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November 18, 2021

What is a Tire ID Number and How Does It Work?

There is a ton of info on the sidewall of a tire, but how many know what all of it means? We’re talking about the Tire Identification Number (often called the “TIN”). This post will attempt to explain all that tire info in an easy-to-understand manner and ensure you make an informed decision when purchasing a new set of tires for your vehicle.

What is the Tire Identification Number, or TIN?

A Tire Identification Number, or TIN for short, is a series of numbers and letters that are molded inside each tire. This number allows you to quickly determine important information about the tire’s make, model, dimensions (in both metric & American units), weight capacity (a very important metric) as well as warranty data.

Tire manufacturers began placing TINs on tires sold in North America beginning in 1974. Originally it contained more information than what we see today; this additional info included things like treadwear rating (basically how long you can expect the tire to last) and max load (how much weight the tire can support at maximum inflation pressure). As time went on, manufacturers decided they would rather leave off some of this data in favor of simplicity.

The TIN has been updated a few times since 1974 when it was introduced. The following is a “timeline” of when these changes occurred:

1974 – the year the tire industry began placing TINs on tires sold in North America 1985 – the first change to Tire Identification Number 2001 – second change to Tire Identification Number 2008 – third & final change to Tire Identification Number (so far)

Keep this timeline of changes in mind as you read through all that follows below. Knowing when each of the changes occurred will help you better understand what each piece of information means. We’ll go into more detail about everything below but here are some quick highlights…

How to Read TIN – Tire Diameter, Construction Type, Rim Diameters, Max Inflation Pressure

The TIN on all tires sold in North America will start with a set of 3 numbers which represents the tire’s approximate diameter. This is not an exact number as it does not take into account any additional space needed for load & inflation but it gives you a good idea as to how big the tire will be. You can find this figure by looking at your vehicle owner’s manual or doing some quick research online. It doesn’t tell you exactly how large a particular model is but it does help narrow things down a bit.

After that first set of three numbers, you’ll see one letter & another number combination – these represent info about the tire construction and are important to know if you have any special requirements for your tire pressure. If you have an all-season or summer tire, the letter will be “M” or “S”, respectively. If your vehicle requires a specific type of tire inflation, it should be included in this area as well. For example, if your vehicle requires a non-temperature sensitive spare tire, there will be a single-digit between these two sets of letters/numbers that indicates how much weight each tire can support.

The final component of the TIN is a single number found at the end which represents the rim diameter in inches. It’s important to note that this number doesn’t represent the size of the wheel but rather how large of an opening exists on that wheel for your new tires to fit into. In other words, you can’t always use a tire that’s larger than your wheel simply because the TIN says it fits – the tire will just stick out of your wheel and rub against things as you drive down the road. If you’re not sure what size of rim your vehicle uses, check with an auto parts store or do some quick research online.

After reading this section, hopefully, you’ll understand why we urge all customers to make sure they know what type of info is represented on their TIN before purchasing new tires! The last thing we want is for them to end up with a set of tires that don’t quite fit and which put them and their family at risk (or worse yet, become stranded somewhere).

If you live in North America, you’ll soon be seeing new TINs with an extra piece of info on them. This will be another letter (or maybe even two) and it’s all part of the tire industry’s efforts to promote fuel efficiency. The idea is that by giving drivers more information about how their tires perform in real-world conditions, they can then take action to improve fuel economy if needed. We’re not sure exactly when this change will go into effect as it has yet to be finalized but we’ll keep you posted as things progress.

How to decode the information on a Tire Sidewall

This section will help you sort out what the information on a tire’s sidewall means. We’ll list each piece of data from largest to smallest as they appear from left to right starting with the bottom of the tire and moving up.

Tire Diameter – as mentioned above, this is an approximation of how large your new tires will appear on the vehicle when they’re mounted. It is not meant to be exact but it’s useful when you’re trying to find out if a certain model will fit in your existing rims or looking for replacement tires that won’t stick out too far

Construction Type – this letter represents how the tire was built and can tell you things like whether it is summer or all-season tire, whether it’s meant for use in higher or lower temperatures and how much weight each tire can support

Tire Type – this letter represents what the tire is meant to be used for. If your vehicle says “LT” on it, that means you have a light truck and that you need an LT tire (typically you won’t see this on passenger cars as those tires are classified as “P”). Also, if your vehicle says “All Season” or “Q”, it means that the tire has a symmetrical tread and is made to be used all year round (the vast majority of tires will fall into one of these two categories)

Tire Width – this number represents the tire’s total width from one sidewall to the other. As a general rule, you should make sure your new tires are within 1/8″ of each other in total width

Rim Diameter – as mentioned above, this number doesn’t represent the size of the wheel but rather how large of an opening exists on that wheel for your new tires to fit into. In other words, you can’t always use a tire that’s larger than your wheel simply because the TIN says it fits – the tire will just stick out of your wheel and rub against things as you drive down the road. If you’re not sure what size of rim your vehicle uses, check with an auto parts store or do some quick research online.

Tire Load Rating – This number represents how much weight the tire can bear safely. The vast majority of vehicles will require a tire load rating of “E” (for passenger cars) to ensure that they don’t break under normal driving conditions

Speed Rating – as mentioned above, this letter represents how fast you can safely drive on the tire. If your vehicle says “C” on it, that means you’re limited to speeds of 112 mph or less (this is usually for low-speed vehicles like small ATVs and lawnmowers)

Tire Construction – this letter lets you know what kind of sidewall construction the tire uses. If your tire says “D” on it, that means it has a diagonal steel belt under the tread for added strength and support. If you see an “L”, that just means there’s a nylon cap over the bead so don’t let this letter fool you into thinking the tire is any different than one without it

Treadwear Rating – this number tells you how quickly a tire wears down under normal driving conditions. A “200” means that the tire will last twice as long as another one with a “100” rating

Traction Rating – this letter lets you know the traction capabilities of your new tires. If you see an “A”, that means they’ll be good for use in wet conditions. A “B” rating means they’ll be great for snowy areas while a rating of “C” or higher means you have nothing to worry about no matter where you live

Tire Sidewall ID – this final piece of data is called the Tire Identification Number (TIN) and it’s just a series of numbers and letters that serves as a unique identifier for each tire. Some tires have the TIN molded onto the side of them – just look at your sidewall to find it

And there you have it – all the information you need to make sure your next set of new tires fits your vehicle looks good on it and gets you where you need to go safely.