The only real connection between driver and road are four handprint-sized pads of rubber. Your engine, brakes and safety features mean literally nothing if your tires are old, bald, or underinflated. That's why Nissan's Easy-Fill Tire Alert is one of the most important features on the market today. It's not quite as cool as Mercedes' emergency deflate feature, but that's not here quite yet.

Underinflation, which is worse that over inflation, forces tires to work at higher heats than when blown up properly, and tires underinflated by 20% wear out the tire 25% faster. There's also less traction, and fuel consumption goes up. Nissan has now sold 9 million vehicles with the feature, and not just the top models. It's currently standard on the Versa, Sentra, Altima, Maxima, Leaf, Kicks, Rogue, Rogue Sport, Murano, Pathfinder, Armada, Frontier and Titan.

Here's how it works. First you park the vehicle, obviously. You leave the ignition in the accessory position, engine off. When you start filling up the tires the headlights and taillights flash. When you hit the correct pressure, usually listed on the driver's side door jamb of the vehicle, the horn beeps. If you overinflate the tire, the horn beeps again, and the hazards flash three times.

According to the National Highway Traffic Safety Administration (NHTSA) there are nearly 11,000 tire-related motor vehicle crashes each year, with 600 deaths. Additionally, NHTSA says that keeping tires properly inflated "can save up to 11 cents per gallon, and can extend a tire's life by 4,700 miles." Now if we can just add Continental's renewable tires to the mix, we'll be on to something.

"Ensuring your tires are inflated to the correct pressure is one very simple step consumers can take to help make their vehicles safer, especially with the start of holiday road trips," said Selim Hammoud, director, NNA Safety Officer, Nissan North America. "Nissan's Easy-Fill Tire Alert takes the guesswork out of filling tires and makes simple vehicle maintenance less intimidating for the average driver."

This is a perfect next step after tire pressure monitoring systems or TPMS. That type of system has been required on all new vehicles in the US since 2007. This Easy Fill feature builds on that, by offering a simple way to know how much air to put in your tires, without carrying around a tire pressure gauge or borrowing one from the gas station. Making important maintenance easy, maybe the most-important maintenance, is something automakers will have to focus even more on as this form of transportation becomes more passive than active.