You might not notice it the first time, but there are a lot of inscriptions on the sidewall of every tire. Even if you look closer, you might not be able to understand what’s written as everything is in code. Knowing what’s inscribed on your tires can help you in emergency situations. Luckily, decoding it isn’t a big deal.
That’s exactly what we are going to explore – what do the numbers on tire size mean and what to look for when purchasing a tire for your vehicle.
What Are The Tire Sizes?
Per standard, tires come in 8, 10, 12, 13, 14, 15, 17, 18, 19, 20, 22, 23, 24, 26, and 28 inches. This standard is applicable to passenger tires, SUVs, light-duty trucks, and minivans—basically, all daily-use or commonly-seen vehicles.
What Do Tire Size Letters Mean?
In most cases, the codes on tires start with letters, for example, P or LT. The letter specifies the specific function or service for which the tire was designed.
1. P-Metric
The most common letter you would encounter would be P, which stands for Passenger tires. These tires are suitable to lift the passenger load and are usually used for minivans, cars, light-duty pickup trucks, SUVs, etc.
2. LT-Truck
The denominations LT can be found as either prefix or suffix in the codes:
LT - Prefix
LT means Light Truck, and when it appears in the prefix, the tires are designed to carry heavy loads like towing a trailer. Therefore, this can be found on light-duty to medium-duty trucks, small pickups, minivans, and SUVs.
LT - Suffix
These tires can be used for all kinds of trucks (light, medium and heavy duty) as well as in sports utility vehicles and full-sized vans.
3. Euro-Metric/Metric
This type of numbering originated in Europe; hence, the name. In this format, there are no letters, either at the beginning or the end. The Euro-metric tires are almost comparable to the P-metric tires when it comes to their sizes, but as for the load-bearing capacity, the euro-metric tires are superior.
These tires are quite suitable for minivans and SUVs and can even be used on all passenger vehicles.
4. T-Metric
The T-metric is used for tires that are to be used as temporary spares in case of malfunctioning of the actual tires. These tires are used as step-in when the moving tires get punctured or become unsuitable for use.
5. C-Metric
The C-Metric denotes Commercial Tires and is made to withstand heavy loads, making them suitable for trucks and other load-carrying vehicles.
What Do Tire Size Numbers Mean?
Section Width Of The Tire
The immediate three numerals that follow the letters tell you the cross-sectional width of the tire, measured in milliliters. You can easily convert it to inches by dividing the value by 25.4.
Aspect Ratio Of The Sidewall
The two digits after the first slash following the section width of the tire is the aspect ratio of the tire’s sidewall.
For example, let's consider the code: T145/70R17 106M.
The 70 denotes that the sidewall distance measured from the wheel rim up to just outside of the tread is about 70% of the section width. If the aspect ratio is lower, the tire has a low profile with a shorter sidewall. On the other hand, if the tire has a high aspect ratio, it's most likely to look like a donut as it has a high profile and longer sidewall.
Diameter Of Tire And Wheel
Let's take the example above: T145/70R17 106M.
The 17 that follows the aspect tire ratio and the letter ‘R’ is the tire and wheel diameter. This is mentioned in inches.
You may be wondering what the letter R is. This position gives you insight into the construction of the tires.
The most commonly seen ones are:
● R - Radial
● D - Bias Ply
● B - Belted
Summing Up
That’s how to decode the essential details on the tire inscriptions. Now you know what the numbers mean on tire sizes. Knowing this can be very helpful as you can easily notify a nearby mechanic about what kind of tire you need in case of tire damage.
