TRUCK SERVICE MANUAL
WHEELS, RIMS, TIRES
Overinflation is also costly because a tire which
is 20% overinflated will produce only 92% normal tire
After 225 km (140 miles) of driving
the pressure had increased to 85
pounds and temperature 93.3 degrees
"Bleeding" of air from hot tires should never be
C (200 degrees F).
practiced. The pressure will be reduced but an increase
The pressure was then "bled" to 70
in temperature will result as soon as driving continues.
pounds and an additional drive made
of 225 km (140 miles). Note the temperature.
The pressure had increased to 73
pounds while the temperature increased
to approximately 104.4 degrees C (220
Note the temperature.
After 322 km (200 miles), the tire
failed from a temperature of over
121.1 degrees C (250 degrees F).
Loading tires beyond their rated capacity is
expensive because tire mileages are rapidly decreased
with overloads. The following chart (Fig. 12) illustrates
how an overload of only 20% will result in tire mileage
being only 70% of normal.
Fig. 11 Chart Showing Effects of Bleeding
The chart (Fig. 11) illustrates a condition where a
tire was started cool with a pressure of 70 pounds and at
a temperature of 26.7 degrees C (80 degrees F).
Fig. 12 Overload vs. Mileage