PS Magazine - TB 43-PS-573

PS, The Preventative Maintenance Monthly

ISSUE 573

AUGUST 2000
PS Magazine - TB 43-PS-573 - Page 3 of 43
PS 573
2
AUG 00
’Course, once you leave the sand you’ll need to increase tire pressure for
driving on hard surfaces. Again, drivers of CTIS-equipped trucks just need to
flip a switch. For everybody else, it’s a tougher job—for safety reasons.
If you have to add
more than 10–15 pounds
to the tires, use the inflator
gauge and hose, NSN
the job. That’ll put 10 feet
of hose between you, the
tire and the wheel as you
reinflate it. It lets you stay
out of the danger zone in
case the tire explodes or
the wheel flies apart.
Avoiding Flats
Try not to run over cactus or brush. Many have spines and thorns that break
off in tires—where you can’t see them—and
work their way through. You’ll have more leaks
than you know what to do with.
Take it easy in rocky, rough terrain. The
sidewalls on radial tires are thinner than bias
ply tires and rocks cut them to ribbons. Small
emplacement excavators (SEEs) are especially
prone to tire damage because they’re right out
there where the going is rough.
Tubeless tires lose air traveling through rocky
terrain when the tire breaks loose from the rim.
So check tire pressure more frequently when
operating in the desert.
During stops, look for rocks caught between
dual tires. Rocks between sidewalls rub holes
in the tires.
ires suffer a double whammy in the desert.
First, there’s the increased heat. Then,
there’s the terrain. You can’t change either,
but you can reduce the damage they cause.
Operating under normal conditions, tires
get hot as they flex under load. When
operating in desert heat, the tires can’t
cool off, causing them to weaken.
Help save your tires by not overloading
the vehicle. Less weight means less
wear and damage. Sure, you’ve got to
move a load, but keep in mind the
capabilities of your trucks and trailers
and their tires.
If you use a lower tire pressure for
driving in the desert, drop your speed,
too, to reduce tire wear from flexing.
Some operator manuals list lower pressures
to give the tires more flotation and traction in sand. Note that this can increase
tire wear if vehicle speed is not lowered.
Tires . . .
Trucks equipped with a central tire inflation system (CTIS) have a setting
specifically for operating in sand, so use it.
M939A1/A2 series
(14.00 x R20)
HIGHWAY
- front & rear
Standard (psi)
60
60
60
60
60
60
60
60
60
80
Metric (kPa)
414
414
414
414
414
414
414
414
414
551
CROSS COUNTRY
- front & rear
Standard (psi)
35
35
35
35
35
35
35
35
35
35
Metric (kPa)
241
241
241
241
241
241
241
241
241
241
MUD, SAND and SNOW
- front & rear
Standard (psi)
25
25
25
25
25
25
25
25
25
25
Metric (kPa)
172
172
172
172
172
172
172
172
172
172
EMERGENCY
- front & rear
Standard (psi)
12
12
12
12
12
12
12
12
12
12
Metric (kPa)
83
83
83
83
83
83
83
83
83
83
ALL MODELS, SPARE
inflate to maximum highway pressure
M923
M925
M927
M928
M929
M930
M931
M932
M934
M936
heh,
heh,
heh!
this
heat
is
killing
my
tires
.
huh?
thanks to
pm
-
-
i'm
ready
for the
long haul
!
Here’s an example for the M939-series trucks:
Rocks stuck between
duals kill tires
Avoid danger zone when reinflating tires
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