According to the Technology and Maintenance Council’s Tire and Wheel Study Group Information Report: 2010-2 Tire Pressure Monitoring and Inflation Maintenance, tires are the second largest investment for a fleet. Because of this, it is critical that tires are properly maintained and managed. The following is a compilation of best practices for tire maintenance, but by no means are fleets limited to these best practices.
Tire pressure systems can provide fleets a means to more closely monitor the performance and status of tires on their vehicles.
A big challenge for fleets is to determine which type of tire pressure system will provide the best return on investment (ROI) or total cost of ownership (TCO) for their individual needs.
Options available
When it comes to tire pressure systems, SAE and NACFE define the following three system choices:
- Monitoring – Commonly referred to tire pressure monitoring systems (TPMS), monitoring systems record and communicate past and current tire conditions. This system can provide real-time information, but only provides notification of an issue. The driver or fleet is required to take corrective action.
- Maintenance – In addition to monitoring capabilities, maintenance systems can add or release air pressure automatically when needed to maintain a preset level on each tire. These systems are commonly referred to as automatic tire inflation systems (ATIS).
- Management – Tire management systems can adaptively alter air pressure through programming dependent upon load, speed and other variables. These types of systems are commonly referred to as central tire inflation systems (CTIS).
There are pressure systems available for both tractors and trailers. It is important to note there are differences in these systems dependent on the type of tire.
Preventive maintenance practices
There are several preventive maintenance practices that are crucial to maintaining the tire life for the fleet. But the most critical factor in tire maintenance is proper inflation. Step one is to measure every vehicle tire for proper inflation, correcting underinflated or overinflated tires. Check tires when they’re cold, or at least three hours after use.
Typically, tires should maintain 85-100 psig, with variances dependent on application, tire construction and manufacturer’s guidelines. Many fleets like to run at one tire pressure setting in all tire locations, as this is the easiest to communicate consistently and for drivers or technicians to remember.
An underinflated tire has a larger ground contact footprint, which increases contact with the road and creates higher internal stresses (heat) in the tire casing. The larger footprint increases rolling resistance, thus requiring more energy/power from the vehicle to rotate the tire. As an analogy, an underinflated tire effectively provides a greater drag against the vehicle's motion similar to an increase in head wind or a slightly dragging brake.
Meanwhile, an overinflated tire decreases fuel economy and overall tire life, leading to an increase in operating costs. Over-inflation can increase the potential for catastrophic tire failure or other issues.
It is important not to overload the tires. The maximum load is dependent on the application. Fleets can avoid excessive heat buildup, which can lead to tire deterioration, damage or failure, by following the tire manufacturer’s recommended allowable load for an application.
Fleets can take a proactive approach to monitor the load using any of the pressure systems mentioned above.
TPMS will notify the driver or fleet of an overinflated or underinflated tire and its location for corrective action at the next service stop.
If the fleet is looking for an even more comprehensive approach, a tire maintenance system can be installed on the vehicle and trailer to not only monitor, but automatically inflate or deflate tires based on a predetermined set point.
The next level of tire pressure systems currently available is the management system, or CTIS, which can be pre-programmed to account for many factors related to road surface and environmental conditions to optimize tractive effort as well as tire life.
Pre-trip inspection guidelines
To increase safety and prevent downtime, a pre-trip inspection is recommended for every vehicle leaving the facility each day. Below are a list of steps to follow for this inspection.
Step 1 - Check tire for proper inflation. If a tire is 20 percent below the recommended psi, it should be checked for damage and repaired or replaced before beginning service.
Dual tires should be within 10 psi of one another. Maintaining proper inflation pressure in duals can minimize the damage caused by mismatched diameter, which will prolong tread and casing life.
The tire inflation system installed on the vehicle will determine the method for inspection:
- No tire pressure system – Check all tires for proper inflation pressure manually. Correct accordingly.
- Monitoring system – Check all tire pressure settings in controller looking for any warnings or other system messages. If any tire is identified, take corrective actions.
- Maintenance system – Check tire system warning indicators once the vehicle is started, but before beginning service. Respond to any indications of issue with corrective action.
It is important to note ambient air temperature and load can have a positive or negative impact on the tires overall life and working air pressure. Ideally, during long journeys from a hot to cold region (or vice versa) the vehicle’s tire pressures should be checked periodically for compliance to specification.
Step 2 - Visually inspect tires for damage or defects, checking for wear, bulges, cracks, cuts or elements that have penetrated the tire.
When a tire maintenance system is present, visually inspect the system hoses in addition to the tire.
Step 3 - Check valve caps to ensure they are present and properly secured.
Step 4 - Check for tread wear by measuring the tread depth. It’s important to know the tire tread depth when new, and then take subsequent tread measurements at the same spot on the tread, close to the center of the groove.
Step 5 - Check wheel for rust, dents and any deviations.
Step 6 - Inspect the vehicle’s suspension.
- Check the suspension to be sure it is fully operational, ensuring it is visually free of any obvious signs of failure in any major component.
- Visually inspect all suspension component fasteners.
- Visually inspect air springs for sufficient and equal pressure, and check to see that the suspension is set at proper ride height. Refer to the suspension manufacturer’s maintenance manual instructions.
- Check that the suspension ride height is within +/- 1/4” of the suspension manufacturer’s recommended height. An improperly set ride height could result in suspension component damage and/or poor vehicle ride performance. Refer to the suspension manufacturer’s maintenance manual instructions.
- Inspect nuts and bolts at the pivot connections, transverse beam connections and axle connections to assure they are properly torqued.
- Check the air spring and shock absorber fasteners and all other nuts and bolts for proper torque, re-torquing as necessary.
- With vehicle on level surface and air pressure in excess of 70 psig, all air springs should be of sufficient and equal firmness. Note that height control valves control all air springs. Check all fittings for air leaks by applying a soapy water solution and checking for bubbles at all air connections and fittings.
- Check all other suspension components for any sign of damage, looseness, wear or cracks, replacing any damaged parts to prevent equipment breakdown. It is important to note only lubricants recommended by your suspension manufacturer should be used. Refer to your suspension manufacturer’s maintenance manual instructions.
Conclusion
Comprehensive tire maintenance and management is critical to maximizing a fleet vehicle’s uptime. There are a number of tire pressure systems available to spec on these vehicles in order to optimize tire monitoring and management. Be sure to complete thorough research to find what’s best for the fleet.
From truck suspensions and brakes to trailer axles, suspensions and landing gear, Bill Hicks, manager of product planning – America, SAF-Holland, has more than 30 years of global experience at SAF-Holland, having held various positions in engineering, service and product planning. Hicks has worked with tire inflation systems for the last 10 years, and is the in-house subject matter expert on ATIS as well as other inflation options. With a BSME from Western Michigan University, Bill is an active member of SAE, holds 18 patents and has co-authored an SAE paper.
