TPMS Sensors : Dial up the Pressure on Safety and Cost Savings
Maintaining proper tire pressure cuts to the heart of fuel efficiency, tire wear and safety—three key concerns for truckers and fleet managers. That’s why it is important to understand how a tire pressure monitoring system (TPMS) works and the critical role of TPMS sensors. These devices perform the essential role of constantly sensing the air pressure of every tire on a tractor trailer and triggering an alert when tire pressure goes outside of safety setpoints. With a timely warning, drivers and fleets can attend to potential tire failures before they happen.
Maintaining proper inflation levels with a TPMS is critical because safe and efficient operations depend on every tire having the right psi.
TPMS Sensors’ Central Role
Sensing air pressure changes in 18 wheels continuously is no easy task. There are two main types of TPMS and each uses different technology. Direct TPMS uses sensors placed inside every tire to monitor each tire’s pressure and temperature. Indirect TPMS relies on wheel speed sensors of anti-lock brake systems to estimate tire pressure based on the rotational speed of tires.
In both systems, information is transmitted wirelessly from the sensor to the driver and/or fleet in real time whenever there are problems.
It only takes one tire to create an unsafe situation, drag down mpg or cause costly treadwear. That’s why fleets need every TPMS sensor in working order to keep every tire properly inflated.
Tire Pressure Monitoring System Benefits
- Improved Safety - Underinflation of tires is the leading cause of blowouts
- Fuel savings - Every 10% reduction in tire pressure equates to an approximate reduction in fuel efficiency of 1%
- Reduced tire costs - Underinflated tires increase wear-related tire costs by an estimated 12%
- Accurate tire pressure – TPMS sensors provide real-time readings that are more accurate than manual gauges
- Driver productivity – TPMS sensors reduce the need for truckers to do manual inspections
- Fleet efficiency – TPMS data received through telematics helps fleets plan maintenance and predict tire needs
How TPMS Works
With both direct and indirect TPMS, sensors transmit readings to the system. The system processes the information and then alerts the driver whenever there’s an issue. When the TPMS feeds into telematics, the system alerts the fleet.
Systems in commercial vehicles—usually direct TPMS—receive data in real-time from sensors that monitor air pressure and temperature in each steering, drive and trailer tire.
When the system detects air pressure below the programmed baseline level or when tire temperatures exceed a set reading, the system alerts the driver and/or fleet along with the tire position that’s at fault. Some systems sound separate alerts for major and minor pressure drops, fast leaks, overinflation or lost signals.
Drivers receive alerts over a dashboard display that usually has an audible and visual component to get their attention. Tire monitoring alerts can come in over a computer or smartphone when TPMS is integrated with fleet management systems through telematics.
Direct Versus Indirect TPMS
Of the two main categories of TPMS, direct TPMS is more often used for heavy trucks. Light trucks and passenger vehicles usually use indirect TPMS, but also employ direct TPMS.
Direct TPMS monitors tire pressure and temperature from a sensor mounted inside the tire. A key advantage of direct TPMS is that there are no inaccuracies when tires get rotated or replaced. The readings are actual because they are direct. These systems can be easily resynchronized after a tire rotation or replacement. Direct sensors can be installed in spares and their long-lasting batteries are good for about a decade.
Indirect TPMS doesn’t directly read tire pressure. It estimates underinflation of tires by measuring the rate of revolution of each wheel. Wheel speed sensors connected to anti-lock braking systems transmit readings to the system which analyzes the information alongside speed, wheel size and other datapoints. When something in the rotation is wrong, the system determines tire pressure is off.
Which is better? Indirect TPMS is less expensive than direct and requires less programming and maintenance over the years. However, indirect is an estimate of psi by its nature. Indirect can also become inaccurate when tire sizes change or tires become unevenly worn. Indirect systems must also be reset after tires are rotated or even inflated.
Five Types of Direct TPMS Sensor
1. Rim mounted sensors connect directly to tire-side of the rim
2. Patch mounted sensors, also known as boot- or embedded-style sensors, attach to the inside rubber of tires
3. Internal valve mounted sensors attach to the valve stem inside the tire
4. External valve mounted sensors attach to special valves on the outside of tires
5. Stem mounted sensors screw right onto standard tire valves
Tire Pressure and Safety
The TREAD Act of 2000 addressed the dangers of underinflated tires head-on. It also established the Federal Motor Vehicle Safety Standard requiring the installation of TPMSs that warn the driver when a tire is significantly underinflated. The standard applies to passenger cars, trucks, multipurpose passenger vehicles, and buses with a gross vehicle weight rating of 10,000 pounds or less, except those vehicles with dual wheels on an axle.
Blowouts are dangerous and happen often. According to a 2006 FMCSA study, there is one blowout for every 18 tires every year on average.
Consequently, TPMS is popular in semi trucks. Although sensors are not required in trucks and vans, the North American Council for Freight Efficiency says 25% to 30% of tractors and 15% of trailers use them voluntarily.
Deciphering TPMS Alerts
When a TPMS alert sounds, it means the tire or tires have air pressure that is below or above a programmed baseline pressure. It signals a tire condition that needs to be addressed to avoid a dangerous situation. It doesn’t mean the tire pressure is outside the range for optimal fuel performance or tire wear. For that reason TPMS shouldn’t be considered a replacement for manual air pressure checks and visual inspections.
A TPMS alert that goes on and off may not be malfunctioning. Fluctuating outside temperatures may be to blame. Tire pressure can drop overnight when temperatures drop, causing an alert. It may turn off when tire pressure increases during the day after temperatures rise or heat is generated by driving the vehicle. When this happens, be sure and check the pressure of every tire and add air to any low tires.
When to Replace TPMS Sensors
TPMS sensors are often replaced at the same time tires are replaced. Although sensors’ batteries can last five to ten years, replacement tires may outlast them. Sensors should be replaced in tandem, lest the batteries fail while the tires are still good.
If a sensor breaks, it is best practice to replace it as soon as possible. Your tire could lose pressure and before you know it be in a dangerous state. Unchecked pressure excursions can also lead to damage to the tire, rim or vehicle.
When to Reset TPMS Sensors
After changing or rotating tires or installing new sensors, you should always reset the TPMS. Some manufacturers advise resetting even after adding air to tires.
Resetting or “retraining” teaches the system to recognize sensors in their new positions. The resetting procedure depends on the TPMS system.
Under Tire Pressure?
Imperial Supplies stocks an expansive array of TPMS sensors and replacement valves as well as tools for programming TPMS and replacing TPMS valves to help fleets keep tire pressure calibrated across the board.
Talk to your Dedicated Account Advisor for the advice and expertise you need to make proactive stocking choices that support uptime and productivity in your shop, throughout your fleet and on the road.