224 wheel TPMS is a radio problem first
Most TPMS questions are simple. A truck has six to ten wheel positions, one receiver, and the job is done. Then somebody asks about a machine with 28 axles and eight wheels per axle, and the conversation changes character.
The largest single machine we have measured carries 224 wheels across 28 axles. The count itself is not the hard part: a single receiver supports up to 256 wheel positions, so 224 fits inside one receiver's address space. What makes 224 wheels difficult is everything around the number — radio coverage along a very long structure, commissioning time, the wheel map, and the alarm logic that has to survive contact with an operator.
Address space is not coverage
The first misconception to clear up is that a high wheel count needs many receivers. It usually does not, but not for the reason people expect.
Radio at 433.92 MHz travels well in free air and poorly through steel. On a 28-axle machine the chassis is a long, dense metal structure, and the receiver is at one point on it. Wheels near the receiver report cleanly; wheels ten metres away, behind three axle assemblies and a hydraulic pack, do not. Adding receivers or repeaters is how you fix the path, not the address count.
That is why the 160-wheel beam carrier we delivered uses two receivers and twelve repeaters for 160 sensors. The repeater count is what the structure demanded, and it was planned before the installation, not discovered on site.
Step one: freeze the wheel map before you buy anything
On a 224-wheel machine, the wheel map is the project. Before sensors are ordered, agree on a naming scheme that survives the whole service life of the vehicle:
- Axle number, counted from a defined end of the machine
- Side, defined by the direction of travel rather than left and right as seen by a fitter
- Position within the axle group — for an eight-wheel axle, inner and outer on each side
Write it down and put it in the maintenance file. When a tire is replaced two years later, the technician has to be able to identify the sensor without guessing. Every mislabelled wheel position becomes an alarm that gets ignored, and ignored alarms are how these systems die.
Step two: plan coverage from the structure
Coverage planning is a drawing exercise, not a specification exercise. Ask for the axle layout, the location of the electrical cabinet, the tank and any large steel mass between them. Then place repeaters along the machine at intervals that give each sensor a short, unobstructed path to something.
Two practical rules have held up in our projects:
1. Treat the machine as several radio zones, not one. Group axles into segments, give each segment a repeater, and chain them back to the receiver.
2. Leave margin. A repeater that is marginal when the machine is new will be unreliable after two years of dust and vibration. Plan for one more repeater than the minimum the link budget allows if the structure is dense.
Both are cheap at design time and expensive during commissioning.
Step three: commissioning is the real cost
This is the step buyers underestimate most. On a 224-wheel machine, every sensor has to be identified, associated with a wheel position and verified. Doing that wheel by wheel on a machine in the yard is slow, so it should be designed to be done in batches, at the bench, before the wheels go on.
Defence against that cost is a sensible kit design: encode or label sensors before installation, commission per axle group rather than per wheel, and run a full-wheel-position integration test before the machine leaves. We run a full wheel-position test on complete machines, because at that count it is the only way to be sure the map in the controller matches the physical machine.
Step four: alarms have to be grouped
224 raw alarm sources will destroy an operator's attention in a week. The system has to present information at the level a human can act on.
A workable hierarchy, from the bottom up:
- Wheel position — actual pressure and temperature, for diagnosis
- Axle group — the smallest unit a fitter can act on
- Machine — one alarm that says "stop and inspect", not 224
Thresholds also need more than one level. A slow leak on one wheel of a beam carrier should raise a maintenance alert; a fast loss on a load-bearing axle should raise a stop alarm. Deciding those two settings, and who receives them, is part of the project, not an afterthought.
What the numbers look like in practice
Some reference points from machines we have actually configured:
- 160 wheels, delivered in ten units. Two receivers, twelve repeaters, 160 sensors. This is the largest wheel count we have put into series production.
- 224 wheels. 28 axles × 8, the largest single machine we have measured.
- 256 wheel positions. The maximum one receiver can address, which leaves headroom above our largest real machine.
- Pressure accuracy ±7 kPa, tire temperature ±3 °C. Internal sensor rated −40 to +125 °C, enclosure IP68.
- Sensor battery life of at least five to six years for the internal type, which matters when opening a wheel takes half a shift.
Data is carried on CAN 2.0B at 250 kbps by default with a 500 ms data period, both software-configurable, and the same platform covers J1939, RS485, RS232, Modbus RTU, PROFINET and UART.
If you are planning a many-wheel machine
The useful conversation is not about sensors. Send the axle layout, the wheel count, the location of your controller and the environment the machine works in. We will come back with a receiver and repeater plan, a wheel map structure and the commissioning procedure — and we will tell you which parts of the machine are likely to be hard for radio.
The figures above come from our own projects. Read how we handle multi-axle vehicles, see the beam carrier installation, or send us the axle layout.