In Gear - Today's Trucking

for a full load will bounce like crazy when
empty or lightly loaded.
Low-spring-rate suspensions could also
help to reduce irregular wear by maintaining
better contact between the tire and
the road.
“Air suspensions typically have a lower
spring rate than leaf spring suspensions,
and they maintain a relatively constant
low spring rate whether the trailer is
loaded or empty,” says Jim Rushe, program
manager for on-highway products at
Hendrickson. “Air suspensions also have
shock absorbers that dampen the suspension
movement, further improving the
suspension’s ability to maintain tire contact
with the road.”
Leaf springs provide a stiffer ride on an
empty trailer resulting in a varying load on
the tire as it encounters irregular road
surfaces, Rushe adds. “Leaf spring suspensions
do not have shock absorbers, but the
leaf springs themselves provide some
damping characteristics.”
In many high-empty-mile applications,
tires and suspensions run either fully
TREADING A BIT TOO LIGHTLY: Normally
loaded, tires have a flat, even footprint. When
empty at highway speed, the only center of
the tread makes contact with the pavement.
loaded or empty, so “tuning” the suspension
and tire pressure to work equally well
at opposite ends of the spectrum is realistically
out of the question.
“For air suspensions, the air pressure is
used to maintain the trailer height, so
changing air pressure would have little
effect on the spring rate,” notes Rushe.
“Leaf springs can be designed to provide
varying spring rates at different loads, but
the amount the spring rate can be varied
is limited.”
Since there are no spec’ing options to
help manage this unique situation, the
duties seem to fall on the maintenance
department’s shoulders. Beckett sees this
issue cropping up constantly in his alignment
shops. He suggests the jump-in
point is careful tire matching.
“Mixing brands and models of casings
in a dual assembly encourages irregular
wear. They don’t all have the same sidewall
flex,” he says. “The more focus on matched
brands, models, circumference, and infla-
In Gear
tion pressure, the better the tires will wear
—even under these conditions.”
And he says shock absorbers on air
suspensions need particular attention.
“That’s where all the damping takes place.
If they’re failing, your tires will fail too.”
Since your fuel costs will be lower in a
half-loaded application, maybe some of
the savings should be allocated to the
maintenance budget. ▲
How much revenue can you
afford to lose? Whether it’s
for billing purposes or DOT
compliance, all CAT Scales are
certified. CAT Scale weights
are guaranteed accurate.
COVER YOUR REAR
with CAT Scale.
CAT SCALE CO.
Walcott, IA
1-877-CAT-SCALE
www.catscale.com
®
JANUARY 2010 43