4WD Tractor TRACTION:  Pulling 550 hp Implement

4WD Tractor TRACTION: Pulling 550 hp Implement

Below is question posed to tire manufacturers from Illinois:

  • In 4WD Tractor application, if implement requires 550 hp and standard duals are not providing adequate traction (can’t go wider with triples), what is your recommendation and how does it compare to tracks on transport & field speed?

Precision Inflation, LLC
Ken Brodbeck: VP of Technology

How to make your 4WD Tread Lightly and Pull Like a Locomotive!

An implement requiring 550 hp is definitely a heavy tillage requirement and demands the tractor be set up specifically for this high draw-bar application.

The tractor must have all three attributes properly set in order to provide comparable draw-bar pull to track machines:

  1. Tires:
    1. Base or standard tires may need to be up-sized to wider and higher load capacity tires
    2. Standard 620 or 710 width tires should be replaced with IF 800/70R38 for the widest and longest footprint possible
  1. Tractor Ballast:
    1. For heavy tillage, 4WD tractors require more ballast
    2. If 4WD wheel slip is over 8 to 10%, more ballast is required
    3. Typically, the rule of thumb is 105 lbs. per engine horsepower
    4. 550 hp x 105 lbs./HP = 57,750 lbs.
    5. Weight split should be 55% front and 45% rear for Ag Applications
    6. Front weight = 31,800 lbs.
    7. Rear weight = 26,000 lbs.
    8. Minimum PSI with IF 800/70R38 tires
      1. Front = 9 psi
      2. Rear = 6 psi
    9. If this is an extreme traction application, most tractors can be ballasted to 60,000 lbs. using the same 55/45 weight split
  1. Tire Pressure:
    1. Quite often the implement or tire dealer will over-inflate the original tires OR use the same smaller tire psi for the larger tires
    2. Over inflation shrinks the footprint and makes the tractor prone to power hop and higher wheel slip
    3. The tractor needs to be weighed on a scale or estimate weight using the tractor manufacturer ballast calculator to determine both front and rear axle loads
    4. Tire pressures then need to be set 1 to 3 psi above the minimum tire pressure unless the machine has a tire inflation system that allows the tires pressure to be maintained daily
  1. Speed:
    1. It is important to note transport speed differences between tires and rubber tracks with heavy hitch loads
    2. Often, rubber belt tractors have speed limits for weight and distance in transport. Tires do not have these limitations.  See rubber track machine advisory placard below:

Bottom Line:

Once you have completed the above 3 steps, the 4WD tire tractor will walk softly and run right with its rubber belted cousin with no problem- just like in the photo below!

And with a $100,000 lower price tag.

 

Camso
Jeff Staab: Product Line Manager – Track Systems

Farming equipment has become extremely specialized to respond to the numerous application requirements of today’s agricultural industry. For the high horsepower tractor range, original equipment manufacturers offer, direct from the factory, vehicles that are equipped with either tires or tracks. As machines keep getting bigger and faster and they pull larger implements, we’ve seen increased demand for tracks from the market. For end-users, the mobility of tracks in many applications remains a key differentiator.

Why Tracks to Increase Traction?

High horsepower tractors have to pull implements at various soil depths, in addition to completing multiple functions in a single pass in the field. Combine this with the need to complete these tasks at higher speeds and/or in as fewer passes as possible, tracks are helping farmers get the work done efficiently, especially when dealing with soft field conditions. In such conditions, performance is in the 1-5% slip range for tracked tractors due to longer and larger footprint, while duals will run in the 8-12% slip range. Slip reduction helps to maintain higher speeds in the field and to take advantage of the tractor and implements’ high performance.

Farmers appreciate the ride quality in the field with the tractor on tracks: they experience less vertical bouncing and no power hops. While they have to give up some ride comfort when roading, they like the narrower transport width going down the road, only 36 inches of track on each side of the tractor, making it more than four feet narrower than a tractor equipped with duals.

 

Maxam Tire International
Greg W. Gilland:  Business Development & Ag Segment Manager

Each agricultural operation requires equipment designed to maximize the pulling or transmission of a tractor’s horsepower (HP) to pull the desired implement through the field.

4WD tractors using tracks have the advantage of a constant footprint on the soil due to the length of the track and available contact footprint over the soil.

The larger the 4WD tractor (increased horsepower), the larger an implement the 4WD tractor can pull.

The options available for ag tires employed on larger 4WD tractors to transmit the machine horsepower, increase traction and ensure the required flotation (as compared to 4WD tracked tractors) are summarized below:

 

In the case of 4WD tractor applications, the choice of machine brand and horsepower available will dictate the options or size of tires that can be employed to deliver the traction expected to pull large implements.

Agricultural tires are designed based on their size geometry, materials and air chamber to carry a certain amount of weight at a given ground speed and to fit a certain wheel base or equipment.

In 4WD tractors the on-going challenge is to reduce the size or width of the tractor despite the fact, that with larger implements on the design board, more horsepower is being applied to all new 4WD tractors coming to the ag market. The below chart created by New Holland for the T9000 summarizes some of the width challenges and solutions offered by various tire options:

One solution, that has been tested with successful results, is to convert a tractor to a larger diameter VF Tire that simultaneously provides the tractor with reduced width solution, greater traction (tread length) and lower soil compaction (air pressure):

Provided below is a table comparing the above tires in terms of load carrying capacity in equivalent 4WD tractor applications based on tire specifications provided by both the Tire and Rim Association (TRA) and the European Tire and Rim Organization (ETRTO):

In summary, when challenged with a 550 HP tractor that needs greater pulling power at reduced widths (no triples – less than 14 feet) convert your tractor to larger diameter tires that can be used in duals giving you greater traction, footprint and reduced machine width. VF Technology continues to bring new solutions that are re-defining the use of tires to meet the growing challenge of larger, more powerful tractors.

When you compare the advantages of tires to tracks, tires are easier to maintain both in terms of mounting, impact of tracks on overall machine weight, vehicle maintenance and the overall fuel efficiency of the tractor. Machine speed and fuel consumption will be based on the load the machine is pulling either in the field or on the road whether with tracks or on tires.

Maxam Tire is actively working to develop VF Technology ag tires to meet the evolving and increasing weight demand of the next generation of ag equipment, with our first VF tire solution being our Agrixtra N (N for narrow) high clearance sprayer VF 380/90R46, with 4WD tractor VF technology coming to market over the next few years.

 

CEAT Specialty Tires Inc.
Jim Enyart: Technical Manager

John Deere 9620R Example

Weight
The first thing to do is determine the actual gross weight per axle. The Base weight of this tractor model is 43,420# and the engine horsepower is rated from 370 to 620 hp. We have to assume we have the 620hp engine.

Ballast
The minimum recommended gross weight should be 62,000# with 60% of the weight on the front axle and 40% on the rear. You need to add a minimum of 18,580# of additional weight via suitcase, axle or wheel weights. If adding weights does not accomplish the gross weights or weight distribution, you can add weight via liquid ballast.

Inflation
Check your inflation pressures on all tires. Normal inflation pressures for this setup would be 10psi in the front and 8psi for the rear tires.  You may be able to lower your inflation pressures but you need to consult the tire manufacturers’ load and inflation tables before you do this. If the gross weight and the distribution is correct and traction is still an issue you should add additional weight approaching a gross weight of 74,400# with the appropriate distribution. This additional weight gets you to 120#\ hp.

We have no information concerning additional weight to the drawbar that would be exerted by our implement so minimal consideration will be calculated into our recommendations.

In Sum
Setting up this tractor with the gross weight at 120#\hp with the correct distribution and correct inflation pressures should provide more than adequate traction.

If that is not the case, another option to consider would be renting or borrowing a smaller implement that has lower power requirements. If this situation is a normal, regular operation you might consider replacing your tires with IF or VF type tires that will provide longer footprints, increased flotation, and increased traction.

 

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

Managing traction is important to controlling costs and efficiencies on a farm. Too much tire slippage can increase fuel and labor costs. The more lugs that can be put on the ground, the better the traction and performance will be. When high horsepower tractors are used with heavy implements, higher air pressures may be required to support the increased weight. Higher air pressures in standard rated tires can lead to less traction, more tire slippage, and a greater increase in soil compaction. Having the ability to reduce air pressures without damaging the tire will give a larger tire footprint and better traction.

Tires with IF and VF technology may help with traction and lead to less tire slippage and better flotation. IF tires are rated to carry 20% more weight at the same air pressures as a standard tire. VF rated tires are rated to carry 40% more weight at the same air pressures as standard tires. If a tire can carry the same weight at 20% to 40% less air pressure respectively, this allows for a larger (wider) tire foot print with more of the tire and lugs on the ground for traction. This allows less slippage and fuel savings. Tires provide better traction as their inflation pressures are decreased. IF and VF tires enable a tractor to carry more weight on the road without having to widen the tractor with triples. They can be used to minimize soil compaction where important. Looking at these tires to replace standard rated tires would be a first step in solving this problem.

When comparing tires with tracks for traction, there are pros and cons with both. Tracks provide more traction and flotation in wet soil and tracks have a longer foot- print. Tracks generally work with less slippage, about 5% compared to 8-15% for tractors. This should give tracks the advantage of pulling heavy equipment where triples can’t be used. Field speeds with tracks should be equal to, and maybe a little better, for tracks in this proposed application.

Often times, farms are scattered, and tractors must be transported on the highway. Pneumatic tires work better with this application.  Another question is the cost of operating a tractor with tires vs. tracks.  The cost of maintaining the suspension on a tractor with tracks is expensive compared to that of a tractor with tires. On a tractor with tires, you basically only have to worry about tires, wheels, and hubs. Tracks are more expensive than tires and there are many more moving parts on a tractor with tracks.

As a comparison, if tires can be used and give the required traction, they are much less expensive to maintain. They ride and handle better, and generally last longer than tracks in highway use.  While there advantages for tracks, the farmer must decide what is best for his application and what costs he can live with.

 

Trelleborg Wheel Systems
Norberto Herbener: OE Applications Engineer

Every farmer strives for the highest efficiency on power and torque transfer from his tractor to the ground. He seeks the lowest slippage, lowest fuel consumption, lowest compaction, and fastest speed possible. Not all conditions can be achieved, yet many combinations can be applied to meet proper needs. Each element must be approached step-by-step.

Ballast

First, we consider the transfer of power to the ground. It begins with balancing the total tractor weight and its power (as the weight distribution depends on tractor power). There are general rules to follow when determining this balance. Heavy tillage must consider between 100 to 120 pounds per tractor engine horsepower. In this case, a 620 hp tractor would need between 62.000 to 75.000 pounds of total tractor weight. As for weight distribution between front and rear axle, it will depend on how much down force the implement applies to the rear axle. Broadly speaking, a starting point of 55% front-45% rear and up to 60% front-40% rear is the right point.

Inflation Pressure

Secondly, focus on how to transmit power to the ground. A track system does not require any adjustments; but remember that the rubber track must be tensioned well, to avoid slippage on the wheel. Tires, on the other hand, must be adjusted; to monitor inflation pressure (per the tire manufacturer recommendations). Once the correct weight for the tractor has been established, we may define the correct inflation pressure, depending at what speed we intendent to drive the tractor.

Speed

On conventional tires, (not IF or VF technology) the load capacity increases when we reduce the working speed (at same inflation pressure). That being said, it is very important to be aware of the machine’s speed that the tractor-implement will be working. Follow the tire manufacturer recommendations to assure the tire footprint is the largest possible for the load; with more lugs on the ground for traction and larger footprint for lower compaction. One point to consider, while using dual fitment, is that the load capacity is reduced by 12% on each tire –meaning that the load capacity should not be doubled. By adding duals, you gain 1.76 times the single load capacity. The reduction is even higher when using triples. Each tire load capacity is reduced by 20%, conveying a triple set will carry 2.4 time the load of a single tire (not 3 times).

IF /VF Tires

On IF and VF technology tires, there is no gain in load capacity when speed is altered. Once the load has been established, the inflation pressure may be determined. The advantage of IF and VF technology tires is that they can carry more load at the same inflation and inflation pressure can be reduced with the same load. A lower inflation pressure means more lugs on the ground and larger footprint with lower compaction. An important point to mention is: there is an opposite relation between traction and flotation. When flotation is increased (for extreme compaction) the lug pressure is reduced on the ground (less traction), and slippage increases. Each farmer will have to find the right compromise between power transfer efficiency (less slippage) and compaction (flotation).

Solutions

With a better understanding of setting up tires on a tractor, we can now discuss solutions to when the tractor does not perform as expected. If there is excessive slippage, it may be because of the following two main reasons. First—too much pull from the implement (meaning the implement requires more power as the tractor can deliver). Or, the tires are not transmitting the power to the ground.

In the first case, the only option is to reduce the implement power needs (for example: reduce the implement penetration) or reduce the working speed. It is also possible that the soil conditions are not normal-optimal for the operation (such as: too wet). Resulting in more power as in normal conditions. In this case, the farmer would need to schedule the work for a better soil condition if possible.

For the second reason, the farmer would need to check first that the inflation pressure is correct (as per tire manufacturer recommendations) for the tractor weight. If correct, and there is no possibility to add triple tires- additional weight may be added (if not yet at the maximum weight allowed). Or the tires may be changed to provide a larger and wider footprint and ensure they are R-1W tread (20% deeper lug height as R1 tires) or the lug design (45-degree lugs, Progressive Traction technology). Also, it is possible to change to IF or VF technology, allowing the reduction of inflation pressure and increase the footprint (more lugs “biting” the soil). This usually requires a change in rims (VF technology uses wider rims).

In most situations, a correct tractor weight and distribution (actual tractor weight – not the manuals estimated weight), with the correspondent tire inflation pressure is enough for an efficient performance. Remember to always consult your trusted tire dealers or equipment dealer for additional information.

 

Alliance Tire Americas
Nick Phillippi: National Product Manager

With massive loads and high horsepower, today’s top-of-the-line tractors are placing huge demands on tires. There are three levels of commitment an operator can undertake when it comes to maximizing the performance of the tires and the equipment: managing the inflation pressure properly (easiest), switching to low-pressure tires (moderate), and, ideally, using a central tire inflation system to maintain optimum pressure (fully committed).

In tires, it’s all about inflation pressure. With a massive tire like an 800/70R38, the difference between 23 psi (which many farmers will inflate to because it’s easy and going to the max seems like the safe choice) and 12 psi (which is optimum for field work) is night and day. Just dropping to that lower inflation pressure is enough to transform his tractor into something he didn’t even know he had.

And all it takes is an air gauge, a tire inflation chart and a few minutes to really get the most out of that $400,000 he invested in his tractor.

The next step, especially with a huge tractor, is switching to VF tires. It is possible to “over-tire” some tractors, as Dallas Ransom discussed in a recent blog. But with a John Deere 9620 or a Steiger 620, you’re talking about 50,000 pounds of machine. Nobody makes a tire too big for that.

With that kind of load, VF tires will pay off all day long, especially because you can handle the same load as a conventional radial with 40 percent less inflation pressure. That allows you to get down as far as 8 or even 6 psi and really give tracks a run for their money in terms of traction and flotation.

Of course, the best way to get duals to maximize traction is to lower inflation pressure in the field and only raise it on the road. Under those conditions, the tires should perform equivalently to tracks at all times—while being a lot less expensive and much easier to maintain.

As much as we in the tire industry would love to see farmers stop on the edge of the field to adjust their inflation pressure, the most practical way to ensure that the adjustments are made would be to install a central tire inflation system (CTIS) on their tractor, especially if he or she has made the investment in VF tires.

CTIS technology allows the operator to adjust inflation pressure with an onboard compressor at the touch of a button. In just a couple of minutes, a set of tires can be adjusted to optimum inflation pressure for either field or pavement, low speed or high. CTIS can be easily retrofitted onto tractors, and can cost less than a set of tires. Especially if a farmer is investing in IF or VF tires, CTIS is a great complement to that.

With all the advantages of CTIS—including better traction, improved flotation, more effective transmittal of horsepower to the ground, increased fuel economy and longer service life from your top-dollar tires—investing in the technology begins to return immediately and a good system can pay for itself very quickly.

 

Titan International, Inc. (Manufacturer of Titan and Goodyear Farm Tires)
Scott Sloan: Ag Product Manager / Global LSW

The key to any high draft load / heavy tillage applications requires three things.

First, the tractor must be ballasted heavy enough to pin the power to the ground.  As discussed in previous articles we recommend 90lbs to 120lbs per horse power as a guideline for total machine weight.  Additional ballast may need to be added to achieve the proper machine weight.

Secondly, along with total weight,  front to rear weight distribution is also critical.  We recommend a 60/40 (front/rear) weight split as a target.

Lastly, once the tractor is ballasted correctly inflation pressure must be set for optimal performance.

Below is an example of loads and inflation which would work on any model tractor:

600+ HP Tractor (Any Brand) Ballast and Inflation Recommendation

Total Machine Weight    62,000 lbs.

Front Axle Weight            37,200 lbs. (9300 lbs./tire)

Rear Axle Weight             24,800 lbs. (6200 lbs./tire)

Recommended Inflation

710 (Duals)RearFront800 (Duals)RearFront900 (Duals)
710/70R429psi16psi800/70R386psi13psiLSW900/50R466psi7psi
IF710/70R426psi12psiIF800/70R386psi9psi
VF710/70R426psi9psiVF800/70R386psi7psi
LSW710/60R466psi12psiLSW800/55R466psi9psi
Singles
LSW1100/45R4612psi*17psi
LSW1250/35R4612psi*17psi
LSW1400/30R4612psi*17psi

*VF agricultural tires when used as singles minimum 12psi (TRA standard)

Tracks machines are different in the fact that they typically sit at or close to the appropriate weight without hanging another piece of iron on the machine.  The down side is that the machine cannot be made any lighter when a lighter less compaction type application is being performed such as planting.

Road transport speeds and distance in track machines are typically reduced due to the wear and tear on the tracks themselves.

In the field I would put up any LSW tire on a wheeled machine against any track machine of similar horsepower and run toe to toe with the track machine.  I have seen time and time again conventional tires tend to not perform as well as tracks or LSW tires due to the propensity to power hop in the field causing the tractor to loose tractive efficiency and therefore being less productive across the field.

Road speeds are also typically higher in LSW equipped machines versus track machines or machines equipped with conventional tires due to road loping issues.  Titan/Goodyear offers expertise in the field with our Ag Specialist Team, with the group’s sole purpose to assist end users with application issues- they will come out and scale equipment and make recommendations on ballast and inflation to ensure optimum performance.

 

Continental Agriculture North America
Harm-Hendrik Lange: Agriculture Tires Field Engineer

As a broad portfolio provider, Continental offers both rubber track and tires for a complete agriculture solution. There are certain applications where each excels and is a better overall fit for the needs of the operation. Farmers should consider investment and maintenance costs, road driving capabilities, transportation width, soil compaction, traction and fuel consumption. To help customers make the right equipment choice, Continental has a team of experienced field engineers who visit and consult with customers in the field. Every application is different, and Continental offers products to meet every need.

Both track and tires can provide superior performance, depending upon the application.

The benefits of  TRACK include:

– Narrower transport width for the same load capacity
– More pulling traction in wet conditions
– Less fuel consumption per acre at high loads and high torques
– Less track width, able to handle row applications in wet and muddy conditions with narrow tracks
– Same footprint area on less track width means less soil deformation energy in total
– No time required to adjust tire inflation pressure
– Less slip rates to transfer the pulling force
– Soil protection, if highest loads needs to be carried (where tires need high inflation pressure)

The benefits of TIRES include:

– Lower investment cost
– Lower vehicle weight
– Lower fuel consumption per acre for lower torque applications, as tracks have more moving parts
– Less heat generation at road speeds
– Lower maintenance costs
– Reduced soil disturbance on end row
– Improved steering on steep inclines
– Uniform soil pressure distribution
– Better ride

Continental heavy-duty farm tires are versatile for applications that need performance in the field and on the road. They have low heat buildup while roading and can be driven loaded and unloaded on both roads and fields. Tires offer low investment and maintenance costs, uniformly distribute soil pressure and are efficient for road transportation. To optimize traction, farmers should reduce the tire pressure to the recommendation stated on technical data sheets. Oftentimes, the inflation pressure is too high creating a smaller contact patch of the tire to the ground which lowers traction.

For an application with full power field work where standard duals are not providing adequate traction and the user isn’t able to go wider with triples, track offers an efficient solution. Continental Trackman rubber track, constructed for the most severe and extreme applications, are able to transfer more torque to the ground and gain greater traction, all with high flotation because of their larger foot-print. This foot-print allows the machine/equipment weight to be distributed across a greater area and lowers the ground pressure, without increasing width as triples would require. Reducing ground compaction equals greater crop yields.

In order to get the power to the ground with the highest horsepower equipment in the marketplace, we recommend market leading guide-lug support system called ARMORLUG®, MAXXTUFF™ wire ply construction providing more ends per inch, and now the patented ARMORLUG® ULTRA that provides 25% more torque capability than before.

 

Michelin Ag
David Graden: Operational Market Manager – Agriculture

As a producer, you are inundated with marketing campaigns, ads, salespeople feeding you opinions as fact, etc. The truth is, if you know what you want to achieve and you know what is available, it will lead you to the decision that meets your needs.

At Michelin, we begin with creating tires based upon a farmer’s value and needs. From there, we teach our sales reps to find the facts and match the right tire based upon those facts. Finally, we close the loop by proving lower total cost of ownership and stand behind our decision by working with you year after year.

In the case of a 4WD machine, pulling an implement that requires 550 hp, there are several cost-effective tire options for you that can do the job. First, begin with listing your needs:

  1. Traction
  2. Torque transfer
  3. Limited width (triples too wide)
  4. Are you concerned with fuel economy?
  5. Do you have the need to travel between fields at a descent rate of speed?
  6. Have you considered soil compaction and the proven effects on yield?
  7. Have you looked at the different machines and price gaps between each?

Typical tire sizes found on these machines are the 710/70R42 and the 800/70R38. I would recommend going with the VF (Very High Flexion) tires in these sizes in the new Axiobib 2 or Evobib. Each of these tires has been extensively tested and marked with “Inflation Systems Ready” on the sidewall, meaning they are designed to optimize your tire pressures based upon your needs- with the simple push of a button.

Let’s take a look at the air pressures required to transfer 550 hp. When calculating the optimum tire pressures, we need to first know what the machine weighs and calculate the proper weight distribution required to transfer that torque to the ground.

At 6 mph, these machines will require about 95 lbs. per engine horsepower. That comes to 52,250 lbs. total. Next, you want about 55% of that weight on the front and 45% on the rear axles. This weight distribution will eliminate power hop and road loping.

For each of these tires, the front axle air pressure for field operation is 9 psi and the rear axle air pressure for field operation is 6 psi. With a PTG central tire inflation system, for roading, you can then increase the air pressure to maximum psi on the sidewall for each tire and travel at maximum machine speed!

The main difference between these two tires is the Evobib will have a much larger footprint at 6 and 9 psi than the Axiobib 2. Due to the shoulder design of Evobib, the footprint of this tire will actually increase by over 28 additional pairs of lugs on the ground at field operation pressures!

So, in addition to transferring 550 hp to the ground, you want higher road speeds, less fuel consumption, increased yields, and an overall lower cost of ownership, our recommendation is to pair a premium VF tire with a central tire inflation system.

 

Firestone Ag
Bradley J. Harris: Manager, Global Agricultural Field Engineering

When users complain about traction in the field, the first thing that needs to be done is make sure the tractor is set up correctly. Loss of traction could be due to under- or over-ballasting of the tractor, too high of inflation pressure in the tires, or using liquid ballast in the tires. Before we recommend different tire sizes, tire technologies or mobile solutions, let’s get the tractor set up correctly.

For a 4WD tractor, the target ballast weight is 110 lbs per engine horsepower in heavy drawbar pull.  A 620 hp 4WD tractor should have a base weight of 68,200 lbs.  The weight needs to be distributed so that 51% – 55% is on the front axle, and 45% – 49% is on the rear axle. The front-axle target weight would be between 34,782 lbs and 37,510 lbs, and the rear weight would be between 33,418 lbs and 30,690 lbs. I recommend using steel ballast to obtain the weight on the tractor. Using liquid ballast does not damage the tire, but liquid does not compress. Since liquid does not compress, it will prevent the sidewalls from properly deflecting, and will make the tire stiffer. This extra stiffness causes the tire from developing a full footprint, reducing traction in the field. By using the ballast calculator provided by the tractor manufacturer, the machine can be ballasted with the available steel weight package, which provides a front-axle weight of 35,500 lbs (52%) and a rear axle weight of 32,700 lbs (48%).

With the front- and rear-axle weights set to utilize the engine horsepower, the minimum inflation pressure for the tires can be calculated. Assuming the tractor has dual 710/70R42 tires, the minimum inflation pressure needed to carry 35,500 lbs on the front axle is 20 psi. The minimum inflation pressure needed to carry 32,700 lbs on the rear axle is 17 psi. Setting the pressure to these weights allows the tires to develop the largest footprint possible. The pressure in the tires also determines what the ground contact pressure is. In this setup, the ground contact pressure is approximately 22 psi on the front axle and 17 psi on the rear axle.

If the tractor is set up correctly, and it still does not seem to have the required traction (excess tire slippage on firm soil), then it is time to look at the IF or VF tires. IF and VF tires allow the tires to carry the same axle loads at lower inflation pressures. The lower inflation pressures allow the tire to deflect more, allowing the footprint to increase in length. The longer footprint allows more tread bars to make contact with the soil, increasing traction. For a 620 hp tractor, Table 1 shows what inflation pressures are needed to carry the axle load:

Table 1: Minimum Inflation Pressure

The benefit of the IF and VF tires to the user is that the standard radial tires can be replaced with the IF or VF tires, with only an investment in the tires. The Firestone IF and VF tires are approved to go on the same rims as the standard radials, making extra spending on wheels or different mounting hardware unnecessary. The lower inflation pressure increases the footprint area, and provides an improvement in traction and a reduction in fuel usage. The lower inflation pressure also reduces soil contact pressure, helping to limit soil compaction.

When comparing four-track systems to wheel setups, it’s important to understand what performance targets are important for the operation. Both setups provide users with various benefits. Wheeled tractors have a lower initial purchase price and lower operation cost. When the wheel tractor is set up with tires that allow for inflation pressures below 15 psi, the wheel tractor will have lower soil contact pressure versus a tracked tractor. In wet soils, a tracked tractor provided better traction performance, because the track acts like a road paver. As the tread of the track engages the soil, it stays in the same position, and the undercarriage moves forward. That is why a tracked tractor does not seem to rut the field up in wet conditions. On a wheeled tractor, the tire is continuously rotating, and in wet soils, the tire pushes the soil, causing ruts.

It doesn’t matter whether a 620 hp tractor has tires or tracks; if the tractor does not seem to have the proper traction in the field, the first step is always to make sure the tractor is ballasted correctly. After the ballast has been corrected on wheeled machines, make sure the inflation pressure is set to match the axle loads; and on tracked machines, make sure the undercarriage tension pressures are correct. If more traction is needed on a wheeled tractor, IF and VF tires will provide a larger footprint, which generates more traction in the field, and could be a lower-cost solution versus purchasing a tracked machine. If the machine is going to be used in wet conditions, a tracked machine may be a better option, but remember that the track machine is still compacting the soil.

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 before use. Ag Tire Talk does not recommend anyone conduct tire service work with exception of Certified Ag Tire Dealer Professionals.

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One Response to “4WD Tractor TRACTION: Pulling 550 hp Implement”

  1. Author Image Jeff says:

    Excellent read!

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