Maintenance Q&A – August/September 2019

Spec’ing new trucks, balancing tires

August-September 2019

Paul Abelson

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Q: I have a 2011 Cascadia that I love, but it’s getting old and costly to maintain. I need a new one. My question is, with all the devices and add-ons on the market today, what should I get to make it as fuel efficient as possible? And is there any risk other than cost and weight to worry about?

A: Great question, but it can get me in trouble if I leave out a product or list only a few manufacturers in a category. Here’s a suggestion. Whenever you park in a truck stop, look for trucks from fleets that are known for being leaders in fuel economy. They’re the ones featured in ads for fuel-efficient products. Make note of how those trucks are equipped differently from your truck.

If you can, talk to some of the drivers of those trucks. Ask what they like or dislike about what their fleets provide. See if there are any unintended consequences, such as difficulties performing a pre-trip inspection caused by aerodynamic wheel covers or increased brake fade due to trailer skirts. Ask, too, what benefits they have found. Many fuel conscious fleets meet regularly with their drivers or publish newsletters that discuss equipment fleet matters including equipment changes.

Since your engine burns the fuel, that’s a good place to start. Many of today’s engines produce full torque at very low rpm, often from 1,000 rpm out to more than 1,400 with very little fall off beyond that. To take advantage of that “downspeed” capability, drive axle ratios are approaching 2.0:1. Remember, it’s torque that moves the goods and gets you up the hills, while the horses give you speed and consume fuel as they do. Specify only as much horsepower as you need and as much torque as you can afford.

Automated manual transmissions have proven themselves to boost miles per gallon and are gaining growing acceptance among drivers. Tires contribute to miles per gallon, so consider low rolling resistance models and wide-base singles.

Have your dealer run some computer simulations with various specifications of engine horsepower and torque, transmission ratios and drive axle ratios. They can project each proposed specification set for relative speed, fuel economy and hill climbing ability. The projections will be relative, not absolute, but they will give you an idea how drivable the truck will be.

An example of unintended consequences is the switch to 6×2 drives. Fleets found they save from 2% to as much as 5% in fuel consumption, and the configuration is lighter by 200 pounds or more. But many switched back to 6×4 because of driver complaints about reduced traction and uneven tire wear between the powered wheels and those being pulled or pushed along. I’ve met very few drivers who are reluctant to talk about their rigs, so ask questions and learn from their experiences.

Other things to consider are automatic tire inflation systems (now available for tractors), aerodynamic devices such as cab extenders to close the gap between tractor and trailer, and devices that direct air around tandems, such as FlowBelow. If you have your own trailer, consider skirts and tails. There are even slotted mud flaps that have been shown to improve miles per gallon in SAE/TMC standardized fuel economy testing.

Just going from a 2011 truck to a 2019 should increase your current miles per gallon by 15% to 20%, with additional improvements coming from the components and accessories you’ll be adding. They add cost but all have relatively short payback. Good luck with your new truck.


Q: Over the past few months, I noticed uneven wear on my trailer tires, and it’s starting to show up on my drive tires, too. Whenever I get home, about every 10 days or so, I give the truck a thorough check. My last tread depth varied across one tread by from 3/32 to about 14/32. I had the truck aligned when I first noticed it, but it seems to be getting worse. Any ideas?

A: When you had the truck aligned, I assume that included the trailer, since that’s where you first noticed the problem. Since we can safely say alignment is not the cause or it has been corrected, the next things to check are shock absorbers. With the problem occurring at multiple wheel positions and because you check regularly and have not found shocks leaking, the next and most likely cause is balance. Contrary to popular opinion, it is a good idea to balance all tires, not just steers.

Normal wear, the wear a tire experiences during normal operating conditions, is not even or uniform. Variations in inflation pressures due to air loss through the rubber, ambient temperature changes, and nonuniform stresses during cornering, braking and accelerating all contribute to uneven wear over time. Studies show that a 295/75R22.5 drive tire will lose more than 30 pounds on its way to 6/32 remaining tread. Even if a tire is balanced initially, uneven wear will unbalance it. Dynamic balancing devices that adapt to change are best. Rings with balls in a viscous fluid are effective but may interfere with brake drums and must be properly sized for each tire. Continuous internal adaptive balancing is possible using small bead-like materials. A packet is placed inside the tire prior to mounting on the wheel. The tire is then inflated with dry air, since moisture may cause the material to clump. When rolling, the packaging disintegrates. Two popular brands are Counteract Balancing Beads and Equal. They are chemically inert and not destructive to the wheel or internal tire structure, essential properties for any such materials. Screened tire valves should be used to prevent clogging and air leaks.

These devices assure continuous balance for the life of the tire, resulting in longer life, more even wear and a better ride. In TMC Type II tests, they have also been shown to improve mileage. LL

 

Paul Abelson, senior technical consultant, is a longtime contributor to Land Line. He’s a member of the Society of Automotive Engineers and a member of the Technology and Maintenance Council. In 1995, TMC awarded him its Silver Spark Plug award. In 2006, he received the Lifetime Achievement Award from the Truck Writers of North America. Although he’s “retired,” he still makes a popular contribution to Land Line readers with “Maintenance Q and A.”