AG Tire Rolling Resistance IMPACT

 

AG TIRE TALK KEY TAKEAWAYS

BKT: “Rolling resistance is significant in transportation and engineering as it impacts fuel efficiency, energy consumption, and overall performance of vehicles and other wheeled equipment.”

MICHELIN: “In general, rolling resistance is the main contributing factor for fuel consumption.”

MAXAM: “Rolling resistance is the force that acts against the forward motion that tire must transmit against the ground when a forward force or engine power is applied.”

YOKOHAMA TWS: “Choosing the correct tire tread design can greatly influence reducing your rolling resistance which will reduce your fuel consumption.”

PRECISION INFLATION: “For the best Fuel Economy for Field and Road and the least Rolling Resistance, you need 2 opposite tire pressures- High Pressure for Road Transport & Low Pressure for Soft Field Performance.  All this can be accomplished with a Central Tire Inflation System.”

YOKOHAMA OFF-HIGHWAY TIRES AMERICA: “In the field, a farm tire encounters increased rolling resistance when it creates a trench and has to push soil out of its way to move forward, or when it slips as it tries to gain traction. That means overinflated tires, narrow tires or tires with poor flotation encounter greater rolling resistance, especially in wet or soft soil.”

 

Michelin Ag
David Graden: Operational Market Manager – Agriculture

Rolling resistance, as it relates to Agriculture tires, is far different from rolling resistance related to vehicles primarily working on hard surfaces. In general, rolling resistance is the main contributing factor for fuel consumption.

In both hard and soft surfaces, you’ll want to optimize your air pressures so as to maximize your fuel consumption but preserve the tread life of your tires at the same time.

For Ag tires, specifically, a higher pressure will produce a smaller footprint on the ground. Of course, this will generate the best fuel economy…on the road.

When you enter a field, however, that same small footprint won’t roll over the soft soil very well and, alternatively, generates very poor fuel economy. Historically, farmers and Ag tire manufacturers, alike, have had to find a happy medium between the two. That is, set the air pressures for the fastest speed the machine will run down the road and to carry the greatest weight it will operate in the field. Michelin answered this happy medium by inventing IF/VF Tire Technology in the early 2000’s, which is an industry standard today.

The question remains, how do we optimize our tire’s air pressure to result in maximum fuel economy, while preserving or improving performance? The answer is, Michelin owned PTG central tire inflation system coupled with the Michelin Evobib!

PTG systems allow a machine operator to preset air pressures based upon the machines activity (i.e. field operation with implement, roading, hauling, etc.) with a simple push of the button. Without stopping the machine, this system will inflate or deflate the tires in preparation for the next activity. Its very design is to optimize fuel economy on the road while also optimizing fuel consumption, traction and floatation in the field. To take it a step further, Michelin created the Evobib Tire, with a unique tread designed to significantly reduce the tire’s contact patch on the road and maximize the contact patch in the field, therefore, amplifying the benefits of the PTG system.

Many American farmers today consider their fuel consumption a simple cost of doing business. However, what if they could reduce that fuel consumption by as much as 10%? That could be a large dollar amount added to the bottom line!

To learn more about PTG, Evobib or even find recommended air pressures for your current set up, reach out to your local Michelin Ag tire dealer and request a visit from a Michelin Ag representative.

 

Yokohama TWS
Chris Neidert: AG Marketing, Training & Development Manager for Trelleborg & Mitas Tires – North America

Let’s establish some kind of definition for “Rolling Resistance”. Rolling resistance is the resistance to the force your tractor must develop to make its tires move on the ground. This resistance is directly proportional to the weight exerted on all the tires of your equipment, whether or not these are drive tires.

The force that resists the motion of a body rolling on a surface is called the rolling resistance or the rolling friction.

Let’s say this another way, when your equipment (tractor) is not moving, its weight exerts a downward force which is met by the force generated by the reaction of the ground. As the tire and the ground are distorted, the tire sidewall flexes while the ground compresses, until both opposing forces become equal. The tire’s rolling resistance therefore results from these two distorting movements.

To show some examples of rolling resistance on a hard surface, check out these simple examples:

Example 1

Railroad cars have steel wheels. On the track, they encounter almost no rolling resistance, because neither of the two components (the steel wheels or the steel track) undergoes any distortion, whatever the load in the car. The traction needed to move the railroad car is therefore very small.

Example 2

Let’s take a look in your garage at your personal vehicle. It has 4 flat tires. It would require a large amount of traction to move it, whereas you would have been able to push it by hand if the tires had been properly inflated.

How to Lower Rolling Resistance / Reduce Fuel in Transport Mode
What tactics can a producer use to minimize energy loss?

Running the correct air pressure will be a huge influence on rolling resistance and minimizing energy loss. We at Trelleborg & Mitas are a huge proponent of running at field pressure and a road pressure.

You can see the two tire pictures below. They are depicting field pressure and road travel pressure. The picture on the left is field pressure and you can see the sidewall squatting. This is because it is being operated at slow speed (5 mph) which enables you to run less air pressure to carry the load. When you get out on the highway you need to increase that air pressure. The higher air pressure at road speed helps the tire to not deform and it reduces heat buildup. The higher pressure reduces rolling resistance and energy loss.

       

Let’s use a load table to further explain.

This is a load table for a 480/80R50 R1-W Tractor Tire. Let’s use an example that the tire must carry 8,000 lbs. We can calculate field pressure and road pressure. We will use 5 LT S for the speed. LT stands for Light Torque and S means we are using a single application and 5 is the speed in MPH. I have put a circle around the approximate load in our table we will use 8,130 lbs. since it is close and not below our target load. We follow that column up until we intersect the psi line. We can run 15 psi in the field for our application. When we go out on the road for transport mode, we will look at the 30-mph row. That will be our road speed. We follow the column up until it intersects the psi line. We will use 23 psi for road speed. Using these two pressures will give you the best of both worlds. Reinforcing that higher air pressure at road speed will reduce the tire’s deformation. This will reduce energy loss and reduce rolling resistance. Fuel economy will improve.

Use of a Central Tire Inflation System (CTIS) will work perfectly for our above example. If that system is not available, we would suggest running the air pressure at the higher number.

What specific tire attributes can help reduce rolling resistance.   Lower Void Ratio Tread Design

Choosing the correct tire tread design can greatly influence reducing your rolling resistance which will reduce your fuel consumption. Shown below are three different tread designs. Tread #1  is showing a very deep lug tire or in some terms it has a very high void ratio meaning there is a lot of space between the lugs. Treads #2 and #3, are vastly different. They have a very low void ratio meaning the lugs or the spaces between the lugs are very small. This will contribute to reduced rolling resistance and improve your fuel economy, tire ride, and tire life.

 

1.    2.         3.   

Depending on your application, you may need tread #1. If you need a lot of traction or operating in a muddy condition, tread #1 will be the choice. However, if your application is mostly road travel or operation, tread #2 and #3 will be your best choice. Shown below are some vehicles or applications that will benefit from the lower void ratio tread designs. Roadside mowing, yard work and tanker transport are applications that require very little traction and spend most of their time on the highway. This equipment and/or applications will benefit from a low rolling resistance tire.

                

 

Maxam Tire International
Greg W. Gilland:  Vice President Global Agriculture

Rolling resistance is used to explain the physical reaction between two objects in contact acting against each other. In the case of all tires, but specifically in AG tires, it is the force that acts against the forward motion that tire must transmit against the ground when a forward force or engine power is applied. There are three forces that the AG tire must overcome to move the tractor in the working direction forward or in reverse (this is true in all tire applications):

• X Force is the forward or backward force to transmit the engine torque.
• Y Force is the lateral forces caused by the side-to-side forces as the tire deforms or achieves “Plastic Deformation” due to the air pressure required to carry the weight, in relation to the Z force or vertical load flexing.
• Z Force is the vertical force caused by the suspended load or vehicle load acting on the tire.

The X Force in the above diagram is the applied force that transmits the engine torque or power which overcomes the rolling resistance also known as tire slip, providing the forward or rear motion to move the machinery. “Plastic Deformation” is the temporary (at times permanent) surface distortion that can occur to the ground. For example, when the tire compresses, it “deforms” the sidewall to flex as it stretches under the vertical load while in contact with the surface. That surface or ground in turn reacts to such force and either changes temporarily or permanently based on the vertical, lateral, and forward forces applied. For example, wet ground or muddy soil can be temporarily deformed, where a hard surface such as concrete is permanently formed. As the tire engages with a given contact area, whether that is loose soil, packed soil, gravel, rocks, or paved surfaces, the force required to overcome resistance to the tire is called rolling friction or drag, which is termed the “rolling resistance”.

The evolution from wood or steel wheels to rubber coated wheels and eventually to rubber inflated tires occurred due to the inherent flexibility rubber exhibits in its ability to transmit the necessary energy to overcome rolling resistance and move the tire forward despite the tire deformation or bulge exhibited when under heavy load. Rubber transmits energy or torque which allows forward motion efficiently overcoming the rolling resistance that acts as a “resistant counter energy” pushing back. Rubber tires experience a physical reaction called “hysteresis” which generates heat and is the result of repeated cycles of rubber deformation (flexing) and recovery with every tire rotation while engaging the above three dynamic forces (X-Y-Z). Therefore, the “hysteresis” effect is both a positive element that permits the forces acting on the tire to allow forward motion while accounting for the energy loss or heat generated by the rolling resistance between the two engaged surfaces of rubber and ground.

Rubber also contains “viscoelastic” characteristics that allow for the rubber tire to deform against operating surface in contact and return to its original condition repeatedly without material failure due to heat under given operating conditions ensuring reliability and endurance. There are other factors that can influence how a tire will perform beyond it’s “hysteresis” or rolling resistance, this includes the surface conditions like the roadbed that can affect the surface adhesion or deformation between the contact areas (tire vs road/ground soil) in summary: the looser the material the greater the friction between surfaces.

Unfortunately, farmers and growers cannot change the physical nor structural elements of their tires to overcome the “rolling resistance” that is inherent in any tire operation. However, farmers can implement the below best practices to achieve improved tire performance and mitigate the impact of rolling resistance:

• Inflate their tires to the correct cold inflation pressure based on the axle load and required work speed so the tire can absorb the heat and overcome the hysteresis.
• The right air pressure will minimize ground compaction and reduce the “Plastic Deformation” of the soil or ground.
• Greater crop yields will be achieved if soil compaction can be minimized by using the best tire footprint based on the right inflation pressure.
• The right air pressure will improve tire wear and reduced sidewall deflection giving the optimum tire gross flat plate or footprint while minimizing hysteresis or rolling resistance.
• The right air pressure will ensure the tire can transmit the forces necessary to overcome rolling resistance, allowing improved fuel efficiency and reduce tire slip.
• The right air pressure will ensure greater productivity in the field as the tire’s footprint and traction will deliver increased traction, overcoming the rolling resistance required to work the field efficiently.

MAXAM’s agricultural product range has been engineered and designed to ensure the optimal contact patch without compromising flotation or traction while ensuring maximum efficiency to overcome any inherent rolling resistance.

 

BKT USA, Inc.
Dave Paulk:  Manager Field Technical Services

Rolling resistance, also known as rolling friction or rolling drag, is the resistive force that opposes the motion of a rolling object over a surface. It primarily occurs due to the deformation of the tire and the surface it rolls on. Smoother surfaces typically offer less rolling resistance compared to rough surfaces.  Rolling resistance increases as torque and speed increases.  This is why it is important to run proper air pressures in the field to reduce slippage (loss of efficiency) and gain fuel economy. It is equally important to run the correct air pressures on the road to reduce rolling resistance (for fuel consumption) and possible damage to the tires.

Factors that contribute to rolling resistance are the deformation of the tire when rolling and under load, deformation of the surface the tire is traveling on, and movement below the surface. Higher loads or under-inflated tires can increase rolling resistance because they cause greater deformation. This deformation requires energy, which is dissipated as heat, creating resistance.  Other factors that play a part in this are air, weight, diameter of the wheel, and mechanical parts such as bearings. Temperature also influences rolling resistance. Some studies have shown that rolling resistance decreases as temperature increases up to a certain threshold (approximately 90 degrees F).

Rubber is not a perfectly elastic material. The primary cause of rolling resistance is called hysteresis.  This is the deformation of the tire that occurs under a load because it doesn’t decompress as quickly as it compresses. This causes a lagging decompression effect on the back side of the tire as it turns. This means that the load distribution on a tire is not uniform, and more of the resistance is on the front side of the tire than on the back. As a tire turns under a load, it is continuously running through these cycles of compression and decompression. This generates heat and is a cause for rolling resistance. This is a reason that silica, rather than carbon black, is being used in some low rolling resistance tires to minimize hysteresis.

Tread compounding and tire construction can increase or minimize rolling resistance. There are different compounds used for different surfaces and various applications. Some are compounded to reduce heat, some are made with chip and chunk resistance, stubble damage resistance, and friction resistance compounds. The body construction of a tire is important depending on the application. Radials tend to run cooler on the road than bias tires. Radials can run with more deflection and traction and less slippage in the field. Rolling resistance causes heat. The less heat a tire creates, the better for the casing. Belt packages used in tire construction can minimize rolling resistance. Most farm tires are made with nylon belts. BKT has rolled out several tires made with polyester belts for improved rideability and to minimize rolling resistance.

The materials and design of the tire or wheel can influence the degree of rolling resistance.

The tread thickness and shape affect rolling resistance. The thicker and more contoured the tread, the greater the rolling resistance. Hybrid tires (lower void to ratio design) can be used with better results where highway usage is high, but you give up traction in the field. Chevron style farm tires give the best traction in the field but have higher rolling resistance and rate of wear on the road. It all depends on where the tires are used and the application they are used in.

Central Tire Inflation Systems (CTIS) are being looked at and/or used by major implement manufacturers. These systems allow the user to increase air pressure or decrease air pressure based on the surface and application. The correct amount of air must be used to carry the load and handle the speed. In the field, the speed is slower and lower air pressures can be used for a larger footprint to gain more traction and minimize soil compaction. On the road, the speed is faster. Higher air pressures should be run to carry the weight at speed and have a smaller footprint to minimize rolling resistance and maximize fuel savings.

Rolling resistance is significant in transportation and engineering as it impacts fuel efficiency, energy consumption, and overall performance of vehicles and other wheeled equipment.

 

Precision Inflation, LLC
Ken Brodbeck: VP Technology

Rolling Resistance is caused by internal and external forces that resist a tire from rolling.

There are 2 major sources:

1. Internal friction or hysteresis inside a rolling tire:
   1. Bias tires have internal friction due to cross ply construction and take more power to roll.
   2. Radials have less internal friction due to radial plies; and therefore, have better fuel efficiency and less internal rolling resistance.
2. Rolling resistance on a hard paved road is minimized by adding more pressure to the tire to reduce the tire deflection.

A large VF tire sidewall bulge is detrimental during road transport!

Moving into the field with a high pressure tire will cause sinkage, vastly increasing rolling resistance. This is called the bulldozing effect.

To reduce soil rolling resistance, one can:

1. Increase footprint by reducing tire pressure to the minimum allowed by the tire type, axle load and speed.
2. Use IF or VF tires to allow higher deflection and lower pressure than standard tires.

Use larger tires and/or add duals or triples

For the best fuel economy for field and road and the least rolling resistance, you need 2 opposite tire pressures!

High pressure for road transport & Low pressure for soft field performance.

Today you suffer from either:

1. High tire pressures for the road, but pay a large penalty in the field.
2. Low pressure in the field and burn more fuel and poor steering on the road.

With CTIS from Precision Inflation, you have the best of both worlds!

Road Transport with High Pressure provides:

1. Best fuel economy with minimal sidewall deflection.
2. Longest tire life, they last 20 to 30% longer with minimal tread scuffing.
3. Cooler tires provide longer tire life.
4. Less sidewall bulge gives crisper steering response for safer driving on public roads.
5. Higher transport speeds (Up to 40 mph), than 20 – 25 mph for rubber tracks.

Lower Field Pressures provide:

1. Larger footprint = better flotation and less bulldozing = Best fuel economy
2. Larger footprint = More traction & Less slip = less ballast required
3. Lower Soil Compaction = Higher yields
4. Less soil rutting and soil erosion
5. Better water infiltration

 

Yokohama Off-Highway Tires America, Inc.
James Crouch: National Segment Manager—Agriculture and Forestry

Rolling resistance is the opposing force that a tire encounters as it tries to move forward. The more rolling resistance your tires encounter, the more energy is wasted trying to overcome it—your fuel consumption increases and your tires may build up heat. It is important to note that all tires encounter some amount of rolling resistance, regardless of whether they are on drive axles or free-rolling ones.

Rolling resistance sounds simple at first, but it is actually a complex set of reactions between a tire and its environment—and the rules are different depending on whether you’re driving on soil, mud or pavement.

In the field, a farm tire encounters increased rolling resistance when it creates a trench and has to push soil out of its way to move forward, or when it slips as it tries to gain traction. That means overinflated tires, narrow tires or tires with poor flotation encounter greater rolling resistance, especially in wet or soft soil.

Your best bet for reducing rolling resistance in those conditions is maximizing flotation and traction. That means operating at the lowest appropriate inflation pressure for your speed and load. Choosing wider tires or duals is the next step, and mounting VF tires and operating them at the low pressures they’re capable of is the gold standard.

On the road, the situation is almost opposite. You want to reduce friction between the tire and the pavement with a smaller contact patch and less deformation in the tire—basically, more inflation pressure.

Tread pattern can also impact rolling resistance. Deep lugs with lots of space between them—just what you want for traction in soil—can increase rolling resistance on hard surfaces. If you do a lot of roading with your equipment, you might want to consider some of the new hybrid tread patterns like the curved block treads on the Alliance 550 or Alliance 363. Those designs offer more biting edges for traction in the field while decreasing the rubber-to-void ratio for a smoother ride and reduced rolling resistance on the road.

Many farmers are put in a bind by rolling resistance because they often have to operate extensively both in the field and on the road. If you do a lot of both, VF radials and a central tire inflation system (CTIS) unit could be a very worthwhile investment that pays off remarkably quickly in better performance, lower fuel bills, and longer tire life. You’ll get less soil compaction and be able to run more quickly on the road, too.

Even without a CTIS setup, a set of good VF or flotation radial tires can go a long way toward reducing rolling resistance and increasing your efficiency, while also reducing soil compaction at the same time.

 

All information is provided in this blog solely to provoke thought. All deductions made from information on this site must be confirmed by Certified Ag Tire Dealer & Tire Manufacturer before use. Ag Tire Talk does not recommend anyone conduct tire service work with exception of Certified Ag Tire Dealer Professionals.