Why do heavy-duty trucks have so many wide tires?

Commercial transport trucks and heavy loads form the backbone of the global economy, moving over 70% of the world's goods via highways. In many countries, commercial transport relies solely on trucks. This makes the importance of truck tires increase daily for the entire world. As a result of these facts and needs, specialized tires must be designed for these demanding tasks. Tire industry engineers have taken on this challenge, sparing no effort in developing this field astonishingly over recent years. Among the most important features distinguishing trucks is the wide tread and the use of multiple tires (duals). What are the benefits of these characteristics? And what motivates engineers to develop truck tires with these specific, recurring features? All these questions will be answered after you read this article, where we've condensed the information to save your time and provide you with the expertise needed by drivers, logistics fleet owners, and even light vehicle owners.

What Sets Truck Tires Apart from Other Tires?

Heavy truck tires are designed based on the unique and significant challenges they face in operation. This presents a major challenge for many tire manufacturers. Truck tires must withstand enormous weights, handle various harsh weather conditions, and operate intensively for long periods without rest. These demanding requirements necessitate designs that focus on load distribution and vehicle stability on the road. Engineers focus heavily on the internal and external engineering design of the tires, which determines whether a particular tire is the right choice for this category. Below, we review the main characteristics that differentiate truck tires from regular car tires.

1. Enhanced Structural Design

Structural enhancements involve developing thick, reinforced sidewalls with additional layers of nylon or steel to withstand heavy loads and resist deformations caused by high pressure. Additionally, the internal layers are reinforced to over 10 plies, compared to a maximum of 6 plies in car tires, which increases puncture resistance and reduces unwanted wear. Finally, the tires are reinforced with a spiral steel belt that enhances stability at high speeds and withstands severe impacts and bumps.

2. Capacity for Massive Loads

According to the European Tyre and Rubber Manufacturers' Association (ETRMA), tires designed for heavy-duty trucks can withstand ten times the load of regular car tires, owing to the significant difference in load capacity and internal air pressure.

• Load Index: For trucks (between 120-150) compared to cars (between 70-100), representing a significant difference of several tons.
• Internal Air Pressure: Trucks (100-120 psi) versus regular cars (30-45 psi).

3. Specialized Tread Patterns

Just as tires require diverse internal structures and manufacturing compositions, they also need specialized engineering techniques for designing tread patterns tailored to their operating environmental conditions. What distinguishes truck tires from others in terms of tread are the deep, winding grooves that rapidly drain water and mud, providing a larger contact patch with the road to stabilize the tires and prevent hydroplaning. These tread patterns are composed of very rigid rubber blocks designed to withstand bumps and impacts with strength and flexibility.

In summary, truck tires fundamentally differ from regular car tires, driven by the distinct demands of each vehicle type. This includes a focus on maximizing the road contact patch and reinforcing the tire's internal walls to provide sufficient strength to withstand the immense pressure during load transportation.

Read also: 5 Differences Between Truck and Car Tires

Engineering and Mechanical Reasons for Using Wide and Multiple Tires in Trucks

Truck tires are designed to meet specific needs, as they are an integral functional component of trucks that cannot be considered in isolation from their operating environment and climate. However, in this article, we will focus on understanding the engineering and physical reasons that necessitate tires being wide and multiple.

Weight Distribution and Infrastructure Protection

When a truck carries a load of 50 tons or more, the force generated by the load's weight is governed by the following physical equation: Pressure (P) = Force (F) / Surface Area (A).  To simplify this equation, pressure is directly proportional to the resulting force and inversely proportional to the surface area. This means that the larger the surface area over which the pressure is applied, the lower the overall pressure and the reduced force resulting from this physical interaction. The process of increasing this area is achieved through two tire characteristics: tread width and the number of tires. When more tires with wider treads are used, the pressure on all tires becomes less than it would be otherwise. This significantly contributes to improving the driving experience and extending the lifespan of all tires. The impact of this distribution on infrastructure is very significant, summarized by the following two points:

• Reducing Road Maintenance Costs: Narrow tires significantly impact asphalt due to concentrated pressure on a small area, leading to potholes. Consequently, the European Union incurs 3.5 billion euros annually in commercial road maintenance costs.
• Geographical Variation: In countries like Sweden and Finland, where icy and snowy roads are common throughout the year, wider tires, up to 50 cm, are used compared to normal conditions. This variation in tire width changes depending on the type of roads and their ability to withstand pressure.

Dynamic Stability Against Weather Conditions

The design of wide and multiple truck tires is not solely for one reason; it also addresses dynamic effects related to natural factors such as strong side winds, which create lateral shear forces that threaten to overturn the truck, or sharp turns where centrifugal force increases with speed and mass. These unavoidable effects in commercial or logistical operations make wide tires an essential component for all heavy commercial truck drivers.

• The Role of Static and Kinetic Friction:

Static friction increases with the contact area between tires and asphalt, preventing tire slippage during acceleration and sudden braking. Kinetic friction, on the other hand, plays a role in dissipating and dispersing the heat energy generated by movement. For this reason, many tire manufacturers intentionally add a blend of silica and synthetic rubber to achieve a balance between flexibility and heat resistance.

• Modern Developments in Tire Stability:

With the increasing number of traffic accidents caused by tire slippage on wet roads or during rainy weather, new systems and technologies have been adopted in tire tread design to enhance slip resistance. These include deep grooves that provide space for faster drainage of water, mud, and other obstacles, giving the tires a larger contact area with the road. All of this is a means to keep pace with developments in roads, trucks, and manufacturing materials, necessitating continuous improvement.

Tire Temperatures

When tires rotate at different speeds on asphalt roads, heat energy is naturally generated from the internal friction between the rubber and the road, and laterally with the air. This heat can rise to high levels, especially if the tire's tread area is narrow or if the truck has a small number of single tires. In some cases, this can lead to a very dangerous tire blowout. Therefore, having a large number of tires helps distribute the total heat generated because the contact area between the truck and the road increases. This reduces the load on each tire and extends the lifespan of all tires. Manufacturers confirm that increasing the number of tires reduces the likelihood of tire blowouts by up to 35% for a calculated 20% increase in the total number of tires.

Providing Safety and Support in Emergencies

Heavy trucks have 10 to 18 tires in some models and types. This large number of tires provides an additional layer of safety for the truck, especially if the tires are wide and multiple. This allows the truck to continue moving even if one tire fails, without the driver losing complete control of the vehicle. This unique feature gives trucks a high capability to avoid constant breakdowns, which pose a risk to other drivers, as disabled trucks will occupy a lane of the highway where maintenance areas are unavailable.

Automatic Compensation Mechanism: If one tire is lost, the load is automatically distributed among the adjacent tires thanks to the following systems:

• Air Suspension Systems: which are a means of adjusting the air pressure within the intact tires.
• Electronic Pressure Sensors (TPMS): These sensors alert the driver in case of a sudden imbalance in tire air pressure, helping to address the problem immediately.

What is the impact of using wide tires on truck performance?

Wide tires, as their name suggests at first glance, have a larger contact patch than others. Tire width directly correlates with various stability and performance characteristics. For trucks, wide tires significantly impact vehicle performance across different roads and loads. Below, we explain to you, dear reader, the various effects of wide tires depending on the road type.

On Dry Asphalt Roads: When asphalt roads are completely dry, this means we have both bad news and good news. The bad news is that tire temperatures will rise more significantly, and the good news is that the tires will be more stable on the road. Between these two points, the effect of wide tires provides the truck with greater acceleration and excellent traction due to the increased contact area on the road, which means more torque. Additionally, it enhances stability, allowing heavy trucks to corner at higher speeds without concern because wide tires offer high road grip, increasing resistance to centrifugal force.

On Winter and Snowy Roads: Wide tires offer a larger tread area, giving the grooves greater ability to drain water, snow, and debris more smoothly. On wet or snow-covered roads, there is an urgent need for sufficient traction to stabilize the truck. Since wide tires come with larger sipes, they can meet this need. Therefore, equipping your truck with wide tires enables you to drive on dry, wet, and snowy roads in all conditions and through all challenges.

On Off-Road and Mountainous Terrains: For trucks operating on mountainous, rough, and construction roads, wide and multiple tires are an excellent option. They come with greater thickness than standard tires, meaning increased resistance to punctures and cracks, along with the ability to handle emergencies thanks to the presence of multiple and dual tires.

Potential Challenges and Drawbacks

With every advantage in any industry, challenges and drawbacks are bound to emerge. To do justice to this article, we will outline the potential challenges and disadvantages you might encounter when using wide and multiple tires on your heavy and medium-duty truck.

Increased Noise:

Wide tires generate more noise compared to standard tires. While not a major problem, this can be annoying for drivers covering long distances and may contribute to increased driver fatigue.

Wheel Compatibility:

In some cases, incorrect tire sizing for the wheels can significantly reduce tire effectiveness, particularly during cornering and maneuvering, and also lead to increased uneven wear.

Fuel Consumption:

Naturally, an increased number of tires and a larger contact patch with the road surface lead to higher fuel consumption. However, this can be mitigated by selecting high-quality tires, such as those offered by Darbk Saudi Tire Company.

Performance and Consumption Comparison: Wide vs. Traditional Dual Tires for Trucks

Comparison Metric

Wide Tires

Traditional Dual Tires

Fuel Efficiency

2.9% improvement in fuel efficiency, potentially saving approximately 728 gallons annually per truck.

Higher fuel consumption due to increased weight and rolling resistance.

Weight

Approximately 70 lbs lighter per tire.

Heavier, reducing permissible load capacity.

Load Capacity

Increased load capacity due to lower tire and rim weight.

Lower load capacity due to increased tire weight.

Maintenance

Less and easier maintenance due to fewer tires to inspect and easier access to air valves.

Requires more maintenance time, with the need to match inner and outer tire pressures.

Stability

Improved stability due to a lower center of gravity, with the possibility of extending the trailer frame by 6 inches

Reduced stability, especially when cornering and at high speeds

Traction

Better grip on dry roads due to increased road contact area

Reduced grip on dry roads

Braking

Superior braking performance and shorter stopping distance due to increased friction during braking

Relatively longer braking distance