Up to 15 percent of the fuel used by a typical vehicle goes into producing energy needed to overcome rolling resistance. Energy is needed to counter road surface friction and losses due to hysteresis when tires flex. This energy loss results in hot tires, especially after a few high speed miles. Countering this is an industry move toward low rolling resistance (LRR) tires that can reduce fuel consumption by 1.5 to 4.5 percent. While this might seem insignificant, every mpg gain is important when eking out greater range from an electric vehicle or meeting the CAFE (Corporate Average Fuel Economy) standard of 54.5 mpg by 2025.
Virtually every EV and hybrid rolls on LRRs and manufacturers equip their regular vehicles with tires incorporating LRR technology. Most tire makers offer both original equipment and aftermarket LRR tires. Tire brands make these tires pretty recognizable with LRR tire or technology names like Bridgestone Ecopia, Michelin Green X, Goodyear Fuel Max, Toyo NanoEnergy, Kumho eco Solus, Pirelli Extra Low Rolling Resistance (ELRR), Yokohama BluEarth, and Continental EcoPlus.
Older LRR tires were noted for their harsher ride because they used much harder rubber compounds combined with stiff sidewalls in an effort to reduce friction and flexing. Newer LRR tires use advanced compounding with silica-based and alternative oils to provide a more pleasant ride. Early LRR tires also had reduced grip and wore more rapidly. This has changed significantly as tire technology has evolved.
The goal these days is to offer LRR tires that not only speak to improved efficiency, but also deliver the traditional performance characteristics desired by motorists. Yokohama’s new AVID ENVigor presents a good example. We’ve found this tire offering excellent traction and a smooth, quiet ride on one of our test vehicles, fundamental requirements on the part of most consumers. Its added benefit is a design that blends these characteristics and low rolling resistance with all-season performance, a projected long tread life, and availability in many sizes to accommodate diverse applications.
It takes petroleum – lots of it – to make a tire. Thus, alternative feedstock materials are being developed that could replace petroleum to help reduce our dependence on oil. Yokohama has developed an orange oil technology that combines low rolling resistance with a good grip, especially in wet conditions. Orange oil, already used in detergents and perfumes, is quite acidic. This keeps the rubber tire compound soft and flexible at a micro level so it grips the road. More importantly, it works in cold and wet conditions when rubber normally hardens and loses grip.
While orange oil provides grip, fine-particle micro-silica helps the nano-blend compound resist wear. As an added benefit, orange oil displaces some of the petroleum used in tire production so both energy and resource savings are achieved. Renewable orange oil comes from orange peels, including waste orange peels. Orange technology is now used in Yokohama’s C.drive2, Geolandar SUV, ADVAN, AVID, and the aforementioned BluEarth LRR eco tire lines that meet three previously conflicting performance criteria – low rolling resistance, long mileage, and excellent wet grip.
Goodyear is working on substituting soybean oil for petroleum-based oil used in producing tires. Besides helping the environment and reducing Goodyear’s use of petroleum-based oil by up to seven million gallons per year, these tires could increase tread life by 10 percent. Goodyear expects to market soybean based tires as early as 2015. Likewise, Bridgestone has developed BioIsoprene, a bio-based alternative for petroleum-derived isoprene used in tire manufacture. One sure way to avoid under-inflation is to use airless or non-pneumatic tires.
Several companies have shown airless tires, such as Michelin, which has been working on its Tweel that combines a tire with a wheel. Bridgestone is developing the Air-Free Concept Tire. Goodyear’s Spring Tire designed for heavy vehicles uses 800 load bearing springs. Resilient Technologies and the University of Wisconsin are developing a non-pneumatic tire, which is basically a round polymeric honeycomb wrapped with a thick, black tread.
In development at Goodyear is a passive self-inflation system that automatically keeps tires properly inflated as they roll down the road. The purely mechanical Air Maintenance Technology system uses a regulator that senses when the tire is at optimal pressure. If pressure drops below this level, an inlet filter in the regulator lets some outside air into a pumping tube that runs around the inner circumference of the tire. As the tire rolls, the tube deforms and causes puffs of air to be transferred from the pumping tube through an inlet valve and into the interior cavity of the tire. Fleet evaluations of the tire are planned to start this year.
Farther in the future are intelligent tires that automatically adapt to changing road conditions. Researchers at the University of Leipzig in Germany are incorporating changeable tire elements that would alter the shape of the tire to suit the road. The system incorporates flexible actuators, piezo-ceramic actuators, shape memory alloys, and smart materials that gather and process information on road surfaces and weather conditions. Data is used to reshape the tread in real time for optimal performance. The time when tires were simple and low tech has surely passed, but that’s a good thing.
If energy-robbing rolling resistance, inconsistent performance, and inconvenient flats become a thing of the past, we’re all for it.