In a tire size of P235/75R15, the "P" designates that is is a passenger tire. The "235" is the width of the tread side to side, in millimeters. The "75" is a ratio of height to width. In this instance the sidewall is 75% of 235. The "R" says that it is a radial tire, which any tire for your passenger vehicle will be. The "15" is the diameter of the wheel in inches. Some manufactures may include an additional letter such as "Z" as in P245/45ZR18, the "Z" gives an indication of the speed rating of the tire.

In a tire size of LT 235/85R16, the "LT" designates that it is a light truck tire. On light truck tires, you also have to consider the load range of the tire, or how much weight each tire can carry.

With so many vehicles being 4X4’s and AWD, it is important on these vehicles to keep all tires the same size, design and tread depth. When purchasing tires for these vehicles consider all four tires as one, as they work together compensating for each other.

Ply ratings are an important factor when purchasing your tires.
They are listed as Load Range B, Load Range C, Load Range D, or Load Range E, these are the most common listings.
A Load Range of B is a 4 ply tire; a Load Range C is a 6 ply tire; a D load range is an 8 ply; and an E Load Range is a 10 ply tire, increasing by two for every letter.

Your load range will be listed on the placard inside the drivers door along with your tire size. It is important to not overload your tires by using a lower load range than required, this decreases your tread life and compromises the safety of your tires.

The speed rating is also listed on the sidewall of a tire.
This is generally listed after the size and load index, which consists of two or three numbers, the letter following is the speed rating.

Examples are:
98T, 101W, 87H, 97Z

These ratings tell you what is the performance level of a tire. The most common ratings are S, T, H, W, V, AND Z. Tthe S and T have the lowest performance level, or what most people would consider the average passenger tire. The H rating will give you more performance while still giving good mileage. The ratings of W, V and Z, are the high performance tires. If you are an aggressive or fast driver, or your vehicle is a sports model this may be the rating you want to consider.

Another part of the speed rating the speed at which a tire can travel for one hour straight before it is compromised. The chart below lists the different ratings:
S= 112 mph     V=149 mph     Z=186 MPH+
T=118 mph     W=168 mph      
H=130 mph     Y=186 mph      

You want to keep the same speed rating on all four tires of your vehicle, as recommended by the manufacturer.

Also on the sidewall will be listed M&S, or possibly M/S. Virtually All passenger tires will have this listing. While this used to indicate that this was a snow tire, that no longer applies. Most all season tires will also have this listed on the sidewall.

The tread design will be listed on the sidewall. Some tires will list the manufacturer as well as the tread design. For example, the Cooper Discoverer H/T on the sidewall indicates that Cooper makes the tire and the tread design is the Discoverer H/T. Just as your vehicle may have a sub model, so do tires in a manner of speaking.
The Discoverer line in Cooper has a few different treads such as the H/T and the Discoverer ATR. Firestone has the Firehawk G/T, as well as the Firehawk SZ50, and the Firehawk Wide Oval . So when looking for the tread design of your tire, make sure you list everything on the sidewall. In addition to what is previously listed, it may also be just a listing of letters, but it will be the larger print on the tire, the manufacturer wants that advertising to be visible.

Let’s talk about dry rot on a tire. A tire has a life of 5 to 6 years. It does not matter if this tire is on your vehicle, in your garage or on the tire store shelf. The ozone affects the components of the tire and breaks them down over time, affecting the safety of the tire.
It is recommended that after 5 or 6 years that you do not use the tire. We run into this with spare tires that have never been on the vehicle.

Even though it appears new, it is starting to break down. We also see this quite often on motor homes and recreational trailers. If you are buying a used trailer or motor home, do not assume that because the tires have a lot of tread on them that they are new or usable.

All tires have a manufacture date on them, this is listed as week and year. This information can be found in the DOT Serial Number.
DOT MA L9 ABC 0301, would be read as follows:
The DOT is the dept. of transportation .
The MA is the plant of origin.
The L9 is a code designating the size
ABC is a manufacturer code
0301, means the tire was made during the 3rd week of 2001
The first two numbers being the week and the last two the year.

I included this in the information page simply because so many people don’t realize that there is a specific tire for trailers. They have an ST before the size. Such a size would be ST225/75R15. This tells me that it is a trailer tire, the ST, and it is a radial tire, the R. Unlike tires for your vehicle, there are bias tires manufactured for trailers.

The radial tire will give you more miles and be able to run at hotter temperatures than bias tires.

You do not want to mix bias and radial tires on your trailer.

Please contact us with any other questions or concerns about purchasing your next set of tires.