PEGGY FISHER: Tread design considerations for commercial truck tires

This is the time of year consumers begin thinking about winter tires.

However, commercial trucks and their operations are radically different from cars, SUVs and pickups driven by consumers to get to work, the grocery store, the soccer field and the occasional trip over the river and through the woods to grandmother's house.

Since trucks are traveling thousands of miles a year generating revenue, they are not going to stop to have their tires replaced with snow tires every winter and changed out again in the spring. That's just too much labor and lost productivity, and it isn't necessary.

Although most trucks don't use special tires for the winter, they do, however, have special needs when it comes to selecting tread patterns. Most fleets rely on their commercial tire dealers for information about the best tires for them to use and the technological advances made in tires.

So it's up to you to be the fleet's tire consultant. And as a consultant, it is usually helpful if you know what you're talking about.

So how do you go about recommending the proper tires for a customer's fleet of trucks that will maximize tire service life and minimize tire cost per mile?

Always start by determining what the vehicle is going to be doing. The characteristics for good performing tires used in on-off road applications or even in urban operations are much different than those used on long-haul, over-the-road trucks.

Tires designed for one application normally will not perform well in different applications.

For example, a line-haul drive tire usually will not have the chipping and chunking resistance that an on-/off-road tire will have while an on-/off-road drive tire will not provide the tread mileage of a line-haul tire in an over-the-road operation.

Line-haul vehicles usually make runs that exceed 500 miles and operate on highways and interstates with few stops. They average 80,000 to 200,000 miles a year. This operation is typical of national, less-than-truckload (LTL) and truckload (TL) carriers.

Regional vehicles normally run about 250 miles a day within a limited multi-state area such as the Midwest, Northeast, Southeast, etc. They usually average 30,000 to 80,000 miles a year and are operated by local grocery stores, petroleum distributors and regional LTL and TL carriers.

Urban pickup-and-delivery trucks operate just in their local area and run very short mileages with a high percentage of stops. These vehicles average 20,000 to 60,000 miles a year and are operated by school bus operators, retail and wholesale stores, package delivery fleets and beverage distributors.

Vocational trucks operate both on paved roads and unimproved roads in gravel, mud and sand at lower speeds and normally run between 10,000 and 70,000 miles a year in highly aggressive conditions. They are operated by construction companies, coal mines, utilities and sanitation companies, to name a few.

Tread patterns

Tread patterns designed for linehaul and regional operations are compounded and designed to produce high tread mileage with resistance to irregular wear and have low rolling resistance for better fuel economy.

Long-haul drive tires with deep treads are designed for maximum mileage, while drive tires with shallower tread depths are designed for maximum fuel economy. Trailer tires with shallow tread depths are produced to minimize irregular wear and maximize fuel economy too.

Tread patterns for pickup-and-delivery operations are designed to prevent damage from hazards that urban tires encounter daily, such as punctures from debris and contamination from oil in city streets and gutters.

They also are compounded for high-turning, low-mileage applications and are designed to provide good wet traction.

Tread patterns designed for vocational applications are imbued with cut-resistant compounds and have stone ejectors and thicker undertread to resist stone drilling and protect the belt package. (Stone ejectors, also known as "stone rejecters" or "platforms" are specially designed, groove side angles that can reduce stone retention in operations that run over gravel or poor asphalt roads where damage and irregular wear caused by stone retention is a problem.)

Because tread designs are usually a compromise of characteristics that enables them to provide good service under a variety of conditions, sometimes some performance requirements may have to be sacrificed in order to obtain others of greater value to the fleet.

Take for example a long-haul fleet that operates in Canada and wants aggressive drive tires that can handle snow and ice its trucks frequently encounter but also wants good fuel economy. To get this high traction quality, however, it may have to give up great fuel economy and settle for average fuel economy.

Therefore, before recommending specific tires to your customer, it is good to prioritize the fleet's requirements by putting the tire characteristics it wants most at the top of the list and those that are not as important at the bottom.

Some typical tire characteristics to consider are:

• Great fuel economy;
• High-mileage treadwear;
• Resistance to irregular wear;
• Resistance to penetration;
• Good steering response;
• Reduced noise generation;
• Good wet traction;
• Good dry traction;
• Good snow traction;
• Good dirt and mud traction;
• Resistance to stone retention;
• Resistance to cutting, chipping;
• Resistance to rib tears, curbing;
• High-speed operation; and
• Low-speed operation.

Besides designing tires for specific applications, tire manufacturers design tires for specific wheel positions: steer, drive, trailing and all-position.

All-position tires are built mostly with the steer axle in mind but also perform well on the drive and trailer axles.

Using an all-position rib tire all the way around the tractor can save a fleet big-time in terms of tire pricing, reducing the number of different tires that have to be stocked in inventory and improving fuel economy.

If a fleet's main concern is fuel economy, all-position tires will improve it since they have a lower rolling resistance than drive tires.

However, using specific-position tires provides better handling and traction because they are optimized for those specific positions and designed for longer wear. And less is more when it comes to trailer tires, since trailer axles are free rolling with no driving force running through them, they can get higher miles with shallower tread.

The deeper tread found in all-position tires is more vulnerable to irregular wear and isn't able to clean itself of snow or slush as easily.

All-position tires are a compromise from the start since they are not the deepest nor the shallowest in tread depth. They are designed without all the special features of position-specific tires so they are not optimum for any position.

Choosing all-position tires may be an option for only a very small segment of fleets that have fuel economy as their primary concern and traction being second.

This would work for regional fleets in the Southwest with flexible scheduling that are not just-in-time (JIT) driven and may only experience severe rains every now and again.

However, if on-time arrival is important, then trucks need to function in all types of weather conditions, and traction becomes the No. 1 priority so position-specific tires should be used.

Once you have the list of your fleet customer's tire requirements prioritized, you can then work on finding the right tires that best suit its needs.

Two tread designs

There are basically two types of tread designs: rib designs and lug designs.

Rib designs have grooves that run circumferentially around the tire. They are usually used on steer and trailer tires since this type of design has the poorest traction qualities.

The patterns can be zigzagged, which provides more biting edges for traction on wet pavement and are ideal for turning and maneuvering in pickup-and-delivery operations or fairly straight with little rolling resistance for high tread mileage and fuel economy.

Straight tread patterns usually also are accompanied by "defense" or "decoupling grooves," which are thin straight grooves on the shoulders of the tire that act as barriers to reduce shoulder wear. They are not normally used in urban applications since they tend to retain stones and can be torn by curbing.

Lug tread designs have blocks and grooves that cut across the crown and add traction and aggressiveness to the tread pattern. They also can have some circumferential grooves as well and are designed for use on drive axles.

Lug tire designs also have two basic patterns: open shoulder and closed shoulder.

Open-shoulder designs have blocks on the shoulder as well as throughout the pattern and have more aggressive traction abilities for operation in rain, mud and snow, while closed-shoulder designs have wide shoulder ribs that are resistant to side forces and permit the use of deep treads that provide high tread mileage in line-haul operations.

Lug tires with shallower tread depths resist squirm inherent in short-haul operations with constant turning and are less prone to irregular wear.

Sipes are tiny notches along the edges of grooves and within tread blocks and can be found in both lug and rib tread patterns of over-the-road tires. Their job is to relieve rolling stresses that start and spread erosion/river wear.

Tire manufacturers today also are producing tires designed with special performance qualities such as resisting side forces and high scrub found in spread-axle trailer applications, providing ultra-high fuel economy in over-the-road operations and delivering good tread mileage on 6x2 tractors with high-torque drive axles.

So it's vital to know not only the operation the vehicle is running in but also the qualities of the vehicle itself.

While spread-axle trailers and 6x2 tractors have been around for years, electric trucks and tractors are a new innovation in the trucking industry, and these vehicles do require different tires than gas- or diesel-powered vehicles.

Since electric vehicles provide instant torque to the tires and electric motors can more than double the amount of torque of their diesel counterparts, their tire tread patterns and compounding must be different from these used on vehicles that have to be shifted through two, three or four gears before getting up to speed.

Traditional tires can wear out up to 30-percent faster on electric vehicles, so tires for these vehicles must reduce the wear from high torque. Their tread designs must also provide extended mileage and reduce rolling resistance, which also will increase the vehicle's range.

They also probably will be made quieter because road noise seems greater since electric vehicles make little noise.

We should expect to see tires designed specifically for electric vehicles in various operations. While they are not here yet, I guarantee you, they will be soon.

Not an exact science

Selecting the proper tread designs for your fleet customers' vehicles is not an exact science. But if you follow a few basic steps you can narrow down the hundreds of tires to choose from to just a few. To do this, follow these tips:

1. Determine the vehicle's type and the operation it will be running in.
2. List your fleet customer's operational requirements.
3. Arrange these requirements in order of importance.
4. Compare the fleet's requirements with the operating qualities of tires designed for the operation, vehicle type and wheel position.
5. Select appropriate tread patterns.

Once you have selected tread patterns that appear to be good fits for your fleet customer, the only way to really determine the performance a fleet will get from these tires is for it to test them.

It's a good idea for the fleet to evaluate two or three tread designs in small numbers to see how they run and wear before it makes a large-scale purchase of one tire tread design.

Peggy can be reached via e-mail at [email protected].