Two-Wheel and Four-Wheel TPMS: What Actually Changes Wheel count changes the housing, the valve interface, the position marking and the kit — not the sensor inside. Here is what to compare before you order.

The assumption that costs people money

Buyers routinely assume that a two-wheel TPMS and a four-wheel TPMS are two different products. It is understandable: the part numbers differ and the boxes differ. But it leads to an expensive mistake — treating a four-wheel programme as new product development, when most of it is a configuration of something that already exists.

The truth is narrower. Wheel count changes the mechanical parts: what touches the rim, and how the kit is presented. It does not change the electronics, the measurement or the radio protocol. Knowing which is which tells you where a supplier can move quickly and where they genuinely have to do work.

What changes when the wheel count changes

Four things, in order of how much trouble they cause.

The housing and the valve interface. A sensor has to attach to a rim, and rims differ. A motorcycle rim is not a car rim; a spoked wheel with an inner tube is not a tubeless alloy; a small scooter wheel is not a quad wheel. The interface between sensor and valve is the part that has to hold air, which makes it the part that has to be right. This is where the real engineering effort sits.

Wheel position marking. A four-wheel kit has four sensors that are not interchangeable in the user's mind. If they all look identical, the fitter guesses, and a guessed installation produces readings that are correct in value and wrong in location. Marking each sensor by position — such as L.F, R.F, L.R, R.R — removes the guess. On two wheels the ambiguity is smaller but does not vanish, because front and rear often run different target pressures.

Kit composition and quantity. Two sensors, three or four. That sounds trivial until you consider packaging, instructions, the spare-parts list, dealer stock and the app's setup flow, all of which are written around a fixed number.

Documentation and packaging. Labels, manuals, language sets and box artwork follow the wheel count and the market. This is the cheapest thing to change and the most common thing to get wrong, because it is usually decided last.

What does not change

This is the part that matters commercially.

• The sensor body. The same sensing element and the same measurement chain sit inside every variant in the family.
• The radio protocol. The same BLE version, band, transmit power and data rate apply across the range.
• The battery. The same replaceable coin cell, with the same behaviour after a battery swap.
• The temperature specification. The same operating and storage ranges, with a wide-temperature variant available at four wheels for markets that need it.
• The app. One application can handle a mixed fleet of two-, three- and four-wheel vehicles, because wheel count is a configuration value rather than different firmware.

If a supplier quotes a fresh development programme for every wheel count, ask what actually differs. If the answer is the housing and the marking, the programme should be measured in weeks, not quarters.

The four configurations we build

Configuration	Typical vehicles	What is specific to it
Two-wheel	Motorcycles, scooters, mopeds	Two sensors, one per wheel; front and rear pressure targets
Three-wheel	Tricycles, three-wheel commercial vehicles	Three sensors; position marking matters more than on two wheels
Four-wheel	Quads, ATVs, light four-wheel vehicles	Four sensors; marking by corner is essential
Four-wheel, wide temperature	Same vehicles in markets with a wider ambient range	A different temperature specification on the same platform

All four use the same sensor platform. One platform covering several vehicle classes is easier to stock, easier to service and easier to keep compliant than four unrelated products.

Why position marking is not cosmetic

Consider a four-wheel ATV with a sensor that has lost its label in the spare-parts bin. Somebody fits it. The app shows low pressure on a wheel that is fine, while a slow puncture on another corner goes unnoticed until the tyre is destroyed.

The fix is not clever software. It is a marking scheme applied at the factory that survives the workshop, plus an app that lets the user confirm which sensor is on which corner. Both belong in the specification, not in a later support call.

What to ask before you order

1. What is the valve interface, and what rim does it fit? Give the rim type, the valve hole and whether the wheel runs a tube. Guessing here is how a pilot batch fails.
2. How are the sensors marked, and can the marking carry our part numbers? Position marking plus your own numbering is the most useful combination for a dealer network.
3. What is in the box, exactly? Sensors, valves, nuts, caps, manual, spare seals — ask for the packing list in writing.
4. Does one app handle all wheel counts? If not, ask how a dealer who stocks several vehicle classes manages the split.
5. Which parts are common across configurations? This question tells you how much of your range is genuinely shared.
6. What is the wide-temperature variant for? It exists for markets whose ambient range is wider than the standard specification covers. If your destination is one of them, say so at the start rather than after a field failure.
7. What is the production reality? Ask for real monthly volumes and real capacity, not a capability statement.

Where the standard specification sits

Item	Specification
Bluetooth protocol	BLE 4.1
Operating band	2400 MHz – 2483.5 MHz
Transmit power	3 dBm
Air data rate	1 Mbps
Receiver sensitivity	−95 dBm @ 1 Mbps
Power	CR1632 coin cell, replaceable
Operating temperature	−20 °C to +80 °C
Storage temperature	−40 °C to +85 °C
Operating humidity	5% – 95%, non-condensing
Sensing element	Infineon

If your market spends a meaningful part of the year outside the operating temperature range, that is a variant conversation, not something to discover in the field.

Where we stand

We build the sensor and the platform ourselves, and we run two-, three- and four-wheel configurations plus the four-wheel wide-temperature version on the same core design. Volume today is more than 10,000 sets a month into the Chinese two-wheeler aftermarket, with capacity of 30,000 sensor units a month. Every sensor is pressure-calibrated on our own test software before it ships, and we run water-immersion, RF-range and protocol verification in house. Certification is handled per market and per project.

If you are planning a range rather than a single model, tell us the wheel counts and the markets and we will map which configurations share parts and which need their own tooling. The sensor specification is on the BPU100 product page, and further reading is on the blog index.

FAQ

Is a four-wheel TPMS just two two-wheel kits? Mechanically, no. The kit is a defined product with its own packaging, marking and documentation, and the valve interface may differ. Electrically and in firmware it is very often the same platform, which is why the wheel count should not trigger a full development programme.

Can the same sensor be used on a motorcycle and an ATV? The sensor electronics can be. The housing and valve interface have to suit the rim, and that is where the difference lives. Confirm the rim type before assuming a shared part.

What happens if a sensor is fitted to the wrong wheel? The pressure reading will be correct but attributed to the wrong position. Marking sensors by wheel position at the factory and confirming the assignment in the app is the practical defence against this.

Is the app different for each wheel count? It does not have to be. Wheel count is a configuration value, so a single app can cover two-, three- and four-wheel vehicles. Ask any supplier how their app handles a mixed fleet before you commit to a range.