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Info from this link: Finding the Right Tires, there are also pictures posted there as well.

What may seem like an easy job, finding the right tire for the application, can have many components. There are many decisions to make when selecting a tire. A few of them include tire size, tread type, load rating needed, radial or bias, and tube or tubeless, all of which can have an impact on the tractor's performance in the application.

Selecting the right tire begins with understanding basic tire information. Read on to learn more about information to consider when selecting tractor tires.
Tires and Wheels
People often use the words tires and wheels interchangeably, but technically that's not correct. A tire is not a wheel.

A wheel, wheel assembly, or rim refers to the metal portion. In the image above, the yellow portion is the wheel, or rim. Wheels and rims can be steel or cast. Cast rims are heavier than steel rims and typically can handle a higher load rating.

The tire refers to the rubber part. In the image above, the tire is the black part.
Tire Sizes
Tires sizes are typically given in either standard sizes or metric sizes, depending on the manufacturer.

Standard size
U.S. designations (sometimes called standard) measure in inches and typically feature a star load-rating system.

The star designation was related to a standard maximum tire pressure. For example, one star meant a a maximum of 18 psi, regardless of tire size; two stars meant a maximum of 24 psi; and three stars meant a maximum of 30 psi.

Load ratings vary based on tire size. This means a small tire and a large tire could both have a three-star destination, but different load ratings.

Standard size example
18.4R30 ***

18.4 = tire section width (inches)
R = radial construction
30 = rim diameter (inches)
*** = 3 star = symbol

Metric size
The metric designations provide measurements in millimeters and use a load index expressed as a three-digit number. This system has a value-based rating of load-carrying capacity, called the load index (LI).

LI relates to the maximum load-carrying capacity of the tire. The metric tire-rating system allows manufacturers to design tires that better meet specification requirements for diameter-to-width and rolling circumference dimensions, which are critical for mechanical front-wheel drive (MFWD) tires.

Metric size example
480/80R30 145 A8 R1W
480 = tire section width (mm)
80 = aspect ratio (percentage)
R = radial construction
30 = rim diameter (inches)
145 = load index
A8 = speed symbol
R1W = tread designation

In recent years, many agricultural tire manufacturers have moved from the U.S. designation (in.) to a metric designation (mm). The metric designation conveys more information and allows tires to be compared by load index.

Conversion between standard and metric tire sizes

Metric to standard conversion:
Divide the metric number (mm) by 25.4 to get inches.

Example: 480-mm section width/25.4 = 18.9-in. section width.

Standard to metric conversion:
Multiply the standard number (inches) by 25.4 to get millimeters.

Example: (18.4-in section width) x (25.4) = 467-mm section width.
Aspect ratio—This number provides the section height of the tire relative to the tire width. The number is related in a percentage. So a 480/80 has an 80 percent aspect ratio. This means the tire's sidewall is about 80 percent tall as it is wide.

Aspect ratio = (tire section height/tire section width) x 100.

Speed symbol—This is the maximum speed allowed for the rated load of the tire.

International speed symbols
Speed symbol
Speed category (km/h)
Speed category (mph)

Tread designation
Tread designation—The tread designation describes the tread and indicates the tire use. Utility tractors typically have R1, R1W, R3, or R4 tread designations.

R1 is the most common tread type used in agriculture throughout the United States and Canada. Sometimes called bar tread, R1 provides good traction for dry-land farming.

R1W offers a deeper tread than a R1 tire. At the center, the tread depth is typically 25% deeper than a standard R1. The deeper treads of the R1W are popular in wetter soils. Many European utility tractors use R1W tires.

R2 has the deepest tread depth. R2 is used for farming extremely wet and difficult conditions. The tread is approximately twice as deep as the R1 tires. R2 tires are rarely used on utility tractors.

R3 offers a less aggressive tread pattern for turf applications. The turf tread pattern reduces potential ground damage, but sacrifices traction. R3 tires are normally wide tires that provide a larger footprint for less compaction. These tires are ideal for turf applications, like mowing parks or harvesting sod. Typically, the tread depth is about half of the tread depth on an R1 tire.

R4, or industrial tread, tires have a tread depth of about 70 percent of an R1 tire. They offer more traction than an R3 tire, but less than an R1tire.

F2 front-tire treads complement the R1 or R1W rear tires. F2 has a multiple rib steer tire tread and is used in general farming conditions. They are normally found on 2WD tractors.

F3 front-tire industrial multiple rib steer tires work well with R4 rear tires. They are normally found on 2WD tractors.

I3 bar-type tread tires look like a small version of the larger drive tires.
Load ratings
Load ratings communicate the maximum load that can be carried by that component. It is important to note there are axle, wheel, and tire load ratings.

The overall load rating of a tractor is determined by the axle, wheel, andtire load ratings. Of those components, the lowest load rating is the restriction. The load rating of the John Deere wheel is at least as high as the load rating of the tire with which it is paired.

In most cases, the tire is the limiting factor regarding load restrictions. This means the tire load index is the most important load rating to know. Refer to the international tire load index numbers chart for information about how the load index relates to pound-carrying capacity.
Radial vs. Bias Construction
Agriculture tires are offered in either bias or radial construction. The tire size relates this information. Bias construction by using a "-". For example a 16.9-30 would be a bias constructed tire. Radial tires have an "R" in the tire size. For example 18.4R30 have radial construction.

Bias tires are preferred for utility tractors that do not perform major tillage operations and do not spend much time on the road and/or are operated for a low amount of hours per year. Bias tires are typically less expensive than radial tires.

Radial tires have a larger footprint than a comparable-size bias tire. This gives radial tires more traction than bias, making them the preferred tire for wet, muddy field conditions or tillage operations. Radial tires have a different type of construction than bias tires. The heavier construction of a radial makes them better suited for operating on pavement.
Tubed vs. tubeless tires
Tires can be either tube or tubeless. Tubeless tires are tires without internal tubes. Tubeless tires typically last longer and are easier to repair than tube tires. Tubed tires are a little more difficult to repair. A punctured tubed tire requires disassembling the wheel and tire to repair the tube.

Tubed tires are normally desired for tires requiring liquid ballast. Placing the liquid ballast inside the tube saves the tire rim from any contact with the liquid ballast.

Ultimately, the selection of tubed tires vs. tubeless tires depends on the application and operator preference.
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