Ag Tire Talk: The Effect of Varying Rim Widths on Radius, Traction and Flotation
QUESTION: What impact do varying rim widths have on tire radius, traction and flotation?
DAVE PAULK, manager, field technical services, BKT USA Inc.: All wheel rims should be selected based on the tire manufacturer’s recommended and alternate options for the specific tire being used. The Tire and Rim Association lists both design rim (recommended rim) and approved rim (alternate rim) widths and contours for agricultural tires.
Using a rim wider than what’s listed in the manufacturer’s options flattens the tread face and the stability of the tractor can be impacted. In hard soil, there is less lug penetration and less traction. Stress is then concentrated in the shoulder area and increases the amount of shoulder tread wear. When the tire’s beads are mounted farther apart than intended, it forces the sidewall of the tire to flex lower than normal. This creates circumferential carcass breaks and sidewall separations.
Using a narrower rim than listed manufacturer options can cause mounting problems and impede the bead from seating properly to the wheel. Increased pressure from the bead to the rim flange can cause possible bead and sidewall separation to the tire and premature rim failure. The tread of the tire becomes rounded and tread wear is concentrated in the center of the tire. Therefore, traction in the field is greatly reduced. We do not suggest going outside listed manufacturer parameters for any reason.
In the right circumstances, it makes perfect sense to change sizes for more flotation, less compaction and more weight carrying abilities. When changing wheels and tires, it is important to ensure that the tires match up to the wheels for load, speed and inflation. This will minimize any future problems with wheels and tire failures.
JIM ENYART, technical manager, Ceat Specialty Tires Inc.: Recommended rim widths are very specific due to the bead seat angle that is built into each ag tire. The recommended rim will have the best bead-to-bead distance for proper seating, maximizing sidewall deflection and providing the best weight distribution within the footprint. This also allows the tire to provide maximum traction and flotation.
If you venture outside the above parameters, the bead may seat, but the carcass of the tire becomes distorted. As you proceed farther from the recommended rim, distortion increases and impacts tire performance and longevity. Traction — and possibly flotation — will be reduced when mounting tires on incorrect rim widths.
When the angle of the rim and bead are not close enough to withstand high torque situations, the tire can demount or slip on the rim.
It’s all about matching angles for the best bead-to-rim seating. Correct bead seating allows the tire to withstand heavy loads under high-torque applications, while maximizing sidewall deflection, footprint, flotation and delivering optimum traction. In short, we always recommend staying within tire manufacturer wheel parameters.
HARM-HENDRIK LANGE, customer solutions engineer, Continental Specialty Tires: Agriculture tires have flexible carcass construction to enable a wide footprint with good traction and low inflation pressure for low soil compaction. This flexibility, especially for tires with high aspect ratios, allows the tire to operate within certain variations in rim width.
Changing or modifying the rim width, along with the flange height, could impact tire performance, since the deflection area in the sidewall will change. A change in the deflection area will have an impact on the ground contact area, affecting traction and flotation. And a different rim width could have an impact on the mounting process, increasing the stress in the bead area.
There are other factors to consider when combining rims and tires. A more narrow rim reduces the tire’s ability to transfer side forces while curving on roads and driving on inclines. It also causes more bending stress in the tire sidewall, especially directly over the bead section, which can bring about earlier aging and cracking, particularly when deflection on the sidewall is high. And a more narrow rim limits the tire’s ability to use the lowest possible inflation pressure for maximum traction and reduced soil compression.
GREG GILLAND, vice president, global agricultural program, Maxam Tire International: All agricultural tires are designed by size to fit on a certain rim seat. Depending on the equipment design or need, rims also are made in various widths to allow the tire to drive or steer the vehicle and provide the best load carrying capability.
The key to a tire successfully carrying the load and delivering expected performance is the capability of the air in the tire to suspend the load and allow the tire sidewall deflection to push the tire footprint, which delivers the rim pull or torque to move in the desired direction.
Each tire manufacturer should offer a recommended wheel width, with acceptable alternative wheels or rim widths that allow their tires to deliver the optimal performance. Selecting the right wheel and tire combination will maximize equipment performance by optimizing load carrying capability and delivering the necessary power to plow, plant, harvest or spray crops.
DAVID GRADEN, operational market manager, agriculture, Michelin North America Inc.: A recommended rim always optimizes traction and flotation. However, all acceptable rims listed by the manufacturer will provide adequate performance.
It’s important to note that wheel width has a bigger impact on lower-profile tires. Tires with a higher sidewall aspect ratio will see less bead area stress than those with low sidewalls. Take, for example, our VF 480/95R50 Yieldbib vs VF 480/80R50 Yieldbib. The sidewall height on the 480/80R50 is about three inches shorter. Due to the larger deflection zone, the taller sidewall will be much more forgiving with a narrower wheel than the lower sidewall.
The tires of today are designed to perform at their maximum potential on recommended wheels. If you choose a narrower wheel, you may change the performance and longevity of your customer’s tire investment. We highly recommend using the recommended wheels, as this will ultimately result in increased traction, better flotation, reduced soil compaction, improved fuel efficiency and even longer tread life. It will give end users a lower total cost of ownership and will add more to their bottom lines.
SCOTT SLOAN, ag product manager/global LSW, Titan International Inc.: With the introduction of increased flexion (IF)/very-high flexion (VF) technology, testing was done to see what performance improvements could be gained with regards to tire longevity. What was determined is that IF/VF tires running on wider rim widths actually saw an improvement in durability. Moving the beads out from the centerline moves the stress and deflection from the beads up into the sidewall, which is designed to flex. This results in enhanced longevity.
In some cases, wheel widths that have not been designated as approved alternates can be selected. As an example, the rim width for a size 650/65R38 is 20 inches, with an alternate wheel being 23 inches. Many flotation sprayer conversions using size 650/65R38 conventional tires have been installed on 18-inch wheels. An issue may occur if that customer decides to convert from standard 650/65R38 tires to IF/VF 650/65R38 tires, installing them on 18-inch wheels. Running the tire at lower inflations and higher deflections on a narrow wheel, in this particular case, will cause premature failure and should be avoided.
My suggestion is if a customer is looking at moving to tire technologies like IF/VF, research current size and wheel recommendations. Wheels and tires work together. To ensure that your customer has the best chance of success, start with a little research.
NORBERTO HERBENER, OE applications engineer, Trelleborg Wheel Systems: When talking agricultural tires, each tire manufacturer makes recommendations for an ideal rim width, in addition to two additional size options to give operating flexibility.
This recommended rim width is calculated by using standardized formulas agreed upon by all tire manufacturers within the Tire and Rim Association. It is determined by three components: tread width; aspect ratio; and technology, such as bias, radial, IF technology or VF technology.
The choice of suggesting what rim to use does not end here, as there are several rim pro les to consider. In certain sizes, these can play a role in influencing the ease of mounting the tire on the rim.
In addition, the rim profile used by the equipment manufacturer will be in uenced by specific axle and space design. With an IF or VF technology tire, the sidewall is reinforced and stiffer when compared to a conventional tire. The recommended rim size is always the next available wider size. If you’re thinking of changing tire sizing on any equipment, as a general rule of thumb, always check on the specification
NICK PHILLIPPI, national product manager, Yokohama Off -Highway Tires America Inc.: Just as important as rim width, in some cases, is rim type, which would be speaking to the rim flange design and the drop center design.
When changing sizes, you have to be aware of the disc offset of the rim — a measure of the relationship between the centerline of the wheel and its disc or mounting surface. Offset is important to make sure your customer’s tire has enough clearance from suspension parts, fenders or even the body of his equipment. If you’re going with a wider tire, you may very well need a rim that is further out for clearance and will need the off-set of the disc to be more positive than the original wheel.
Finally, make sure that the rim and wheel assembly is capable of carrying the load your customer will be putting on it. Recommended wheel widths are very important when it comes
to helping your customers get all that they have paid for in a tire. Sure, you may use a narrower or secondary recommendation. But unfortunately, your customer could lose a variety of benefits and may not even know it.
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.