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Truck TPMS 101

TPMS101

In order to help reduce the costs of operating commercial vehicles, we believe that it’s essential to educate our customers about fleet safety technology. Below are some frequently asked questions regarding truck TPMS:

What is Truck TPMS?

How is tire pressure measured?

Are there different types of TPMS sensors?

Do tire sensors have different capabilities?

What features are most vital in a TPMS monitor?

What is TPMS vs. ATIS (automatic tire inflation system)?

What is Truck TPMS?

The acronym generally stands for ‘Tire Pressure Monitoring System’, which is a means of detecting or monitoring the level of air pressure in a tire and reporting it. It can also be short for ‘Tire Pressure Maintenance System’, a set of procedures and steps to properly maintain a tires operating condition in different environments. As an example, the second term may also include tire inflation as part of the maintenance solution.

How is tire pressure measured?

Tire pressure is most often measured by utilizing a wireless sensor, which is usually screwed directly onto the valve stem or mounted inside the tire. This allows for each tire to be monitored individually in real-time. The actual pressure level, as well as each tire’s temperature is then displayed on a small unit in the driver’s view inside the cab. With more advanced systems, this information can be provided to a fleet’s facilities in real-time.

Are there different types of TPMS sensors?

Yes, part of the lack of deployment of a truck TPMS is due in part to unclear and inaccurate information. Since each company focuses on their apparent strengths, fleets are left to filter through all types of data creating a difficult comparison. Let’s look at some of the metrics that can be compared equally for tire sensors:

  • Cap-style Sensors: As the name implies, these are large valve caps that screw on the valve stem. In order to add or remove air, they must be removed each time and maintain a quality air seal when they’re threaded back on. Since they’re external, they must withstand exposure to outdoor elements and are prone to being lost or placed on the wrong tire.
  • Flow-thru Sensors: This type also threads onto the valve stem, but as the name implies allows for air to flow through the sensor. This means that the sensor does not have to be removed and repositioned each time air is added or depleted. Think of it as an extension of the tire’s valve stem since they never have to be detached from the tire. These sensors must also withstand exposure to these outdoor elements.
  • Internal-mount Sensors: Internally mounted sensors are installed inside the tire, often with a large metal band secured around the wheel or adhered to the tire casing or wheel. Having them mounted inside allows the sensor to be protected, but may require additional installation hardware.
  • Dual-purpose Sensors: A type of sensor that has the ability to be installed either externally mounted on the valve stem or inside the tire. Given that they are designed for exposure to the elements, the advantages include:
    • Sensor can be installed either aftermarket or OEM
    • Provides the option for moving the sensor from internal to external mount and vice-a-versa
    • Limits having to inventory multiple types of truck sensors
    • If the sensors are mounted internally and a tire breaks down, the sensor can be externally mounted by road service

Do tire sensors have different capabilities?

Yes. Not only do tire sensors vary in how they are installed, they can differ greatly in measurement accuracy, operating reliability and practicality of use. Tire monitoring systems are tools like any other; the ones that provide maximum usefulness and value are often finely engineered. Of a well-designed commercial tire sensor, the most common features to consider are:

  • Pressure Sensing Technology: There are two common methods used to measure direct truck tire pressure levels, they are:
    • Baseline Reference: This type of sensor uses the tire’s air pressure level when first put on as a baseline or reference pressure. If the pressure decreases by a set percentage, usually 12.5% and 25%, the system provides an alert. If the sensor is removed to air up, it must be replaced within 60 seconds or a new baseline reference is established. This can lead to false alarms since the new baseline is usually established at an elevated temperature.
    • Absolute Pressure: This sensor type is designed to measure absolute tire pressure, which is the true pressure inside the tire (referenced to atmospheric pressure). Similar to a house thermostat, it reports the true temperature in the structure regardless of the conditions outside. Having the ability to measure absolute pressure allows the user to set specific warnings and alarms as desired, increasing tire maintenance results.
  • Sensor Programming: Most sensors must be programmed or associated to a tire position during installation or field replacement. This is sometimes done using a seperate instrument such as a sensor scanner or reader. Other systems require a serial number to be manually entered into the monitor for each sensor and must be reprogrammed again if removed. Additionally, there are systems that require a powered cab monitor to be placed into a programming mode to detect a sensor during installation. This generally requires more than one individual to install the system.
  • Sensor Battery Life: The life a sensor battery can range from as little as 18 months to 10 years. Typically the shorter battery life sensors require battery replacement, which at a minimum needs removal from the tire to return to the factory or to open the sensor to replace a battery. Caution must be used to prevent moisture from entering the sensor. Both replacement methods require reprogramming the sensor and repositioning on the vehicle.
  • Sensor Pressure Accuracy: The accuracy of the readings for a sensor determines the quality of the data received, but even more importantly the ability to truly detect leaking tires. Sensors with an accuracy of 1% or better (over entire operating temperature range) and a resolution of .1 PSI is necessary to measure more than rapid or catastrophic leaks.
  • Sensor Temperature Accuracy: Heat destroys tires often as a result of low tire pressure. When the pressure is low, the sidewalls of a tire flex rapidly (sometimes referred to as micro-flexing) leading to deformity and breakdown of the tire casing from elevated temperatures.  Look for a sensor that has a +/- 2% accuracy over the full automotive-grade temperature range. That specification should be -40°C to 125°C, not an arbitrary range since it is at the higher temperatures where the greatest damage occurs.

What features are most vital in a TPMS monitor?

Here too you will find a number of discrepancies between commercial vehicle tire pressure monitoring devices. While there are a number of specific features that can be considered, they mostly fall into either the Basic Display type or the Intelligent Computer type, which consist of:

  • Basic Display TPMS Monitor: The most common type is a fixed in-vehicle, display monitor, with no real computing capabilities. They generally consist of a simple LED indicator or LCD static graphical display showing tire locations on a vehicle. They solely indicate when an alarm condition occurs and are not meant to offer operating environment flexibility. Simple to operate, but lack many desired capabilities or computing intelligence beyond displaying tire alarms. They may have a limited communication interface to connect to an in-vehicle computer, but usually require an additional device to enable its use. These unintelligent, often consumer-grade monitors don’t generally reflect a cost commensurate with their restricted capabilities.
  • Intelligent TPMS Monitor: Current technology has led to the intelligent TPMS monitor, which are not only capable of highly advanced and accurate tire monitoring, they store months of data which can be sent via various integrated telematics interfaces. They can best be described as an intelligent computer platform or black box. Despite the rapid ROI that a quality TPMS can provide, that investment should contain some or all of the following:
    • User-friendly color touch-screen display utilizing modern intuitive display icons
    • Data memory storage so that a truck or trailer on the road for months retains critical information to analyze upon return to a facility
    • Capable of monitoring both the tractor & trailer with effortless trailer exchange
    • Software and hardware upgradeableto protect the user’s investment
    • Ability to report/configure locally and via a web portal
    • Operates fixed in a vehicle and as a portable device
    • Utilizes RFID technology

What is TPMS vs. ATIS (automatic tire inflation system)?

Each provides value on their own. Monitoring alone may not be enough and Inflation alone isn’t enough. You must consider that both require some type of human intervention to be effective. Also, there are no tractor inflation systems on the market, so it makes practical sense to protect those tires with a quality and reliable commercial truck TPMS. To help gain further clarity, let’s define the role of each:

  • Tire Inflation: This technology is meant to force air into a tire in the case of a small leak while driving and allow the driver to get to a place where the tire can be fixed. They often have a LED light on the trailer to indicate if an excessive leak is detected, but do not provide the driver or dispatch critical information such as which tire, how severe, leak rate and tire temperature. In some cases an inflation system may not be able to keep up with the leak or worse yet, stop the leak from becoming a blowout.
  • Tire Monitoring: This technology helps both the driver and the dispatcher become aware of tire conditions that may require action to properly maintain tire life and prevent tire blowouts. Furthermore, an advanced computer monitor can provide valuable data for preventative maintenance based on predictive failure analysis and such things as comparison of tire brands for specific applications.

Understanding that each technology brings value to proper tire maintenance, it becomes clear that neither solution alone can ensure you never have a flat tire. Forcing air into a tire has its advantages only if it is not masking a bigger problem that TPMS can reveal. Adding a tire monitoring system to an inflation system will allow others besides the driver to identify a tire issue, helping the driver to know when to take action. Ultimately it is about proper tire maintenance and actionable information that reduces tire expense and limits a fleet’s liability.