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Rolling rewards

Low rolling-resistance tires reduce fuel consumption


October 8, 2012
by Howard J Elmer

The phrase “carbon footprint” is used often these days, particularly by government, and I suspect that its meaning is just as often misunderstood.

Most drivers tend to think of their carbon footprint as being determined entirely by fuel consumption. And while everything about fuel (from production, through transport, to final usage) adds up to a carbon footprint, burning gas by itself is not the end of a car’s environmental impact.

Even all-electric vehicles have to claim some carbon footprint. Why? Because while they don’t burn fossil fuel and produce carbon through combustion, the process that makes their electricity does—like coal-fired electricity generation and the transition of that power to their batteries. Then you can add the carbon footprint of the production, and the eventual disposal of the batteries and the rest of the car. Frankly, these calculations can get complicated and boring very quickly; that’s why people lose interest.

Another phrase that’s been getting lots of media and advertising play is “low rolling resistance”. This phrase refers to a type of tire. A low-rolling-resistance tire rolls further with the same amount of energy input, meaning less fuel is consumed getting the tire going and keeping it in motion. Transport Canada describes these low-rolling-resistance tires as a class that improves fuel consumption and greenhouse gas (GHG) emissions by 2.5 to three percent.

Tires, like every part of a vehicle, require energy to move down the road. Part of that energy is used to overcome air resistance (drag), friction and the rolling resistance of the tires. A driver has to live with most of these characteristics. However changing tires can alter this equation.

How? Consider that more than 80 percent of a vehicle’s fuel energy is lost to various forces of drag. But, adding low-rolling-resistance tires can help reduce this loss by making vehicles easier to roll down the road. In fact, recent studies performed by manufacturers, as well as third-party evaluations, have found that low-rolling-resistance tires can help reduce a vehicle’s fuel consumption by as much as 4.5 percent.

Yet one tire is really not that different from another, right? They are made of rubber and are round—but that’s where the similarities end. Research has revealed that chemical changes (at a molecular level) could create new type of tire—a low-rolling-resistance tire.

At a Bridgestone event the concept was explained this way: Better carbon footprint = less friction = fuel savings. To be able to control how the various chemicals and additives of a tire go together, engineers have to operate at a molecular level. Over time they determined that just stirring the pot didn’t mix everything evenly. Instead, they had to organize those
different bits (polymers, black carbon, and silica) using a technique called Nanostructure-Oriented Properties Control Technology. The process fixes the various molecules into a preset pattern creating a much tighter, tire, self-supporting tire.

In fact, Bridgestone’s tire (the new Ecopia) sidewalls are so stiff they give energy back to the tire which otherwise would be lost as heat. This process really is the trick no matter who the manufacturer is.

Rubber compounds in a tire give off energy in the form of heat as they deform during rotation. The amount of energy required by the tire to deform is called rolling resistance. Tires that have a low rolling resistance require less energy to deform. It’s this reduced energy loss that in turn reduces fuel consumption and emissions.

Studies by the US Department of Transportation seem to also reinforce what Transport Canada is saying. Replacing high-rolling-resistance tires can result in as much as $100 in annual fuel savings—or hundreds of dollars over the life of the tire. Since this breakthrough, several companies have introduced lines of low-rolling-resistance tires in just the past couple of years.

The following is a sample of some of the newest low-rolling-resistance products available from the tire companies. It is by no means a complete list, however it will introduce the idea of saving fuel and saving the environment through a reduced carbon footprint.

Bridgestone Ecopia

Bridgestone says alternative powertrain sales will reach 1.8 million units by 2015; this number only translates into 12 percent of new vehicle sales, however for these buyers saving fuel and a “green” footprint seem key to the buying decision; so a low-rolling-resistance tire seems an obvious choice. The Ecopia is rated for 110,000km of tread wear and is available for a wide variety of vehicles. This tire was tested by letting two identical Honda Civics coast down identical ramps (kind of like a soap-box derby) and across a flat asphalt parking lot. The Ecopia-equipped Civic rolled about 15 percent further than the non-Ecopia-equipped car. Bridgestone claims around a four percent fuel economy improvement with their product.

Michelin Green X – Energy MXM4 Tire

Michelin offers a series of tires under its “Green X” label. Some of these are currently found on Mercedes, Infiniti and Buick cars as original equipment offerings. One of its newest tires is the Energy MXM4. It is said to be quiet, comfortable, wear evenly and, of course, go farther with each tank of gas. The tire is offered with a 70,000-km tread wear limited warranty and is available in sizes 235/65R17, 255/55R18, and P235/55R17.

Michelin uses sunflower oil, more common in cooking, to create the unique rubber compound they use. It turns out that sunflower oil used in the patented Michelin Helio Compound technology allows this new tire to maintain its edge in wet and snowy weather while still delivering safe all-weather handling.

Continental CrossContact LX20 with EcoPlus Technology

Continental CrossContact LX20 with EcoPlus Technology

At last year’s SEMA show in Las Vegas, Continental showed its new CrossContact LX20 tire with EcoPlus Technology. It was subsequently awarded “Best New Tire and Related Product” at the show for its innovative low-rolling resistance and fuel-saving features.

This tire is now Continental’s premier all-season tire, aimed specifically at the light truck, SUV and crossover market. Developed to deliver improved fuel economy and better tread wear, it also has the benefit of achieving a stopping distance 34 feet shorter than the leading competitor in independent wet braking tests.

Continental’s EcoPlus technology consists of two main factors, Tg-F polymers and +Silane. The Tg-F polymers are temperature-activated functional polymers that increase compound bonding. These improve wear and the low rolling resistance of the tire. The second part is the +Silane. This additive improves the tire’s grip on slippery roads. It also improves stopping distances.

The CrossContact LX20 comes in sizes to fit 15- to 18-inch rims and has an 110,000-km (or 72-month) warranty.

Goodyear Assurance CS Fuel Max

This newest Fuel Max tire—the CS—is aimed at the SUV, light truck and crossover market and follows up the successful launch of the original Fuel Max. Goodyear expresses its savings saying they estimate reduced energy needs will save up to 4,000km worth of gas over the life of four tires.

The first Fuel Max tires were introduced in 2010 and sold three million units; these were intended for cars. They are now original equipment on vehicles like the Chevrolet Volt, Chevrolet Cruze Eco, Ford Fusion S and
Toyota Prius.

Goodyear says these new tires are built with a centre wet zone that will enhance traction in wet and light snow conditions. The outer dry zone is meant to improve handling and grip for confident maneuvering. The CS gets reinforced construction (and new tread designs) to handle a variety of vehicle weights in the SUV, light truck and crossover category.

These CS tires are available for 16- to 19-inch rims and come with a 105,000-km tread life limited warranty.

Pirelli Scorpion Verde

This new tire is introduced as part of Pirelli’s “Green Performance” range of products to cover low-rolling-resistance tires. Like most companies, Pirelli has used nanotechnology to make compounds that deliver better thermal stability, have less heat dispersion due to friction and consequently lower fuel consumption and reduce carbon emissions.

Interestingly though, they point to the elimination of highly aromatic oils—which are potentially harmful to both people and to the environment—as being a breakthrough in their manufacturing processes. They say they are now safer, as well as having reduced their impact on our environment. The results are perhaps best expressed in their Green Performance philosophy. This is a global ecological viewpoint: Pirelli believes that the use of materials which aren’t derived from petroleum, together with integrated solutions for the automobile industry will reduce the impact on the environment.

The Scorpion Verde is specifically aimed at high-performance SUVs. Its tread has an optimized pitch sequence and phasing as well as longitudinal siping and high lateral siping density as well. The tire’s large contact patch has four, wide longitudinal groves for stability. It fits 17- to 20-inch rims and has an 80,000-km limited tread wear warranty.       c.a.r.