The right tire choices will make a lasting difference
Ryder Truck Rental Canada has more than 106,000 tires on the ground at any moment in time. About 39,000 of them will be replaced every year. So there’s little surprise that Brian Edwards, manager of technical sales support, is focused on finding the best options.
“Tire cost is the single-largest piece of the truck’s maintenance cost,” he observes. But there is no single solution; no one tread that fits all. The perfect choice needs to consider where the tire will be mounted, how it will be used, and even the routes it will travel. Then there is the matter of weighing the promises to improve traction, control irregular wear, reduce on-road breakdowns, or enhance fuel economy.
“There are a lot of different things that go into defining what creates value for a fleet,” says Paul Crehan, director – product marketing at Michelin Truck Tires North America. “You’re always balancing multiple features.”
In urban settings, Edwards wants a tire that will work in several applications. Too many options will strain tire replacement inventories. “If we had a specific tire for every application it would be overwhelming,” he says. It is not the only way supply chains play a role. Wide-base tires have been rejected so far because they are harder to source in more remote areas. When it comes to regional equipment, meanwhile, the focus turns to durability in a bid to support retreading programs. But the heavier loads in Western Canada demand drive tires with aggressive open shoulders – the voids between individual lugs along a tire’s outside edge.
The longhaul tires easily hold the greatest promise for a long life. Their routes are straight and the time off road is limited.
“The longer you can prevent the initiation of irregular wear, the more likely you are to get the maximum number of miles out of that tire,” says Greg McDonald, engineering manager – corporate accounts with Bridgestone North America. In the case of a steer tire, this will mean features including a tread that is not too deep, and some form of “decoupling” groove to separate the tread’s outer edge and the tire’s shoulder.
But even the expectations for longhaul tires can change. Ryder Canada once focused on tires which “wore like iron” and offered the best mileage for every 32nd of an inch, Edwards says. Rising fuel prices and new emission standards limiting greenhouse gases shifted the focus to Low Rolling Resistance (LRR) designs.
Some of the added fuel economy is realized by using two different compounds in the tire, with the underlying layer flexing more easily than the material touching the surface of the road and consuming less energy, Crehan explains. The U.S. Environmental Protection Agency’s SmartWay program offers its stamp of approval to the tires which have proven the biggest fuel economy gains.
Transport Canada research unveiled during the Private Motor Truck Council of Canada’s 2013 annual conference even proved that the gains have been made without sacrificing winter traction or durability.
Low Rolling Resistance tires could boost fuel economy 3-6% depending on how many are used, McDonald says. On a typical tandem tractor and tandem trailer, 18% of the savings will come from the steer axles and 39% will come from the drive axles, but the remaining 43% will include the trailer tires. “If fleets are paying really detailed attention to the rolling resistance of the tractor tires, but they’re just putting anything [such as a tire designed for a different wheel position] on the trailer, they’ve already defeated half of their fuel economy program as far as tires go,” he says.
Increasingly, the fuel economy promises are the most important factors of all, Edwards says. “The old days of the mega-traction type tire is going to go away.”
The pick-up and delivery fleets which spend most of their days on city streets face a different challenge. Here, the overriding interest involves compounds which promise to resist cuts and tears as they bounce through potholes and over railway tracks, McDonald says. Added material in a sidewall can offer a protective barrier against curbs, while deeper treads on the drive tire offer more rubber to scrub away before retreading. If the truck spends all of its time on a well-maintained road, a drive tire with a deep rib design will place more material on the ground and boast a slower wear rate than a lug-type tire.
Some of the most complex tire choices involve a mix of operating conditions, like a truck that splits its time on and off the road, or travels most of its kilometres on a highway but spends one-third of the time making tight turns in an urban environment.
“There are a lot of different vocations,” says Brian Buckham, commercial brand marketing manager for Goodyear North America. “It’s hard to design one tire for dump trucks and the same tire for waste haulers because they all have different service conditions.” But there are times the needs overlap. A work truck or cement truck used in construction, but spends most of its time on a paved road, may be able to use a mixed service tire. In these tires, fleets looking for extended tire life will want big, stable blocks that hold their shape as the tread enters and exits the tire’s footprint, he says. “If it starts squirming or slipping, that’s what creates the faster wear.”
Treads which have stone ejectors – raised areas inside a tire’s voids – can help to push out the stones that will otherwise be trapped and drill into the tire. This can even be an important feature outside a job site. “Sometimes they pull into their own yard and it’s gravel,” Buckham observes. “Every time it goes through the footprint, those [ejectors] will flex a little bit and will work stones out.” He also prefers blocks with tapered sides. “When you have grooves that go straight up and down, and if you start running through gravel with a similar width, they [the stones] will get in there and they’ll never get out.” Once that stone breaks through to the tire’s belt, the wires will rust and the casing will be damaged. At best that will need to be repaired. At worst it might mean the casing cannot be retreaded.
Retreadability can certainly be a key factor when looking to reduce costs over the life of a tire. It is why Edwards balks on deals for offshore tires that seem too good to be true. Their casings might be rejected long before their time.
Maintenance practices make a difference, too. Ryder, which measures tread depths during every Preventive Maintenance inspection, saw a dramatic increase in the number of casings available for retreading once it began removing tires after treads wore down to 4/32”. “We have very little if any stone drilling,” Edwards says, referring to a common threat posed by shallower treads.
The focus on tire life also extends well beyond the wheel end. The length of the frame, reinforcements and axle choices can all influence tread wear. “Air suspension has served the Canadian fleet particularly well,” Edwards adds, referring to the shift away from spring suspensions on single-axle straight trucks in 2008/09.
While some fleets are adopting tire pressure monitoring systems, he suggests there is no alternative to regular checks with a calibrated tire gauge. (“A hammer is accurate to plus or minus 60 psi,” he jokes.) Challenges such as uneven wear can also be spotted with an up close and personal look. Anything off by more than 10 psi is inspected and re-inflated.
Looking at the tires rolling through his shop, Edwards is largely impressed by advances over the last decade. “The changes they’ve done, the makeup, the rubber compounds that they’re using today, they seem to be better with every iteration.” But claims are not taken at face value. Ryder’s maintenance group in Miami works with vendors to establish specific spec’s. Tests by the fleet will typically include hundreds of tires. “That gets you pretty meaningful data,” he says.
It isn’t the only way that data plays a role in the decisions. The fleet continues to track everything from tread depths to casings. “Our tire folks can pull down a particular fleet of trucks or type of truck or specification of truck,” Edwards says. The costs per kilometre reflect everything from road failures to service calls, tread life, casing life, irregular wear, safety and reliability. “None of these criteria are second to any other.”
No matter what the application, Crehan says fleets should ask themselves a key question before buying any tire: “What is the sort of thing you just can’t live with?” A fleet without any just-in-time demands may be willing to accept an increase in roadside tire failures in exchange for a lower acquisition price. Its counterpart that hauls milk, which could spoil if stranded for too long, will approach the question a different way.
Knowing why any tire is removed, what it looked like when it removed and why a challenge occurred, a fleet is in a better position to choose the best option, McDonald says. “What tire is going to fit [your] needs?”
Coffins and Casings
Batesville Logistics, a private fleet which delivers coffins in Canada and the U.S., tracks its tires from the day they’re purchased to the end of their lives. During a recent meeting of the Technology and Maintenance Council of the American Trucking Associations, terminal manager Randy Obermeyer offered some insight into his fleet’s tire program.
- Costs per kilometre — The search for a perfect tire looks to balance fuel economy and cost per kilometer – but the costs look well beyond the price of a virgin tire. Calculations also consider ongoing maintenance, the value of casings and retreads. A fleet that proactively replaces shocks to extend tire life would also want to include that price, he says as an example.
- Tire gauges — Tire pressures are inspected every time a truck crosses a fuel island, arrives in a shop, or when his local tire supplier visits. This is on top of a driver’s pre- and post-trip inspections. Tires on steer axles, trailers and dollies are inflated to 100 psi, but drive tires are at 95 psi.
- Retreading — Casings will only be retreaded if they have been in service for up to 60 months with a maximum of two repairs, none of which can be on the shoulder or include a section repair. Trailer tires are the exception. Those casings can be retreaded within 72 months and with a maximum of two repairs, one of which can be on the shoulder, and one of which can include a section repair up to 33 mm in size.
- Reselling – Retreading is not the only option as a tread begins to scrub away. “Run the tire down to a certain point and sell them as used tires,” Obermeyer suggested.