AG Tire Talk Key Takeaways
MICHELIN: “Improper Lead/Lag can cause more rapid tire wear, increased fuel consumption, transmission unit wear, loss in power and performance, and deterioration of topsoil.”
TRELLEBORG: “Lead/Lag is a condition that exists on MFWD (Mechanical Front Wheel Drive) tractors. Since the front tires are smaller than the rear tires, the front tires have to rotate faster to cover the same distance as the rear. To ensure correct Lead/Lag, we use RC (Rolling Circumference) – Distance covered in one complete revolution of the tire on an asphalt road.”
PRECISION INFLATION: “On a Mechanical Front Wheel Drive (MFWD) Tractor, the Front Tires should turn 1 to 5% faster than the Rear Tires…Otherwise, they FIGHT each other.
BKT: “When doing a tire change, or conversion, on a MFWD tractor, you must know the Lead/Lag Ratio…tire sizes can be changed on MFWD tractors, but they must stay within the same Lead/Lag Ratio based on the Rolling Circumferences.”
MAXAM: “Our Agricultural Tire Catalog contains both the tire Rolling Circumference and the tire RCI Value to assist farmers or growers in ensuring the tires chosen for their equipment can operate within their tractor gear ratio limits or needs.”
YOKOHAMA: Rolling circumference is the key factor in lead/lag problems. Some of the challenges include the fact that a tire in a specific size from one manufacturer may be a few inches larger or smaller in diameter than a tire of the same size from another brand, or that a worn tire of a particular size can be inches shorter in outer diameter than it was when it had all of its tread.
FIRESTONE: To correct an undesirable Lead/Lag Ratio you can change Front Tires to a Larger or Smaller Rolling Circumference.
Michelin Ag
David Graden: Operational Market Manager – Agriculture
Tire conversions are very common, especially with newly purchased machinery. Often time, it is less costly to purchase a new machine with whatever the manufacturer specs or however the manufacturer configures the machine. They tend to assume producers will make the necessary adjustments for their specific needs and applications. Unfortunately, this isn’t necessarily true in many cases. This is where your tire manufacturer can help.
At Michelin, we are equipped with the knowledge and experience to help you set up your machine for the absolute greatest efficiency and overall success. This is especially important when it comes to changing your tire sizes, whether you want to achieve more tractive capacity, floatation, improve fuel economy, change row widths, etc. Whatever your objective is, it is vitally important your tires fit within the allowable parameters of your machine’s transmission. Calculating the Lead/Lag of your machine will give you the most accurate information you need to make an informed decision on which tires to fit to your machine.
On the other hand, Improper Mechanical Lead/Lag tire fitment could lead to:
• Increased Fuel Consumption
• More Rapid Front & Rear Tire Wear
• Significant Wear on the Transmission Unit
• Poor Overall Tractor Performance
• Abrupt Front Axle Engagement
• Loss in Power & Performance
• Deterioration of Topsoil
*Most tractor manufacturers impose a mechanical lead of between 0% and 6%. This lead is specific and may vary depending on the manufacturer and the vehicle.
To calculate Mechanical Lead, you will need the following information and plug it into the below formula.
• RC Rear: Rear Tire Rolling Circumference (specified in the Technical Tire Databook)
• RC Front: Front Tire Rolling Circumference (specified in the Technical Tire Databook)
• R: Inter-Axle Ratio or Mechanical Gear Ratio (this is fixed initially by the manufacturer and can be found in the manual of all tractors)
Let’s look at a real-world example of why you would need to calculate mechanical lead and what that looks like.
You have a used John Deere 7710 with Titan 420/85R28 High Traction Lug on the front and Firestone 520/85R38 RAT 23 degree on the rear. The front tires are worn out and you want to replace them with Michelin Agribibs.
At this point, you could play with the calculations to see what your maximum and minimum RC measurements are to widen your options, however for this example, you want to fit that machine with a 16.9R28 Agribib because this size is dimensionally the same and the other options would require purchasing a new wheel. Using the below calculations, your new mechanical lead would be +3.9% and well within the parameters.
If your machine is already fitted with the tires you want, but you’re seeing the above signs of improper mechanical lead, you check this by doing the following:
Step 1 – Use chalk to mark your front and rear tires with a vertical line from the edge of the wheel to the ground
Step 2 – MAKE SURE YOUR FRONT AXLE IS DISENGAGED (out of 4WD)
– Drive the machine forward until the rear tire has completed 10 full rotations. Count the number (N) of rotations the front tire completed
Step 3 – FRONT AXLE ENGAGED (in 4WD)
– Drive the machine forward until the rear tire has completed 10 full rotations. Count the number (N1) of rotations the front tire completed
Of course, if you currently own Michelin tires or are planning to convert your tires to Michelin, the easiest method is to contact your local sales rep and have them do this! While they are there, you may as well ask them to help you distribute the weight of your machine for maximum torque transfer and properly set your air pressures.
Trelleborg Wheel Systems
Chris Neidert: Marketing, Training and Development Manager – AG
LEAD/LAG is a condition that exists in a MFWD (Mechanical Front Wheel Drive) Tractor. Since the front tires are smaller than the rear tires, the front tires have to rotate faster to cover the same distance as the rear. MFWD tractors are designed with a very specific ratio between the front and rear axles.
So to avoid excess front tire wear, excess tire slippage or even damaging the transmission and front axle when changing tire sizes, you must change the front and rears in the same percentage.
Basic Definitions
RC (Rolling Circumference) – Distance covered in one complete revolution of the wheel on an asphalt road. It’s measured according to ISO11795 at the specific tire nominal load and nominal inflation pressure. This RC value is the one you can find in the Tire Manufacturer’s Databook. Depending on each manufacturer internal tire design and objectives, the RC values between tire manufacturers can vary for the same tire size.
Lead/Lag – It refers to the difference in covered distance for the front tire comparing it with the distance covered by the rear tires. It is directly related to the transmission interaxle ratio and the size of the tires. The value is expressed in percentage and a positive value (Lead) means that the front axle will cover more distance than the rear. A negative value (lag) will mean that the rear tires will be pushing the front slower tires. A too high positive value will cause the front tires to wear more quickly and is most common on tractors with mechanical front wheel drive (MFWD). An industry accepted and desired value is a lead of 1-4%.
RCI – “The tire industry has developed the RCI (Rolling Circumference Index) system based on the OD (Overall Diameter) of tires to assist in the proper of selection of tire size combinations that will work.”
Let’s explain Inter-Axle Ratio:
- The front wheels of a tractor are smaller than the wheels on the rear axle.
- At the same driving distance the number of wheel revolutions is different on front and rear axle.
- A differential gear unit has to be installed between both driven axles to compensate this difference.
- The gear ratio of this differential is called “Gear Factor”.
Mechanical Front wheel drive tractors (MFWD) and the relationship between the front and the rear axle, called Inter-Axle Ratio, is part of the tractor design to assure the best traction performance and to avoid transmission issues. A typical IR (Interaxle Ratio) is between 1.25 to 1.35 and is specific to each tractor model and front axle configuration. This means that the front axle will turn 25 to 35% faster than the rear axle to cover the same distance with the tires.
The above illustrations show the starting point and the ending point of a mark on the tire when the tractor covers a certain distance with a typical interaxle ratio of 1.33. The front tire will turn approximately 33% more than the rear tire to cover the same distance.
Now. Let’s look at what happens when the interaxle ratio is not taken into consideration when changing tire sizes.
Changing only Rear Tire to a Larger Size (Front Axle LAG) – The below illustration represents when changing only the rear tire and to a larger size. As a larger tire has a higher Rolling Circumference (RC) it will cover a larger distance with every axle rotation. If the front tire is not changed to larger size, it will be covering the same distance as before and will be “slower” compared to the rear tire. This is considered that the front tire lags compared to the rear tires that will be pushing the front one. This will put strain on the transmission. Steering ability will be compromised, and tractor efficiency is greatly reduced. This is a situation we want to avoid at any cost.
Changing only Front Tire to a Larger Size (Front Axle LEAD) – The below illustration is dealing with changing only the front tire to a larger size. The front tire will cover more distance than the rear tire. This will cause the front tire to pull the tractor too much and will put high strain on the transmission and increase the front tire slippage with a front tires quicker wear of the tread.
There are several methods than can be used to calculate the current Lead/Lag when changing tire sizes. For this example we will use the Rolling Circumferences of the Front & Rear Tires.
- Start with the RC’s (Rolling Circumferences) of the Front & Rear Tires for the Specific Tire Sizes & Brands CURRENTLY ON TRACTOR.
- Calculate the ratio between the two RC’s (Rolling Circumference Rear / Rolling Circumference Front).
- Find the same information for REQUESTED NEW SIZES.
- Calculate the ratio between the two RC’s (Rolling Circumference Rear / Rolling Circumference Front).
- Calculate the Rolling Circumference Ratio between the two NEW sizes.
- Check if rim change is needed?
- Make sure the load carrying capacity of the new tires are adequate.
Comparing Both Ratios we need to stay within Plus or Minus 1% of the Original Ratio.
Let’s go through an example of making a tire substitution.
CURRENT Tire Sizes Front & Rear
- Front tire size = 14.9R30 (380/85R30) Rear tire size = 18.4R42 (480/80R42)
- RC front tire = 166.9” RC Rear tire = 218.5”
- Current Tire Ratio = 218.5 / 166.9 = 1.309
REQUESTED New Sizes
- Front tire size = 540/65R28 Rear tire size = 650/65R38
- RC front tire = 166.1” RC Rear tire = 216.9”
- New combo ratio = 216.9/166.1 = 1.306
We must stay within plus or minus 1%
- Current Tire Rolling Circumference Ratio = 1.309
- The New Tire Rolling Circumference Ratio must be within +/- 1% = 1.322 or 1.296
- Our New Tire Rolling Circumference Ratio = 1.306
- This new ratio is within the two numbers- this new combination is ACCEPTABLE.
BKT USA, Inc.
Dave Paulk: Manager Field Technical Services
MFWD (Mechanical Front Wheel Drive) Tractors have become popular for farm use and other applications. They are versatile and can be used in 2 WD and 4 WD modes.
Most MFWD Tractors have different sized drive tires on the front and rear. Since they can be used in 4 WD, the tractor transmission must be geared where the tires roll close to the same rate of speed. The fronts are always turning faster, since they are smaller. Tractors are set up at the factory with the correct tires to match up with the front to rear gear ratio (or Lead/Lag Ratio). Problems with performance and damage to the drivetrain can occur if the wrong sizes are used in replacement.
When someone is buying a new tractor, they will get the right set-up for their application from the dealer. When a used tractor is bought from another part of the country, it may be necessary to consider different widths, either wider or narrower, for the new application. In these instances, knowing how to determine the correct sizes, and whether they will work, is important to protect the equipment and the tires. Many times, when changing tires, new wheels may be required to be purchased. Wheels and tires are very expensive. It would be a waste of money to buy something that causes future problems.
Tire sizes can be changed on MFWD Tractors, but they must stay within the same Lead/Lag Ratio based on the rolling circumferences. The rolling circumference of a tire is the number of inches that tire travels in one revolution. If the Front Tire is too small (the rolling circumference isn’t great enough), they will turn slower than the Rears. The same thing can happen if the Front Tires are correct, and the Rears are too large. The Rear Tires will push the Front Tires (too much Lag). If the Front Tires are too Large, or the Rears too Small, the Front tires will pull faster than the Rears (creates too much lead). This can cause premature tire wear and transmission problems.
Most tractor setups have a Positive Front Lead (or slippage) of 1% to 5%. The positive front slippage allows for better steering and better front tire wear. When considering tire sizes other than what came on the tractor, it is best to stay within this 1-5% window.
When doing a tire change, or conversion, on a MFWD tractor, you must know the Lead/Lag Ratio. This can be obtained from the equipment manufacturer or tractor dealer. Once a user knows the Lead/Lag Ratio, there are several ways to determine if the conversion tires will work.
RCI (Rolling Circumference Index) charts can be used to determine if tires will work. Rear tractor tires are categorized with a RCI number, usually somewhere between 33 and 50 depending on size. The tires on a specific RCI line have close to the same rolling circumferences. By finding the Original Equipment tires on the RCI chart, you can determine the steps between the sizes. If changing sizes, a user would need to make sure the new tires have the same number of steps.
An example is a tractor with 480/80R46 Rears and 380/85R34 Fronts. This is a 5-step set-up on the RCI chart. Other sizes chosen would also need to have 5 steps to work and not cause a lead/lag problem. On the RCI chart, if a user picks a tire on a line above or below the original size, they must do the same with the corresponding tire. After choosing the tires, it is always best to check the rolling circumferences and the math to make sure they will work correctly. (Shown below)
Another way to determine if conversion tires will work is by doing some simple math. By multiplying the rolling circumference of the front tire by the lead/lag ratio and dividing this total by the rolling circumference of the rear tire, the user should get a number between 1.01 and 1.05. If the number is less than 1.0, the front tires are too small. If the number is larger than 1.05, the fronts are too large. An example is using the 480/80R46 (RC 231.1) rear and the 380/85R34 (RC 177.3) front with a 1.332 lead/lag ratio. When multiplying the front by the lead/lag ratio (177.3 x 1.332), it gives a total of 236.1636. Dividing 236.1636 by the rolling circumference of the rear tire (231.1), it gives a total of 1.0219. This number falls between 1.01 and 1.05 and is an acceptable positive lead.
Most farm tire dealers are very good at determining whether a particular tire (or tires) will work. It’s their business and desire to keep users out of trouble with Lead/Lag issues. Lead/Lag issues can cause premature tire wear and transmission problems. On the flip side, with the correct tires, the tractor will perform like it should, and be a valuable tool to the farmer.
Precision Inflation Systems
Ken Brodbeck: VP of Technology
What is Lead/Lag or Overspeed/Underspeed? Lead is how much faster the Front tires are going compared to the Rear Tires. Lag is just the opposite.
On a Mechanical Front Wheel Drive (MFWD) Tractor, the Front Tires should turn 1 to 5% faster than the Rear Tires. Otherwise, they FIGHT each other which can cause:
- Excessive Strain on the Tractor Drive Line.
- On hard surfaces and light loads in the field, the faster tire is trying to push or pull the other, wasting fuel and causing faster unnecessary tire wear.
- Basically, the axles fighting each other act like you are lightly riding the brake wasting fuel.
How can we measure our current tractor tire setup and, when we change tires, how do we calculate the new tires Lead/Lag in the most precise way?
To check your current tractor, with 3 people, do the following:
- Find a level hard surface 250 feet long, take the tractor to one end, ready to drive to the other end.
- Mark the left Front RIM, in 8 spots, use Duck or masking tape, Mark Rear at the bottom. With tape, you can easily re-zero the rear tire.
- Engage front axle, driver goes straight at walking speed while,
- 2nd person counts front wheel revolutions and 3rd counts 10 rear tire revolutions
- 3rd person tells driver to STOP @ 10 REAR Revolutions.
- 2nd person writes down total front revolutions to the closest mark on front tire.
- Back tractor up and stop front tire at 0 and reset rear mark to bottom by moving tape.
- Repeat with front axle engaged and count 10 rear revolutions to DOUBLE CHECK.
- Back tractor up to start and stop with front tire at 0 and reset rear mark to bottom.
- Disengage front axle, count 10 rear revolutions, stop, write down front revolutions.
- Repeat counting a 2nd time with front axle disengaged to DOUBLE CHECK,
- To calculate whether tractor has lead or lag, use the formula:
- Lead or Lag = Front Revs Engaged / Front Revs Disengaged
Example 1:
Front Revs Engaged – 14.375
Front Revs Disengaged – 13.875 14.375 / 13.875 = 1.036
IF the number is greater than 1, then the tractor has LEAD, 1.036 -1 = .036 OR +3.6%
Example 2:
Front Revs Engaged – 13.875
Front Revs Disengaged – 14.5 13.875 / 14.5 = .957
IF the number is less than 1, then the tractor has LAG, .957 – 1 = -.043 OR -4.3%
To select correct tires for front and rear axles by using an RCI chart, please see Precision Inflation, LLC segment at :
AG TIRE SIZE OPTIONS/CONVERSIONS: Why, When, How ? | AGTireTalk
Maxam Tire International
Greg W. Gilland: Business Development & Ag Segment Manager
As the Agricultural Industry has evolved from 2WD Tractors to Mechanical Front-Wheel Drive or Mechanical Front-Wheel Assist tractors (MFWD or MFWA: same machine-different name), tires have also evolved in design, materials, functionality, and performance. Ag tires are designed by size or footprint to fulfill the following specific functions:
- Carry the load
- Transmit the torque (or driving power)
- Provide direction
The challenge for all tractor manufacturers is that agricultural practices around the world differ based on crops grown, soil conditions, moisture content, and environmental conditions. Original equipment manufacturers have adapted their tractors to deliver solutions that are flexible to the evolving global market by providing machinery with tires of different diameters or widths allowing farmers or growers to adapt the equipment to meet the specific needs of their crops.
One of the key tools that are used to adapt or convert from one Ag Tire to another is the RCI or Rolling Circumference Index. The RCI is the rolling circumference or the distance a tire travels in one rotation or revolution. To pull implements using a powered front axle known as Mechanical Front Wheel Assist or Mechanical Front Wheel Drive Tractor in the field, a farmer must have a clear understanding of how the tire’s RCI impacts the tractors’ ability to transmit the engine torque to the ground. In essence, the smaller front tires must travel faster to stay in the same ratio or time sequence as the larger rear tires turn or travel when rolling forward or backward. In other words, the front tires will turn more times as the tractor moves forward for every rotation of the rear tires. To effectively operate the difference between a Smaller Front Tire and a Larger Rear Tire, each MFWD Tractor must maintain a balance between positive slippage or front tires pulling, and negative slippage when the front tires are slower or lagging therefore resisting the push from the rear tires. This balance is the tractor gear ratio also known as, the Lead or Lag Ratio.
The following are general rules related to ensuring the right Tractor MFWD or MFWA lead, or lag considerations are taken:
- The ideal tractor gear ratio between the Front Axle and the Rear Axle (IAR or Inter-Axle Ratio) ranges from 1.2 to 1.5
- For the Front Tires to pull successfully and produce the right amount of torque or pulling power with the right slip to stay within the tractor-gear ratio, the proper tire slip needs to be between 0% (0.01%) to 5% (5.00%) = positive slip.
- If you have too much positive slip ratio (above 5%) you will have excessive work by the front tires pulling the rear tires equates to a loss of efficiency and higher fuel consumption.
- If you have a negative slip result, the front tires will experience a braking effect that creates a loss of pulling power, more fuel consumption, and reduced steering capability. Each OEM publishes their recommended gear ratio for each model MFWD or MFWA tractor they manufacture.
- Tire manufacturers should provide their tires’ rolling circumference (RC) or the RC Index (RCI) values in their published product data to allow growers to calculate the right size tire fitment from front to rear for their equipment to ensure the right amount of positive slippage or pulling power for the given gear ratio.
- For most Tractors, the IAR requires that front tires be five steps smaller than rear tires based on their RCI Index value.
- Front to Rear Gear Ratio Tire Slippage Calculation: (Front Tire RC x Tractor OEM L-L Gear Ratio)/Rear Tire RC) – 1) 100 = Slip%
- See the provided example below:
MAXAM publishes in our agricultural catalog both the tire rolling circumference and the tire RCI value to assist farmers or growers in ensuring the tires chosen for their equipment can operate within their tractor gear ratio limits or needs. Both farmers and growers at times will also consider changing tires by either selecting a bigger tire combination or a wider-width tire to improve their traction, flotation, or pulling capability. Below is the MAXAM example of tires having similar diameters but different widths within the same RC or RCI permitting a quick determination of what is the best tire geometry suited to meet their field or crop production needs. Using the above equation and the RCI data, as well as the OEM tractor gear ratio value, any grower can quickly determine if their equipment will allow switching or evolving to larger tires without compromising their required gear ratio slip rate percentage. In all cases, please ensure the tires are inflated as required or recommended to carry the expected axle load so they can effectively transmit the engine torque or power to the ground either in the field or on the road.
The MAXAM Agricultural Tire Data Book and Catalog provide all the technical specifications that include RC, RCI, and diameter specifications to assist growers in determining any technical information necessary to support their equipment needs or potential tire size evolution.
Firestone Ag
Greg Jones: Global Field Engineering Manager
Lead/Lag, sometimes referred to as Overspeed/Underspeed, are conditions found in tractors that can impact wear and tear on the Front and Rear Tires as well as the machine’s powertrain. Calculating for Lead/Lag helps reduce these problems and maximize tire performance over time.
Lead/Lag refers to the relationship between the speed of the front wheels and the speed of the rear wheels. See the chart below for specific definitions and ideal calculations.
If the Front and Rear Wheels move at the same speed, the tractor would have Zero Lead/Lag. On Mechanical Front Wheel Drive (MFWD) Tractors, the gearbox, which can negate the difference in tire size or axle speed, is how we arrive at a 0% Lead.
When the tractor is driven on-road, it’s important to keep the front wheels in neutral to minimize strain on the drivetrain.
As farmers prepare to calculate Lead/Lag, they can consult their local Firestone Ag Dealer and the Firestone Ag Databook (page 190) for support.
For further support, please refer to the RCI chart (page 169) in The Firestone Ag Databook for proper tire size groups with the correct lead percentage. The Firestone Ag field engineering team will be happy to help growers with this, if needed.
How is the calculation done, and how does it ensure optimum tractor and transmission performance?
There are two ways to calculate Lead/Lag: manually and mathematically.
Manually
The four-step manual process requires three people and is done in the field. One person drives and the other two document the rotations of the front and rear tires respectively. For a sample calculation, reference page 190 of the Firestone Ag Databook online.
- Mark the front and rear tires on one side of the tractor using a piece of chalk. Draw one line on the side of the rear tire starting at the six o’clock position and ten evenly spaced lines on the side of the front tire.
- Find a long, straight piece of ground with firm soil on which to drive the tractor and begin conducting the test. Start with the chalk line on the rear tire pointing straight down. With front wheels engaged, drive the tractor forward. Using the chalk line as a guide, have one person count the number of revolutions of the rear tire and another person count the number of revolutions of the front tire. When the rear tire has made exactly 10 revolutions, stop the tractor and write down the number of revolutions the front tire made to the nearest tenth of a revolution. To ensure an accurate reading, repeat the procedure at least one more time.
- With the front wheels in neutral (disengaged), repeat the process. After the rear tire has made ten revolutions, stop the tractor and write down the number of revolutions the front tire made to the nearest tenth of a revolution. Again, it’s a good idea to repeat the procedure at least once to ensure your reading is accurate. When you have accurate readings with and without the front wheels engaged, you’re ready to calculate the percentage of lead or lag.
- Divide the number of revolutions of the front tire with the front wheels engaged by the number of revolutions of the front tire with the front wheels in neutral, and then subtract one. If the resulting number is greater than zero — a positive number — the tractor has a lead condition. If the resulting number is less than zero — a negative number — the tractor has a lag condition.
Mathematically
Firestone Ag field engineers can also help farmers calculate Lead/Lag. Gather the gearbox ratio and the Rolling Circumferences of the Front and Rear Tires. The field engineer will enter this data into a formula and provide the Lead/Lag percentage. Once you have the calculated Lead/Lag, either in the field or with the help of a Firestone team member, you can determine if you need to make adjustments. The ideal Lead/Lag is 2%, but 0-5% is acceptable. Anything under 0% is a Lag condition and needs to be corrected immediately.
To correct an undesirable Lead/Lag ratio you can change front tires to a larger or smaller rolling circumference.
- For a lead condition greater than 5%, change to a smaller tire.
- For example, if you have a tractor with 6% lead, use a front tire that is 4% smaller.
- For any lag condition, change to a larger tire.
- For example, if you have 6% lag, use a front tire that is 8% larger.
It is important to note that an equivalently sized IF/VF tire will typically exhibit a lower rolling circumference than its standard (e.g. non-IF/VF) counterpart due to the increased deflection inherent to its design. It is consequently recommended to confirm that the correct percentage lead will be maintained when switching one or both axles to IF or VF tires.
Making these changes will help minimize wear and tear on the equipment’s drivetrain as well as both the front and rear tires.
Contact Firestone’s Field Engineering team for further questions and assistance at 1-800-847-3364.
Yokohama Off-Highway Tires America, Inc.
Blaine Cox: National Product Manager—Agriculture, Golf and Turf
The gearboxes of mechanical front wheel drive (MFWD) tractors are designed around a specific size relationship between larger rear tires and smaller front ones. The front wheels turn slightly faster, or lead, helping the tractor deliver 4-wheel-drive performance. An appropriate lead ratio should be 0 to 5%—ideally 3%.
However, if the relationship between front and rear tire circumference is changed, the wheels will turn at different rates than they are supposed to. The result can be excessive lead, when smaller front wheels are rolling even faster than they should and pulling on the rear axle, or lag, when the front wheels that are too large slow the rear axle down and create a braking effect on the tractor. The phenomenon can be even more pronounced when turning. Excessive lead, or lag, can cause accelerated tire wear or even cause transmission damage.
Rolling circumference is the key factor in lead/lag problems. Some of the challenges include the fact that a tire in a specific size from one manufacturer may be a few inches larger or smaller in diameter than a tire of the same size from another brand, or that a worn tire of a particular size can be inches shorter in outer diameter than it was when it had all of its tread. That can significantly affect rolling circumference. Another change that can impact circumference is if you changed loads on one end or the other. And, of course, air pressure changes can affect lead/lag, too.
Another wrinkle is that a VF tire has more sidewall flex than a standard radial of the same size, so the outer diameter is different, even for same-size tires made by the same manufacturer.
Some of the most common causes of lead/lag problems are:
- Selecting the wrong-sized replacement tires on one of the axles
- Installing new tires on one axle while keeping worn ones on the other
- Using VF tires on one axle and standard radials on the other
The rolling circumference is the critical measurement when it comes to keeping replacement tires in the proper ratio. With today’s computerized tractors, there’s very little wiggle room for putting the wrong-sized tires on your tractor. You could cause expensive damage to your gearbox.
The bottom line: talk to your tire dealer to make sure your choices keep your MFWD tractor performing its best.
Please see our AG Tire Databook page for complete listing of Rolling Circumference Data from all of the above leading manufacturers: https://agtiretalk.com/databooks/
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.