Farm tyres live a double life: the same tyre carries the machine down a hard road and then works in soft soil, and the pressure that is right for one job is wrong for the other. That is the specific problem agricultural machinery has, and it is why a pressure reading taken once at the start of the season tells a farm very little.
This article covers why it matters, what the failure modes cost, how a system is specified for farm duty, and what happens on a farm that has no mobile coverage.
Two pressures, one tyre
On a road truck the pressure is set once for a load case and checked occasionally. Agricultural machinery is different in kind, not just in degree:
- On the road the tyre needs to be firm enough that the sidewall is not worked against the rim on every turn and every pothole.
- In the field the tyre needs to be soft enough to spread the load, so the machine does not sink into wet soil and so the ground under the wheels is not compacted.
Compaction is the expensive one, and it is invisible on the day it happens. A wheel running too hard presses the soil structure flat; the yield cost shows up in the following season, not in the workshop. Sinking is the visible version of the same mistake - a machine spinning in a wet field is losing time that the harvest window does not give back.
Tractors: front and rear are not the same problem
A tractor is not one pressure target with four tyres. The front and rear tyres are different sizes and carry different loads, and the load changes when ballast is added or an implement is coupled. A machine with a different implement is a different load case on the same rubber.
That is why thresholds on this class are set per position or per axle group rather than one figure for the whole machine. A single number forces the operator to choose which axle to run wrong.
There is also the practical matter of valve access: external sensors screw onto the valve and can be changed in the yard, while internal sensors have to go inside the tyre and are the better choice where the wheel is exposed to impact. On farm machines the decision is usually made rim by rim, not for the whole machine.
Harvesters: the load changes by tonnes within one pass
A harvester leaves the field empty and comes back full, and that difference sits directly on its tyres. An empty machine and a full grain tank are two load cases, and the pressure that suits one is not automatically right for the other.
The harvest window is measured in days. A machine stopped for a tyre is not a repair bill - it is crop that will not be cut on time. That is why on this class the argument is not "does TPMS save tyres", it is "does it let me find a soft tyre before it becomes a stopped machine". Sampling the pressure once a week answers neither question.
Load-sensing alarms are the practical answer: thresholds set against the empty and laden weights, so a full tank does not trip a false alarm and a slow leak is still caught.
Sprayers and trailers: weight arrives as liquid or grain
The same logic applies to a sprayer, where the tank weight arrives as liquid, and to an agricultural trailer, where it arrives as grain. On a sprayer the load also shifts the centre of gravity as the tank empties, which changes how the tyres are worked through the day.
No network on the farm - this is the part that changes the design
This is the difference between agricultural work and port or mining work, and it is the point most specifications miss. A port has connectivity and a mine often has a site network. A farm in a remote area frequently has neither.
The good news is that the core system does not need it: sensors send to a receiver on the machine, the receiver drives a cab display or feeds the machine controller, and the alarm logic runs on the machine. Pressure, temperature and alarms all work with the data staying local.
If a farm does want machines linked to an office, that is a radio-link project rather than a tyre project: it has its own payload, its own server and its own range question. We treat it as a custom build with a per-project quote rather than a catalogue item, because no two farms ask for the same payload.
What the hardware actually is
The system is the same architecture we use on cranes, stackers and haul trucks, specified for farm duty:
- Sensors on each valve position - external screw-on, or internal where the wheel is exposed. Sealed to IP68 on the industrial line.
- One receiver on the machine, up to 256 wheel positions, so a tractor and a trailed implement fit within one unit's capacity.
- One interface of your choice - CAN, RS232, RS485 or Modbus RTU, chosen at the factory, one per unit.
- A cab display where the operator should see the values directly, or the machine controller where the data should be part of the machine's own logic.
- Repeaters only where the layout demands them; on a tractor and trailer that is usually a single well-placed unit rather than a chain.
The parameters we publish for this line: 433.92 MHz licence-free radio, pressure accuracy ±7 kPa, temperature accuracy 1 °C (error ≤ ±3 °C), 10 ms receiver-to-bus period, 10-30 V DC supply, receiver sealed to IP68.
Who buys this, and how it is fitted
Two routes exist and they are genuinely different projects:
- Dealers, farms and cooperatives retrofit machines that are already working. The fitting has to fit around the season, and the buyer wants the alarm in the cab, not a dashboard nobody opens.
- Machine builders fit at the factory, where the data can go straight into the machine's controller and the display becomes a line item rather than a retrofit kit.
Knowing which one you are changes the specification more than any product choice does.
The machine classes this applies to are covered in more detail on the agricultural machinery page, with separate pages for tractors and harvesters. If you are specifying the hardware, the receiver and sensor range is the place to start.
Questions worth asking before you buy
- How is the alarm delivered? If it only appears in an app, it will not be seen while the machine is working.
- What happens when a sensor is missing? The system should show a defined absence value, not a silent zero - a missing wheel must not look like a healthy one.
- Who plans the radio layout? A supplier who quotes without asking for the axle layout is quoting a box, not a system.
- Does it work with no coverage? For farm work, this should be the first question, not the last.
If you tell us the machine, the wheel count and whether the site has mobile coverage, we can reply with the configuration and say whether the cab display or the machine controller is the better place for the data.
FAQ
- Does a TPMS for agricultural machinery need mobile network coverage?
- No. The sensors, the receiver and the cab display work as a standalone system. Network is only needed if the farm wants to see the data somewhere other than the machine.
- Why do tractor tyres need different pressures on the road and in the field?
- A firm tyre protects the sidewall on a hard road; a softer tyre spreads the load in the field so the machine does not sink and the soil is not compacted. The two jobs want different pressures on the same tyre.
- Can one receiver cover a tractor and its trailer?
- Up to 256 wheel positions per receiver, so the capacity is usually not the constraint. Send the wheel count of the combination and the repeater layout is planned against the axle layout.