Radial vs. Bias

As the drawing here shows, radial tire construction is substantially different from bias tire construction. The crossed plies of the bias tire run diagonally from bead to bead. In a radial tire, the carcass plies run in a radial direction from one bead to another. Radial tires also have stiff belts in the tread area that restrict growth and stabilize the lugs when they contact the ground. Radial tires have more supple sidewalls than bias tires that, in combination with the stiff belts, provide traction and efficiency superior to bias tires.

Tubeless 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.

Tire Size Nomenclature

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. See Millimetric Size Marking for a more complete description of this sizing system.

Sidewall Info

On both sidewalls of all tires is the brand name in large letters, a size marking, a tire name such as “DT810,” and a panel giving the maximum pressure for that tire, the load corresponding to that pressure, and the maximum speed for which that load is valid. If your operating conditions are different from those on the sidewall, you must consult extended load tables in the Titan Tire Catalog.

Ply Rating / Star Marking / Load Index

The load and/or pressure capacity of a tire is shown in the ply rating (bias tires), the star marking (conventional radial tires), or the load index (metric radials). It can describe tire strength (ply rating), rated inflation capacity (star marking), or rated load capacity (load index).

Ply Rating – Used by bias tires and some older radials. Ply rating is an indication of carcass strength and not the actual number of fabric plies in the tire. Maximum rated loads and pressures are different for each tire size with the larger tires operating at lower pressures for a given ply rating.

Star Marking – Used by conventional-sized farm tractor radials. Star marking is an indication of rated inflation pressure: 1 STAR farm tractor tires are rated at 18 psi, 2 STAR farm tractor tires are rated at 24 psi, and 3 STAR farm tractor tires are rated at 30 psi. Loads vary with tire size.

Load Index – Used with metric radials. Load index is an indication of rated load with each load index number corresponding to a certain load (see table on “International Load Index”). If two tires have the same load index, they will carry the same load, but not necessarily at the same inflation pressure.

MFWD Lead / Lag Calculation

On mechanical front wheel drive (MFWD) tractors, front and rear rolling circumference must be matched to the tractor front-to-rear gear ratio. For further details see “Rolling Circumference” section.

Rim Selection

It is important to always mount a tire on a rim that is approved for it. Not only must the width be correct, but also the flange contour (i.e. DW, DD, F, L, ...) must be the one recommended for the tire in question.

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. See “Rim Types” and “Approved Rim Contours” sections for the list of recommended and alternate rims.

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 with possible tire sidewall separation or premature rim failure at the heel radius. On a narrow rim the tread of the tire is rounded, as with the over-inflated tire, treadwear will be concentrated in the center area of the tread and traction in the field will be reduced.

Drive Tire Designs

See the “Industry Standards and Selection Chart,” which is an excellent guide for determining the type of service for which a tire is intended.

R-1 is the most common type of lug tire used in the United States and Canada and is the tire to use for general dry land farming. Goodyear R-1 tires include the UltraTorque®, Dyna Torque® radial and Duratorque®.

R-1W tires were introduced in Europe for the wet soils found there. They fill a gap between the R-1 and R-2 tires and provide the right tire for areas with wet, sticky soils. The “W” signifies wet soil service. R-1W tires are defined as having 20% deeper tread depth than an equivalent R-1 tire, but actually range from 15 to 35 percent deeper. Goodyear R-1W designs include the Super Traction Radial, Optitrac® DT824™ and DT820™.

R-2 tires are for cane and rice and other crops grown in wet muck or flooded fields. R-2 tires are about twice as deep as R-1 tires. Goodyear R-2 designs include the Special Sure Grip® TD-8 and Special Sure Grip TD-8 Radial. Although R-2 tires are excellent in the service for which they are intended, the widely-spaced lugs can cause problems with wear and vibration when roaded. R-2 tires also do not pull as well as R-1 tires in the drier soils typical of crops such as corn and beans.

R-3 designs such as the Goodyear All Weather® and All Weather Radial are used on turf or in sandy areas where the disturbance of an aggressive lug-type tire is not wanted. R-3’s shallow, button-style treads are not designed for hard pulling, but may give surprisingly good traction on smooth, dry surfaces.

R-4 tires are found on tractors with backhoes and/or frontend loaders at construction and other industrial sites. These tires have shallow, durable lugs. R-4 examples include the Goodyear IT510® Radial, IT525™, and Industrial Sure Grip.

HF-1,HF-2, HF-3 and HF-4 are types of a high flotation tire referred to as Terra-Tire®. In comparison with conventional tires, these tires have a wider cross section, a larger air volume, and operate at lower inflation pressures. The net result is a flotation effect for go-anywhere performance – despite terrain, despite load. The HF-1 is a Rib Tread similar to an R-3 tire. The HF-2 type is a regular lug tread similar to an R-1 tire. The HF-3 type is a Deep Lug Tread similar to an R-1W tire. The HF-4 is an extra deep lug tread similar to an R-2 tire.

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-1W.

For an explanation of all codes see Industry Standards and Tire Selection chart.

Flotation / Compaction

Flotation is defined as “the ability of a tire to resist sinkage into 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 pore spaces that allow root growth, the transport of plant nutrients, and rapid absorption of rain water. Compaction is defined as a decrease in the volume of these pore spaces. There are two different concerns: 1) subsoil compaction which is dependent on the total weight of the vehicle and 2) surface disturbance which is highly related to the average pressure between the tire and soil. For a given load, the tire 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 2 psi for a radial and 2 to 3 psi for a bias) than the inflation pressure in the tire. It is important to remember that the published contact areas are correct only at that tire’s rated inflation pressure and rated load. To compare the flotation characteristics of different size tires, use the load/inflation tables to determine the pressure corresponding to your load per tire. If you are looking for flotation, the tire that will carry the load at the lowest required inflation pressure is best.

Terra-Tire is a specifically designed high flotation tire. The large ground contact area of Terra-Tire flotation tires effectively distributes load over a relatively broad area, providing a reduction in unit ground pressure in comparison to conventional tires. This reduction in ground pressure means less soil compaction and less ground disturbance—on the farm or on the golf course. It also means improved mobility, permitting the Terra-Tire 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 increased flotation over single tires depending on how you set them up.

If you want TRACTION, add weight to your tractor up to the published load capacity for the tire using the appropriate row (single, dual or triple) from the tables in the “Load and Inflation” section. Inflation pressure must be increased to match the load using the same table. Be careful not to exceed the manufacturer’s maximum load rating for the axle. If flotation is not a concern, higher load capacity single tires used at higher load and pressure will increase traction and be more efficient and maneuverable than dual or triple tires.

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 according to the “Load and Inflation” tables and the “Optimum Tractor Tire Performance” section.

Compared to single tires, duals and triples can allow you to both increase traction (more weight) and improve flotation (lower inflation pressure) if only moderate increases in ballasting are made. However, 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, the spacer 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.

Liquid/Air Fill With Duals

A few years ago, the recommendation was to put liquid only in the inner tire, but new information has changed the guidelines. All tires on an axle should be filled to the same level, which should not exceed 40% (4 o’clock valve stem position). Likewise, all tires on a given axle should be inflated to the same pressure. See the section on optimizing your tractor to find the current rules concerning the use of liquid ballast.

Mixing Radial And Bias Duals / Unmatched Duals

There is no reason why you cannot mix radial and bias tires on the same axle. Of course you don’t get the full benefits of radial tires when you mix them with bias, but the result is still better than dual bias tires. The radial tire would typically be mounted at the inside dual position. A guideline to follow when dealing with unmatched duals is that the larger diameter of the two unmatched duals should be at the inside position.

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 a problem. 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 characteristics — does not work as efficiently. Moreover, the tightly stretched overinflated carcass is more subject to weather checking and impact breaks.

Pressure Adjustments For Slow Speed Operation

Higher loads are approved for intermittent service operations at reduced speed. This is shown in the footnotes under the “Load and Inflation” tables for rear and front tractor tires operated at speeds up to 5 mph max. To carry the increased load at this speed, the pressure MUST be increased as shown in the footnotes to reduce tire deflection and assure full tire service life.

Furrow Drive Wheel Tires

In mold board plowing operations, where tires on one side of the tractor are run in the furrow, inflation pressure in the furrow tire should be increased 4 psi over the rated value. The additional pressure compensates for the additional load being carried by the furrow tire and reduces sidewall buckling tendencies in bias tires under high torque.

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 down side. It is recommended that the inflation pressure in the rear tires be increased for additional stability. For base pressures 12 psi and above, the pressure should 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 load carried by the tractor drive axle(s). For more pull, more weight should be added. The effect of added weight will be in proportion to the figures in the following table. For each 100 pounds added to the rear axle of the tractor, the average drawbar pull will be increased by:

Rim Slippage

In attempting to obtain maximum tractor drawbar pull, tube valves are occasionally torn off because of slippage of the tire bead on the rim. Tubeless tires, although immune to pulled valves due to slippage, may still suffer abrasion on the base of the bead after prolonged operation with the tire slipping on the rim. Tire slippage on the rim may be caused by:

• Low inflation pressure for load.
• Improper seating of tire bead on rim.
• Use of thick soap solution or improper mounting lubricant in mounting the tire beads to the rim.
• Inadequate tire size or strength rating for the high torque requirements.
• Undersize rim — consult Titan Customer Service for specialized equipment needed to determine if rims are out of spec.
• Poor rim knurling on bead seat.
  

When one of the first three conditions is responsible for the problem, tires should be demounted and tire beads and rims carefully cleaned. Tire should then be remounted and inflated to 35 psi to properly seat the tire beads on the rim. The precautions found in this handbook MUST be observed. If tube type tire, the tube should then be completely deflated and then reinflated to recommended operating pressure.

Where inadequate tire size or load capacity is the problem, a change to a higher load capacity and/or larger tire size will be required. Determine tire adequacy by checking the “Load and Inflation” tables.

If it is determined that the rim is undersize or has poor knurling, then it must be replaced.

Roading 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 make contact with 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 from the “Load and Inflation” table will even the load distribution across the face of the tread resulting in more uniform wear.

Farm 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. Later, a premature 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 attack by oxygen and ozone. Although Titan and Goodyear farm tires use considerably more of the materials that protect against ozone and oxygen than car or truck tires, care should be taken in storage conditions to get full life expectancy from your tires.

Because tires readily absorb oil, grease, fuels and other solvents, they 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 ozone attack can escalate until rubber degradation can cause tire carcass 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.