Agricultural Mechanics: Service of Tires & Wheels (PDF)

# AGRICULTURAL MECHANICS ## 8206-B ## SERVICE OF TIRES AND WHEELS ### INTRODUCTION When we think of modern agricultural tractors, equipment, and vehicles, it is hard to visualize them with any thing other than rubber tires. This has not always been true. Rubber tires and tracks have propelled Am...

# AGRICULTURAL MECHANICS ## 8206-B ## SERVICE OF TIRES AND WHEELS ### INTRODUCTION When we think of modern agricultural tractors, equipment, and vehicles, it is hard to visualize them with any thing other than rubber tires. This has not always been true. Rubber tires and tracks have propelled American farming from the age of steel wheels and tracklayers to the space age in a half century. Rubber tires and tracks offer many advantages over steel wheels and tracks. They provide smoother rides, faster and easier transportation of vehicles, tractors, and implements over roads; and more economical field operations with less weight and compaction. The agriculturalist of tomorrow will need different types of tires to meet the needs for his or her operation. The tire industry provides many specialized tires and tracks for vehicles and farm equipment. However, the cost may run into the thousands of dollars each. Thus, the agricultural business person and/or operator who drives the equipment must know how to select, care for, and maintain these tires or tracks to ensure a long service life. ### CLASSES OF RUBBER TIRES There are two general classes of pneumatic tires (filled with compressed air) that are used in agricultural applications. - **Over-The-Road-Tires** are designed for road and highway use. They flex faster for high speed use and thus generate more heat than off-the-road tires. They are used for speeds over 30 mph. - **Off-The-Road-Tires** are designed to carry heavy loads and provide increased traction at lower speeds. Off-the-road-tires must be tougher to absorb shocks from rocks, stumps, and bumps; withstand cuts and abrasions; and accommodate increased torque loads. Some tires, such as large truck tires, may be designated to satisfy both conditions. ### TYPES OF TIRE CONSTRUCTION #### PARTS OF A TIRE - Tread Depth - Tread - Direction of Rotation - Sidewall - Rim - Valve Stem - Shoulder - Body Plies - Bead - Air Container ### TYPES OF TIRE CONSTRUCTION A diagram illustrates the following types of tire construction: - **Belted Bias Ply** - **Bias Ply** - **Belted Radial Ply** Within the two classes, there are three basic designs or types of tires used in most agricultural applications. They include: - **Bias Ply:** is the original tire construction design in which the ply cords run from one tire bead to the other at an angle. Alternate plies of the body run in opposite directions. This bias construction gives rigidity to both the sidewall and the tread. Advantages of bias ply tires include basic simple construction, dependable traction, and average mileage performance. - **Belted Bias Ply:** is similar to the design of the bias tire except the body is surrounded by fairly rigid belts. These belts are composed of cords which surround the tire body underneath the tread. The cords have much less angle than the cords in bias ply tires. The belts reduce tread motion during contact with the road, thus improving tread life at higher speeds. The arrangement also gives rigidity to the sidewalls and to the tread. This design improves mileage, improves traction, and provides greater tread impact resistance. - **Radial Ply:** is the newest construction design which utilizes one or more body plies with the cords running in a right angle from bead to bead. Located on the top of these body plies and directly under the tread area are two or more belts or thread plies. These belts prevent "squirm" in the tread area and provide lateral stability to the tire. Advantages of radial ply construction over bias ply or belted bias ply tires include: - better fuel mileage - greater impact resistance - fewer tire failures - smoother ride - improved thread support - quicker steering response - increased surface contact with ground or road - longer tire life - improved stability Cord belts for tires are made of rayon, nylon, cotton, polyester, and steel. Each cord and layer of cords or belt is separated by a resilient rubber. It is not a recommended practice to mix different designs of tires on the same vehicle at the same time because of the differences in the road handling characteristics, traction, etc. ### TIRE SIZE AND TYPE CODES **Passenger and Light Truck Tires:** The Tire and Rim Association and the Rubber Manufacturers Association have established specifications to standardize the different size, types, and quality of tires and rims. The new "P-Metric" system has been adopted by most tire manufacturers. It is used on most passenger and light truck tire sizes to replace the older numeric (7.75-14) and the alphanumeric (F R 78-14) systems. Basic information for the new system is stamped or molded on the sidewall of the tire. The letter "P" stands for passenger and indicates the tire is designed primarily for use on passenger cars and light vans. LT in the place of the P means light truck. Light truck tires are suitable for use in most agricultural businesses such as on farm and ranch pickup trucks and highway trailers. The number 195 represents the section width of the tire in millimeters from sidewall to sidewall. The number 14 is the diameter of the rim in inches the tire is to be mounted on. Some manufacturers still use parts of the older numeric system which gives tire width in inches for some light truck and trailer tires. For example: a 7.50/16 is approximately the same size as a LT 235/85 R16. The number 85 is the tire series; 85 indicates the tire section height is 85 percent as high as the section width. The R means radial ply design construction. A D in place of the R means the tire is a conventional bias ply tire. M/S indicates the tire has been designed for improved traction in mud and snow conditions. Ply rating is an index of tire strength and does not necessarily represent the number of cord plies in the tire as it once did. Some manufacturers may also include the type and number of plies used on the sidewall and tread areas with the ply-rating. A treadwear rating and a traction and temperature rating are comparisons to government standards. A three-digit number (200, 210, 280, etc.) is an indication of the expected treadwear life. A tire with a rating of 200 would last approximately twice as long as government standards with a base rating of 100 under normal conditions. A higher number indicates a higher quality tire which will normally wear longer. Traction and temperature ratings are designated by the letters A, B, and C. Tires with an A-rating can be operated at higher temperatures without possible failure. The load-range rating is an indication of the load carrying capacity of the tire at the recommended inflation pressure. Also included on the side wall is an indication of whether the tire is tubeless or tube-type. **Tractor and Implement Tires:** Tractor and implement tire codes for agricultural use are divided into three basic groups. R-series are used for rear traction tires on most tractors. They are also used as the front traction tires for four wheel drive and power assisted front wheel drive tractors. F-series tires are used as front or steering tires for tractors, combines, cotton pickers, etc. I-series tires are considered implement tires for use on plows, equipment, trailers, etc., that carry heavy loads. Tractor and implement tires use the basic numeric system to indicate tire size. Within each series, there are different tread designs, patterns, ply ratings, load ratings, lug angles, tire qualities, etc., to meet individual customer needs. | Type of Tire | Code | |-------------|------| | **FRONT TRACTOR** | | | Rice tread | F-1 | | Single rib tread | F-2 | | Dual rib tread | F-2D | | Triple rib tread | F-2T | | Industrial tread | F-3 | | **DRIVE WHEEL TRACTOR (REAR)** | | | Rear wheel, regular tread | R-1 | | Cane and Rice, deep tread | R-2 | | Shallow, non-directional tread | R-3 | | Industrial, intermediate tread | R-4 | | **IMPLEMENT** | | | Rib tread | I-1 | | Traction tread | I-3 | | Plow tailwheel | I-4 | | Smooth tread | 1-6 | For example: The 18.4R-38 R-1 would indicate a regular tread radial design rear tractor tire that has an 18.4-inch section width from sidewall to sidewall. It is to be mounted on a 16-inch wide rim that is 38 inches in diameter. The R between the numbers indicates it is a radial ply design tire. If there is no letter between the numbers, the tire is a regular bias ply design tire. All other factors being equal, radial rear tractor tires can increase traction for six to ten percent over bias ply tires because of a longer and wide footprint. Radial design tires also create less rolling resistance. The ply rating is still used to indicate the relative carcass or body and sidewall strength of bias ply design tires. The higher the ply rating, the stronger the tire and the greater the load carrying capacity. Radial R-series traction tires are currently using a newer star system to replace the ply and load ratings because of the differences in tire design. Tires are one, two, or three star rated within a given tire size. The more stars, the higher the loading carrying capacity. The number of stars is also an indication of the recommended inflation pressure. One star (*) tires are rated at 18 psi, ** tires at 24 psi, and *** tires at 30 psi. Some I-series implement tires may have additional information in the size code. An 11L-16SL would have an 11-inch section width, but the "L" would indicate it is a "low section height" tire. The section height is less than 75 percent as high as the section width. Standard size implement tires have approximately the same section height as section width. Low section height implement tires can carry from seven to nine percent more weight as the same size standard tire. The "SL" means it is "service limited" or that the maximum load limit is rated at speeds less than 25 MPH. Many tires require inner tubes (tube-type or TT) while others are tube-less (TL). Tube size must be matched with the tire's size for proper fit. Also, inner tubes for use in radial ply design tires flex just as the sidewalls flex and must be designed and manufactured differently than bias ply tubes. Use only inner tubes marked "Radial" in radial ply design tires. All agricultural type tires can be considered tube-type tires unless they are specifically marked "tubeless." #### RIM SELECTION To obtain proper tire performance and for safety, always use recommended tire and rim sizes. The proper rim and tire diameter sizes must be matched as well as the proper tire and rim width sizes. For example: It is possible to pass a 16" diameter tire over the lip or flange of a 16.5" size diameter rim. However, it cannot be inflated enough to position itself against the rim flange. If an attempt is made to seat the tire bead by overinflating, the tire bead will break with explosive forces and may cause serious injury or death to the operator. Tire and rim width size must also be correct so that the bead will seat properly against the flange of the rim. ### INFLATION AND TIRE DAMAGE The single greatest cause of tire damage is improper inflation. Tires will slowly lose pressure over time even without a puncture. The result is unnecessary stress on your tires, early and irregular tread wear, and poor gas mileage. No matter what brand of tires you have on your farm tractors, implements, or automobiles, they can't deliver their best performance without the correct air pressure. Properly inflated tires permit all of the tread to contact the ground, yet are not soft enough to flex excessively. #### Overinflation: Overinflated tires do not fully contact the ground. The center of the tread wears. Because the tire is more rigid, the flexing characteristics of the tire do not perform efficiently. Also, the tightly stretched carcass is much more subject to impact type damage caused by curbs, rocks, stumps, etc. #### Underinflation: Underinflated tires flex excessively every time the wheel turns. This results in high internal heat build-up and premature cord failure. Underinflation is indicated by excessive wear of the sides of the tread while the center is relatively unworn. Continuous operation at reduced inflation pressures may result in cord separation or a series of flex breaks in the lower sidewall area. While an underinflated drive tire may pull slightly better in some soil conditions, this is usually not worth the risk of tire damage that can occur in such an operation. #### Tire Inflation Rules 1. Always check and inflate tires when they are cold if possible. When tires are hot, the air is expanded thus increasing the pressure several PSI. Never "bleed" air pressure from warm or hot tires thinking they are overinflated. This results in the tire pressure being too low when the temperature becomes normal. 2. If a tire becomes low during operation, adjust the pressure to the same as other tires of the same size on the machine or vehicle. Recheck after approximately 30 minutes to be sure the pressure is still correct. 3. It is more difficult to estimate the pressure of radial design tires by visual inspection because of the way the sidewalls bulge. Use a tire gauge regularly to check tire pressures. 4. Always use a liquid-type tire gauge when checking pressures in tires with liquid ballast. Check pressure with the value stem located in the lowest possible position. 5. Never use the vapors from a LP-gas tank to inflate tires. The vapors are very explosive. They expand as the tire heats up with use. The smallest spark or even static electricity from your hair or clothing can be enough to ignite the vapors while inflating, mounting, or dismounting tires causing it to explode. One possible exception to the above rules may apply. Some equipment operators manuals and tire manufacturers often recommend that rear tractor tires be "overinflated" several PSI if the tractor is to be roaded over hard "black-top or concrete" roads for more than several miles at a time. This will help prevent excessive wear on the outer ends of the traction bars. It is recommended that the tire pressures be lowered to normal levels when the tractor is put back into normal field use. There are many other causes of tire and wheel damage. They may include: stubble wear, weathering, spinning, cuts, side wall breaks, grease and oil damage, punctures, and cord breaks from impact. Stubble from various types of crops such as corn, cotton, or shredded brush can be rigid enough to puncture a tire and/or cause fast tread wear. Rubber ages or deteriorates when exposed to direct sunlight and other elements of the weather for long periods of time. If possible, jack-up equipment, lower tire pressure and protect tires from the sun and moisture when they are not being used for extended periods of time. Excess grease, oil, and other petroleum products can also cause rubber tires to soften and deteriorate. Always avoid conditions that cause tires to spin and/or expose them to objects that may cut or puncture them. Sidewall breaks are caused when tires are operated at low pressures for long periods of time, when they are overweighted to increase traction, or when the vehicles are overloaded. Impact damage to tires and/or bent or broken rims occur when vehicles are driven over large rocks, stumps, chuckholes, curbs, etc. Tires can also be punctured by misplaced nails, glass, equipment parts, sharp rocks, bones, etc. Often it is not the puncture that damages or ruins the tire, but the sidewall damage when tires are operated with low pressures caused by the punctures. ### MOUNTING AND DISMOUNTING TIRES AND WHEELS There are many different types of tires and rims used in the agricultural industry. Each has specific procedures to safely mount and dismount them. Specialized tools and equipment are available to mount and dismount tires without causing damage to tires, tubes, and rims or personal injury. Over inflation and improper mounting techniques can cause a tire to explode with great force. It is beyond the scope of this topic to go into details on proper tire mounting and dismounting procedures. Always consult the proper operators manual, technical manual, tire industry handbook, and/or a trained tire repair person for specific procedures. Your life or health may depend upon it. ### TORQUING LUG BOLTS, WHEEL CLAMPS, AND FRAME BOLTS Checking and maintaining proper torque of lug bolts, frame bolts, and wheel clamps are just as important as maintaining proper tire inflation. As needs in agriculture have changed, equipment and vehicles have increased in size. Higher horsepower engines have increased the power transferred through the power train and tires or tracks to the ground. The total amount of weight equipment and trailers can carry has also increased. Vehicles and equipment travel at much higher rates of speed. This increased horsepower, weight, and speed has required an increase in the size and strength of lug bolts, clamps and metal wheels. It has also increased the torque required to properly tighten them. No longer will a standard lug wrench or a one-half inch drive break-over handle supply sufficient leverage to properly torque the bolts on many types of agricultural equipment. For example: the torque specifications for the lug bolts and wheel clamps for a larger four-wheel drive tractor may be as high as 500 foot/pounds. Even many smaller two wheel drive tractors require 300/pounds of torque on rear wheel lug bolts. Five hundred foot/pounds of torque is equivalent to 100 pounds of force applied to a lever 5 feet long. It is difficult, if not impossible to estimate the force you may be applying to a handle; even if there was sufficient room for a five feet long handle. It is often tempting just to use an air impact wrench and tighten bolts as much as possible. This procedure may be safe if the air supply is constant and the person can verify the strength of the impact wrench. Bolts can work loose if not tightened using the proper techniques. Lug bolts or clamps can also stretch and weaken if over torqued which may be equally dangerous. Imagine the damage and/or injury that could occur if even a small front wheel and tire came off or become loose because of improper torquing procedures. It is important to always use proper equipment and follow procedures outlined in an operators manual. ### BALLASTING Modern off-the-road machines are designed with adequate horsepower to move heavy loads under normal conditions. Slippage is the power lost due to the spinning of the traction tires or tracks on the soil surface. Rolling resistance is the power used to get the tires to roll over or through the soil. Rolling resistance increases in wet, spongy, or loose soil conditions. Traction is the effective usable power to push or pull a load that results from the machines ability to grip the soil or other surfaces to overcome slippage and rolling resistance. Traction and slippage are dependent upon: 1) tire tread or track design, 2) inflation pressure, 3) amount of contact area between the tires or tracks and the soil surface, 4) soil types and moisture conditions, 5) and the machine's weight. Often, a machine's total weight is not sufficient or is not correctly distributed for optimum traction and stability. Additional ballast or weight can help increase traction but will also increase rolling resistance. Tractor tires develop traction in relationship to the amount of weight upon them. The greater the weight, the more the lugs or tread can grip the soil and increase traction. However, there is a trade-off. Increasing weight decreases thread wear from spinning and increases traction. But, it also increases the stress on the sidewalls and power train as well as increases soil compaction. Most agricultural tractors are designed to provide maximum performance between approximately 10 and 15 percent slippage of traction tires when pulling a heavy load in average field conditions. Tire traction can be judged by: 1) looking at the tire tread pattern left in the soil, and 2) counting the number of revolutions the tires make in a given distance with and without a load (see student topic # 8201-A). - **Too Much Weight:** Clear, well-defined lug marks with no indication of track or dirt movement in moist soil means there is too much weight. - **Proper Weight:** Ballast and slippage are correct when lug marks in the center of the track start to crumble, but the outer edges are still well defined. There is no standard amount of weight that should be added because conditions constantly change. The operators manual and/or local implement and tire dealers can provide general guidelines for the weight-per-horsepower ratios for different operating conditions. It is up to the equipment owner and operator to monitor slippage and add or remove ballast as field conditions change. - **Too Little Weight:** If lug marks or tracks are entirely erased, there is too little weight. Ballast can be added in several ways. One popular method is to add water inside the rear traction tires on two wheel drive tractors and the front and rear tires on four wheel drive or mechanical front wheel drive tractors. A mixture of water and calcium chloride (to prevent water from freezing) weighs approximately 11.8 pounds per gallon. Charts are available which show the capacity of different size tires and the recommended amount of water and calcium solution to add for different conditions. Special valve stems and equipment are required to be able to pump the water in and out of the tires. A common practice is to determine the total amount of weight needed for the most severe pulling conditions. Water is added for only a portion of the total amount needed. Cast iron weights are attached to the tire rims or tractor frame for the additional weight. The cast iron weights can then be easily removed for more efficient operation when not needed for lighter field work. ### TRACK USE IN AGRICULTURE Steel tracks have been used on several designs of agriculture and industrial tractors ("dozers") for many years. Steel tracks are designed for use in muddy, rocky or loose soil. Tracks are also designed to allow a larger ground contact area thus increasing traction. However, most steel tracks are designed for slow speed rough terrain conditions at less than approximately two MPΗ. Tracked vehicles could not be "roaded" from one field to another without excessive track wear. Steel tracks and rollers represent up to 20 percent of the initial purchase price of a dozer and up to 50 percent of the repair and maintenance costs over the life of the machine. #### Rubber Track and Roller Even with the best maintenance and operating conditions, the expense and heavy weight of steel-track tractors prevented many from being used in higher speed (3 to 8 MPH) agricultural field operations. In the last few years, with the use of new technologies, research engineers have developed long wearing rubber tracks and rollers that show many possible benefits to the agriculture industry. - Continuous rubber tracks reinforced with steel cables show great promise for increasing the contact area with the ground to increase traction and at the same time reduce soil compaction. - Rubber tracks have also been adapted for use on large implements, combines, grain carts, etc., which can help eliminate severe soil compaction and flotation problems. - As tractors and equipment become larger, maximizing traction and flotation while minimizing weight and soil compaction are becoming very serious problems facing agriculturalist and soil conservationist. A diagram shows a comparison between a rubber track and a typical rubber wheel in terms of footprint. The illustrations show the results from tests that compare the average ground contact area and amount of soil compaction between two tractors of comparable size and weight. One was equipped with dual radial tires and one equipped with continuous rubber tracks. It is beyond the scope of this topic to go into details of the service and repair of steel or rubber tracks equipment. Please consult the appropriate operators or technical manuals for further information. ### ACKNOWLEDGEMENTS Dr. Joe Muller, Curriculum Specialist, Instructional Materials Service, developed and organized the information in this topic. ### References: - Consumer Tire Guide, Tire Industry Safety Council, Washington, D. C. - Farm Tire Application Guide, The Firestone Tire and Rubber Company, Akron OH. - Tires and Tracks, Deere and Company, Moline IL. - Farm Tire Handbook, Goodyear Farm Tire Marketing Department, Akron, ОН. - Farm Tire Handbook II, Successful Farming - Meredith Corporation, Des Moines, IA. - The Total Field Machine, Caterpillar Inc., Peoria, IL.