From a physics standpoint, how do ag tires and tracks interact with the soil differently? Why do tracks have a different optimum slip compared to tires, and what specific applications does each lend itself to perform best on?

In this edition of AG Tire Talk, officials from ag tire manufacturers outline the most important capability and performance differences between tires and tracks to help ag tire dealers better inform their customers. 

Robert Bender, product manager and tech support, off-highway tires, Ascenso Tires North America: Tires and tracks have the same basic job: transferring power to the ground while carrying and distributing the weight of the machine. They just go about it differently. Those differences impact everything from flotation and traction to ride quality, slip, fuel efficiency and roadability. Both systems have applications where they perform extremely well. 

Tires are essentially flexible air chambers. The air pressure inside the tire carries the load while the casing flexes to create the footprint. A properly inflated radial or very-high flexion (VF) tire creates a longer footprint that helps spread the load while improving power transfer to the ground. That footprint becomes the contact patch responsible for both traction and weight distribution. 

One of the biggest advantages tires have is flexibility. Tires absorb shock better in the field and on the road, generally ride smoother and allow for higher transport speeds when inflation pressures are correct. The biggest challenge with tires is often the simplest thing to change: air pressure. Most farm tires are overinflated because pressures are rarely adjusted for changing loads, speeds or applications. That’s where I’m hopeful central tire inflation system technology continues to help gain traction in agriculture. 

The flexibility of the casing and inflation pressure are two major components of the traction equation with tires. The third is lug penetration. Those three things together determine how efficiently the tire can pull through the soil. Tires rely on controlled slip to create traction, with an ideal operating range generally around 8% to 15% slip and roughly 11% being near ideal. As a tire moves through the field, it continuously creates a new footprint and new lug engagement with the soil. 

When one part of that system gets out of balance, efficiency drops quickly. An overinflated tire creates a smaller footprint. A smaller footprint reduces the number of lugs that are engaging the soil. Reduced lug engagement increases slip. Increased slip raises fuel consumption, reduces traction efficiency and increases the risk of both soil damage and tire damage. 

Tracks work differently. They rely on a large, consistent footprint to transfer power to the ground. With a track system, the footprint is always there. As the machine moves, the track rolls over itself like a conveyor belt while maintaining a large contact patch. Because of that large footprint, tracks typically operate at much lower slip percentages, ideally somewhere in the 2% to 5% range. 

The same thing applies with tracks. Once slip moves outside the ideal range, efficiency drops quickly. Excessive slip with tracks tends to smear or polish the soil surface rather than aggressively digging. That’s why a tracked machine can get stuck without necessarily digging a deep hole. One major advantage to tracks is that the lower slip percentages often correlate to improved traction in high-draft load, deep tillage or scraper applications. 

The trade-off is roadability and versatility. Track machines are generally rougher riding, operate at slower transport speeds and tend to experience more heat-related wear issues during extended road travel. 

When it really comes down to it, both tires and tracks have their place. I’m honestly still a tire person. While I absolutely believe tracks serve a purpose and I’ve sold and installed plenty of them over the years, I still believe tire technology offers the most versatility across the industry as a whole. 

In soft soil conditions where flotation is critical, or in heavy draft applications where maximum traction and shear force transfer matter most, tracks can absolutely shine. But agriculture covers a massive range of applications. From narrow row crop farming where a 9.5-inch tire is needed to prevent crop damage, to loader work, transport applications and general farming, where road speed matters, tires still win in my book. 

Obviously, there is a lot more to it than simply saying one is better than the other. At the end of the day, it comes down to matching the machine setup to the application. There is a place for both tracked and tire machines, and there probably always will be. Different tire technologies and different track systems all perform differently depending on the application. Understanding the operation, the conditions and the expectations are what ultimately lead to the best outcome for your customer. 

Dave Paulk, manager, field technical services, BKT USA Inc.: Contact pressure, footprint size, ground area and the degree of soil deformation are all results of the impact of tires or tracks on the soil and are strictly related to the specific design of products, but also are highly influenced by other factors, such as the load they carry and the conditions of ground contact. 

Tracks have a larger footprint area, spreading the load more evenly, which creates a smoother contact surface and reduces the soil disturbance. This specific feature allows for a better distribution of load and pressure on a wider footprint, being synonymous with reduced compaction. Also, their improved flotation and reduced risk of slippage ensure better performance even in wet, muddy or clay soil conditions. 

Focusing on tires, inflation pressure plays an important role. Inflation can be adjusted and regulated to reduce ground-bearing pressure. In dry, sandy and loamy soils, tires operating at lower air pressures have an increased footprint area on the ground. This translates to reduced compaction, crop preservation and improved soil productivity. 

Let’s look at slippage. A very low slip indicates that a tractor is underloaded and not operating at maximum tractive efficiency. If slip becomes excessive, tractive efficiency decreases, resulting in high soil compaction and disturbance. Tracks generally operate at lower slip rates than tires, often in the range of 2% to 5% under field conditions, because their large uniform contact area helps distribute weight more evenly and minimize slippage. They are especially effective in wet, soft soils, where improved flotation is important. Tracks also perform well in demanding, high-pulling tasks such as tillage and planting. 

Soil compaction is primarily influenced by the machine’s total load. Tire systems can minimize compaction by adjusting air pressure to match the required load capacity, improving weight distribution and reducing ground pressure. Tracked tractors are generally heavier than their tire-equipped counterparts, resulting in higher loads. However, tracks maintain a consistent contact area with the ground. This fixed, extensive contact patch helps distribute the weight more evenly than tires. 

Most tire-equipped tractors are lighter and rely on air pressure to determine the ground-bearing pressure on the soil. When tire pressures are reduced below 20 psi, the load is spread over a larger footprint, helping minimize soil compaction. When comparing the percentage of soil compaction between tires and tracks, tires operated at moderate pressures — around 25 psi to 35 psi — can perform similarly to tracks. However, at higher pressures — 35 psi and above — tracks typically cause less soil compaction. 

Trevor Wilson, marketing specialist, Maxam Tire North America: Tracks and tires move across soil differently at a fundamental physics level, and that difference determines which one belongs on your customers’ ag equipment. Understanding how each system generates traction, manages ground pressure and responds to slip gives you the information to make that decision based on your operation rather than on assumption. 

The honest answer for most farming operations is that neither tracks nor tires are uniquely superior. The right choice depends on soil type, seasonal moisture conditions, implement load requirements and the proportion of your work cycle that involves road travel. In consistently wet, heavy soils where high-horsepower drawbar work is the primary task, tracks deliver a real, physics-based advantage. 

In mixed conditions with significant road travel and varying soil moisture, a properly specified VF radial tire running at optimized inflation pressure competes directly with tracks on soil protection and traction while cutting down on operating costs. 

A tire generates traction through a single, concentrated contact patch. The size of that patch is directly controlled by inflation pressure, tire size and axle load. Lower inflation pressure increases sidewall deflection, which lengthens and widens the footprint. A larger footprint distributes the machine’s weight across more soil surface area, reducing ground pressure in pounds per square inch and improving flotation in soft conditions. 

Traction depends on the interaction between the tread lug and the soil. As torque is applied, the lug shears into the soil surface. The soil resists that shear force, and the reaction pushes the machine forward. On firm ground, this system is highly efficient. On soft or wet ground, the soil shear strength is lower, meaning the lug breaks through the surface before the full reaction force is generated. The result is slip, which produces rutting, compaction below the disturbed layer and wasted fuel. 

A track distributes machine weight across a contact area determined by track width and the length of ground contact between the front idler and rear drive sprocket. This geometry produces a lower ground pressure than a tire of equivalent width on the same machine, because the load is spread over a much longer surface.  

The traction mechanism for a track is different from a tire in one important way. Rather than relying on individual lug shear at a single contact patch, a track engages the soil across the entire length of its ground contact. The track links apply force progressively as the machine moves forward, distributing shear stress across a larger soil volume. This is why tracks maintain traction in conditions where a tire would spin out. The soil does not need to resist the full shear force at a single point. It only needs to resist a fraction of it at any given moment across the full track length. 

There is an important qualifier: Weight is not distributed evenly across a track’s contact patch. The rollers and idler wheels concentrate load at specific intervals along the track, creating localized pressure points that exceed the average ground pressure figure. In very soft or saturated soil, those concentrated points still cause subsurface compaction.

Tracks perform best in wet, soft or saturated field conditions, where soil shear strength is too low for a tire to maintain traction without excessive slip; primary tillage in heavy, wet soils where drawbar pull requirements are high and ground conditions are marginal; operations where surface rutting is a significant concern and the field must remain passable throughout the season, and when used on high-horsepower row crop tractors pulling full implement loads in variable spring conditions where soil moisture changes across the field. 

Tires perform best in firm-to-moderate field conditions, where soil shear strength is sufficient to support efficient traction within the tire’s contact patch; roading and transport between fields, where tracks are limited and incur significantly higher wear costs on hard surfaces; mixed operations that require both field work and road travel in the same day, and operations where operating cost is a primary constraint. 

Modern VF radial tires address the soft ground limitation more effectively than any previous tire technology. By operating at inflation pressures below 15 psi while carrying full axle loads, VF tires create a contact patch that rivals what a track delivers in many field conditions. The tire’s sidewall does the work that air pressure previously handled, and the result is a longer, flatter footprint with significantly lower ground pressure than a standard radial or bias ply tire at equivalent load. 

Yokohama TWS ag group: There has always been discussion about what system is better: tires or rubber tracks. Both systems have their advantages and are not exclusive one to the other. Equipment type and size, field usage, soil type and condition and customer preference will play a role in what system works best. Agricultural rubber tracks are part of an engineered undercarriage system designed mostly for high-power, high-weight agricultural machines operating in demanding conditions, as it is a more expensive option. 

Rubber tracks have been developed to support high machine loads; offer the most consistent traction on uneven terrain; improve surface load distribution; maintain productivity in certain soil conditions, and deliver a smoother ride in very uneven soil conditions. Tracks and tires complement each other where operating margins become critical. When comparing the same equipment, buying and maintenance costs are higher for the rubber-track version as more components are involved. 

Rubber tracks perform best when soil bearing capacity is reduced; draft force is remarkably high, like in scrapper applications; machine stability is critical to the operation, and harvesting cannot be delayed due to soil with excessive high moisture. 

In standard or mixed conditions, modern VF agricultural tires already deliver excellent performance and can adapt to different conditions. Plus, they are more versatile with equipment that changes uses, like field operation and roading, where inflation pressure can be adjusted to provide the best performance. Tires also allow a larger range of adaptation, such as changing inflation pressure to adapt to changes in load. Equipment equipped with tires normally allows for higher speeds versus rubber track versions. Tires also can accommodate load bonuses.