Tractor Tire Codes Made Simple

Confused By All the Numbers on Your Tire?

Start with identifying your wheel diameter, tire size and type.

This is pretty straightforward. The diameter of your wheel will be important information when shopping for wheel weights.

Now note the Load Index and Speed Ratings in the above decoder.

The load rating is the maximum amount that can be carried by the single tire. The load rating is ALWAYS related to a certain speed and to the nominal inflation pressure. See chart below:

Then take a look at the speed rating for your tire:

Let us say you have a 151A8 or 151/A8 tires. 151 would be the load index so a single tire can carry 7600 pounds at the correct inflation pressure at the rated speed. A8 would be the speed rating. In this example the tire could safely travel up to 25 mph with proper inflation and under normal (level ground) conditions. If you have four of these tires installed and the weight is distributed evenly, you could carry a total amount of 30,400 pounds up to 25 miles per hour. The total carrying capacity of 30,400 pounds includes the weight of everything. You, Your machine, Your ballast, Your implements, and the amount of material weight in your loader.

Note: The front axle weight and rear axle weight of your tractor are often different. While there are some ballpark methods to guesstimate the weight per axle or weight on each tire, it is usually better to actually weigh your tractor correctly. Get a correct weight of the entire machine and a correct weight of each of the axles.

Simple enough? Yes and No. Determining the values of the codes on your tire is pretty easy. Unfortunately, it can get complicated depending on the work to be performed, the typical operating speed, and the terrain conditions. Since the load ratings are tied to the speed ratings, a “plus up” or “load bonus” in carrying capacity on conventional tires is possible with correct inflation pressures at lower speeds. Bias ply tires, unlike radial tires are not made to run at lower air pressures. With Bias Ply Tires: ALWAYS verify they are not being overloaded. For more guidance, check this resource of very good information.

Sub Compact, Compact, and Small Utility Tractors with Bias Ply Tires DO NOT always have the code numbers readily available on the side of the tires. In these cases. you must read all the warning and data sections on the tires and should also consult your owner’s manual for the correct information. Many are in plain English and state the max load, speed and inflation pressures.

We recently looked at a new L2501 tractor equipped with a LA525 loader on a dealer’s lot. The rear tires stated a “6 PLY RATING” and the number 412373 on the side of the tire. We find that tire to be a Titan Trac Loader 15×19.5 bias ply tire. On one website it is listed as a skid steer tire with a max load speed rating of 6130 pounds at 5 mph with 30psi inflation pressure. On another website it is listed as a 129/A8 tire which would give us a load speed rating of 4080 pounds at 25 mph with 30psi inflation pressure. Both are correct as speed impacts load rating. For the application on a skid steer, the speed would be much slower than on the tractor, thus enabling more load carrying capacity.

The older term of ply rating still used in the above example goes back to the days when bias ply tires were constructed of layers of cotton fabric. Ply rating referred to how many layers, or plies, of cotton had been used in the tire’s construction. The number of plies determined the strength of the tire.

Today, tire plies are no longer made of cotton. Tires are constructed using fewer, stronger, plies. The term “ply rating” no longer refers to the actual number of plies. Instead, the ply rating indicates an equivalent comparison to early cotton constructed bias ply tires. Most tires that list a ply rating like “6 Ply Rating” will also list maximum load, speed, and correct inflation pressure.