What two types of Tire Pressure Monitoring Systems (TPMS) are there? First, there is Indirect TPMS, and then Direct TPMS. Let's look at how they differ:
An Indirect TPMS doesn’t measure tire pressure. It doesn't electronically process the same kind of measurement you might see with a tire gauge. Instead, an indirect TPMS relies on wheel speed sensors of anti-lock brake systems. It measures how fast your tires are rotating and sends a signal to your on-board computer, which interprets the relative size of your vehicles' tires and compares to other operational data, like speed. When a wheel spins faster than expected, the computer can interpret this as an underinflated tire and will alert the driver.
Here are a few disadvantages of Indirect TPMS:
May inaccurately measure the wheel revolution rate if you put a bigger or smaller tire on your vehicle
May be unreliable when tires are unevenly worn
A reset is necessary after properly inflating every tire
A reset in necessary after after routine tire rotation
Cannot measure or display absolute pressure values
Direct TPMS uses pressure monitoring sensors within each tire to monitor specific pressure levels – not just wheel revolution data from the anti-lock brake system.
Sensors in a Direct TPMS may even provide tire temperature readings. The Direct TPMS sends this data to a centralized control module where it’s analyzed, interpreted, and, if tire pressure is lower than it should be, alerts the drive on the dashboard. A Direct TPMS usually sends all this data wirelessly. Since each sensor has a unique serial number, your vehicle can distinguish itself from other vehicles and can also provide pressure readings for each individual tire.
Here are a few advantages of Direct TPMS:
Can deliver actual tire pressure readings from inside the tire
Not prone to inaccuracies because of tire rotation/tire replacement
Simple resynchronization after tire rotation/tire replacement
Batteries inside the sensors usually last around eight years