Two Types of TPMS Systems

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:

Indirect TPMS

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

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
• A vehicle's spare tire can also use a Direct TPMS

For more information on TPMS systems and parts, visit our JohnDow.com/TPMS.