When it comes to medium- and heavy-duty trucks, small increases in cost-per-mile can have a major effect on the bottom line. After all, you can’t shrink the distance between two points, and driving and maintenance improvements can only improve the lifespan of a single tread by so much. To get better returns beyond that, you have to get more retreads from the casing. In order to that, you have to put your detective hat on and take a closer look at the causes of casing failure.
The first step is to understand the different causes of failure and how to recognize them. Some failures are environmental and come from how the tire is used or maintained. Bob Eck, vice president of the TA Truck Service Commercial Tire Network, says that it’s important to understand the different causes of failure and to understand whether they are a result of usage or construction issues.
Eck mentions stone drilling, casing separation and some large injuries to the casing can prevent retreading. In the case of, injuries, the casing may be technically salvageable, but it may not be worth the expense, rather than simply replacing it with a new tire.
In some cases, the source of a failure can be easily identified by external inspection, Eck says. Other times, there is no way to really know what went wrong without using more modern diagnostic tools.
“Sometimes, a visual inspection is just not enough to determine the severity of an injury,” Eck says. “It takes advanced technology like shearography to see things like potential zipper ruptures that you just cannot see from the outside.”
Once you’ve assessed the source of a casing failure, it’s important to look at the full picture painted by the data points. Understanding which tires are failing is a good start, but if you want to have a good idea where you are getting value, you have to understand why a tire fails.
“Comparing the percentage of tires rejected of each brand tells you very little about the quality of that brand of casing,” says Jerry Southergill, manager of the technical department at Marangoni Tread North America. “In our most recent study, which included 145,582 casings, 27% of the tires rejected were rejected due to maximum repair limits exceeded; 15% of the tires rejected were rejected due to road damage; 11% of the tires rejected were rejected due to excessive age.”
That means, according to the Marangoni study, a full 53% of failures are more related to end-user driving and maintenance practices than the quality of the casing.
On the other hand, Eck says that failures due to ply gap, thin inner liner or pulled loose cords are likely related more to the construction quality of the casing than the usage. Southergill adds belt package separations, liner separations, bead separations and rust migration to that list.
Once you learn to recognize some of the tell-tale signs of failure (see sidebar on the left), it’s still important to document what you find. Once you account for damage and maintenance failures, you can start to factor in miles traveled and upfront cost to determine a total cost of operation. More importantly, you can don the deerstalker hat and wooden pipe, because you are a retread detective.
And you are on the case.
Dealing with Damage from Stone Drilling
In some cases, removing your tires from service a little earlier will actually improve your tire budget. If the environment you operate in subjects your tires to stone drilling, then it is advisable to remove them before extensive damage is done to the casings that will result in them being non-retreadable. Stone drilling occurs when sharp stones become caught in the tread grooves and cut through the undertread to expose the belt package to the elements.
If the tread is less than 6/32-in. deep, this damage will probably cause the tire to be rejected by the retreader due to the resulting rust in the belt package. These pictures show the extent of the damage after the tread has been removed during the retreading process. If it is retreaded, it will require extensive skiving that may result in an inferior product.
On the other hand, a retreaded tire, using the right chip-resistant compound, can remain in service at a much lower tread depth than the new tire without resulting in the same degree of damage.
High-quality retread rubber specifically designed for off-road applications is made of chip-resistant rubber and will protect the casing much better than the tread compound of a virgin tire.
With proper tire management, that same casing will be able to be retreaded a second time to maximize your tire budget. If the retreader determines that the casing is not a good candidate for another drive tread, they should consider downgrading it to be used one more time with a shallow trailer tread.
— Contributed by Jerry Southergill, technical department manager at Marangoni Tread North America.