Years ago the U.S. government wisely mandated tire pressure monitoring systems (TPMS) on passenger cars for all the wrong reasons. Audi takes a rather unique approach to this mandate using indirect measurement rather than individual tire sensors and the upside is significant.
Back when Ford Explorers were flipping and rolling along the highways of America and other countries in unusually large numbers (but similar vehicles were not), a circular firing squad was formed to place the blame. First up, you. You were blamed for being dumb and lazy and not checking the air pressure inside your tires. Next, Ford. Its ancient leaf-sprung, and not-independent rear suspension coupled with a tall tippy vehicle. Finally, the tire maker, whose tires on the upside down Fords with the victims inside often showed the tell-tale signs of having treads delaminated from the tire structure. Out culture being what it is, the automaker and tire maker could not assume all the blame, so the government accepted a compromise.
That compromise now costs every new car buyer hundreds of dollars. Tires are now required to be monitored for deflation. Single-tire deflation was not the cause of all the accidents in the Ford Explorer tragedies, but nonetheless, on we went. Initially, automakers looked at was asked of them, and they used indirect measurement. They simply monitored the wheels’ speed using the existing anti-lock brake system (ABS) sensors. If one wheel was rotating slower than the rest, it meant that a tire had lost pressure. Problem solved, and at almost no cost.
However, most automakers didn’t stop there. They instead opted to use a sensor inside each wheel to read the pressure. Thus, they could set a minimum, or a standard deviation from the other three tires to detect a low-pressure event (flat). The problems started there. This method costs hundreds of dollars, and the sensors have been driving owners nuts ever since. They sometimes get a little out of whack or stop working. The people that make the expensive sensors have great videos explaining why you’d be crazy not to use them.
However, there is another issue for snow-belt car owners that want to have two sets of rims with two sets of tires. Buying two sets of sensors is very expensive and installing new sensors on the car often means re-initializing the system to recognize the sensors. A hassle and an un-needed expense. Audi, has standardized on the indirect method since 2011, and it makes using two sets of tires/rims much easier.
This is not some theoretical advantage. I use two sets of wheels for my 2007 Highlander that has the indirect system. My neighbor Bob has a 2015 Audi S4 performance sedan. He also uses two sets of wheels. We can swap our 3-season wheels and tires for our winter set easily at home, or have it done at a local shop for nearly free. Our alternatives would be to strip the rubber off the rims twice per year, or buy added sensors and the hassles that come with that method.
Audi is not alone. A few other automakers have returned to the indirect method on selected models. Kudos to Audi for recognizing that this method jives very well with its heavy reliance on Quattro AWD and those customers that want the safety and performance of dedicated winter wheels and tires.
Top image courtesy of Audi, second and third images courtesy of Tire Rack.