Indirect tire pressure monitoring systems work via the antilock braking and electronic stability control (ESC) systems. As a result they are less costly, but currently not as accurate as direct TPMS.
To improve the precision of indirect systems, Audi and NIRA Dynamics, a Swedish company with expertise in signal processing and control systems, have jointly developed second-generation indirect TPMS.
This system signals the tire pressure loss for each individual tire and is able to detect both a puncture and diffusion. For these reasons it is the only indirect TPMS that meets the US FMVSS138 regulations.
The advantage of indirect TPMS is that you do not need costly and complicated wheel-mounted electronics and separate hardware, Victor Underberg, responsible for ESC and tire pressure monitoring systems at Audi said.
Moreover this indirect system ensures the functionality of TPMS over the entire life of the car.
Audi concedes that direct TPMS can have certain advantages like showing the tire pressure and temperature in the infotainment screen, but says that it can be significantly more expensive for the customer.
It is our experience that customers are not ready to pay extra for such a system, especially when they also have to buy it for winter tires, causing the risk that drivers will not take notice of the warning system any more, Underberg said.
The risk could be that in countries where separate winter tires and rims are used, drivers will simply avoid the expense of paying twice for a direct system and physically block out the warning light with tape.
According to Underberg, in the EU where TPMS are set to become mandatory, the outcome of ongoing discussions about the competing systems is expected in March.