On the Surface
of the Tire/Road Relationship
Anyone who has been around the tire business for any length of time has heard or participated in discussions about how well competing brands or types of tires perform. Equally well known is the wide variety of conclusions some "experts" derive from their "experience."
It brings to mind an observation one old-timer friend of mine muttered whenever one of his peers was preaching about their findings – "that’s the thing about his experience, it’s his."
Nevertheless, it’s sometimes difficult to comprehend how some operators, especially in the trucking industry, can have such vastly different opinions about how well certain tires deliver their expected value. Often, the real answer is right at their feet.
So Many Reasons …
The truck configuration typically comes into these discussions early. Effects of engine torque, wheelbase, single vs. tandem drive, steer axle setback, fifth wheel location (weight distribution), empty vs. loaded miles, alignment settings, and other variables have been studied and ordered by tire manufacturers and many industry observers.
Driver impact has also been investigated, especially relating to truck fuel economy. Interestingly, a correlation between driver habits and the durability of other drivetrain components, including clutch, universal joints, and tire wear, is generally accepted by most experienced maintenance managers.
Seasonal differences have also been studied. Most users agree that longer overall treadlife is achieved if new tires are applied during the fall or winter seasons so that initial wear occurs at cooler ambient and road temperatures.
Road Surface a Key Contributor
There is, however, one major and often overlooked variable that can account for large differences in tire wear performance. The effects of different road surfaces, while producing an obvious influence, are often underestimated or difficult to quantify.
A wide variety of industry studies have shown that variations in road type can significantly affect tire wear and also influence other performance factors. For example, truck fuel economy is generally improved when running on harder surfaces like concrete vs. softer pavements, such as multi-level asphalt. The theory here is that a softer surface deforms more under the pressure of the tire footprint, causing additional energy to be lost in rolling resistance.
However, in this instance, any correlation between fuel economy and tire wear is suspect, since surface deformation is not necessarily related to the surface abrasion characteristics that have a primary influence on wear.
Historically, some industry testing has shown differences in treadwear and traction on new vs. worn road surfaces of the same pavement type. This is likely caused by the "polishing" effect whereby tires round the sharp edges of aggregate in top layers of the road material. Different road surface finishing techniques, such as type of brushing or rolling, can also influence tire traction and treadwear.
Tread Wears Faster in Some Locales
Many tire engineers agree that the basic road mix itself is often a major factor in determining wear rates and tread life expectancy. In recent years, there has been much study of road building materials with an eye toward improving the durability of pavement. And there has been added focus on bridge surfaces, where cracking and internal moisture contamination can lead to premature structural corrosion in climates that experience frequent freeze-thaw cycles. Information is now being shared more freely among state and federal highway engineers, resulting in more standardization of pavement mix specifications.
Most of these mixes, however, include the use of locally quarried aggregate. Differences in rock types can be very significant. Both the origin of the quarried rock and the fracture mechanism when it is crushed to size are important.
For years, rental car fleets and package delivery operators, with large numbers of similar, locally domiciled vehicles, have recorded tire wear differences caused by local aggregate variations. For example, certain areas of Florida are well known for having up to 40% to 45% faster tire wear than national averages, due to locally quarried aggregates that contain coral and other shell-type materials. The geologic origins of road surface aggregate in other areas of the country are equally well known for fast/abrasive tire wear.
The percentage and severity of elevation changes in local roads can also be major factors, especially in combination with stop-start driving cycles. Many suburban areas around Pittsburgh, for example, are known to produce rapid tire wear of this type.
Similarly, curved roads, especially in combination with higher speeds, can dramatically reduce tire treadlife. The primary mechanism at work in these examples is abrasion at the tire/road interface.
Crowning and Alignment
Wear differences can also result from running on primary vs. secondary roads, even if both have similar pavements and finishes. Most secondary roads are crowned (high in the middle and tapering down on both sides), while many modern primary roads are simply sloped slightly from one side to the other, sufficient for water drainage.
Vehicles finely tuned for neutral alignment on level surfaces may tend to pull slightly on sloped roadways, requiring small but consistent steering inputs to maintain direction.
Alternatively, many of today’s large trucks riding on modern radials employ small side-to-side variations in camber, caster, or axle setback to improve straight ahead road feel on interstates. This contrasts with generally higher camber and toe-in settings, which were more appropriate back when crowned roads and bias ply truck tires were dominant.
As you can see, depending on where your fleet customer is based and when its trucks travel, there can be dramatic differences in tire wear rates – and in overall tire performance. So, there really is some truth to the old timer’s observation about individual experiences. It all depends on where you’re from and what type of rocks you drive on.