How To Read Tire Size?

Learning how to read tire size is an important step in selecting the right tires for your vehicle. Tire size is typically displayed on the sidewall of the tire, and it includes a series of letters and numbers that provide information about the tire’s size, construction, and load carrying capacity. Let’s simplify things.

Reading tire size you are going to see something like P215/65R15.

• P indicates that this is a tire for passenger vehicles
• 215 is the width of the tire in millimeters
• 65 is the aspect ratio, which means that the sidewall height is 65% of the width
• R stands for radial construction
• 15 is the diameter of the wheel that the tire is designed to fit on, in inches.

Let me explain the main things to know about each below.

P (For Passenger Tires)

P215/65R15 89H

At the start, you get to see either a “P” or a “LT” (for the most part). These basically tell you what type of tire it is. P stands for Passenger (tires), whereas LT stands for “Light Truck” (tires).

Learn all about LT here.

Although both would have similar inner build of polyester casing, steel belts and nylon cap plies, LT sizes get to have a stronger overall construction, so they get to be more durable in comparison.

And so where their more robust plies allow them to carry more weight, the heavier construction limit the steering response a little bit on roads.

In other words, LT sizes get to have stronger weight ratings and these sizes are built to carry a heavier weight, (of vehicles such as trucks). Passenger tires on the other hand are lighter, and can’t bear as much pressure because of their weaker inner make up.

Width

P215/65R15 89H

The next number tells, how many millimeters is the tire’s width, (which some also call tread width).

The wider the tire the better the overall grip, as more surface area of the rubber is available to meet up with the road. Though at the same time, that also means increase in the rolling resistance, meaning less overall fuel economy.

In other words you can say, grip comes at a price (literally).

For Your Info: You can actually safely put on 20 mm wider tires on your rims. They call it plus-sizing. For example if the vehicle has 205/65R15, you can either put on 215/55R15 tire or even 225/50/R15 to increase the contact patch with the road and with it overall grip.

Aspect Ratio

P215/65R15 89H

Aspect ratio is simply the thickness of the sidewalls. It tells what the ratio of it to the width of the tire. In other words, you can say, its the percentage of the tire’s width.

So in case of 215/65, it means the sidewalls are 65% of 215 and that is 139.75 mm.

Sidewall thickness is very important, as if the aspect ratio is too low, (consider low profile tires here), the overall comfort is compromised.

Though you do improve handling and stability with it at high speeds.

Too thick the sidewalls, and your vehicle would feel much more bouncy.

For Your Info: Did you know, that the most common all-terrain tire size is 265/70R17.

R – Radial

P215/65R15 89H

Some folks think R stands for “rim” or even worse “radius”, it just tells you about the internal make up of the tire, radial.

On this type of construction, the plies are plied over each other underneath in a perpendicular angle (to the center line of the tire).

Its the new type of construction that you mostly see with all the newer tires, and it talked about in contrast to Bias-Ply construction which is denoted by symbol B.

I have talked about them both in detail here.

Rim Size

P215/65R15 89H

The 15 at the end simply tells you about the size of the rim, it’s diameters in inches.

Here there are 2 things to make sure of. One of course you get the tire according to your rim.

And two, make sure there is not a lot of offset to the rim. Meaning, there’s no gap between the rim and the tire’s mounting.

A positive offset means the mounting surface is closer to the outside of the wheel, while a negative value tells you that it’s closer to the inside. If not aligned these can push the tire out sideways during turns, compromising on a lot of performance areas, like wear, handling and so on.

Load Index

P215/65R15 89H

Load index is the measure of how much weight a tire can carry on it. This numerical code stamped on the sidewalls simply corresponds to the assigned maximum weight.

For example taking the size 89, the tire indicates that its designed to take on 1279 lbs.

The higher the load index, the more larger the weight bearing capacity.

Also don’t confuse yourself with load index and load ratings, see the difference here.

Speed Rating

P215/65R15 89H

Similar to load index, speed ratings tell you about the maximum amount of speed a tire can handle safely.

This letter code is stamped right next to the load index number without any gaps, and corresponds to the speed number in mph/km/h, telling you about the maximum speed.

For example letter H tells that the tire can handle up to 130 mph. Similarly other letters such as S, T , U, V, W and so on, do the same.

For Your Info: Some folks think that the speed rating of a tire is the same as the maximum speed a vehicle can reach. That’s not the case. Its just the maximum speed that the tire can handle over a prolonged period without fail. Read that again.

For better understanding, learn these things about speed ratings.

One more thing: There’s a lot of confusion about the ZR rating, so it’s better you get it out of your way here.

What Else Is There?

In addition to tire size (P215/65R15 89H), you should also consider the following things.

UTQG Ratings

UTQG ratings are a set of standards set by the National Highway Traffic Safety Administration (NHTSA) to provide consumers with information about a tire’s tread wear, traction, and temperature resistance.

Traction grades range from AA (highest) to C (lowest) and temperature grades range from A (highest) to C (lowest), whereas tread wear is indicated by a number (100 to 1000, the more the better the tread life).

Inflation Pressure

On the tire sidewalls, this will be written as something like “Max Load XXX kg @ XXX psi” and it indicates the maximum weight that the tire can safely carry when inflated to the specified pressure.

Make sure you keep the inflation pressure in check, as it really affects the tire’s overall performance.

DOT Code

This is the code that shows the tire was manufactured after the year 2000 and met the safety standards set by the US Department of Transportation.

When getting a tire, make sure you buy the one with latest manufacturing date.

To Sum Up

So overall when reading tire size, make sure you know what is the difference between LT and P metric sizes, what is the width and aspect ratio of the tire.

What does R (Radial) mean? And how it’s different from Bias Ply.

And what load and speed ratings suit your drive the most.

Lastly some other things to keep in mind is the tire’s optimal air pressure values, tread depth, and tire’s DOT code (manufacturing date).