Tires are one of the most critical components on a Class 8 vehicle, and it is crucial to properly spec and maintain tires to improve safety, minimize the risk of a roadside violation and maximize fuel economy.
The Commercial Vehicle Safety Alliance (CVSA) has released a new Inspection Bulletin that outlines the tread depth measurement of evolving commercial motor vehicle tires. “An evolving tread design is a tread pattern that experiences a significant and noticeable transition in appearance as the tire wears down from the new state to the worn state,” CVSA said when announcing the new guidance. “As the tread wears, some features disappear, while new features are revealed.”
In an instructional video CVSA posted online, Jeremy Disbrow of the Arizona Department of Public Safety demonstrated how to measure the depth across each of the major tread grooves, including evolving tread grooves, on a tire.
Mike Hasinec, vice president of maintenance for Penske Truck Leasing, said all tires have a treadwear bar, and when the tire gets worn down to the point where this bar is even with the tread, it’s time to replace the tire. “Taking tread depth measurements in the wrong area, such as on top of that wear bar, can give you the wrong reading, and you’ll end up changing the tire sooner than you may need to,” he explained.
The U.S. Department of Transportation requires 4/32" on a steer tire and 2/32" on a drive tire as the minimum allowable tread depth, Hasinec said. Penske has a 5/32" and 3/32" minimum requirement, which ensures tires are changed before the tread gets too low.
Penske will even change drive tires earlier than 3/32" in northern climates. “Drivers want to feel comfortable that they have adequate tread in case of snow, for example,” Hasinec said. “We may do so at 8/32" to 10/32".”
Hasinec said Penske works to match the tread design to the application of the vehicle. “We want a tread that fits the application and has a long life,” he said. “If you can spec the right tire, you can get longer tread life and have better fuel economy.”
Lug designs allow better traction and are desired if there is some off-road driving required or if drivers will encounter inclement weather, such as snow, Hasinec explained. “Straight or rib-tread designs allow better fuel economy and perform well in the rain, but don’t provide the traction drivers need/want for snow, gravel, etc.,” he added.
For example, fleets operating in South Florida that don’t need to prepare for snow, could run a ribbed tire and have a longer life and better fuel economy. “If you’re in the Northeast or North Central regions, you have to be concerned about inclement weather, so you run a lug design,” Hasinec said.
SmartWay certified tires are required in many cases on certain vehicle types, especially in California. “The SmartWay designation meets EPA standards and helps with fuel economy,” Hasinec said. “OEMs build new units with SmartWay tires to meet the GHG requirements they need to achieve overall for specific categories of new vehicles.”
With drive tires on a SmartWay tread, the outside shoulder is almost a rib, and rib tires get better fuel economy compared to a lug pattern. However, SmartWay tires, due to the rubber compound, typically don’t last as long, Hasinec explained.
Maintaining tires is very important as proper maintenance can provide better fuel economy and allow the truck to carry the appropriate load for which the tire is rated.
“Underinflation, for example, will decrease your fuel economy and payload capability. Underinflation can also contribute to irregular wear and premature replacement,” Hasinec said. “Maintaining your tires and their alignment properly also contribute to other components' longevity as well as reduce driver fatigue. In the end, tires are very important when it comes to overall safety.”
1. Are our routes mostly stop and go city driving? These applications do well with a rib design as well as a shallower tread and harder rubber compound.
2. Do we have a mix of some distance between points A and B before we start having multiple stops on our routes? For this scenario, fleets will want a little deeper tread design (more 32nds) and still possibly a rib design.
3. Are our routes predominately regional and are the number of stops minimal? Similar to above, these applications could benefit from a little deeper tread design (more 32nds) and still possibly a rib design. They may also opt for a fuel economy tire, such as the SmartWay designation.
4. Are our routes primarily over the road, with a majority all highway? In this case, a deeper tread, SmartWay designation tire works well.
5. Do we go off-road, at locations such as construction sites, gravel yards, etc.? With this application, fleets should consider a lug design for drive tires to get better traction.
6. Do we run our vehicles in parts of the country that experience inclement winter weather? A lug design for the drive tires to get better traction is the desired selection.