A trailer tire can lose pressure at 65 mph without sending much feedback through the steering wheel of the tow vehicle. A slow leak may remain unnoticed until heat damages the casing, the tread separates, or the tire comes apart. By the time you see rubber in the mirror, the rotating tread may already have damaged the fender, wiring, lights, brake lines, deck, or nearby cargo. A sudden impact failure can still happen without warning, but many trailer tire failures begin with pressure loss or abnormal heat that can be detected early.
That is where a trailer tire pressure monitoring system, or TPMS, helps. Sensors on or inside the wheels send pressure and temperature information to a dedicated monitor, smartphone adapter, or compatible factory truck display. A quality system can warn about a slow leak, rapid pressure loss, excessive pressure, abnormal temperature, or a lost sensor signal while you are driving. External-sensor systems can often be installed in 20 to 45 minutes, while internal sensors require professional tire service. TPMS cannot prevent every blowout, but it can give you time to slow down and stop before a manageable tire problem becomes an expensive roadside failure.
Why Trailer Tires Blow More Than Truck Tires
The problem is not that every trailer tire is automatically weaker than every truck tire. Trailer tires simply face a difficult combination of operating conditions. Many trailers sit unused for weeks, lose pressure between trips, remain exposed to sunlight, and then go directly into service under a heavy load. Multi-axle trailers also scrub their tires during tight turns, and uneven cargo placement can put substantially more weight on one wheel position than another. Add road-hazard damage, aging rubber, a dragging brake, a hot wheel bearing, misalignment, or speed beyond the tire’s rating, and heat can build quickly.
Modern ST, or Special Trailer, tires should not all be treated as 65-mph tires. Current ST tires carry a speed symbol or published manufacturer speed rating, and those ratings vary by model. Common trailer-tire symbols include L for 75 mph, M for 81 mph, and N for 87 mph, but the marking on the exact tire controls. Never assume that a replacement tire has the same speed capability as the tire beside it, and never treat a higher speed rating as permission to ignore load, inflation, road temperature, or trailer stability.
An ST235/80R16 Load Range E tire may be rated for a maximum load of 3,520 lbs at 80 psi cold, but that figure is not universal to every tire of that nominal size. The exact tire manufacturer’s data book and sidewall markings must be followed. Its full rated capacity is available only at the specified cold inflation pressure, and the load capacity decreases when pressure decreases. Do not estimate the reduced capacity with a generic percentage. Use the tire manufacturer’s load-and-inflation table, and never exceed the ratings of the tire, wheel, valve stem, hub, axle, or trailer.
A 14,000 lb GVWR tandem-axle trailer also does not automatically place 3,500 lbs on every tire. Some trailer weight is transferred to the tow vehicle through the coupler or gooseneck, while cargo position, road crown, suspension geometry, and side-to-side imbalance can make individual wheel loads unequal. The safe way to evaluate the setup is to compare the trailer’s certified GAWR and recommended cold inflation pressure with actual scale weights and the ratings of every tire and wheel. When possible, obtain individual wheel-position weights rather than relying only on the total trailer weight.
Federal Motor Vehicle Safety Standard No. 138 requires TPMS on passenger cars and on covered multipurpose passenger vehicles, trucks, and buses with a GVWR of 10,000 lbs or less, excluding vehicles with dual wheels on an axle. Trailers are not included in that federal TPMS requirement. Unless your truck and trailer are equipped with a compatible factory trailer-monitoring system, the TPMS in the tow vehicle monitors the truck’s tires only. It has no information about the tires behind the hitch.
Cap Sensors vs Internal Sensors
This is the first major decision when buying a trailer TPMS. Both types can report pressure and temperature, but their installation, serviceability, valve-stem requirements, and temperature readings differ. External sensors are usually the simplest choice for an existing trailer. Internal sensors offer greater protection from weather and physical damage but involve tire-shop labor.
Cap Sensors (External)
Standard external sensors thread onto the valve stem in place of the ordinary valve cap. Installation does not require removing the wheel or dismounting the tire. When air is needed, you normally remove the sensor, adjust the tire with an accurate gauge, reinstall the sensor, and check the connection for leakage. Many kits include locking nuts or anti-theft sleeves that secure the sensors with a small wrench.
Flow-through sensors are a larger external alternative. They allow the tire to be inflated without removing the sensor, which is convenient on trailers that require frequent pressure adjustments. Their extra size and weight place more leverage on the valve stem, so manufacturers commonly require metal valve stems for flow-through sensors. Some lightweight cap sensors are approved for either rubber snap-in or metal stems, but you must follow the TPMS manufacturer’s instructions and inspect each stem for cracks, looseness, or age-related deterioration before installation.
External sensors remain exposed to water, road salt, sunlight, impacts, theft, and damage from curbs or brush. Their sealing o-rings must be clean and correctly seated, and a loose or damaged sensor can create a valve-stem leak. After installation, apply soapy water around the connection and watch for bubbles. External sensors also measure temperature at or near the valve stem rather than directly measuring the hottest part of the tire carcass. The reading is still useful for spotting trends and major differences, but it can be influenced by outside air, sunlight, brake heat, and wheel temperature.
The current TireMinder A1AS is one example of a premium external-sensor system. It combines a 5.5-inch color display with smartphone connectivity, can display as many as 22 programmed tire positions, and is specified for pressure readings from 0 to 199 psi with accuracy of plus or minus 1 psi. Kits are available with different numbers and styles of transmitters, and a signal booster is used to improve communication between the trailer and tow vehicle. It should not be confused with a basic solar-only monitor; the A1AS is a full display-and-smartphone system.
Internal Sensors
Internal sensors are installed inside the wheel. Some attach to a dedicated valve-stem assembly, while others are secured to the wheel with a band. Because the sensor is inside the tire, it is protected from theft, weather, road debris, and accidental removal while adding air. An internal sensor also measures the temperature of the contained air more directly than an external valve-cap sensor, although it still does not measure every hot spot in the tire carcass.
Installation requires removing the tire from the wheel. The technician must position the sensor correctly, avoid damaging it during mounting, replace any required seals or valve hardware, inflate the assembly to the trailer manufacturer’s specified cold pressure, verify that the sensor communicates, and rebalance the wheel when appropriate. If an internal sensor or its battery later fails, the tire generally must be dismounted again. Batteries in many internal sensors are sealed rather than user-replaceable.
The TST 507 product family currently includes internal band-mounted sensors as well as external cap and flow-through versions. Internal sensors are also used by compatible factory trailer TPMS packages from Ford, General Motors, and Ram. These OEM systems use brand-specific sensors and truck hardware, so compatibility must be confirmed by exact truck model, model year, installed options, wheel design, and sensor frequency before the tires are opened.
Choosing a Display and Receiver
The sensor is only one part of the system. The receiver must maintain a reliable connection through the truck cab, trailer structure, cargo, and the distance between the axles and dashboard. On a long gooseneck, enclosed trailer, or trailer carrying dense equipment, a properly installed signal repeater or booster can be just as important as the sensor style. The display must also make an alarm obvious without requiring you to study a phone while driving.
Dedicated Dash Monitor
A standalone monitor mounts on the dash or windshield and provides audible and visual warnings without relying on cellular service. Depending on the model, it may display several tires at once or cycle through individual wheel positions. Better systems identify which tire triggered the warning and distinguish between low pressure, rapid pressure loss, high pressure, high temperature, low sensor battery, and lost signal. Alert limits should be configured around the trailer manufacturer’s recommended cold pressure and the TPMS manufacturer’s instructions.
The current TST 507 color system uses a 3.5-inch widescreen display and supports cap, flow-through, and internal sensors. The platform can be configured for multiple vehicles and a large number of tire positions, monitors pressures from 1 to 218 psi with published accuracy of plus or minus 1.5 psi, and provides low-pressure, high-pressure, fast-leak, and high-temperature alerts. Current trailer kits include a repeater, which is valuable on equipment trailers and goosenecks. TST cap sensors can be used on suitable rubber or metal stems, while its flow-through sensors require metal stems.
The EezTire E618 is another current dedicated-display option. It uses a 4.5-inch color monitor, can support up to 26 tire positions, and is designed for pressures up to 210 psi. It offers configurable pressure and temperature alarms and can be paired with standard external or flow-through sensors. That capacity is far more than a typical tandem-axle trailer needs, but it can be useful for an owner who wants to monitor a truck, trailer, spare, and additional towable equipment through one system.
Bluetooth App-Based Systems
App-based systems send trailer sensor data through a wireless adapter to a smartphone. They reduce dashboard clutter and may integrate with Apple CarPlay or Android Auto when the phone, vehicle, and application are compatible. TireMinder’s Smart TPMS is a current example, and the A1AS combines an application with its own dedicated display. An app system can work well when the adapter continues handling alarms even if the phone screen is off, but phone permissions, Bluetooth settings, audio routing, battery-saving modes, and operating-system updates can affect how notifications appear. For frequent commercial hauling, a dedicated display or a combined display-and-app system is generally easier to monitor consistently.
Systems That Integrate With Your Truck
Select Ford trucks can use Ford’s trailer TPMS hardware to display individual trailer pressures in the cab, provided the truck has the required factory or accessory harnesses and compatible equipment. Properly equipped Chevrolet and GMC trucks can use GM-specific internal trailer sensors with the In-Vehicle Trailering App to show trailer pressure and temperature; GM notes that its system does not monitor the spare tire. Certain Ram trucks also offer trailer TPMS when properly equipped. These are not universal plug-and-play systems, and an aftermarket receiver generally cannot be made factory-compatible merely by plugging a generic module into the OBD-II port or brake-controller harness. Check the truck’s VIN-specific equipment, owner’s manual, sensor part number, sensor frequency, wheel requirements, and maximum supported tire count before buying an OEM kit.
How Many Sensors Do You Need?
Every tire carrying the trailer on the road should be monitored. A single-axle trailer needs two active road-tire sensors, a tandem-axle trailer needs four, a triple-axle trailer needs six, and a tandem-dual gooseneck needs eight. Add one more sensor for the spare when the selected aftermarket system can monitor a stationary spare. A spare sensor is useful for catching slow pressure loss during storage, but it does not eliminate the need to check the spare with a gauge before departure. Some factory-integrated systems cannot monitor a spare, in which case it must be inspected manually.
| Trailer Type | Typical Tire Count | Sensors Needed (with spare) |
|---|---|---|
| Single axle utility | 2 | 3 |
| Tandem axle utility / cargo | 4 | 5 |
| Triple axle car hauler | 6 | 7 |
| Gooseneck equipment trailer | 4 to 8 | 5 to 9 |
Install: What It Actually Takes
For cap sensors, begin with the trailer parked long enough for the tires to be cold. Cold generally means the trailer has been parked for at least three hours and has not been driven far enough to heat the tires. Inspect the tires, wheels, and valve stems first. Measure every tire with a dependable gauge, adjust each one to the cold pressure specified for the trailer and tire setup, and confirm that the pressure does not exceed the ratings of the tire, wheel, or valve hardware.
Program or pair each sensor in the wheel position shown in the system’s instructions. Labeling the sensors before installation helps prevent left-front, right-front, and rear positions from being mixed up. Install the sensors with the supplied seals, locking rings, and tools rather than adding an arbitrary extra quarter-turn. Over-tightening can damage an o-ring, sensor body, or valve core. Once the sensors are fitted, leak-test every connection with soapy water and verify that the monitor displays the correct position and pressure.
If the kit includes a repeater, do not leave it in the box. Mount and wire it according to the manufacturer’s instructions, commonly near the front of the trailer or another protected location with reliable 12-volt power. The booster improves range and helps the receiver overcome interference from the truck, trailer frame, enclosed body, batteries, and cargo. A simple four-sensor external installation may take approximately 20 to 45 minutes, but troubleshooting stems, routing repeater wiring, or programming multiple trailers can take longer.
Do not apply one universal alarm setting to every TPMS. Some systems ask you to enter the recommended cold baseline pressure and then calculate warning levels automatically. Others require separate high- and low-pressure values. Depending on the product, a low-pressure warning may be set approximately 10 to 15 percent below baseline, while the high-pressure threshold may be set around 20 to 25 percent above it. Temperature logic also varies. Some TST instructions use 158 degrees Fahrenheit as a default high-temperature setting, while TireMinder products use their own programmed alert logic. Follow the current manual for the exact model instead of copying generic settings from another brand.
Internal sensors require a qualified tire shop. The tire must be dismounted, the sensor and any new valve hardware installed, the tire remounted, and the assembly checked for leaks and balance. If you are ordering a new trailer and prefer internal sensors or a compatible factory truck integration, discuss it before delivery so the wheel style, valve openings, sensor kit, truck compatibility, and tire-shop work can be coordinated. Spencer Trailers can help determine what information the installer will need for the trailer and tow vehicle.
What to Expect From the System Day-to-Day
A properly configured TPMS should be easy to live with. Before departure, turn on the monitor and confirm that every road tire is reporting, that the readings are reasonably consistent, and that no low-battery or signal-loss warning is present. That check is valuable, but it does not replace measuring cold pressure with an accurate gauge. A sensor can report a believable but incorrect value, and a monitor cannot inspect a valve stem, wheel, tread, sidewall, lug nut, hub, or suspension component.
Tire pressure changes with ambient temperature even when no air has leaked. As a general tire-care guideline, pressure may change approximately 1 to 2 psi for every 10-degree Fahrenheit change in temperature. Tires can also lose roughly 1 to 2 psi per month under normal conditions, with higher-pressure commercial tire types potentially losing more. A trailer that is 8 to 10 psi low after sitting for only a few weeks may have experienced a major temperature change, but it may also have a puncture, leaking valve, damaged bead, cracked wheel, or loose external sensor. Investigate the cause rather than repeatedly adding air.
Pressure normally rises as tires warm during driving. Do not bleed a hot tire down to the recommended cold pressure, because it may become dangerously underinflated after cooling. Instead, compare tires on the same axle and watch for one position behaving differently. A tire whose pressure rises unusually fast may be overloaded or underinflated. A high-temperature reading at one wheel can also point to a dragging brake, failing bearing, or hub problem, although an external sensor’s temperature is influenced by the wheel and surrounding air. Slow down safely, stop in a suitable location, and inspect the entire wheel area before continuing.
External sensor batteries commonly last around one to two years, depending on the sensor, battery type, climate, storage, and use. Current replaceable-battery sensors may use CR1632 or CR2032 cells, but the correct type must be confirmed from the sensor or manual. Keep the proper batteries, spare o-rings, valve caps, and sensor wrench in the tow vehicle. Replace batteries as a set when several were installed at the same time, and recheck the sensor seals after opening the housings. Internal sensor batteries may last several years, but many are sealed and require sensor replacement when exhausted.
Learn the difference between an actual tire warning and a temporary signal interruption. If the monitor loses one position, do not assume the tire is safe simply because no low-pressure alarm appeared. Confirm the repeater has power, inspect the sensor, and check the tire manually. A TPMS can warn about a developing leak, but it may not provide advance notice of an immediate impact rupture, tread separation, wheel failure, or a tire damaged after the sensor has stopped communicating.
Which System Should You Buy?
For most owners pulling a tandem-axle equipment, utility, or cargo trailer on Indiana highways, the TST 507 cap sensor system and the EezTire E618 are credible dedicated-monitor choices. Both offer configurable alerts, replaceable external sensors, expansion beyond four tires, and product families that have been established in the RV and trailer market. The TST 507 is especially flexible because the same display platform supports cap, flow-through, and internal sensors. Choose cap sensors for the simplest installation, or flow-through sensors with approved metal valve stems when frequent inflation access is important.
Owners who want a large display plus smartphone functionality should consider the TireMinder A1AS. It can accommodate far more tire positions than a normal equipment trailer requires, making it useful for a truck-and-trailer combination, a tandem-dual setup, or an owner who manages multiple configurations. TireMinder’s i10 and Smart TPMS products provide additional display and app-based options. Compare the exact kit contents carefully because the number of sensors, sensor style, display, charging equipment, signal booster, batteries, and mounting hardware vary by package.
For a long gooseneck, triple-axle trailer, or tandem-dual trailer, prioritize reliable signal coverage and enough programmed positions rather than choosing a sensor solely because the trailer exceeds a particular GVWR. A repeater should be treated as essential when the TPMS manufacturer includes or recommends one. Internal sensors can make sense when the trailer operates in brush, mud, jobsites, or other environments where external sensors are likely to be damaged, or when compatible factory integration is desired. Their benefits must be balanced against tire-shop installation, sealed batteries, and the cost of replacing a failed sensor.
Expect to spend a few hundred dollars for a dependable current system. A quality four- to six-sensor package with a dedicated monitor and repeater commonly falls in the approximate $250 to $500 range, while larger sensor counts, touchscreen displays, flow-through hardware, internal sensors, OEM integration components, and tire-shop labor can push the total higher. Prices and kit contents change, so compare the complete package rather than the advertised starting price. One avoided roadside tire failure, damaged fender, torn wiring harness, or ruined load can easily cost more than the monitoring system.
If you are shopping for a new trailer and want to discuss which setup makes sense for your haul, reach out to the team at Spencer Trailers. Bring the year, make, model, and installed towing options of the truck along with the trailer’s axle count, tire size, cold inflation pressure, wheel type, valve-stem type, and spare-tire arrangement. And if you want to see what we currently have in stock that fits your needs, check the full inventory. Choosing a system with the correct pressure range, sensor count, stems, repeater, and display from day one makes it much more likely that the TPMS will remain useful for years.
One last thing: TPMS does not replace a proper pre-trip inspection. Check cold pressure with a gauge, confirm that every tire is appropriate for the trailer and load, inspect the tread and sidewalls for cracking, cuts, bulges, exposed cords, punctures, or unusual wear, and examine the wheels, stems, lug nuts, hubs, bearings, brakes, and suspension. Verify that the spare is inflated and that the jack and lug tools can handle the loaded trailer. Let the TPMS monitor pressure and temperature while the trailer is moving, but do not ask it to detect damage that only a careful walk-around can reveal.
