In Gear - Today's Trucking

would occur at the same rate on a loaded
or empty tire, whereas the regular wear
would be slowed. The irregular wear patterns
become more pronounced sooner.
This could lead to the assumption that
running light or empty is the root cause of
the accelerated wear.
Mike Beckett of MD Alignment in Des
Moines, Iowa, disagrees with that assumption—to
a point. He was once called upon
to settle a dispute between a fleet owner, a
tire maker, and a trailer maker. A large
portion of the trailers in that fleet were
burning through tires in about 25,000
miles, Beckett says.
“The fleet ran 250- to 450-mile headhauls
and returned empty. Through all the
finger pointing, the high percentage of
empty miles incorrectly emerged as the
principal culprit,” Beckett says.
Upon inspecting the fleet, Beckett found
higher-than-normal incidences of loose
wheel bearings, improperly matched tires
in dual assemblies, and improper inflation.
“Once all the problems were rectified—
and they went to a quality tire—the fleetaverage
miles-to-pull leapt to 150,000
miles. Was it the high empty miles? No, it
was poor maintenance,” he says. “The fleet
wasn’t taking the right steps to correct
the problem.”
CHANGING THE FOOTPRINT
Idaho Milk Transport is a textbook case of
a high-empty-mile fleet. Based in Burley,
Idaho, the food-grade tank carrier runs a
lot of dedicated trailers loaded one way
and back empty. Leased owner-operator
Tony Head says he has switched to
running a closed-shoulder drive tire to
minimize cupping along the edge of his
dual drive tires.
“I used to run lug tires, but the edges
cupped out real quickly,” he says. “And I
see more center wear on the company’s
wide-base single trailer tires.”
Shawn Estes, IMT’s fleet services facilities
manager, agrees with Head’s observations,
and while he notes that proper
alignment can solve some of the cupping
problems, he says running light seems to
make the problem worse.
“The unloaded tires just skip down the
road without any weight to bear down on
the tire,” says Estes.
The tread surface is generally pretty
In Gear
SHOCK ABSORBER MAINTENANCE
Even the best shock absorbers won’t last forever, though one might not suspect
a problem from outward appearances. While TMC strongly recommends establishing
a shock replacement interval, RP 643 stresses that no two operations or
vehicles for that matter will experience shock deterioration at the same rate. As a
guideline, TMC suggests replacing shocks when installing new tires.
Visually inspect the shocks during the “A” service, or every 10,000 to 20,000 miles.
Examine the shock body for damage, dents, cracks, etc. Inspect the mounts and bushings
as well for deformation or looseness, and watch for raw oil leaking from under the
dust tube. An oily residue on the shock body is acceptable and considered normal
under some conditions. Liquid oil running down the shock body demands a replacement
(see accompanying photo).
During the “B” service, check the body of the shock for elevated temperature after a
short drive. It should be obviously warmer than the surrounding hardware. If not, it’s not
doing its job, and it has likely failed. Consequences of running on failed shocks include
ride deterioration, excessive vibration, and eventually cupping of the shoulder ribs on
tires. Hopefully you catch a failed shock before it begins to wear out your tires.
close to flat, or square with the road, at
operating pressure. Under load, contact
with the pavement is pretty even across the
tread face, but when empty at normal operating
pressure, the center of the tread tends
to be slightly higher than the shoulder. This
is more acute at high speed, where centrifugal
force also acts on the tread causing
it to extend outward at the center.
What you have is an egg-shaped foot-
print, with the center of the tread having a
slightly larger circumference than the
edges. This increases the scuffing action
because the edges are not revolving at the
same rate as the center of the tread.
“In addition,” notes Bridgestone’s Guy
Walenga, “an unloaded tire that bounces
along the road actually slows while it is
airborne causing a minor bit of scuffing
each time it regains contact with the road.”
JANUARY 2010 41