Tyre Pressure Monitoring Systems Explained… why every off-roader should have them?
A tyre pressure monitoring system (TPMS) is an easy upgrade that can save you big time, both financially and literally.
BEING ABLE TO monitor your tyre pressures while driving has many benefits. Firstly, you can check tyre pressures with a simple glance at a digital display. Secondly, a TPMS will alert you of an unexplained drop in air pressure, which can potentially save a tyre before it’s damaged beyond repair. Thirdly, you can monitor the individual air pressures and temperatures in each tyre as you drive in different conditions, and adjust them if necessary, optimising vehicle ride and handling and extending tyre life.
Original Equipment TPMS
While many modern vehicles are equipped with a TPMS as standard equipment, sometimes these are basic units that use existing OE vehicle hardware to alert the driver of a discrepancy in tyre pressures. These systems are referred to as indirect TPMS, and they work on the principal that a deflated tyre will have a different circumference, and therefore different wheel speed, than a fully inflated tyre. Indirect TPMS can therefore utilise the wheel-speed sensors that are already fitted as a part of a vehicle’s ABS and stability control systems to warn of tyre deflation via additional software.
Indirect TPMS doesn’t measure a tyre’s inflation pressure, just its apparent pressure based upon external data, so it can only provide a warning when there is a discrepancy in tyre pressures; it can’t actually inform you of how much pressure is in each of your vehicle’s tyres.
With indirect TPMS, the driver often has to calibrate the system via a reset button, which must be performed when all tyres are correctly inflated, otherwise it will provide incorrect data. This limits the effectiveness of TPMS for four-wheel drivers who regularly adjust their tyre pressures depending on the terrain in which they’re driving.
Direct TPMS uses battery-powered sensors fitted to each wheel to measure the actual air pressure and air temperature inside each tyre, providing real-time data to the driver.
There are a number of different direct TPMS products on the market, most of which use a battery-powered sensor on each wheel that transmits a radio signal to a receiver mounted inside the vehicle. The receiver usually consists a dash-mounted screen that displays pressure/temperature information from each tyre simultaneously.
Some direct TPMS products use a sensor mounted inside the tyre to monitor inflation pressure and temperature. The sensor itself is either affixed to a band (like a big hose clamp) to the inside of the rim or mounted in place of the standard tyre valve stem.
The advantage of a sensor mounted inside the tyre is that it is generally the most accurate place to measure inflation pressure and temperature, and it is protected from the outside environment, which may include dust, mud and water, as well as the potential for off-road impacts. An internal sensor also allows for easy tyre inflation and deflation without the need for sensor removal. On the downside, an internally mounted sensor cannot be moved from vehicle to vehicle without removing the tyre from the rim. These types of sensors can also be damaged when a tyre is changed, especially if the person performing the tyre change is not familiar with the location of the sensor, or the way in which it is mounted.
Another style of direct TPMS consists a sensor that is simply screwed on to the outside of the tyre’s standard valve stem in place of the dust cap. Although more prone to damage than an internally mounted sensor, especially when driving off-road, external sensors have other advantages: they can be moved from vehicle to vehicle; if a tyre is damaged beyond repair the sensor can be easily fitted to the spare tyre; and the sensor’s battery can be easily replaced if necessary. Most external sensors will be supplied with security rings to ensure they don’t separate from the valve stem, as well as to minimise the chance of theft.
Regardless of the style of sensor you think will best suit your requirements, there are some other features to look for when choosing the right TPMS.
Some TPMS products will work with more than four sensors, so you can monitor the tyres on your vehicle as well as those on a trailer. If you haul a dual-axle trailer, make sure the TPMS you select can monitor up to eight tyres at once.
Look for a TPMS with a dash-mounted backlit monitor that has a user-friendly interface, and one that displays tyre pressure and temperature information in a logical and easy-to-read format. The monitor needs a power source, so for ease of use look for one that can be plugged into your vehicle’s 12V DC power supply, or one with rechargeable internal batteries. Also examine the way in which the monitor is mounted to your vehicle; options include windscreen suction cups, dash-mounts and units that plug straight into a 12V accessory outlet, so opt for the one that best suits your vehicle. Some TPMS monitors also include a USB charging port for other electrical accessories.
Make sure the TPMS provides both visual and audible warnings when a tyre begins to deflate, such as a buzzer and a bright red light; the sooner you become aware of a tyre deflation, the greater the chance a repair will be possible before irreparable damage occurs.
Most aftermarket TPMS products allow you to set the inflation pressure at which the deflation alarm is sounded, which is an important feature for four-wheel drivers who regularly adjust tyre pressures to suit different driving conditions, such as driving on gravel roads, in mud or on sand.
There are a number of TPMS products on the market for less than $100 but, as always, you get what you pay for. A good quality TPMS kit with four sensors will usually cost from around $300 and up, and while this might seem like a significant outlay, it’s still less than the cost of a 4×4 tyre, so if it saves just one tyre from irreparable damage then it’s money well spent.