Low Rolling Resistance Tire Primer
Do your tires matter? Seriously, how much do those rolling pneumatic cushions underneath your vehicle make a difference, as long as they’re balanced and don’t have a flat?
Some might say this is a ridiculous statement – and it surely is – but the way many people maintain their tires suggests they are treated as out-of-sight, out-of-mind.
And this is all the more ironic given there are now many “low rolling resistance” tires that may incrementally save fuel and money. This means not taking care of what you have can be like a double whammy: Not only are many not taking advantage of the most efficient options, they may even be hampering the efficiency of their existing black rubber Os.
Estimates say 86 to 91 percent of Americans have improperly inflated tires which sap fuel economy by up to 3 percent when underinflated by 20 percent. This is like losing coins daily from one’s pocket. Day after day these wasted gasoline ounces add to an estimated 2.8 billion gallons wasted out of 134 billion gallons annually burned.
The good news is you have choices. Myriad details behind “rolling resistance” are enough to make up their own article, but in brief, low rolling resistance tires are defined as those which minimize energy wasted as heat; they thus curtail fuel usage, and by extension – in the case of petrol-powered vehicles – they reduce emissions too.
This said, it remains a case of caveat emptor. There are measurable ride quality, handling, and braking differences between competitive brands and all tires must contend with trade-offs that may always exist.
Tire engineering involves compromises between diverse – at times mutually opposing – performance goals, but present designs are so good, they may even pay for themselves while making only minimal trade-offs.
Tires: A Critical MPG Variable
Lower rolling resistance tires have become a top choice for automakers picking from the menu of potential solutions to meet present and future efficiency mandates.
We keep hearing about the “all of the above” approach deemed necessary to inch toward the “54.4” mpg target (actually low 40s on window sticker) required by 2017-2025 Corporate Average Fuel Economy (CAFE) rules.
The reason why many solutions are needed is there is no single magic bullet – no super-duper long-range, fast-charging, electric vehicle yet affordable for the masses; and while efficient hybrids do exist, they may not meet the needs of all consumers and must still burn fuel.
Among myriad fuel-saving variables, the number-one contributor by far is the type of vehicle one chooses in the first place.
Beyond this, tires are estimated to optimize a vehicle’s mpg from perhaps 2 percent to – as GM says – up to 7 percent, and perhaps more.
When we set out researching this topic, one question we were interested in was to what degree low rolling resistance tires could upgrade any vehicle’s efficiency? How close, we wondered, could just changing your tires net the efficiency gain of a hybridized version of a given vehicle?
Unfortunately, swapping tires will not likely achieve a hybrid’s benefits without the hybridization, but they stand to incrementally help.
Compared to stock tires, the Tire Rack estimates low rolling resistance tires increase fuel savings by up to double when installed on cars that deliver 25-30 mpg and up to quadruple for light trucks and utility vehicles delivering 12-15 mpg.
While our focus is on efficiency, we mentioned “trade-offs” and we’ll remind you of an important one: safety and control are part of what you gain – or lose.
Essentially, “safety” is a function of grip, thus control – in whatever condition, be it dry, wet, snowy, or icy. If you have improved traction, with all other variables being equal, your vehicle can brake in shorter distances, track in inclement conditions with greater sure-footedness, and corner under higher lateral acceleration.
All-season designs strike a compromise between durability and grip to handle conditions encountered in any region or on any road. While some strictly eco-minded folk may sneer at sports cars as wasteful, one of the benefits offered by their softer, stickier – and not as long-lasting – sport rubber is improved traction, at least on dry surfaces. There also are versions of grippy sport-compound tires for winter driving which increase control on wet or snowy roads while still doing surprisingly well on dry roads.
In contrast to high-performance tires, low rolling resistance rubber and general all-season designs place a higher priority on acceptable grip and increased durability under normal conditions, but do give up some traction at the extreme. While performance tires are a key to aiding and abetting enthusiasts at the limit, their traction could also simply mean better chances of performing emergency or evasive maneuvers – for those with the skills and presence of mind in tricky or panic-inducing situations to negotiate them.
In more blunt terms, if you choose all-season or low rolling resistance tires, you must accept potentially longer stopping distances, less cornering traction, and possibly other critical performance characteristics. In exchange, you get a longer-lasting all-round performer suitable for workaday conditions. The question then becomes what is your risk tolerance, and where are your priorities? Are you willing to give up a little extra grip for a tire that returns better mileage?
If you own a hybrid or plug-in car with eco tires, or even an ordinary passenger vehicle with all-season radials, this choice was already made for you by the automaker.
Stock tires are usually a decent compromise, but there may be better choices available, and new tires regularly come out that claim a superior compromise than before.
One of the more comprehensive tests showing this was a 2009 comparison of then-latest generation low rolling resistance tires by the Tire Rack (see video). It showed stock Goodyear Integrity tires allowed a 2009 Prius to stop on wet pavement from 50 mph in 131.8 feet. This lagged behind six newer green tires – including two from Goodyear – that stopped in distances ranging from 105.2 feet to 112.5 feet.
Even the worst of these beat the Integrity – which formerly shipped with Prius models beginning in 2004 – by 19.3 feet. This is enough to make the difference between stopping for a light or finishing in the middle of an intersection.
In contrast, the Integrity beat all comers in the dry, with a 96.7 foot stop from 50 mph. The six others were not far off ranging from 97.2-101.2 feet. Similar results in cornering were noted. In the dry, the stock Prius tire led the pack by a bit, and in the wet, it was last place.
In choosing a tire, you must therefore determine your priorities while understanding tires remain your only contact to the road. It’s thus worth the research to weed through to the best compromise for your driving habits, region and preferences.
Green Tire Choices
A complete test of all tires available is beyond the scope of this article and the following briefs are just to get you started. All these tire makers play up their green credentials, and sell products also in Europe where the urgency is arguably perceived as greater.
Not unlike EV propulsion battery chemistry, specifics of tire tread rubber composition are a closely guarded secret. The Tire Rack’s Vice President Matt Edmonds tells us tire engineers may work in the center of buildings with no windows under stringent security to protect intellectual property.
Tire rubber can be a mix of organic and inorganic materials including carbon black, and silica – sand. Newer formulations are continually being touted by various tire manufacturers.
Aside from a tread’s contour, sipes and grooves, its unique rubber blend is what separates a stellar tire from an also ran, and would-be copiers of effective chemistries may find it difficult or impossible to reverse engineer a finished tire rubber compound.
So, some of the obfuscation in the fuzzy world of tire makers’ products is to deliberately protect market advantage from prying competitors, not just to keep consumers from comparing apples to apples.
Bridgestone’s Ecopia tire is its flagship line aimed at achieving its global goal to improve rolling resistance by 25 percent in all of its products by 2020. The aim is also to reduce CO2 from its entire product lifecycle by 35 percent per sales by 2020.
Its green technologies include “NanoPro-Tech” which is said to reduce rolling resistance by controlling the interaction between polymer, filler materials and other rubber chemicals at the molecular level. Another technology is a low rolling resistance “Fuel Saver Sidewall Compound” that is said to 1) return more energy to the tire and, 2) reduce heat generation compared to a traditional sidewall.
Like several other makers, the company is using silica to improve wet traction by increasing flexibility of the tread compound. Of course its exact blend is top secret, as is the case for all.
Bridgestone also uses 5-percent recycled rubber sourced from ground-up post consumer tires in the tread compound.
Overall, it says Ecopia models can decrease rolling resistance from 36-42 percent. This is said to improve fuel economy compared to other Bridgestone tires by up to about 4 percent.
For instance – and most leading manufacturers have similar examples to offer –Bridgestone says its Dueler H/L 422 Ecopia Crossover/SUV Touring All-Season tires demonstrate 42-percent lower rolling resistance than its Dueler H/L Alenza (size: P215/70R16). Randomly calculating gas at $4 per gallon, assuming a 15-gallon tank, and one fill-up per week, Bridgestone calculates annual savings of 31 gallons of fuel amounting to $126.
In four years, that’s $504 saved – nearly enough to pay for the tires. And, since gas prices are expected to increase, so will potential savings, so this could be a minor hedge against rising fuel prices.
More info can be found at its Web site.
Continental’s low rolling resistance tire models include its premium replacement tires, the ProContact with EcoPlus Technology, recently launched PureContact with EcoPlus Technology, and its CrossContact LX20 SUV and light truck tire is available in some OE fitments as well as for replacement applications.
“Continental’s technology for expanding the limits of the target conflict of LRR vs treadwear and wet grip is EcoPlus Technology,” said Joe Maher, product manager passenger tires for Continental Tire. “EcoPlus technology consist of two main components; Tg-F Polymers – temperature activated functional polymers that increase compound bonding improving the wear and fuel efficiency, and +Silane – + Silane additives enhance the grip on slippery roads. EcoPlus Technology is used in three products: ProContact EcoPlus, CrossContact LX20, and PureContact
We also asked what Continental could tell us in greater detail about its technology.
“EcoPlus Technology is a combination of innovations which include compound technology but is not limited to compound,” said Maher. “Continental Tires involvement in O.E., where rolling resistance is a high priority, keeps us working to expand our knowledge base. This knowledge can also be shared in other products. EcoPlus Technology, depending on the product, can include construction and sidewall compound too. Continental develops for balanced performance, therefore no one design or construction fits all applications.”
Yokohama has previously used its Orange Oil infused in the tread chemistry for tires not specifically called “low rolling resistance,” but now is presenting it as ideal for these as well. Calling orange “the new green,” Yokohama’s touts its AVID Ascend and related low rolling resistance tires. Although manufacturers more often compare their new products to their existing products, Yokohama’s Dan King, senior vice president of sales and marketing, does cross compare.
According to King, “independent test results reveal that the Ascend can last up to 6,000 more miles than the Michelin HydroEdge.
Testing also shows the Ascend rolls 11-percent easier than the Michelin HydroEdge. Yokohama says this saves 58 gallons of gas over the life of the tire. Plus, the Ascend’s CO2 reduction is better by over 1,000 pounds.
“Not every manufacturer has mastered the technology,” says Fred Koplin, director of marketing communications for Yokohama Tire Corporation, “so the trade-off becomes apparent in their tires.”
Yokohama has long been a competitive maker, and its Web site has more info.
While Yokohama targets the HydroEdge, that is not Michelin’s top tire at this point. In April 2012 Michelin launched its Defender series, in sizes to fit 93 percent of cars and SUVs sold. The company says it is the “greatest standard passenger car tire the company has ever made,” and offers a 90,000-mile warranty, while not compromising on braking distances compared to “a leading competitor.”
Generally, the tire also promises fuel savings, and all-season performance, as does the Energy™ Saver A/S which has previously been called its most fuel–efficient passenger car tire and is specified as original equipment some cars.
Finnish-based Nokian, pronounced “no-kee-en” is unique in that it was green before green was cool. Or, as Robert Hepp, VP of Strategic Planning at its Vermont-based U.S. headquarters says, the company has long striven to make each tire the lowest possible rolling resistance for its intended application. It thus has no separate line of specific low rolling resistance tires, instead it considers them all as such – even its highly regarded winter tires which are said to have low rolling resistance compared to other winter tires.
Overall, Nokian says it continues to pioneer tires offering safety and environmental friendliness. The company is using non-toxic HA (high aromatic) oil-free production in the development of the rolling resistance of tires.
In 2006, in recognition of its development work, Nokian Tyres received a commendation for its eco-friendly tires in the Finnish round of the European Business Awards for the Environment competition.
Recall also that we said the latest crop of low rolling resistance tires is better.
Nokian said while it’s competitive now, more is yet to come as the video shows – a 64 percent improvement is pending with a prototype compared to an existing eco tire.
“Goodyear’s Assurance Fuel Max has a fuel-saving tread compound to help save 2,600 miles of gas over the life of a set of tires. Assurance Fuel Max is a fuel-efficient, low rolling-resistance tire, but it also offers performance that most consumers wouldn’t expect from a fuel-efficient tire,” said Davis. “This includes a Wet Tread Zone with dual Aquachannel grooves, a Dry Tread Zone with solid shoulder blocks, and zig-zagging micro grooves and center tread notches.”
At the same time, the primary goal of efficiency is met, he said.
“Assurance Fuel Max tires reduce rolling resistance by 27 percent and provide up to 4 percent greater fuel efficiency compared to the previous Assurance tire,” said Davis.
“Goodyear’s Fuel Max tire offers these advantages that many consumers might not realize – the fuel efficiency benefits (4 percent improvement in fuel economy), a 65,000-mile treadwear warranty, no drop-off in traction or braking performance, and a full range of tire sizes – to fit more than 80 percent of the cars in this segment.”
Davis reminded us Goodyear’s Fuel Max Technology was chosen as the exclusive fitment for the Chevy Volt. Also, he said, Assurance Fuel Max tires are original equipment on many other fuel-efficient vehicles – Toyota Prius, Ford Fusion, Chevy Cruze Eco and more.
Other Tire Companies
Top tire advice
Properly inflate your tires and, using a reliable tire gauge, check pressure monthly when tires are cold. Be sure that the valve stems are capped to keep dirt out and seal against leakage.
Do not overinflate. This increases wear on the center of the tread. A tire is designed to run with the vehicle’s weight spread correctly in the road contact zone.
Tires should be rotated at least every 6,000 to 8,000 miles and alignment should be checked once a year. Misaligned tires can cause the car to scrub, which lowers mileage and causes unnecessary tire wear.
Pending US Tire Label Law
It’s not hard to notice that “green” is generally “in.” For tire makers, this means mpg and emission improvements equal bragging rights and, they hope, profitability.
To date, when we read about a manufacturer’s new super green eco tire that is “X-percent better,” a good question of the tire seller’s marketing copy is X-percent better than what?
Often the answer is the new tire is compared to an outgoing tire or other tire model still in the manufacturer’s own model range. Or, performance claims against competitors might be made without sufficient qualifying info. Tire selection has often been an apples-to-orange semi-educated guess.
Published reviews from sources with no conflict of interest can put us ahead of the curve, but then you must trust the reviewers’ objective measurements and subjective impressions are accurate.
The not-so-great news is this is not likely to change much any time soon. The better-than-nothing news however is Congress has charged the National Highway Transportation Safety Administration (NHTSA) with putting more objective data into the hands of consumers.
But it NHTSA is quite late. In 2007 as part of the Energy Independence Security Act, NHTSA was tasked with devise rules for a new tire label law by December 2009. This label is intended to list 1) rolling resistance, 2) wet traction and tread wear. The idea was to empower consumers to easily compare trade-offs between rolling resistance, traction, and durability.
In June 2009 NHTSA did propose a rule, and was beaten back to the drawing board following comments by industry stakeholders.
NHTSA is expected to return with revised rules March 2013, to be followed by another 60-day open comment period by the same stakeholders including tire makers, tire sellers, and the Rubber Manufacturers Associate of America (RMA), among others.
Other criticism for the first proposed rule included NHTSA’s desire to slice tire rolling resistance scores into a 100-point scale. This, the RMA objected to saying it should divide that scale of 100 into fifths, with tires falling into categories A,B,C,D, or E, or the like. NHTSA is expected to follow the RMA’s 2009 recommendation for the five-point scale.
The RMA had been instrumental in advocating the label law be immplemented in the first place, and a spokesman for it told us it does believe once they’re finalized they will help consumers. Others think so too, but it is a question. Matt Edmonds, vice president for The Tire Rack told us a five-point scale may have value but could also muddy the waters for some consumers.
He said working off of a hundred-point scale coarsely divided into fifths, consumers may try to expedite a numbers comparison, and, as one example, possibly go with an 81st percentile tire that nonetheless ranks in the A category for rolling resistance that edges out one in the B category that actually scored 79th percentile. Here are two tires actually off by 2 percentage points, but one scores a more prestigious-looking “A” and the other a “B.” Further, the one in the B may be better in other performance categories not measured. In commenting on a similar law in Europe, Goodyear has noted it tests 50 categories to grade its tires, not only three, and as you may see already, there are many considerations aside from rolling resistance, wet grip and treadwear.
Since a label law would only highlight a few out of many variables to be considered in judging a given tire, more comprehensive published reviews will definitely still be needed.
As of Nov. 1, Europe became the first to implement its new tire labeling law which covers two out of three variables the U.S. intends to label: 1) rolling resistance, 2) wet traction, and, 3) noise. The embedded video from Continental gives a rather idealized view of how this is supposed to play out.
The view that independent published reviews will be needed is also held by the Europeans, who are leading the world in this push with intent to further empower consumers to choose the best tire, and, it is implicitly hoped, the most eco-friendly tires.