July 23, 2013

News & Features

Tire innovations to be pumped about

New York Times News Service

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Bridgestone's air-free tire concept is being developed for use on electric golf carts, lawn mowers and low-speed vehicles. (Bridgestone)

The steady flow of reminders to keep tires at the automaker's suggested inflation levels — even President Barack Obama chimed in — demonstrates just how far the demands of auto maintenance have diminished. With spark plugs that seem to last forever and oil-change intervals stretching to 10,000 miles and more, many owners continue to slack off when it comes to looking after tire pressure.

But the day when drivers never have to pump air into their tires may be coming. Goodyear has developed a self-inflating tire technology intended to keep commercial truck tires at the proper pressure, saving fuel and reducing tread wear. The system, which Goodyear calls Air Maintenance Technology, automatically keeps tires inflated without the need for electronic controls or external pumps.

The key is a clever pumping device — essentially a flexible tube nestled inside the tire — that operates in much the same way a person's muscles push food through the digestive tract in continuous pulses. As the tire rotates, high pressure caused by the vehicle's load compressing the tire repeatedly deforms the embedded tube, generating a pumping action.

If the pressure inside the tire falls below the required level, a regulator lets outside air into the pumping tube, where it is pressurized and sent through a valve into the interior cavity of the tire. And all of this happens automatically, without any action by the driver.

Underinflated tires result in a loss of about 3 percent in fuel economy, according to government and industry research.

A $1.5 million grant from the Energy Department's Vehicle Technologies Office is helping Goodyear to speed up demonstration of the system for commercial vehicles. The company has also received a grant from the Luxembourg government to support research there on a similar inflater for consumer tires.

How about car tires that never need inflating at all? The Tweel, a concept for a combined wheel-tire assembly proposed by Michelin in 2005, has been inching forward. The Tweel tried to take pressurized air out of the tire equation altogether, using flexible polyurethane spokes that support an outer band of tread material.

Such non-pneumatic tires would never need filling and would be immune to punctures. Although a flat-proof, no-air tire is an exciting notion, the original Tweel would vibrate considerably above about 50 mph, producing excessive noise and heat.

So Michelin aimed the Tweel for use at low speeds, introducing the X-Tweel SSL, a non-pneumatic tire-wheel for skid-steer loaders, those do-it-all machines used in landscaping, construction, contracting and farm businesses. The single-piece Tweel SSL replaces some 23 components that make up a standard pneumatic tire.

Skid-steer loaders with pneumatic tires typically experience several flats a month, Michelin says. To reduce maintenance downtime, many owners fill their tires with foam or replace them with solid tires, resulting in vehicles with poor traction, handling and ride comfort. The damage-resistant X-Tweel SSL wears longer than conventional tires and also provides excellent traction, Michelin says.

The Tweel is no longer alone in the airless tire category, though.

Bridgestone has introduced its air-free tire concept, a prototype design with recyclable thermoplastic ribs serving as the central load-supporting elements. The design seems to resemble a crisscrossing mesh of polymer leaf springs. Bridgestone says that the concept tire offers sufficient comfort and performance for use on electric golf carts, lawn mowers and various low-speed buggies.

Yokohama Rubber has developed a full-size, non-pneumatic concept car tire called the Youmyaku. The prototype features a honeycomblike network of curving flexible ribs around a large metallic hub.

None of these technologies are going into a passenger car tire anytime soon, though, so drivers still need to remember to pump it up.

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