Tires - Inflation Pressure Adjustment
Bulletin
1317
Issue Date
December 19, 2003
Market
Canada
Title:
ADJUSTMENT OF TIRE INFLATION PRESSURE
Model
All Applicable Models
REVISION NOTICE:
- December 14, 2006: 2005 - 2009 model years have been added to Applicable Vehicles.
Previous versions of this TSB should be discarded.
INTRODUCTION:
The purpose of this bulletin is to provide additional details regarding the tire pressure warning system, as well as provide guidelines for temperature compensation of tire pressure -- taking into account changes in ambient temperature and actual tire temperature.
Seasonal temperature change can dramatically alter tire pressure. In addition, popular pencil type tire pressure gauges and service station air pumps have been proven on many occasions to be inaccurate and misleading.
Low Tire Pressure Detection Timing:
The tire pressure at each wheel is monitored when the ignition is ON. If the tire pressure falls below Threshold value while the ignition is ON, the warning light will illuminate.
Tire Pressure vs. Tire Temperature:
Air in a tire expands and contracts as the temperature of the tire changes, changing the tire's air pressure. Tire temperature is dependent on "cold" tire pressure, driving distance and speed, ambient temperature and road surface temperature. The "cold" tire pressure for the 4Runner is 220 kpa (31.9 PSI), shown as 32 PSI in the Owner's Manual.
When adjusting tire pressures for your customer, you have to consider all of these factors, plus the difference between the temperature in the workshop and the lowest outside temperature you expect to have in your area in the next few weeks.
"Cold" tire pressure, as recommended by the tire manufacturer (and shown on the tire pressure label in our vehicles), is generally considered to be the pressure in a tire that has not been driven the previous 4 hours, and has been parked outdoors.
APPLICABLE VEHICLES:
- All Vehicles equipped with Direct TPWS
WARRANTY INFORMATION:
TIRE PRESSURE ADJUSTMENT:
Recommended Tire Pressure Adjustment:
As noted above, there are many variables that can affect tire pressure in operation. However, you can use these guidelines to optimize the pressure when you set it in the workshop:
- Use a high quality accurate tire pressure gauge, and check its accuracy regularly.
- Consider the difference in the air temperature in the workshop and the lowest ambient temperature you expect in the next few weeks (especially in winter).
- Use the chart (Figure 1) to compensate for temperature of the tires when you adjust the pressure.
- Use temperature compensation Example 1 for the spare tire.
Temperature Compensation Example 1:
Assumed conditions:
- The vehicle has been parked overnight outside your shop (vehicle has "cold" tires), or is the spare tire for the vehicle.
- The vehicle's spare tire pressure is being adjusted.
- Your workshop temperature is 68�F (20�C), and you expect the lowest ambient temperature in your area to be 14�F (-10�C).
Calculations:
- Compute the temperature difference between the seasonable lowest temperature and the workshop temperature: 68�F (20�C) -- [14�F (-10�C)] = 54�F (30�C).
- Using the tire pressure chart (Figure 1), find the intersection of the cold tire line at the point corresponding to 54�F (30�C), and read off the value on the tire pressure change axis. In this case it would be about 4.6 PSI.
- Compute the actual tire pressure the tires should be filled to: 31.9 + 4.6 PSI = 36.5 PSI.
In this example the tires would need to be filled to 37 PSI to compensate for the seasonal temperature difference.
Temperature Compensation Example 2:
Assumed conditions:
- The vehicle has been driven to your shop on surface streets for about 30 minutes (vehicle has "warm" tires).
- Your workshop temperature is 68�F (20�C), and you expect the lowest ambient temperature in your area to be 14�F (-10�C).
Calculations:
- Compute the temperature difference between the seasonable lowest temperature and the workshop temperature: 68�F (20�C) -- [14�F (-10�C)] 54�F (30�C).
- Using the tire pressure chart (Figure 1), find the intersection of the warm tire line at the point corresponding to 54�F (30�C), and read off the value on the tire pressure change axis. In this case it would be about 6.7 PSI.
- Compute the actual tire pressure the tires should be filled to: 31.9 + 6.7 PSI = 38.6 PSI.
In this example the tires would need to be filled to 39 PSI to compensate for the seasonal temperature difference and the heat in the tires from the short drive to your dealer.
Temperature Compensation Example 3:
Assumed conditions:
- The vehicle has been driven to your shop on the highway for at least 60 minutes (vehicle has "hot" tires).
- Your workshop temperature is 68�F (20�C), and you expect the lowest ambient temperature in your area to be 14�F (-10�C).
Calculations:
- Compute the temperature difference between the seasonable lowest temperature and the workshop temperature: 68�F (20�C) -- [14�F (-10�C)] = 54�F (30�C).
- Using the tire pressure chart (Figure 1), find the intersection of the hot tire line at the point corresponding to 54�F (30�C), and read off the value on the tire pressure change axis. In this case it would be about 9.0 PSI.
- Compute the actual tire pressure the tires should be filled to: 31.9 + 9.0 PSI = 40.9 PSI.
In this example the tires would need to be filled to 41 PSI to compensate for the seasonal temperature difference and the heat in the tires from the long, high-speed drive to your dealer.
From these examples you can see that while the "cold" tire pressure specified for the tires is 32 PSI in the owner's manual, you may need to inflate the tires to 41 PSI, or more, depending on seasonal weather conditions and initial tire temperature.
Tire Pressure Chart: