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 answers, will appear in our Commercial Tire Dealer section every other month. For complete answers, click on www.agtiretalk.com.
QUESTION: How do you know when R-1/R-1W tires need to be replaced? What rules should be followed to ensure maximum performance and why do overall tire diameters vary slightly by manufacturer?
Dave Paulk, manager, field technical services, BKT USA Inc.: A general rule of thumb is that when a tire gets below about 20% of its original tread depth, it may be time to start shopping for new tires, depending on the use of the tractor. Soil types and the amount of moisture also play a role in how effective tires are when they start wearing down. Care should also be taken to protect tires by not driving directly over stubble in the spring. Stubble damage can chip away the outside rubber in the tread area and expose cords underneath. GMO technology is great for yields, pests, wind, etc., but terrible for tires. Rubber is no match for the hardness of GMO stalks, especially after they have been in the elements all winter. The overall diameter in radial tires can differ between brands because of maximum growth rates and other factors. Metric-sized radial tires between manufacturers are generally close to the same overall diameter and rolling circumference and can be inter-changed between brands when needed. When replacing one tire that has been damaged, the tread depth needs to be matched closely with the older tires. This may require replacing a couple of tires if the older tires are 25% or more worn. When replacing tires and matching to older tires, the same load indexes should be used. Different load indexes recommend different air pressures for carrying capacity. It is best to use the same brand on an axle and match up a tire with the same brand whenever possible. With mechanical four-wheel drive tractors, make sure tire rolling circumferences closely match when using other brands. With radials, brands can usually be mixed. Different brands can be used on the front and the rear if the lead/lag ratio is within limits. If R-1Ws are used on the rear, they should also be used on the front. Tread patterns should be close to the same in order to ensure good traction and mobility. Maintaining equipment and tires regularly is important to reducing downtime and fuel expenses over the long term.
Greg Gilland, vice president, global agriculture, Maxam Tire North America Inc.: In the agricultural industry, it is how the equipment is utilized or the inherent operational requirements that will affect the tire replacement cycle. As agricultural tires are considered off-road and not U.S. Department of Transportation-regulated, there are no firm rules to determine when an ag tire absolutely needs to be replaced. In all cases, Maxam recommends utilizing ag tires for the longest possible time, regardless of the type of tire R-1 or R-1W - if the tire can be safely utilized to meet operational requirements and therefore achieve the most value for the tires in question.
David Graden, operational market manager, agriculture, Michelin North America Inc.: Natural rubber has a shelf life, much like the loaf of bread in your pantry. When it comes to replacing ag tires, we highly recommend replacing all tires across the axle with the same brand. You will find slightly different overall diameter - and even section width - measurements between manufacturers. This is due to the allowable variance in standard tire sizing. With regard to replacing all tires on both axles when one gets damaged, this is not necessary. However, you may need to adjust the air pressures between front and rear axles to avoid road loping or power hop. Road loping is typically caused when the gap between front and rear tires overcomes the mechanical ratio - even when the front power is disengaged. Power hop is typically incurred when front tires have more tractive capacity than the rear. The bottom line is that air pressure changes the overall diameter of the tire. When you also change the lug depth by replacing worn tires with new, the overall diameter of those new tires in relation to the worn tires has been also been altered.
Chris Neidert, marketing, training and development manager, ag, Trelleborg Wheel Systems: There are many things to take into consideration when considering replacing tires due to a worn tread. Application will be the main driver. If your customer is just using the tractor on very hard surfaces such as concrete or hard pan, where effective traction is not as important as the tire load carrying capability, many times you can delay the replacement decision and let the tires run down closer to a smooth tread. On the other hand, tires need to provide effective traction. If your customer’s tractor can display the current wheel to ground slippage, you can monitor the amount of slip that is being produced in real time. An acceptable wheel to ground slippage will be ranging between 5% and 15%. You can monitor slippage and once it goes above 15% on a regular basis, the tractor will start to lose traction and efficiency. This loss in traction efficiency represents an increase in fuel usage and increased time to do field work. Tire replacement should start to be considered. If your customer’s tractor is not equipped with a slip meter, once the tire gets below 25% of the original tread depth you should start to consider tire replacement. As discussed above, additional slipping will start to happen - taking more time to complete work and using more fuel.
BLAINE COX, national product manager - agriculture, golf and turf, Yokohama Off-Highway Tires America Inc.: There are a few situations in which you absolutely need to replace an R-1 or R-1W tire immediately - if you see an oblong bulge that indicates a rupture in the casing or if excessive wear has exposed belt wires or ply fabric. Those conditions are unsafe and must be addressed at once. Ozone cracking, which you can spot by a network of spiderweb-like cracks and the loss of elasticity, can also be a reason to replace tires. When it comes to regular lug wear, the right time to replace an R-1 or R-1W tire can be more of a matter of taste, economics and the kind of use your customer expects from the tire. For tires that are used in the field, watch for excessive slip. Properly inflated tires should slip 10% to 15% in dry soil. If you you can’t monitor slip, step out and look at your tire prints in the soil. Optimum slip will leave just a little crumbled soil in the center of the tire track, while excessive slip will leave a blurry print or piles of kicked-up dirt. When it comes to maximum performance, the most important thing you can do for your customer’s tires is inflate them properly. That will ensure that the sidewalls have the proper amount of flex and support, the tire’s contact patch is the optimum size and shape and that it will get the most even wear. Operating at the proper inflation pressure maximizes tire performance and tire life. Another aspect of tire engineering is the outer diameter of a tire, which can vary from one design to the next, so not all ag tires in a specific size are exactly the same height. Tread depth differences - such as those between an R-1 or R-1W or an R-2 - can also cause a difference in overall diameter
