What ±7 kPa means in practice
Seven kilopascals is about 1 psi, or roughly 0.07 bar. On a heavy-duty tire running at several hundred kPa, that is less than one percent of the working pressure.
Put differently: an alarm threshold that triggers a real response is usually set at 20 to 25 percent below target pressure. At a 700 kPa target that band is well over 100 kPa wide. Against it, a 7 kPa measurement uncertainty is noise. For the job TPMS exists to do — catch a tire that is going down before it destroys itself — ±7 kPa is comfortable.
So the honest answer to "is ±7 kPa enough" is: for almost every industrial machine, yes. The more useful conversation is about everything around that number.
Accuracy is one term in a bigger budget
A pressure reading is the output of a chain, and the chain has more than one error term. Buyers who only compare the headline figure miss the terms that dominate in service.
Temperature. This is the biggest one, and it is physics, not product quality. In a sealed tire, absolute pressure rises and falls with absolute temperature — roughly 2 to 3 kPa per degree Celsius on a tire at several hundred kPa. A tire that reads 700 kPa cold can read noticeably higher after an hour of highway or haul-road work without a single gram of air being added. That is why a TPMS has to report air temperature alongside pressure: without temperature, you cannot tell a real leak from a hot tire. Our temperature channel is ±3 °C, and the compensation happens in the controller or the display using both values.
Calibration. Every unit we ship is pressure-calibrated on the line. Batch calibration is faster and cheaper, and it is the reason two sensors from the same box can disagree with each other by more than either disagrees with the truth. Ask whether calibration is per unit or per batch. It is an easy question with a revealing answer.
Repeatability. Operationally, repeatability matters more than absolute accuracy. What a fleet manager needs is that the same wheel gives the same number at the same pressure, today and in two years, so that trends are real. A sensor that is slightly offset but perfectly repeatable is more useful than one that is accurate on average and noisy.
Update period. Our default data period is 500 ms, software-configurable. A fast blowout is not really a measurement problem — the pressure collapses faster than any sensible alarm threshold. A slow leak is the opposite: it might lose a few kPa per day, and catching it is about repeatability and trend, not about the third decimal place.
Where ±7 kPa is not enough
Three cases, stated plainly, because it is better to lose a project you cannot serve than to win one you cannot.
Very low inflation pressures. If a tire runs at a low pressure — an off-road or specialty application where the working pressure is a small fraction of a heavy truck's — then 7 kPa stops being one percent and starts being a meaningful share of the reading. If your alarm band is only a few kPa wide, you need a different sensing class.
Laboratory and validation work. If you are characterising a tire, qualifying a rim, or measuring pressure as part of a research programme, you want a reference-grade instrument, not a monitoring sensor.
Very fine leak detection on a large fleet. Catching a 2 kPa per day leak reliably requires a tighter repeatability budget than a monitoring product is designed around. You can still find leaks with a trend, but the confidence interval is wider.
In all three cases the right answer is a different product, not a longer datasheet. We would rather tell you that in the first email.
The questions that reveal whether the figure is real
Ask any supplier these before you compare numbers.
- Is ±7 kPa specified over the whole temperature range, or only at room temperature?
- Is calibration per unit, and against what reference?
- What is the resolution you report, and does the reading get filtered before it is transmitted?
- Does the sensor report temperature with the same timestamp as pressure?
- What happens to accuracy after the sensor has been hit or has sat at pressure for five years?
- Can I see the pressure response in the protocol documentation, so I can design the alarm logic around the real figure?
A supplier who can answer questions four and six has thought about integration. A supplier whose answer to every question is "±7 kPa" has given you a brochure.
Accuracy in the field is a mounting question too
Two installation details change what you actually read.
Where the sensor sits. An internal sensor measures the air chamber directly. An external sensor measures through the valve, which is the same air but a longer path, and it sits where ambient heat and impact can affect it.
Whether the wheel is being read at all. A sensor that is missed by the radio link is worse than an inaccurate one, because the system may report the last known value. On long machines this is solved by repeater planning, not by tightening the sensor specification. Our production configuration for a 160-wheel beam carrier uses two receivers and twelve repeaters.
Designing an alarm around ±7 kPa
A workable rule set looks like this:
- Set the warning band well outside the measurement uncertainty — tens of kPa, not a few.
- Use temperature-compensated pressure, or your alarms will fire on hot afternoons.
- Make the threshold configurable per axle, because steer, drive and trailer positions do not run at the same pressure.
- Watch the rate of change as well as the absolute value. A tire losing pressure steadily is a different event from one that is simply hot.
- Log the raw value. Trends are what catch slow leaks, and trends need history.
Our configuration tool covers wheel count, sensor IDs and thresholds, and the alarm semantics are documented with the protocol so your controller can decide, not just display.
Summary
±7 kPa is enough for industrial monitoring: it is roughly 1 psi, under one percent of a heavy tire's working pressure, and far inside any sensible alarm band. It is not enough for research-grade measurement or for very low-pressure tires, and no honest supplier should tell you otherwise.
See the TR100 specification for the full sensor and receiver data, or the CAN bus TPMS page for how pressure and temperature are delivered on the bus. If you send us your target pressure and the alarm band you intend to use, we will tell you whether ±7 kPa fits.