) Corrected caster:  2.5º  (3.5 - 1.0) Change required: +1º