Issue link: http://read.dmtmag.com/i/34501
MAINTAINING THE TIRE Air pressures on all newly delivered equipment should be verified for the application/operation prior to the vehicle being placed in service. Verify that any pressure monitoring or inflation system is correctly set for your fleet application on the delivery of any new equipment. Proper maintenance is important in order to obtain maximum performance. INFLATION PRESSURE The most critical factor in tire maintenance is proper inflation. No tire or tube is completely impervious to loss of air pressure. To avoid the hazards of underinflation, lost air must be replaced. Driving on any tire that does not have the correct inflation pressure is dangerous and will cause tire damage. Any underinflated tire builds up excessive heat that may result in sudden tire destruction. The correct inflation pressures for your tires must incorporate many factors including: load, speed, road surface, and handling. Consult a MICHELIN ® Truck Tire dealer or MICHELIN data books for the proper inflation pressures for your application. See the Introduction for complete listings of the MICHELIN data books. Failure to maintain correct inflation pressure may result in sudden tire destruction and/or improper vehicle handling. Additionally it will result in irregular wear. Therefore, inflation pressures should be checked weekly and always before long distance trips. Check inflation pressures on all your tires at least once a week, including spares, before driving when tires are cold, especially when vehicle is used by more than one driver. The ideal time to check tire pressures is early morning. Driving, even for a short distance, causes tires to heat up and air pressures to increase. Generally, as a radial tire revolves during operation, heat is generated on the inside of the tire at 4 degrees per minute. However, the tire loses heat at the rate of 3 degrees per minute with dissipation throughout the casing and air flow around the tire. After 40 minutes of continuous operation, the tire temperature has increased 40 degrees Fahrenheit. As the air temperature inside the tire increases, the inflation pressure also increases. Thus, a tire inflated to 80 psi cold would now be at 85 psi. Because the inflation pressure has increased, the amount of tire flexing has decreased, which decreases the amount of heat generated per minute to 3 degrees per minute. Assuming the heat dissipation factor is still 3 degrees Fahrenheit per minute, the net temperature change is nil (0). This is called thermal equilibrium. Always inspect valve stems for proper installation and torque, and verify there is a good airtight seal by use of a leak detector type spray such as a water/soap solution applied from a spray bottle. It is also a good practice to 36 Section Three: Extending Tire Life periodically check existing fitments for slow leaks with this method. Never bleed air from hot tires, as your tires will then be underinflated. Make sure to check both tires in a dual fitment. Pressures should be the same. Maximum allowable difference between dual tires or between axles should be no greater than 5 psi. Remember, a drop in ambient temperature results in a drop in tire pressure. More frequent checks may be required during cold weather conditions. Avoid outdoor air pressure checks when the temperature is below freezing. Ice can form in the valve stem, thus promoting leaks. Check inside a heated facility if possible. Use an accurate calibrated tire gauge to check pressures. (Do not use “Tire Billys” to hit tires as an inflation check. This is an unreliable method.) Unless otherwise recommended by tire manufacturer for optimized tire performance, use the tire inflation pressure shown in the application data books for the particular axle load. Exceeding this pressure could result in reduced traction and tread life. Never inflate to cold pressure beyond the rated capacity of the rim/wheel. However, for steering tires, it is common practice to use higher inflation pressures than necessary to carry the axle load to reduce free rolling wear. Following are two examples of applying the previous considerations to an operation where the user mounts new 275/80R22.5 LRG (with a data book maximum of 110 psi tires) steer tires and desires to increase the air pressure in order to see if this will help alleviate the occurrence of free rolling wear. Example 1: If the axle load is 10,310 lbs., then the table in the data book specifies a corresponding pressure of 85 psi. Then the user can increase the pressure 15-20 psi above that to 100 or 105 psi. Example 2: If the axle load is 12,350 lbs., then the table in the data book recommends 110 psi. As this is the maximum load of the tire, only a 10% pressure increase is permitted. Thus the adjusted pressure would be limited to 120 psi. This procedure should not be applied “across the board.” If satisfactory tire performance and wear are being obtained with “table” pressures for a given load, then leave well enough alone. Overinflation can cause an increase in road shocks and vibrations transmitted to the vehicle as well as an increase in tire failures from road hazards. NOTE: In no case should the maximum capacity of the wheel/rim be surpassed. Consult wheel/rim manufacturer’s specifications. NOTE: The following illustration is based on the recommended inflation pressure from the data book for the load being carried.