How to Read Load Inflation Table

 

AG Tire Talk Key Takeaways

MICHELIN: “Reading a Michelin Agricultural Tire Load/Speed Inflation Table is essential for optimizing tire performance, safety, longevity, efficiency and even maximizing yield.”

ALLIANCE: “Knowing the proper pressure for your ag tires isn’t as simple as checking the sidewall or looking up a number in a catalog. Getting it right involves knowing your machine, terrain, and workload and dialing in tire pressure using your tire manufacturer’s inflation tables.”

TRELLEBORG / MITAS: “What carries the load of a tire?  The answer is AIR.”

BKT: “When referring to the Load and Inflation chart, this gives the load carrying capacity of a single tire. If a user needs 10,000 lbs. of weight carrying capacity on the rear tires, and there are two tires, each tire will need to be able to carry 5,000 lbs. each.”

MAXAM: “Depending on the amount of weight and the desired speed, each tire will need to have their cold inflation adjusted to ensure that the tire casing and resulting tire footprint is optimized to best suit working conditions.”

 

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

Let’s look at reading an Agricultural Tire Load Speed Table, then go through an exercise of calculating what air pressure to recommend.

Our example below shows the Load Speed Table for a 600/70R30 158D Trelleborg TM900HP tire.

• You can determine how much air pressure is needed to carry a certain load at a certain speed.
  • Example – how much air pressure is needed to carry 9,370 lbs. at 40 mph. The answer is 35 psi.

When I conduct a training class discussing tire air pressure, one of the first questions I ask is….What carries the load of a tire? The answer is AIR.

 Calculating the correct tire air pressure is crucial to the tire’s performance. Running the correct air pressure will not only reduce compaction, but it will also provide more traction, a better ride and longer tire wear.

Let’s go through an example of selecting the correct tire air pressure.

Selection of Tire Pressure

First, some basic statements about inflation air pressures. The inflation pressures refer to tires at ambient temperature. The values given in the load tables represent the “reference pressure” for the load and speed condition shown. The actual pressure of the tire must be established in accordance with the mechanical characteristics of the vehicle, the additional load from the use of equipment as well as the load conditions.

These values can be obtained from the “load/pressure/application tables according to the use. We will deal just with tractor tires in our example.

Factors to Consider:

• On road at various speeds or road speeds.
• On field at HT “high torque” (plowing, heavy ripping, etc.)
• On field at LT “low torque” (seeding, surface working, etc.)

Our value we calculate will be the LOAD PER TIRE.

If possible, weigh each axle of the equipment using reliable scales.

Make sure you use the load tables that are designed for the specific brand of tire(s) for which you are making the air pressure calculation. Do not use another manufacturer’s tables.

First, calculate the load per tire. For our example we will use a MF Model 8700 tractor.

Tractor’s total vehicle weight = 23,810 lbs. This is derived from either customer info, weighing the tractor or the manufacturer’s specs.

For a MFWD (Mechanical Front Wheel Drive) Tractor I like to go with a weight distribution of 40% on the front 60% on the rear. You can see our per tire load calculation below. I have also listed the front and rear tire sizes. 420/85R30 and 480/80R50 respectively.

From our earlier calculation, we have determined our front tire load is 4,762 lbs. per tire. We also determined that our Condition of Service is 5 mph speed in a HT (High Torque) application.

To make our front tire air pressure recommendation, we go to our load table for the size 420/85R30 which is our front tire size. We look to the left of the load table and find our Condition of Service which is 5 mph HT S. S stands for a single tire application. We then move along that row until we find our per tire load of 4,762 lbs. Many times, the load table will not have the exact load so we will approximate where that number will be in the table. I have put a red circle in that position. We then move vertically up the table until that arrow intersects the PSI row, which is the air pressure row expressed in pounds per square inch. I have put a red circle in that position. So, for our front tire air pressure recommendation we will use 15 psi.

In summary, use a reliable source to get your starting equipment weight. Use the manufacturer’s load tables. Make sure of the particular application. Use a reliable air gauge to set the pressures.

 

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

For Example: Size 480/80R50 159 A8/B

Shown is an expanded Load and Inflation Chart for above size.

The 159 Load Index means that this tire will carry 9,640 per tire running single at 30 mph. Since this is a radial tire and can run at lower air pressures based on the load on the tire, weight carrying capacity per tire is shown at corresponding speeds. This chart shows the weight carrying capacities at different air pressures at different speeds when running singles. When a user is running duals, they must multiply the weight capacity by .88 for duals and by .82 when running triples, to get the correct weight carrying capacity. These coefficients are used to get some safety margins in case duals/triples fitments are used in slight different conditions (e.g. inflation pressures, pattern wear, etc.). A user can determine the best air pressure to use based on their load by using a chart such as this.

Included in this chart are weight carrying capacities at 5 LT (5 mph at Low Torque) and 5 HT (5 mph at High Torque). Per TRA guidelines, Low Torque applies when the primary torque involved is used to propel the tractor. Tractors pulling carts and trailers are considered operating at Low Torque when operating on slopes 11 degrees (20%) or less. High Torque applies when there is a load on the drawbar or hitch (e.g. plowing, harrowing, etc.). This includes ground engaging equipment or dragging objects. They are operating in a High Torque Mode when operating on slopes greater than 11 degrees (20%). Notice that the load carrying capacities are different between HT and LT.

The accurate weight per tire can be determined by weighing the tractor through a weight platform. This helps to determine the amount of air pressure that should be used. There are several things to keep in mind when weighing the tractor. The implement being used should be attached.

When referring to the Load and Inflation chart, this gives the load carrying capacity of a single tire. If a user needs 10,000 lbs of weight carrying capacity on the rear tires, and there are two tires, each tire will need to be able to carry 5,000 lbs. each. This will give the 10,000 lbs. of capacity needed. Using the chart above, a user could run 12 psi per tire to carry 5,210 lbs. at 30 mph. This is a simple example to show how the calculation works.

If the implement is on a 3-point hitch, the rear should be weighed with the implement up. This will be the greatest weight on the tires. The front should be weighed with the implement down. This puts the greatest weight on the front. For optimal performance on field and drivability on road, always target to around 60% of the load on rear axle and 40% on front axle. To reach this condition, a ballast on front axle is sometimes needed.

Always consider worst case scenario when setting the air pressures. Use the Load and Inflation chart to set the inflation to the highest speed the tractor will run and carry the required weight. By doing this, you are safe in the field and on the highway between fields. If the weight capacity needed for the rear is too great with a standard tire, using a VF tire could be a much better option.

If the implement is on the drawbar, weigh the rear tires with the implement folded up or picked up. Weigh the front with the implement folded down or set down. This puts the most weight on the tire positions and gives a good indication of the amount of air needed. On the pull behind implement, weigh the inside tires that carry the most weight when transporting on the road. Set the air pressure based on the highest speed to carry the required weight.

The reason for looking at worst case scenario on air pressures is for use on the road at higher speeds. The faster the speed, the less the load carrying capacity of the tire. The slower the speed, the greater the load carrying capacity. If a tire is run on the highway under inflated and overloaded, it can’t properly dissipate the heat. This will cause sidewalls and tread areas to separate and result in plies separations. Although lower air pressures can be run in the field at slower speeds, air pressures would need to be taken up for the highway. If worst case scenarios are used, this takes air pressure out of the equation and minimizes problems.

CTIS systems (Central Tire Inflation System) are beginning to become more commonly used and are offered on some tractors, combines, and equipment. With this system, a user can reduce pressures in the field to get better performance from the tires. Traction is increased and ground pressure (soil compaction) is minimized. Flotation is increased as the footprint of the tire is larger to spread out the weight of the tractor or implement over a larger area. When leaving the field to travel on the road, the user can increase air pressures to handle the speed and the weight. When using CTIS systems, weighing the tractors is still required to figure out which air pressures to use at field speed and which to use at highway speeds. Use the scenarios discussed earlier to get the most accurate weights.

In summary, air pressures carry weight and help dissipate heat. If the correct amount of air pressure is used for the weight and speed, this minimizes the potential for a multitude of problems.

 

Yokohama Off-Highway Tires America Inc.
James Crouch: Alliance’s National Segment Manager–Agriculture

Knowing the proper pressure for your ag tires isn’t as simple as checking the sidewall or looking up a number in a catalog. Getting it right involves knowing your machine, terrain, and workload and dialing in tire pressure using your tire manufacturer’s inflation tables. Online inflation pressure calculators and apps are gaining popularity, but I still find a good old-fashioned pencil and paper work best.

Before You Begin Calculating

There’s no all-purpose inflation pressure. Consequently, you need to ask a few key questions before making any calculations:

• What kind of machine are you running?
• What size tires are on the machine?
• What configuration are you using (singles, duals, triples)?
• What task are you doing? (planting, roading, combining, etc.)?
• Where are you operating (flat fields in Iowa or 20% slopes in Washington)?

If your equipment doesn’t have a central tire inflation system (CTIS), there are two other questions you’ll need to answer:

• What’s the heaviest implement or load you’ll pull or carry?
• What’s the highest speed you’ll travel?

Establish Tire Load

Determine the axle load to start. The most precise way to figure out axle load is to weigh your equipment as field-ready as possible. If you don’t have scales on the farm, contact your local co-op, most have drive-over scale pads. Another option is to contact your Alliance representative—they often carry portable scales when traveling.

If you don’t have time to weigh your machine or need to make a quick calculation, you can use a tractor’s horsepower to calculate its weight. MFWD and 4WD tractors generally weigh between 100 and 130 pounds per horsepower. For example, a 300-horsepower tractor typically tips the scales between 30,000 and 39,000 pounds. For MFWD tractors, weight is typically distributed 40% to the front and 60% to the rear. For 4WD tractors, the split is usually 55% front and 45% rear.

Calculate weight per tire by dividing axle load by the number of tires on the axle. (Duals? Divide by two. Triples? Divide by three.) If you’re running duals or triples, increase the calculated load per tire by 12% for duals and 18% for triples. This compensates for temporary overloading caused by bumps, curbs, and uneven terrain.

Consult Inflation Tables

With the weight per tire calculated, find your tire size and model on the manufacturer’s website. Manufacturers provide a load index and speed rating for every tire. These classifications are standardized by the Tire and Rim Association (TRA) and indicate the maximum speed a tire is designed for and its load-carrying capacity.

Manufacturers also provide tables recommending the speed a tire can travel while inflated to a particular psi and load. For non-CTIS equipment, I calculate the inflation pressure for the worst-case scenario. That is, the fastest speed it will travel and the heaviest load it will carry.

CTIS Changes Everything

Without CTIS, you have to set your tire pressure for the worst-case scenario—the highest speed and heaviest load. However, with CTIS you can optimize tire pressure for the actual conditions you’ll encounter. With the push of a button, you can increase pressure for travelling at high speeds on the road or decrease pressure to maximize traction and reduce compaction in the field.

CTIS allows you to realize the full potential of your tires—improving fuel efficiency, increasing service life, enhancing traction, and reducing compaction. In fact, CTIS can outperform tracks when it comes to compaction reduction.

Boots on the Ground

Proper air pressure is key to maximizing tire performance. Alliance’s Whole Farm Concept—a commitment to providing low-pressure tire solutions for every piece of equipment that enters the field—works best when tires are correctly inflated.

 

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

At first glance, an agricultural tire load inflation table is hard to interpret. However, it contains valuable information that determines the correct cold air pressure, weight being carried by the tires, and the overall central inflation system methodology.  Below, we’ll dive into a helpful guide to read the MAXAM load and inflation tables to ensure you receive the best value for our products.

Each of our radial tires is designed to operate on or off the road based on the speed and physical load being carried by each axle. “Cold” air inflation pressure management is the key to optimize how well a tire can perform on any equipment for any given speed, load, or application on or off the farm. Radial tires are particularly sensitive to the impact of cold air inflation as 80% of any given load is carried by the compressed air. Please keep in mind that the casing, tread belts, and rubber components only account for 20% of the total weight being carried by the tire, therefore the air pressure is the most critical component to the tires’ success.

Depending on the amount of weight and the desired speed, each tire will need to have their cold inflation adjusted to ensure that the tire casing and resulting tire footprint is optimized to best suit working conditions.

Below, we examine the impact of air pressure for two working conditions at 5 mph (Field Work Speed) and at maximum speed of 40 mph (Transport Speed) for the same tire load:

1. Select the Working Speed…Example: 5 mph or 40 mph
2. Determine the Load per Tire based on the tire Load Index…Example LI157 = 9100 Lbs
3. Determine the correct cold inflation air pressure based on the given speed and the load per tire

The above example gives us two different air pressure results depending on the load index of that tire versus the desired speed for that give application:

• At 5 mph or Field Working Speed the tire cold inflation pressure necessary to carry the Load = 15 PSI
• At 40 mph or Transport Speed (Maximum) the tire cold inflation pressure necessary to carry the Load = 23 PSI

Due to evolving work conditions in all agricultural applications, the following factors must also be assessed and considered when selecting the “correct” cold inflation air pressure:

• The axle load or weight being carried
• The desired speed to achieve the optimum productivity
• The desired tire contact patch or footprint at a given air pressure to reduce soil compaction.

Each of the above factors dictates the capability of tires to achieve their purpose of moving a given load from point to point. Weighing the machine when configured to its maximum load per axle allows the best information to be applied to determine the best operating cold inflation pressure per axle or tire size.  As a rule, lower torque or slower field work speeds allow Ag tires to use lower air pressures to carry significant loads. The tire sidewall deflects as needed and increases the tire tread contact area, thus reducing soil compaction while simultaneously improving traction. Conversely, when moving a machine or platform from one field to another, air pressure must be increased as the higher transport speed requires more air pressure to adjust to the higher heat generated by the increased velocity and load being carried. The above air inflation factors are further affected by the impact to tire load due to dual or triple fitments on the same axle. Below are the tire load adjustments based on either using tire in dual or triple fitments:

• When operating Ag tires in duals with four (4) tires on an axle the weight carrying capacity is adjusted from 100% down to 88% or -12% lower carrying capacity or what is termed its “equivalent load.”
• When operating the tires as triples on an axle using six (6) tires across one working axle from side to side, the weight carrying capacity is adjusted by -18% or 82% for its “equivalent load.”
• The -12% or -18% weight reduction adjusts the air pressure on all four or six tires to reduce or minimize the impact of load transfer from one side of the axle to the other.
• Despite the lower load carrying capacity of the equivalent load, you are also distributing the load on the axle across four or six tires, thus reducing the air pressure requirement, improving the footprint on the soil.
• Once you have determined the “equivalent load” per tire you can adjust the air pressure per tire for the required speed either in the field or for transport.

Central inflation systems on any powered ag platform permit tire air pressures to be changed almost immediately, allowing the optimal pressure to be added to the tires to achieve the desired load carrying capability for a given speed. Although this technological solution is becoming more accessible and popular across the Ag industry, for most growers and farmers, the current solution is to select the highest air pressure necessary based on the machine’s fully loaded weight with its heaviest implement or trailer hitched. This determines the load on the front and rear axles. The next step is to adjust to the highest air pressure necessary to meet the operating speed based on their field work or transportation needs without having to make manual changes on the go! In addition to the above axle load considerations for duals or triples impacting the machine’s air pressure needs, you must also consider the below front or rear axle requirements caused by the load distribution per axle by platform (general guidelines):

• 2WD Tractors: 35% of the total weight is on the front axle and 65% of the weight is on the rear axle.
• MFWD/MFWA Tractors: 40% of the total weight is on the front axle and 60% of the weight is on the rear axle.
• 4WD Tractors: 55% of the total weight is on the front axle and 45% of the weight is on the rear axle.
• Combine / Harvesters: 70% of the total weight is on the front axle and 30% of the weight is on the rear axle.
• Floaters: 30% of the total weight is on the front axle and 70% of the weight is on the rear axle.
• Self-Propelled High Clearance Sprayers: 48% of the weight is on the front axle and 52% on the rear axle.

MAXAM recommends the following best practices:

• Inflate tires to the correct cold inflation pressure based on the axle position, number of tires, axle load and required work or transport speed.
• Greater crop yields will happen if soil compaction can be minimized by using the best tire footprint based on the right inflation pressure by axle configuration, position, axle weight distribution, and speed required.
• The right air pressure will improve tire wear and reduce sidewall deflection, giving the optimum tire gross flat plate or footprint allowing improved fuel efficiency with reduced tire slip.
• The right air pressure will also ensure greater productivity in the field as the tire’s footprint and traction will be fully optimized.

 

Michelin Ag
David Graden: Global Account Manager – Agriculture

Reading a Michelin Agricultural Tire Load/Speed Inflation Table from the Michelin Databook is essential for optimizing tire performance, safety, longevity, efficiency and even maximizing yield. These tables provide data that help determine the correct air pressure based upon the tire’s load and speed conditions.

How to read the table:

Each row in the table corresponds to a specific combination of load (in pounds or kilograms depending on your country) and speed (in mph or kph). The columns list the recommended inflation pressures (in psi or bar) for those conditions. To calculate Michelin’s recommended air pressure for a given tire:

1. Identify the tire model and size from the sidewall of the tire
2. Weigh each axle to determine the actual load per tire, which is the total weight supported by the axle divided by the number of tires on that axle. Then divide by 0.88 (for dual fitment) to represent up to 12% weight shift for varying ground slopes. In many instances, we will also recommend adding 6 psi for use on slopes of more than 20%, when using single tire configurations.
3. Match the load and operating speed to the closest values in the table. Here is where it gets slightly more complicated: if your weight per tire falls between the printed values, take the higher printed value and subtract the lower printed value. Then, divide that number by the number of psi difference corresponding to each of the printed values (see example below). The answer to this calculation will be your recommended air pressure.

Example: Let’s say a John Deere 8R410 weighs about 38,000 pounds. 55% of that weight is on the rear and 45% of the weight is on the front.

Rear Tire: Duals: 480/80R50 Agribib 2 for up to 30 mph

38,000 x .55 = 20,900 lb Rear Axle ÷ 4 tires = 5,225 ÷ 0.88 weight shift = 5,938 lb/tire

From the databook above @ 30 mph row, 5,995 (12psi) covers our weight requirements.

 

Front Tire: Duals: 420/85R34 Agribib 2 for up to 30 mph

38,000 x .45 = 17,100 lb Front Axle ÷ 4 tires = 4,275 ÷ 0.88 weight shift = 4,858 lb/tire

Using the above table, I’ll take 4,805 (17psi)on the 30 mph row and add 1 psi to cover the 4,858 weight required to carry the load. In this case, 18psi is the front tire recommendation.

Finally, if we take a Central Tire Inflation System (CTIS) into account, this calculation changes. A CTIS allows operators to adjust the tire pressure on the go, adapting to changing field and road conditions. This recommended air pressure and flexibility:

• Reduces soil compaction by lowering pressure in the field
• Improves fuel efficiency and tire wear by increasing pressure on the road
• Enhances traction and flotation, especially in soft soils
• Improves yield, based upon several 3^rd party studies

When using CTIS, the Michelin table still services as the baseline, but operators can fine-tune pressures dynamically within the safe range provided. In this case, we highly recommend your machines be weighed with each implement (loaded) you will use throughout the year. Program the necessary air pressures for each of these into your system and your all set!

In summary, understanding and applying the Michelin Load/Speed/Inflation Table, accurately calculating per-tire load, and leveraging CTIS can significantly enhance agricultural productivity and tire performance, adding significant value to your bottom line.

Please reach out to your local Michelin dealer or sales representative for help or advice on the above.

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.