Spicer Tire Pressure Control - Manual (Page 2)

crowns or sharp break overs this can become
an important issue. It can also be noted how-
ever, that higher nominal speed capability
stemming from the improved ride and control
when traveling cross-country at reduced
pressures may allow the operator to traverse
some obstacles that could not be crossed at
lower speeds.
Customers should be reminded that one need
not actually install a tire pressure adjustment
system on their vehicle to determine if
reduced pressures will work in their opera-
tion. Manual reduction of tire pressure and
reduced speed operation until tires can be
re-inflated will allow most users to prove the
benefits to themselves with a minimal invest-
ment in time or money. It should also be
stated that the use of reduced tire pressure
will not prevent one from ever becoming
stuck again, especially when you consider the
prospects that you will be operating in places
where you may not have been previous to
using lower pressures.
How are tire pressure settings
developed?
Tire pressures have been developed to pro-
vide the sidewall deflections appropriate for
various tire sizes. Of course, one must
remember that reduced operating speeds are
required to use these reduced pressures.
Generally, tire manufacturers specify on-high-
way tire pressures to achieve sidewall deflec-
tions of 10-13%. These pressures allow
operating speeds up the tire design limit. Off-
highway deflections are typically 20-22% and
limit vehicle speeds to 35 mph. Emergency
pressure settings may go to 30% deflection,
with a typical speed limit of 10 mph.
The vehicle owner should always select tire
pressures with the assistance of their tire
supplier. The Tire and Rim Association has
developed reduced pressure and speed charts
to assist in selection of tire pressures.
When did Dana start making tire
inflation systems?
Dana is the world’s leading provider of central
tire inflation systems, having acquired the tire
management businesses in 1999.
Over 35,000 systems have been provided
since 1987 to numerous military and
and commercial programs. These systems
are fielded worldwide and were proven
in Operation Desert Storm as a vital
element of tactical wheeled vehicle mobility.
Several important features account for the
success of the product, among them:
- Depressurized control line strategy
which extends seal life, eliminates tire
leakdown when parked and provides
“fail safe” operating capability.
- Speed sensing to assure that tires are
not operated continuously at cross
country pressures when traveling at
highway speeds.
- Simple push button operation using
pre-set terrain based pressure modes.
- Electronic pressure supply sensing to
assure proper integration with brake and
other on-board air systems.
The Spicer ® Tire Pressure Control System,
was introduced to the commercial market in
1994. It is presently available from Kenworth,
Western Star, Volvo, Mack and Peterbilt.
Dana continues to work toward wider
availability of the system.
Tire Pressure Control was created by building
on the same technology used successfully in
the military systems. The following list
represents some of the many enhancements
that have been integrated into the commercial
version:
- Multiple channel operation, allowing the
independent control of pressures on
steer, drive and trailer tires.
- Integration of the wheel valve into the
hub cap using a rotary joint on non-
driven axles to simplify installation and
improve reliability.
- Introduction of diagnostic tools using
either industry standard devices or
personal computers, simplifying
troubleshooting and repair.
- Publication of troubleshooting, and
service manuals as well as driver
instructions and in-cab aids to improve
driver understanding of systems.
- Wheel valve design improvements to
increase system reliability with longer
trailer combinations and reduce
sensitivity to control system leaks.
- Pneumatic controls design changes to
reduce sensitivity to control system
leaks.
- Introduction of new steer axle products
up to 14,600 lbs. capacity to improve
routing of air to steer wheel ends.
Does Spicer TPCS fit Meritor
drives? Which ones? How about
others?
Spicer drive axle air seal hardware was
developed to fit on the Spicer “R” spindle
configuration. Dana uses this spindle on sin-
gle axles between 21,000 and 26,000 lbs.
capacity and on tandems from 40,000
through 52,000 lbs. capacity. The “R” config-
uration meets industry standards for fitment
of wheel end hardware (hubs, bearings, seals
etc.), however individual axle manufacturers
have latitude outside of the specific dimen-
sions for the bearings and the seals to
accommodate manufacturing processes and
other considerations.
Historically, the Meritor “R” configuration has
differed from the Spicer configuration specifi-
cally in the width of the outer bearing journal.
It is Dana Corporation’s understanding that
the spindle configuration of the Meritor prod-
uct was changed in 1999 to accommodate
the hardware required to equip their axles
with Spicer TPCS. The hardware will also fit
on spindles from some other axle manufac-
turers. We have found that Mack tandems of
38,000 lbs. and 50,000 lbs. will accept the
hardware without modification, however their
44,000 lb. axles will not. Dana will review
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