Green tyres make fewer compromises

By Rex Roy, Crain staff (AN)

Detroit, Michigan -- Low-rolling-resistance tyres improved vehicle fuel economy when they were introduced in the 1970s. But mileage gains came at a cost: long wet braking distances and poor handling grip.

But now, as the price of gasoline and federal corporate average fuel economy standards rise, Continental AG, Michelin and Bridgestone Corp. are responding with new tyres that offer improved fuel economy and shorter braking distances.

New material technology and construction techniques help deliver the benefits.

Boutique polymers

Specially engineered rubber polymers help Continental reduce rolling resistance and improve braking performance in its recently introduced ContiEcoContact 5 tyre.

Proprietary short- and long-chain molecules in the tyres' so-called Black Chili material react in different ways when the tyre rolls straight ahead vs. when braking or cornering.

The long-chain molecules in Black Chili help provide low rolling resistance and improved fuel economy when the tyre is not stressed.

But when the tyre reacts to braking or cornering forces, the short-chain polymers are physically excited into action. The molecules immediately stiffen, boosting the ContiEcoContact 5's grip.

When demand for braking or handling passes, the short-chain molecules relax and the tyre returns to its low-rolling-resistance state.

Meanwhile, Michelin's Energy Saver tyres feature a new siping technique that indirectly improves fuel economy. Sipes are the tiny cuts in the tread of new tyres.

Michelin's intricate grooves and cuts within individual tread sections help reduce heat buildup in the tyre tread. Lower heat makes for a tread compound with lower rolling resistance.

Shorter distances

Tyre makers are reluctant to provide precise data on fuel economy and braking distances. They prefer percentage comparisons with other tyres because, they say, performance data vary by vehicle and test conditions.

Continental says the ContiEcoContact 5 has 10 percent better wet braking, 7 percent better handing and 20 percent better rolling resistance than the ContiEcoContact 3.

Michelin reports that its Energy Saver All-Season tyre has 31 percent better rolling resistance than the Michelin Harmony line of touring tyres. The two tyres perform almost identically in wet braking.

But even manufacturer-provided data show some compromises. Michelin offers an 80,000-mile warranty on its Harmony line while the Energy Saver's warranty is just 65,000 miles, highlighting the tradeoff in tyre life.

"Tyre engineering is all about overcoming compromises," says Continental's Markus Fischer, an engineer responsible for ultra-high-performance products. "It's easy to engineer a tyre that does one thing well. It's another to create a tyre that does all things well."

Automakers' acceptance

The ContiEcoContact 5 is standard on the Mercedes-Benz SLK and BMW X5.

Michelin's Energy Saver All-Season tyre is used by four major automakers. Notable vehicles include the 2012 Toyota Prius V and the 2012 Buick LaCrosse with eAssist.

The Bridgestone Ecopia is standard on the Nissan Leaf EV.

Continental, Michelin and Bridgestone declined to reveal pricing for automakers. But retail prices for replacement tyres indicate that the latest-generation energy-saver tyres are priced in line with the units they displace.

From Automotive News (A Crain publication)