Two cars can have the same warning light and the same job, watch the tyre pressures, yet go about it in completely different ways. Knowing which system a car uses explains why one needs a button pressed after every top-up and another shows a live figure for each corner.
Direct TPMS: measuring the pressure
A direct system puts a small sensor inside each wheel, usually built into the valve. It measures the actual air pressure and radios it to the car several times a minute. Because it reads each tyre individually, it can do things an indirect system cannot:
- Show the real pressure for each tyre on the dashboard
- Name the specific tyre that is low, rather than just warning in general
- Spot a problem even when all four are low together
The trade-off is hardware. Each sensor runs on a sealed battery that lasts roughly five to ten years, and when it dies the whole sensor is replaced; there is no changing the battery alone. The sensors also need looking after at every tyre change: a fresh valve core and seal, and care not to damage them when the tyre is levered off. That servicing, and any replacements, are handled when new tyres go on, built into the fitting whether the new set is bought locally or online from Tyres.co.uk or a similar tyre retailer.
Indirect TPMS: inferring it from wheel speed
An indirect system has no pressure sensors at all. It uses the ABS wheel-speed sensors the car already has and watches for a tyre that is turning slightly faster than the others. A tyre losing pressure sits a little lower, its rolling radius shrinks, and it has to spin marginally faster to keep up, which the system reads as "this one is going soft".
That approach is cheaper and needs no maintenance, but it comes with limits:
- It gives no actual figure, only a warning
- It is slower and less precise, and can struggle to flag all four dropping together evenly
- It must be reset after any pressure change so it relearns the new baseline, as covered in the reset guide
Which a car has
The quickest tell is the dashboard: a car that can display a pressure figure per tyre has a direct system, while one that only gives a light and relies on a reset button after inflating is almost always indirect. The valves are another clue, direct systems often use sturdier metal valve stems that house the sensor, rather than the simple rubber valves on an indirect car.
Neither design is outright better. Direct trades cost and eventual sensor replacement for accuracy and the ability to name the low tyre; indirect trades precision for being cheap and maintenance-free. Both do the core job, warning before a soft tyre becomes a dangerous one.
From the workshop: the surprise for a lot of people is the bill when a direct sensor dies on a four- or five-year-old car. They're not expensive each, but they tend to go around the same time, and a relearn on top adds a bit. It's worth budgeting for, the same way you would brake pads.
Sources and accuracy. The technical descriptions and sensor battery life here reflect typical industry practice at the time of writing and vary by manufacturer. The car's handbook confirms which system it uses. If anything here looks wrong, get in touch and we will check it and put it right.
Common questions
What is the difference between direct and indirect TPMS?+
Direct TPMS uses a pressure sensor inside each wheel that reads the actual pressure. Indirect TPMS has no sensors and instead uses the ABS wheel-speed signals to spot a tyre rotating faster because it has gone soft. One measures pressure; the other infers it.
Which is better, direct or indirect TPMS?+
Each has trade-offs. Direct is more accurate, can name the low tyre and show a figure, but the sensors cost money and eventually need replacing. Indirect is cheaper and maintenance-free but less precise and must be reset every time pressures change.
How do I know which type my car has?+
If the dashboard can show an actual pressure for each tyre, it is almost certainly direct. If it only gives a warning light with no figures, and has a reset button to press after inflating, it is usually indirect. The handbook confirms it.
Do TPMS sensors need replacing?+
Direct sensors do, eventually. They run on a sealed battery that lasts roughly five to ten years; once it dies the sensor is replaced, usually when new tyres are being fitted. Indirect systems have no sensors to replace.