One of the first things to consider is the type of sensor that is used with the TPMS. Is it external to the tire/wheel assembly or internal? External TPMS sensors usually are screwed onto the valve stem in place of the valve cap and can be damaged by curbing, stolen, forgotten to be reinstalled after adjusting inflation pressure, and are not very accurate in measuring temperature since they measure the pressure in the valve stem which is cooled as the vehicle rolls down the road and heated up when parked in the sun. Their advantage is that the tire does not have to be demounted to install the sensor which initially may save time.
Internal TPMS sensors whether mounted on the wheel, on the tire innerliner or attached to the base of the
valve stem are protected from the outside environment and more accurately measure temperature. This
enables them to more quickly generate overheating alerts that prevent axle end fires and wheel offs due
to frozen bearings. They have the disadvantage of being mounted when the tire is off the wheel but in a
normal tire maintenance program, this step can simply be added to the mounting/demounting process. As
a general rule, liquid tire additives (sealants, balancers and coolants) should not be used with internal
Some sensors have non-replaceable batteries. They usually last between 5 and7 years. Other sensors’
batteries can be replaced and usually have shorter lifespans. The question you must ask yourself is whether
you want to be replacing batteries periodically or simply replacing the sensor after several years of
operation. It is important to remember that you shouldn’t only be considering the sensor price but its total
cost over its useful life. Some sensors appear expensive until factoring in the expected sensor life,
replacement costs over the vehicle’s life, level of effort to perform tire service and on-going maintenance
costs. Looking at all operational costs from a longer perspective may change which sensors are truly the
most cost effective for your fleet’s operation.
Another big factor to consider is the degree of complexity in changing the wheel position to which a TPMS
sensor is assigned. This is one of the biggest challenges fleets report with maintaining tire pressure
monitoring systems. Tire/wheel assemblies in normal fleet operations can be rotated frequently on the
vehicle and to other vehicles depending on the fleet’s maintenance processes. If moving and reassigning
wheel positions is complex and cumbersome, the risk of not properly assigning sensors to their actual
wheel position increases greatly. If alerts are generated for tires in the wrong positions, confidence in the
system is lost when these tires are checked and found to be fine.
Also correcting all the sensors’ wheel positions on the vehicle can be aggravating and time consuming.
Some sensors address this problem by permanently assigning a wheel position to each sensor. However,
this can add another degree of complexity to tire maintenance. The easiest way to change sensor positions
is in TPMS 2.0 systems that enable you to make changes through software. Sensor positions can be verified
and changed as required quickly and easily.
Another key consideration is whether the sensors are permanently programmed for a specific target
pressure. If, for example, a sensor is programmed at a target pressure of 100 psi and to send alerts at
85 psi, when the fleet wants to change its target pressure or alert setting, it will have to change its sensors.
However, if the target pressure and alert thresholds are stored in the cloud rather than in the sensor,
changes can be quickly and easily made any time the fleet wants while the vehicles are on the road. Many
fleets have found that as they become more comfortable with their TPMS 2.0 systems, they were able to
tighten their alert thresholds and squeeze even more savings from their new, efficient and effective, tire
management programs. Being able to change target pressures and alert thresholds easily makes this
Another thing to consider is that if changes to target pressure and alert thresholds have to be made to the
sensors, these changes can only be made to one vehicle at a time when the vehicle is on hand. However, if
changes are made through the TPMS 2.0 solution’s software, these changes can be made to one vehicle, a
group of vehicles, or the entire fleet immediately with a click of a mouse and are accomplished over-the-air.
When choosing a TPMS 2.0 system, one should also think about the flexibility of the system and the ability to change sensor types if it is found that the sensors selected do not work well in the fleet’s application. (For example, the external sensors originally chosen by a fleet are found to be prone to damage, exhibit a high replacement rate and an internal sensor is determined to be more appropriate.) Keeping this in mind, you should ask, “Does the TPMS only provide one type of sensor or does the user have the ability to change sensors without changing the vehicle electronics? If different sensors are offered, can the vehicle electronics read both types of sensors so that the sensors can be changed out through attrition or do all of the sensors have to be changed at one time?”