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Below
are basic illustrations that in principle can be applied
to either tractor or trailer tandem alignments.
Shown
to the right in Figure A.1 is a properly aligned
vehicle diagram.
In
Figure A.2 we see drive axles that are parallel
to each other but not perpendicular to the chassis
centerline. The drives in this example create a "thrust
angle" to the right at the rear of the vehicle. Turning
the steer wheel slightly to the right will align the
drives and steers to run parallel but the vehicle will
"dog track". Even though lateral forces on the steers is
minimal, this can result in asymmetrical steer tire
wear.
In
Figure A.3 the illustration shows the most severe
condition that occurs. Here the drive axles are neither
parallel to each other nor perpendicular to the chassis
centerline. The drives are forcing the vehicle to turn
left so the driver must turn right to compensate. This
will result in the most severe fast and irregular wear.
Recent studies also indicate that the steer tire on the
side in which the drives are closest together will wear
into an out-of-round condition as well.
Figures
A.4 and A.5 illustrate recommended
tolerances for tandem axles.
A.4
- Axles are to be perpendicular to chassis centerline
within 1/8" when measured from axle end to chassis
centerline, or 1/4" when measured from left to right
axle end.
A.5
- Axles are to be parallel to each other within 1/8"
when measured at axle ends. |
