Indirect Tire Pressure Monitoring Systems Making A Comeback On Some Imports - Tire Review
Indirect Tire Pressure Monitoring Systems (TPMS) are the systems that do not have air pressure sensors inside the tires. Rather, they detect a low tire by comparing relative wheel speeds via the Anti-lock Brake System (ABS) wheel speed sensors. Older indirect TPMS are not as sensitive to changes in tire pressure as direct systems that actually monitor the air pressure inside the tire, but they are not as expensive either. Even so, the vast majority of vehicles that have TPMS use direct systems rather than indirect. Federal law requires the TPMS to alert the driver if the pressure inside a tire has dropped more than 25% below the recommended inflation pressure. Many vehicles abandoned indirect systems for direct systems to meet the federal mandate. One of the weaknesses of older indirect systems is that they may not turn on the warning light if all the tires are underinflated by a similar amount. If the recommended pressure is 32 psi, but all the tires are 24 psi (down 25%), the system won’t know there’s a problem because all the tires will be rotating at the same speed when the vehicle is being driven. New systems are taking advantage of better wheel speed sensors and modules to make indirect systems work. But even the newer systems suffer from the inability to read the tire pressure when the vehicle is sitting still. Source: www.tirereview.com
