Tires - Best Pressure For Load Application

89ford06

^33GTIRE - LOAD CAPACITY VERSUS INFLATION PRESSURE

^ TIRE - P - METRIC PASSENGER TIRES USED ON LIGHT TRUCKS

^ TIRE WEAR - EFFECTS OF INFLATION AND LOAD

Article No. 89-9-16

LIGHT TRUCK: 1984-89 ALL LIGHT TRUCK LINES

ISSUE: Tire wear can be affected by inflation and load. Good tread life is dependent on maintaining proper air pressure in the tires. Other factors that affect tire wear are:

^ alignment

^ speed

^ road surfaces

ACTION: Keep tires inflated to the recommended pressures to obtain maximum tread life. Use the following charts and procedures to arrive at the best tire pressure for each load application.

FIGURE 1:

The chart in Figure 1 shows the affect of inflation and load on tire tread life. Use the chart by finding the specified inflation pressure for the vehicle as shown on the certification label and locating that pressure on the specified inflation pressure on the chart. The affects of actual air pressure and load can now be read directly off the chart.

Tire load carrying capacity is a function of tire design and inflation pressures. Each tire has molded into the sidewall a maximum pressure for a specific usage. Use the following guidelines to determine load carrying capacity.

FIGURE 2:

^ For P-metric passenger tires on passenger cars, the values are as shown on the tire.

^ For P-metric passenger tires on light trucks, the load ratings are reduced to 91% to reflect the "harsher" truck environment, Figure 2.
^ For light truck style tires used on light trucks, the values are as shown for tires used in single wheel applications.

^ For light truck style tires used in dual wheel applications, the tire capacities are derated.

Often, inflation pressures for specific vehicles are less than maximum capacity because the load to be carried is less than the maximum tire capacity.

Inflation pressures for originally installed size tires on a vehicle are shown on the vehicle certification label along with the tire size and rated capacity for the axle system. Check the size and inflation information on the label to properly inflate the tires. Be sure that the same size tire is actually on the vehicle and then inflate it to the label's specified pressure. If other than original size tires are on the vehicle, the label's pressures are probably not correct

To find proper pressures for other than original tires, use the following procedure.

1. Obtain both front and rear axle capacity ratings (GAWRR and GAWRF).
2. Divide each number by 2 to obtain the capacity at the tire.

FIGURE 3:

3. For single wheel usage, look up the pressure in the proper chart which will meet the needed capacity, Figure 3.

4. Check the tire side wall label to see if it permits inflation to that pressure. If lower load range tires were installed (i.e., C vs. D or E), the tires may not have the needed capability.

5. Divide the value found in Step 2 by 2 again to obtain individual tire requirements for dual rear wheels.

6. Using a dual wheel inflation pressure chart, Figure 3, determine correct pressure to achieve adequate load capacities.

7. Consult the local tire outlet or the tire manufacturer's home office about tires not shown in the tables.
OTHER APPLICABLE ARTICLES: 87-10-11
WARRANTY STATUS: INFORMATION ONLY
OASIS CODES: 3300