Traction vs. Flotation: How to Optimize Each and Use Flat Plate to Measure Contact
Modern Tire Dealer has partnered with AG Tire Talk to provide answers to insightful questions that farm tire dealers have about farm tire technology. This is the next installment in our ongoing series, which is designed to help farm tire dealers better connect with their customers. A trending question, followed by an abridged version of the answers, will appear in our Commercial Tire Dealer section every other month. For complete answers, check out www.agtiretalk.com!
QUESTION: What is the difference between traction and flotation, how do you optimize each and how do you use flat plate as a measurement tool?
Nick Phillippi, national product manager, Alliance Tire Americas Inc.: Traction and flotation can have a complicated relationship. Sometimes they work together and other times they can work against each other. Understanding both can help farmers make appropriate tire choices. From a tire engineering standpoint, traction, or tractive force, is the maximum amount of force that a tire can place against the surface for forward movement. Flotation is the ability of an object to remain on top of a surface.
Optimum flotation is going to be very dependent on soil types and soil conditions. If you’re in sloppy, thin mud, wide tires can provide plenty of flotation to keep you on the surface, but that slick soil will offer very little traction. If you’re in heavy soil, where a shallower lug can gain traction but you want to minimize soil compaction and rutting, you want more moderately sized lugs and a really large footprint from wide flotation tires or very-high flexion (VF) tires.
Of course, in farming, you don’t get the same conditions every day. The problem is that many people select tires based on the most extreme conditions they may encounter, rather than according to more typical use scenarios. That can lead to inappropriate choices. For instance, an R-2 tire may be helpful for a week or so during a particularly wet midwestern spring, but it would wear too quickly, ride rough and tear up fields most of the year.
You have to think about the conditions you operate in over the course of a whole year. Do you want a rounded contact patch for digging into the soil — which is characteristic of a bias-ply tire — or the flatter, broader contact patch that you see with steel-belted radials? Think about what gets you through your soils, how much slip you can tolerate, how much compaction your soils can take, and what your tolerance is versus the cost of fuel, tires and maintenance.
Dave Paulk, manager, field technical services, BKT USA, Inc.: Modern tractors are designed to transmit power from the engine to the ground. Transmitting that power requires moving traction to the soil surface. Traction determines how efficiently this power is used.
When the engine delivers too much power to the tires and friction to the soil is minimized, tires will spin. Most modern medium- to high-horsepower tractors need added ballast to minimize wheel slip and maximize traction. The weight is determined by the type of implements being used.
Traction can be impacted by air pressure, flotation, and the contact area with the soil. A greater contact area and less inflation pressure will generally increase traction.
Flotation tires are designed to deliver maximum traction while minimizing soil compaction. They have wider footprints to distribute the weight of the tractor, combine, cart, or implement over a wider area of soil. Flotation tires can roll over loose or wet soil and minimize damage by not creating deep ruts. They can be used in free rolling or drive wheel applications and can carry a large amount of weight. Increased flexion (IF) and VF technology have contributed to the versatility of flotation tires.
The flat plate measurement of a tire is the contact area of the tire to the soil in square inches. The greater the contact area of a tire’s footprint, the better the weight is distributed over the soil. Distributing the weight over a larger area reduces soil compaction and can increase traction. Row crop applications are limited to wider flat plate measurements by row width. If row width is not a concern, as in tillage or minimum tillage applications, a larger flat plate works well for traction.
By managing the footprint of the tire, a farmer can increase traction and lower fuel costs. Managing the power of the tractor ensures that the tractor is weighted correctly and horsepower is efficiently used. Managing ballast ensures the horsepower of the tractor is moved to the ground, where it has the greatest value and is most efficiently used. And managing tire inflation pressure means using the right amount of air for the weight of the tractors and implements in motion.
Jim Enyart, technical manager, CEAT Specialty Tires Inc.: Flotation is the ability to remain on or near the soil surface as you are moving across that surface. Flotation is directly related to the weight and the footprint of the tires that are carrying that weight. The larger the footprint, the better the flotation. And the lighter the weight, the better the flotation. When you are increasing the footprint and/or reducing weight carried, you are reducing the weight per square inch or down pressure.
Tire selection is key to maximizing footprint. Adding more tires, wider tires, larger-diameter tires, higher load-carrying capacity tires, higher aspect ratio tires or IF and VF tires can help achieve this goal. There are really no industry standards for comparing footprints. In general, using the flat plate or footprint calculations as a tool to increase flotation is quite easy. The larger the footprint, the better the flotation. Utilizing the footprint to increase traction is not so clear-cut. In some cases, the smaller the footprint, the better the traction — because you simply increase your weight per inch or per unit area.
The biggest problem is wanting to maximize traction to optimize efficiency while your minimizing compaction potential to keep from reducing crop yields. Flotation and traction are almost on a teeter-totter. As flotation increases, traction decreases due to reduced ground pressures. As flotation decreases, traction increases. These opposing effects are not so dramatic under low-torque applications but they can be quite extreme in high-torque situations.
Harm-Hendrik Lange, agriculture tires field engineer, Continental Agriculture North America: In farming applications, traction and flotation tires have different operational tasks, although they are partly used together in many cases. The best example is a large slurry tanker being pulled by a large tractor across a field.
What´s the main difference between traction and flotation tire applications? For creating traction, and to achieve the maximum footprint possible, it is often required to have the maximum number of lugs connected with the ground. But sometimes, maximum traction requires getting through a small layer of wet mud or loose surface material to grip the more solid soil layers below. This means that a little increase in tire pressure can, in certain cases, further increase the traction potential. But this always depends on the actual condition of the ground.
The main task of the flotation tire is to reduce rolling resistance for low pulling force at high loads, especially on deformable surfaces, like dry sand or wet soils. The pressure in flotation tires should not be much higher than the inflation pressure of tractor tires.
Keep in mind that while a driven tire actively works against the “bulldozing effect” by rotating, a non-driven tire needs to be turned by outer forces. With deeper track depth and small tires, the “bulldozing effect” becomes more and more significant as the tire is pulled against the soil wave. This means small tires with higher inflation pressure levels waste much more energy to fight against the soil wave in front of the tire.
Rick Harris, regional sales manager, GRI Tires: Flotation is the tire’s ability to reduce the impact on field conditions, like soil compaction. Traction is the tire’s ability to accomplish work with fewer resources, such as fuel, labor, time and mechanical wear and tear.
Radial tire technology increases traction and flotation simultaneously, much like a drag slick at the start line. The tire’s sidewalls absorb the engine’s torque, allowing the tread to remain in full contact with the ground and produce optimal traction.
The flat plate provides the ability to evaluate the contact patch of the tread at recommended inflation pressures. A larger tread contact patch promotes increased traction and flotation. A greater surface area reduces the amount of equipment and cargo weight supported by each section of the contact patch, increasing flotation and mitigating soil compaction.
Greg Gilland, business development and ag segment manager, Maxam Tire International: Traction is the term used to explain how a tire overcomes the friction between the surface of the rubber tire and the ground. Flotation is the ability of a tire to stay on the surface of soft ground, soil or snow without rutting or digging into the surface or ground, thus limiting the tire from overcoming the friction or providing traction.
In agricultural applications, tires are designed to deliver the optimal traction or flotation based on their size, load capability and compounding. In all cases, assuming the right tire size has been chosen, the key to delivering the best possible traction or force to overcome friction is the air pressure for a given load. When operating with a tractor in the field, the coefficient of traction is measured by the slip of the tires.
If you work in the field at higher road inflation pressures, you will likely experience higher tire slip and tires will float less, creating higher compaction. If you road a tractor at lower inflation pressure levels, you will have less slip but higher rolling resistance, which leads to faster tire wear and increased fuel consumption. The tires also will provide less comfort and lower lateral stability.
If you find that slip is too high or low, check your inflation levels and verify the load distribution from front to rear. Add or remove ballast, as required, and adjust the working depth of any towed implement.
David Graden, operational market manager, agriculture, Michelin North America Inc.: In sloppy soil conditions, there can be such a thing as too much flotation and not enough traction. On the other end of the spectrum, you can have too much traction and not enough flotation.
To achieve the best of both traction and flotation, I would recommend an IF or VF tire, with astandard R1W lug, at the proper recommended air pressure. If your machine weight distribution and air pressures are set properly, there is little that can stand in your way of getting the job done.
To take it a step further, you could also use gross flat plate as a tool to determine which tire is best for you. Gross flat plate, or contact patch, is basically defined as the footprint a tire puts on the ground.
When measuring gross flat plat for standard radial tires, the footprint area is measured at maximum load and pressure for a 20 mile-per-hour application. When measuring gross flat plate for IF/VF tires, however, calculate for the tire’s maximum speed schedule at maximum load and corresponding air pressure.
Gross flat plate is not linear, which means the measurement at max load and pressure will not be the same at operating conditions. As you go down in pressure and load, the increase in gross flat plat is exponential. Depending on the size and volume of the tire, the growth from max load and pressure to least load and pressure could be up to a 30+% difference.
Scott Sloan, ag product manager, Titan International, Inc.: Traction is the force that causes a moving thing to stick against the surface it is moving along. Lack of traction can cause excessive tire to slip, which equates to poor fuel efficiency and loss of productivity. This can be corrected in a number of different ways — the first being that the tractors total weight is properly ballasted to the amount of horsepower. Typically, 100 pounds to 120 pounds per rated horsepower is the appropriate target. The correct weight will utilize the tractive efficiency of the tires in order to transmit the power properly to the ground.
To gain more floatation, minimize the ground bearing pressures to increase the buoyancy or floatation of the machine. The heavier the machine, the more ground contact area is needed to carry that load.
The trick comes with balancing both traction and flotation. Understanding the give-and-take between traction and floatation gives growers a chance to choose the best fitment for their machines.
One method used to balancing traction with flotation is to dual or even triple tires on equipment. However, as with any dual or triple configuration, depending on the soil conditions, this will result in rutting or loose soil being pinched, and a berm will be created between the tires.
Another method that has been gaining popularity is to replace duals with super singles. This immediately reduces the rutting in the field. It also narrows up the machine, making it easier to maneuver in tight areas. ■