Of tires, fuel economy, and regulation

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Many things affect fuel economy – wind, weather, temperature, vehicle aerodynamics, vehicle speed and of course tires. So you have to look at many different factors when you are looking to improve fuel economy.” –Tim Miller, marketing communications manager, The Goodyear Tire & Rubber Co.

So I got the good fortune to sit through a very interesting workshop on truck tires during the National Private Truck Council’s 2010 meeting this week in Cincinnati, made all the more interesting as three of the top and toughest competitors in the truck tire market – Goodyear, Michelin, and Bridgestone – lowered their collective fists, if you will, to offer private fleet managers insights into how truck tires impact fuel economy and how their fuel savings potential is being tapped for a range of environmental issues.

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Tim Miller, Goodyear’s marketing communications manager, started things off with a look at all the factors affecting tractor-trailer fuel economy today, highlighting the role tires play in delivering greater fuel efficiency.

Interestingly enough, it’s the little stuff – proper tire inflation and alignment – than can accumulate big fuel economy deficits if fleets don’t manage these maintenance items carefully.

Miller said each 10 psi (pounds per square inch) tires are underinflated results in a 1% in fuel efficiency, with out-of-spec wheel alignment on both the tractor and trailer leading to a 1% to 2% loss in fuel economy.

“Poor wheel alignment also increases tire wear, meaning you lose tire life as well as fuel,” he stressed.

[More of Miller’s comments are in the clip below.]

Vehicle speed, though – especially highway speeds – hits fuel economy far harder than tires, Miller said. Between 55 and 75 mph, aerodynamic drag has three times as much impact on fuel efficiency as the rolling resistance of the tires, with every 5 mph increase between those speeds typically resulting in a 0.5 mpg loss in fuel economy – a hit of 7%.

The type of trucking operation, too, though greatly influences fuel economy – to the point where fuel-efficient tire designs won’t do much good.

For example, Miller said fuel efficient tires would be wasted on the low speed/start-and-stop operations typically found with urban delivery routes, while only marginally helping high speed/poor aerodynamic trucking applications such as car hauling.

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Fuel efficient tires really offer a big bang for the buck, though, in high speed/high aerodynamic operations such as tanker fleets, he stressed.

One interesting side note in all of this – tire fuel savings actually increase as the tread wears down, meaning that older tires typically save more fuel than new ones, Miller said. Along with that, he stressed that fleets need to understand that the “real world” fuel savings a tire provides almost never equals what such tires produce in controlled field tests (such as SAE’s Type II test), much less the laboratory.

“The ‘real world’ contains wind, poor pavement, poor weather, traffic congestion, vehicle aerodynamics, and a host of other issues we as tire makers factor out in our various tests,” he explained. “That’s why the fuel savings tend to be smaller.”

That being said, tire manufacturers are constantly trying to find ways to mitigate such factors, as Don Baldwin, product marketing manager for Michelin Americas Truck Tires explained.

[See some more of Baldwin’s comments in the clip below.]

One tactic is making sure tires fit well to the truck wheel, for an imperfect fit causes the tire to “wiggle” or move. “That extra movement creates heat – and the energy lost in creating that heat comes right out of the truck’s fuel tank,” he explained. “Now, we’re working with more elastic compounds to try and reduce the creation of heat – to reduce that energy loss – but they are not always the best compounds for traction or long life wear. That’s part of ‘balancing act’ when making truck tires.”

One reason Michelin in particular strongly pursued the development of “wide base” tires to replace the dual tire configuration found on the rear axles of tractors is reduce overall tire and wheel mass – as less energy and thus fuel is required to “push” less mass down the road – but also to reduce excess tire movement, too.

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“No two duals are ever inflated perfectly, so one is always carrying more load than the other, and that makes each dual behave differently,” Baldwin explained. “Different behavior” in this case means “different movement” and that can increase fuel expenditure, so having one tire and thus one tread perform in a unified fashion alleviates this concern.

Aside from “wide base” tires, Baldwin said the focus is to create tires that have a little wider footprint for better traction, yet need less tread as a result – a design that offers a better fuel economy profile due to less tread depth (mirroring the advantages of older, worn tires) yet without a corresponding loss in expected life to removal.

“Little by little, we’re lessening the trade offs,” added Guy Walenga, director of engineering for Bridgestone’s commercial tire products. “No longer must fleets give up mileage or traction to get better fuel economy.”

The tricky part here is that such “fuel saving factors” are drawing the attention of regulatory agencies – particularly at the state level.

[Walenga delves into how the voluntary specs espoused by the Environmental Protection Agency’s SmartWay program are now mandatory in the state of California – all due to rules hammered put by the California Air Resources Board or “CARB.”]

In the case of the CARB, commercial trucks operating in California – even if they are domiciled outside the “Golden State” – must use so-called “SmartWay specs,” including tires approved under the program.

This applies on to Class 7 and Class 8 trucks hauling 53-foot dry van or refrigerated trailers, though Walenga expects CARB – and potentially other states as well – to add more configurations as the EPA adds them to the “SmartWay” program.

“Right now, 13 to 14 other states – such as Nevada, new Mexico, Arizona and some eastern states as well – are considering following CARB’s path here,” he said.

One thing to note, though: CARB allows fleets to use retreaded tires under its SmartWay spec mandate – something EPA does not – as long as the tire casing is one of the 70 different tire models currently approved under the SmartWay program.

At the end of the day, Walenga expects fleets nationwide will begin to shift to a single “SmartWay” spec for their tractor-trailers in order to keep their operations environmentally compliant regardless of what state they happen to be driving in – and that includes using one type of tire for everything, too.

“Not too long ago, we used to have one tractor-trailer configuration for long-haul operations and one for pickup and delivery,” he said. “Over time, with improvements in truck design, fleets could use one truck to do it all. We expect the same may happen with fuel efficient truck tires.”

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