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Tire Tech Guide

There are many different tires available for your truck. From a 33" street tire for your racecab, to a 38" mud-terrain for you serious off-roaders, XDP carries a wide range of combinations to fit your needs. But where should you start when you're trying to pick out that new set of tires for your truck? Follow along below for our complete guide on how to decipher and convert tire sizes, understanding load ranges, choosing a tread pattern & more!

Tire Size

The first place to start when choosing a new tire for your truck is determining what size tire you already have (if replacing), or if changing to a different size, what size can your vehicle configuration accommodate. In either case, your likely first step is looking at your current tire to find out what size you currently have. You will find the size of your tire on its sidewall, displayed as either an Inch Size or a Metric Size.

Standard Inch Sizes are displayed in inches using a Diameter x Width x Wheel Diameter format. For example 35 x 12.5 x 20.

Metric Tire Sizes can be a bit more tricky to decipher. They are displayed in a Section Width / Aspect Ratio x Wheel Diameter format. A common example is 325 / 60 R 20. Metric tire sizes are often confusing, but luckily you will find a handy calculator and more information below that will help you convert your metric size to a standard inch size.

Metric Tire Size Conversion Calculator

/ R
Example: 325 / 60 R 20

Standard Size
x x

Understanding Metric Tire Sizes

Typical Metric Size Format


The three pieces of information needed to convert metric tire sizes to standard inch sizes are Section Width, Aspect Ratio and Wheel Diameter. The metric size can be found on the sidewall of your tire. Below, we will define what each section means, as well as provide a step-by-step guide on how you can convert a metric size to a standard size. First, let's decipher a metric size code.

Section Width
The first three digit number in a metric size is the section width. This is the measurement from sidewall to sidewall in millimeters. Using our example size above, the section width is 325 millimeters wide.

Aspect Ratio
The second set of numbers is the aspect ratio. This ratio is the percentage of the tire sidewall to its cross section. In our example above, this number is 60. This means that the sidewall height is 60% of the section width (325mm).

Wheel Diameter
The final set of numbers in a metric size is the Wheel Diameter. This number refers to the diameter of wheel the tire is being mounted to. Following the example, this number is 20.

Converting Metric Sizes to Inch Sizes

Much like metric sizes, Standard Inch size tires have three main components, diameter, width and wheel diameter. Below we will show you how to convert the metric example above to a standard inch size.

Step 1: Converting Width
Standard width can be calculated by converting the metric section width from millimeters to inches. There are 25.4 millimeters in one inch, so we can divide the section width by 25.4.

325mm / 25.4 = 12.8" Width

Step 2: Wheel Diameter
Wheel diameter is the easiest of the components to calculate between Metric and Standard sizes. The wheel diameter is provided in inches for each configuration.

20 = 20" Wheel Diameter

Step 3: Calculating Overall Diameter or Height
Now that we have figured out the Width and Wheel Diameter, we can use this information to calculate the overall diameter of the tire in inches. This is calculated by multiplying the aspect ratio as a decimal percentage and the width, twice, since there is a sidewall on the top and bottom. Then add this number to the wheel diameter.

(12.8*.6) + (12.8*.6) + 20 = 35.35" Overall Diameter

Now we have converted all of the measurements of a metric tire into a standard tire, making the overall standard size:

35.35" x 12.8" x 20"

Common Metric to Standard Conversions
265/70R16 30.6 x 10.4 x 16 265/75R16 31.6 x 10.4 x 16 285/70R16 31.7 x 11.2 x 16 285/75R16 32.8 x 11.2 x 16
295/75R16 33.4 x 11.6 x 16 305/70R16 32.8 x 12 x 16 315/75R16 34.6 x 12.4 x 16 385/70R16 37.2 x 15.2 x 16
245/70R17 30.5 x 9.6 x 17 245/75R17 31.5 x 9.6 x 17 255/75R17 32.1 x 10 x 17 255/80/17 33.1 x 10 x 17
265/65R17 30.6 x 10.4 x 17 265/70R17 31.6 x 10.4 x 17 275/70R17 32.2 x 10.8 x 17 285/70R17 32.7 x 11.2 x 17
285/75R17 33.8 x 11.2 x 17 295/70R17 33.3 x 11.6 x 17 305/70R17 33.8 x 12 x 17 315/70R17 34.4 x 12.4 x 17
255/55R18 29 x 10 x 18 255/70R18 32.1 x 10 x 18 265/60R18 30.5 x 10.4 x 18 265/65R18 31.6 x 10.4 x 18
275/65R18 32.1 x 10.8 x 18 275/70R18 33.2 x 10.8 x 18 285/75R18 34.8 x 11.2 x 18 295/70R18 34.3 x 11.6 x 18
305/60R18 32.4 x 12 x 18 305/65R18 33.6 x 12 x 18 325/60R18 33.4 x 12.8 x 18 325/65R18 34.6 x 12.8 x 18
265/50R20 30.4 x 10.4 x 20 265/60R20 32.5 x 10.4 x 20 275/60R20 33 x 10.8 x 20 275/65R20 34.1 x 10.8 x 20
285/55R20 32.3 x 11.2 x 20 285/60R20 33.5 x 11.2 x 20 295/60R20 33.9 x 11.6 x 20 295/65R20 35.1 x 11.6 x 20
305/50R20 32 x 12 x 20 305/55R20 33.2 x 12 x 20 325/50R20 32.8 x 12.8 x 20 325/60R20 35.4 x 12.8 x 20

Load Range / Ply Rating

The load range is also known as ply rating — a term that dates back to the days of bias-ply tires, which had different numbers of ply layers. More layers indicated a better and stronger tire. Today, ply rating still refers to the strength of the tire, but since fewer, stronger plies are used, the numbers have been replaced in some cases by load range letters.

Load RangePly RatingMax Pressure
B435 psi
C650 psi
D865 psi
E1080 psi
F1295 psi

Tire Class / Construction

There are many different classes of tires, which will be designated by letters before or after the size. These classes convey two things, Ply Rating, which speaks to load carrying capability, and tire type. Most diesel light duty applications will utilize a LT or "Light Truck" class tire. These tires are typically heavier weight capacity tires, which fall into the C (6 ply), D (8 ply) or E (10 ply) load range.

Smaller diesel SUV/car applications fall into the P or "Passenger" class of tire. Even some smaller light duty (1/4 and 1/2 ton) truck applications can fall into this class. Passenger tires usually carry a standard B (4-ply) load rating.

These classes of tires are constructed as either a Radial or Bias-Ply. The type is designated by either a "R" or "B" letter before the wheel diameter in the size. The more common of the two, Radial, have steel belts that wrap the tire perpendicular to the tread pattern. Due to the design, radial tires stay flatter in the tread pattern and allow the sidewall to flex. This results in better traction, fuel mileage and substantially better wear.

Bias-ply tires have belts that wrap the tire diagonally or in an "X" pattern. Bias-ply tires cause the tread to compress together, which can increase heat build-up, as well as inhibiting traction particularly on wet surfaces. Bias-ply tires, however, do tend to hold up better over time. So on rarely used vehicles, Bias tires may be a better choice.

Tread Pattern

Tires are offered in MANY different unique tread patterns. Choosing a tread pattern often corresponds to your intended use of the vehicle. The most common styles of tire associated with trucks are All-Terrain and Mud-Terrain tires.

All-Terrain Tires are the choice for all-around performance on a variety of surfaces. They combine a semi-aggressive tread pattern with the handling of a street tire. These tires are perfect for the enthusiast who uses their truck as a daily-driver or tow-rig, but also likes to do some light off-roading.

Things start to get more serious with a Mud-Terrain Tire. Mud-Terrains give you the most aggressive tread pattern for optimum performance off-road. Equipped with a more "open" tread pattern, these tires give your ride that traditional off-road look. While still capable for on-road use, using Mud-Terrains on the street usually result in more in-cab road noise, or "humming".

XDP Tire Blog

Still want to know more about tires before you pick out a set for your rig? Check out the Tires 101 and Tires 102 Blog articles on the XDP Blog. Each article is written by XDP’s in-house tech team of industry veterans with over 35 years of combined experience. There you will find information that you need to help you decode many of the markings on the sidewall of your tires. Learn what to look for so you can figure out things like tire speed ratings, load index, PSI rating, and more!


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