Eco Tires: That’s How We Roll

eco-tires-leadThe tires we roll on have characteristics that can differ greatly. Carefully chosen, a new set of tires can make your time behind the wheel quieter and the ride smoother, while others can deliver a harsher ride and transmit an unacceptable level of road noise to the cabin. Tire designs and compounds can also greatly influence handling and performance, which is one of many reasons tire manufacturers devote so much time and resources to advanced tire development and then proving their prowess on the track.

Beyond a focus on ride quality, performance, and tire life, an important trend in recent years has been the continuing refinement of low rolling resistance (LRR) tires that aim to improve fuel efficiency. Such tires are used on virtually every electric and hybrid vehicle for obvious reasons. Many automakers also equip their conventional vehicles with LRR tires since every little bit helps on the way to achieving the best possible fleet mpg average for their model lineup. All are keenly aware of the challenges ahead in meeting the mandated Corporate Average Fuel Economy (CAFE) requirement of 54.5 mpg by 2025. Driving on tires with lower rolling resistance is a small but important part of the strategy.

goodyear-tire-manufacturingTire rolling resistance has the potential to positively influence urban fuel economy up to 4 percent and 7 percent on the open road. As a rule of thumb, a 10 percent reduction in tire rolling resistance will result in a one to two percent improvement in vehicle fuel economy. Hyundai presents a great example. The automaker’s Sonata Eco model gains about one mpg more in the city and three on the highway mainly through the use of LRR tires and smaller wheels, in this case 17-inch versus 19-inch on the standard model.

Drivers shouldn’t be surprised if fuel efficiency actually drops when worn tires are replaced with new LRR tires, even if they’re the same size, type, and brand. Simply, as tires wear their rolling resistance gradually drops, about 20 percent during the life of a tire as the tread depth and mass decreases. The payoff will come over time and not necessarily during the first miles running new LLR tires.

green-tire-treadVarious techniques are used to reduce rolling resistance. Reducing internal friction is one way that comes with no noticeable change in grip characteristics during braking and cornering. Another is changing the tread compound, which can change grip. This sometimes, but not always, means a tradeoff between fuel economy and performance.

Early LRR tires were noted for their harsher ride, a result of using much harder rubber compounds and stiffer sidewalls in an effort to reduce friction and flexing. Newer LRR tires use advanced compounding with silica-based or alternative oils to provide more pleasant ride characteristics. Early LRR tires also had reduced grip and wore more rapidly. This has changed significantly over time as tire technology has evolved.

nissan-leaf-tireEven so, the primary mission of LRR tires is minimizing rolling resistance and addressing safety considerations like wet weather handling and traction. Those looking for tires focused on high performance diving are not likely candidates for LRR tires.

Choosing replacement LLR tires for a Prius, LEAF, Volt, or other electric or hybrid can be relatively easy. Just replace the tires with ones identical to those that originally came with the car. Automakers producing ‘green’ cars spend considerable effort working with tire manufacturers in selecting the right LRR tire to maximize efficiency of a specific model. Still, there are quite a number of aftermarket tires developed for electrics and hybrids so choices are many.

SONY DSCFor example, Yokohama’s AVID S33D LRR all-season tires for third generation Toyota Prius hybrids and other small cars reduce fuel consumption while retaining all-season traction.  Like the AVID, the Yokohama Geolandar G055 BluEarth tires we’ve been testing on a crossover vehicle feature the company’s advanced, lightweight Airtex inner liner that combines the elasticity of rubber with the lightness and superior gas-barrier characteristics of plastic to reduce tire weight and rolling resistance. This tire, like others in the Yokohama line, uses orange oil tread compound to enhance performance and decrease the use of petroleum in tire production.

Among other low rolling resistance tire options on the market is Goodyear’s Assurance Fuel Max, which uses a special fuel-saving tread compound that reduces rolling resistance by up to 27%. Goodyear claims this nets up to 2,600 miles worth of gas savings over the life of four tires. Michelin offers an array of GreenX tire options including Defender, Primacy, and Energy Saver A/S tires. Efficiencies are achieved through multiple strategies including the use of a more rigid tread block to lower rolling resistance and silica-based tread compound to keep tires running cooler. Toyo’s Versado Eco Touring all-season tires are designed to improve fuel efficiency for hybrid, electric, and other vehicles using naturally derived tread compound materials, a low rolling resistance design, and a recycled polyester casing to conserve natural resources.

michilin-geolander-tireWhile plenty of LRR tires are offered for a wide range of vehicles, it’s not always easy to choose since efficiency comparisons are not yet available. Traction, wear, and temperature resistance ratings are to be found but efficiency is glaringly missing, although there is hope.

The National Highway Traffic Safety Administration (NHTSA) has proposed a tire label that would provide wet traction, tread wear, and fuel efficiency (rolling resistance) ratings on a 0-100 scale for replacement tires. It has also done extensive testing to generate data for such a label. While not yet implemented, this will be of real value to those shopping for tires that will deliver improved environmental performance in the future

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