Tractor Ag Tires – Important Things You Need To Know

Tractor Ag Tires – Important Things You Need to Know

by Paul Bruggeman - Tractor Tire Pro Phoenix, Arizona

What is the Difference between Bias Tractor Tires and Radial Tractor Tire? Which Tractor Tire is better? 

What is the Difference between Bias Tractor Tires and Radial Tractor Tire? While they do the same thing and produce the same result at the end of the day, there are differences between the Radial Tires and Bias Tires. Each tire is built differently, and the differences are only important in terms of performance and your application.

Bias Tractor Tires

In Bias Tires, the individual cords that make up each layer of the tire run at angles across the body of the tire from one bead to another. Most run at a 45-degree angle relative to the face of the tire, and also run at opposing angles with each tire ply. Cords make up the tire plys, and in Bias tires they are made of layered nylon, rayon, polyester, and other materials. Because Bias-ply tires are built with multiple layers of these rugged materials weaved diagonally from tire bead to bead, a rugged, stiff tire sidewall. This sidewall characteristic has an advantage when it comes to load carrying capacity and sidewall puncture resistance, which is very important in tractor and farm tire applications.

Radial Tractor Tires

Radial tires also have stiff belts in the tread area that restrict growth and stabilize the tires when they grip the ground. Unlike Bias Tires, Radial Tires have more flexible sidewalls than bias tires, and this flexibility combined with the stiff belts, provide better traction and efficiency superior to bias tires the plies run in a radial direction from one bead to another. Radials can have better traction and reduced soil compaction.

Tubeless Tires vs Tube Type Tires

Tubeless tires have been used for many years on combines and industrial tractors and have recently been adopted at all wheel positions by leading tractor manufacturers. They operate at the same inflation and have the same load capacity as equivalent tube type tires. Not only do tubeless tires provide higher reliability and easier puncture repair, but also lower assembly costs than tube type tires. When used with calcium chloride solution, rim corrosion is not a problem as long as you maintain the proper inflation pressure to keep the tire bead firmly on the rim’s bead seat. This seals outside air away from the rim and controls corrosion. A dismounted rim will rust quickly if not rinsed with tap water immediately.

Understanding Tire Sizes and What They Mean 

Conventional sizing – This is probably the most common size marking system in use today. Examples would be 7.50-16, 11L-15, 13.6-28 and 18.4R38. The first number is the nominal cross-section in inches, which is followed by a dash (-) to indicate bias construction or an “R” to indicate radial construction. The number after the dash or “R” is the nominal rim diameter. Metric sizing – This new tire marking system has the approval of the International Standards Organization (ISO). Examples are 320/90R46 and 710/70R38. The number before the “/” is the nominal cross-section in millimeters. After the “/” is the aspect ratio, “R” indicates radial construction (“D” for bias or Diagonal), and then the nominal rim diameter.

Tractor Tire Rims and Wheels

This is a more extensive subject than can be covered here, but I will run through a quick overview of tractor rims and wheels.  There are many different types of tractor rims and wheels to suit a wide variety of applications. You may have heard of one or two of these different types like double bevel rims, deep well rims, powershift wheels, rim and clamp tractor wheels, waffle wheels, waffle wheel center inserts, direct bolt wheels, axle mount wheels, direct bolt dual wheels, single bevel rims, rod style prime rims, rod style duals, and many others. The most important information that you need to know to buy the right rims for your tractor are the wheel diameter and rim width. You can learn much more about how to measure tractor wheels in the article Tractor Tires and Rims - How to Measure Tractor Tires and Rims in 4 Steps.

Use of A Rim Wider Than Recommended 

Using a wider rim results in flattening of the tread face. This effect may improve traction in some looser soil conditions. In hard soils, however, the flatter tread penetrates less effectively and tractive effort is reduced. Additional stresses concentrated in the shoulder area tend to increase the rate of shoulder treadwear. By spacing the tire beads farther apart, the sidewalls are forced to flex in an area lower than normal and this can result in circumferential carcass breaks and/or separation.

Use of A Rim Narrower Than Recommended 

This condition brings potential mounting problems because the rim shield or flange cover molded into most drive tire designs tends to interfere with the seating of the tire beads on a narrow rim. Once mounted on a narrow rim, the tire rim shield applies undue pressure on the rim flange withpossible tire sidewall separation or premature rim failureat the heel radius. On a narrow rim the tread of the tire isrounded, as with the over-inflated tire, treadwear will beconcentrated in the center area of the tread and traction inthe field will be reduced.

Tractor Tire Treads and Designs

R-1 is the most common type of lug tire used in the UnitedStates and Canada and is the tire to use for general dry landfarming. Tractor tires R-1 tires include the UltraTorque, DynaTorque Radial and Duratorque.R-1W tires were introduced in Europe for the wet soilsfound there. They fill a gap between the R-1 and R-2 tiresand provide the right tire for areas with wet, sticky soils. The “W” signifies wet soil service. R-1W tires are defined ashaving 20% deeper tread depth than an equivalent R-1 tire, but actually range from 15 to 35 percent deeper. Tractor tires R-1 designs include the Super Traction Radial, OptitracDT824 and DT820.R-2 tires are for cane and rice and other crops grown in wetmuck or flooded fields. R-2 tires are about twice as deep asR-1 tires. Tractor tires R-2 designs include the Special SureGrip TD-8 and Special Sure Grip TD-8 Radial. AlthoughR-2 tires are excellent in the service for which they are

High Flotation tires have a wider cross section, a larger air volume, and operate at lower inflation pressures. The net result is a flotation effect for anywhere performance no matter the terrain or the load. This type of tire usually features a Deep Lug Tread similar to an R-1 tire. In wet soils, tread depth is the biggest factor affecting traction in wet soils, but as the soil dries out, deep lugs turn from assets to liabilities. In soil conditions most prevalent in North America, an R-1 tire will pull better than an R-1. For an explanation of all codes see Industry Standards and

Flotation / Compaction Tractor Tires

Flotation is defined as “the ability of a tire to resist sinkageinto the soil.” If a tire is not able to stay on top of the soil,it will leave a rut under which the soil texture is disturbed.It is a concern in loose, wet, or easily compacted soils.Agricultural soils need to have air and water-filled porespaces that allow root growth, the transport of plantnutrients, and rapid absorption of rain water. Compactionis defined as a decrease in the volume of these pore spaces.

There are two different concerns: 1) subsoil compactionwhich is dependent on the total weight of the vehicle and 2) surface disturbance which is highly related to the averagepressure between the tire and soil. For a given load, thetire that will carry the load at the lowest required inflation pressure will provide the greatest flotation and the least surface disturbance and compaction. This is because the average pressure under a tire is a little higher (about 1 to 2psi for a radial and 2 to 3 psi for a bias) than the inflation pressure in the tire. Flotation tires are specifically with a large ground contact area which effectively distributes load over a broader area, providing a reduction in unit ground pressure in comparisonto conventional tires. This reduction in ground pressure means less soil compaction and less ground disturbance. It also means improved mobility, permitting you to traverse mud or snow or soft sand that would often bog down a conventional tire.

 Singles / Duals / Triples

Duals or triples can give you increased traction or increasedflotation over single tires depending on how you set them up. If you want FLOTATION from your duals or triples, run your tractor at the manufacturer’s minimum weight/HP ballasting recommendations and decrease inflation pressure to match the lighter load Compared to single tires, duals and triples can allow you to increase traction (more weight) and improve flotation (lower inflation pressure) if only moderate increases in ballasting are made. Remember that duals and triples increase your tractor’s rolling resistance and decrease traction efficiency.

Dual Attachment Systems

While rim-mounted duals are easier to take on and off, thespacer band between the two rims decreases ground clearance. Axle-mounted duals are more flexible because they allow you to change spacing. Axle-mounted duals are also better at transmitting high torque.

Tire Pressure

Tire Overload or Underinflation

Overloading and underinflating a tire both have the effect of over-deflecting it. Under these conditions the tread on the tire will wear rapidly and unevenly, particularly in the shoulder area. Radial cracking in the upper sidewall area will be aproblem. With underinflated bias drive tires in high torque applications, sidewall buckles will develop leading to carcass breaks in the sidewall. While an underinflated drive tire may pull better in some soil conditions, this is not generally true and not worth the high risk of tire damage incurred.

Overinflation

Overinflation results in an under-deflected tire carcass. The tread is more rounded and wear is concentrated at the center. Traction is reduced in high torque service because both width and length of the ground contact area are reduced. The harder carcass with reduced flexing characteristicsdoes not work as efficiently. Moreover, the tightly stretched overinflated tire carcass is more subject to weather checking and impact breaks.

Side Hill Work

When working back and forth on the side of a hill with a slope exceeding 11 degrees (20% grade), the tires of a tractor will alternately be on the downside. It is recommended that the inflation pressure in the rear tires be increased for additional stability. For base pressures 12 psi and above, the pressureshould be increased 4 psi. For base pressures below 12 psi, the pressure should be increased by 30%. When one side is continuously operated in the down slope position, it is only necessary to increase the inflation pressures on that side.

Drawbar Pull and Tire Slip

The amount of drawbar pull available depends on the loadcarried by the tractor drive axle(s). For more pull, moreweight should be added. 

Roading of Tractor and Farm Tires

Tractor tires operate most of the time in field conditions where the lugs can penetrate the soil, and where all portions of the tread contact the ground. In operating on hard roads in an underinflated or over-loaded condition, the tread lugs distort and squirm excessively as they enter and leave contact. On highly abrasive or hard surfaces, this action wipes off the rubber of the tread bars or lugs and wears them down prematurely and irregularly. Using the correct inflation pressure will even the load distribution across the faceof the tread resulting in more uniform wear. Tractor and implement tires are designed for low speed operations not exceeding 25 mph (some radial tires are also rated for 30 mph). If tractors or implements are towed at high speeds on the highway, high temperatures may develop under the tread bars and weaken the rubber material and cord fabric. There may be no visible evidence of damage at the time but later on a failure may occur, which experience shows was often started by the overheated condition that developed when the unit was towed at a high speed.

Tire Storage and Care

Stored tires and tires on stored implements should be protected from exposure to the elements as much as possible. Although tractor tires and farm tires are very durable, they do readily absorb oil, grease, fuels, and other solvents that cause them to deteriorate. Tractor tires should never be stored on oily floors or adjacent to volatile solvents. These tend to leach the protectants and will damage and weaken tires. Mounted and unmounted tires should be stored away from motors, generators and arc welders because these are all sources of ozone. Ozone attacks rubber, causing it to crack perpendicular to any applied stress. These cracks expose more surface and can escalate until rubber degradation can cause tire failure. Even minor ozone induced surface cracks can form an access route for foreign matter to penetrate the tire when it is put back into use. Since heat and light also degrade tires, care should be taken to make sure that they are stored in a cool, dark place. Tires should be protected from sunlight, either under shelter or at least covered with an opaque tarp. To store tires mounted on rims but not on a tractor, reduce inflation pressure to about 10 psi and store vertically, standing tires on their treads. Tires off rims can be stacked evenly on their sidewalls, but never so high as to distort the bottom tire. To protect tires on a machine in storage for six months or more, block up the machine to reduce stress on the tires. With the tires off the ground, pressure can be reduced to 10 psi. If it is not possible increase inflation pressure to 25 percent above that required for the actual load on the tire to decrease tire deflection. The machine should be moved from time to time to change the location of stress concentrations in the tire ground contact area. Make sure that you remember to reset inflation pressure to the recommended operating value when the machine is restored to service.

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