How to Measure Tire Size KW: tire service


Getting a tire’s measurements is an integral part of selecting good tires for your vehicle. Most often the tire measurements would be printed along the side of the tire, but if by chance they’re not many people may not know which measurement to make or how to interpret the numbers they see.

Knowing how to read, interpret and and measure your tire’s diameter, width, aspect ratio and tread depth is all crucial information you’ll need in order to find the ideal tire. In this article we’ll break down the elements and teach you how to measure your tire’s size.

How To Determine Tire Size

After you have come to the conclusion you need to buy tires, you’ll need to know which size is correct for your vehicle. This information can be found on the inside of your driver’s side door jamb or in your owner’s manual.  To ensure that your current tires or potential replacements are right for your car, it’s a good idea to have a working knowledge of how tire sizing works.

If you, similar to many others, are unsure of how to read a tire’s measurement it can feel like a confusing and frustrating time. But don’t worry, if you ever feel too over your head,  there are alternatives. A good tire retailer or a tire shop can help advise you on which tire is best for your car, your needs and can answer any questions you may have.  Since there are so many optional tire sizes which can have different load capacities and certain wheels could require a different rim, diameter or inflation pressure. An authorized tire retailer is one of your best resources to have around if you’re having trouble.

Metric Sizing

Most cars, SUVs and light pickups (under ½ ton) will come with tires that are either marked with a “P” for P-Metric or  no preceding letter, if there is no letter this is called  Euro-Metric. For P-metric tires this means that your tire is standardized for a passenger car type tire. But if you have an E-metric there will be no letter and it will start immediately  with a number sequence (which could be 225/70, R16, 98H)  Euro-metric means that your car is an european passenger tire type.  Both P-metric and Euro-metric size tires are used on most passenger cars and light pickups.

Now we’ll quickly go over what it means if you have a SUV, van or pickup truck. With these kinds of vehicles you may see a different type of size designation on your placard that is specific for heavy duty or light trucks and vans. The two kinds of sizes in this category are LT-Metric and Euro=Metric Commercial (this can also be called C-type). They are both still considered metrics so they would have the same structure as P-Metric and Euro-Metric but do have some differences. The main difference is that in accompaniment to a  sequence there will be two load index numbers and a load range.

Load index refers to a specific load capacity listed in an index. It usually will  begin with a 1 and end with 150. Numbers in the loadad index represent the carry capacity. For passenger tires there are two types of load types: standard load and extra load. If there is an XL on your ties, this means they are extra load tires.

There are other types of tires that you may see like spares, a temporary spare will be marked with a “T” indicating so. If you see a size that has a “ST” this means special training and is only used for trailers.


The first number to appear in your tire size is the width, most often in millimeters. This indicates the correct tires for your vehicle.

Tire width refers to the measurement from one sidewalk to the other. For example, if a tire had a measurement of P22, this means it’s a passenger vehicle and has a width of 225 millimeters.

Aspect Ratio

After the slash mark, the next number you’ll see is for the aspect ratio. This will tell you how tall your tire profile is. Aspect ratio is done in percentages, so if you see something like P225/70 this means that the tire height is 70% of the width.

Lower aspect ratio tires, such as a 60 series, generally have better vehicle handling performance advantages when compared to higher aspect ratio tires.


After the aspect ratio comes a letter that indicates the type of internal construction maintaining your tire’s stability: P225/70R16 91S.

There are two types of construction that you may see on the sidewall of a tire:

Next following the aspect ratio comes a letter that indicates the internal construction. You can see a letter. You will either see an R for radial or a “D”, “B”, or “-” for diagonal or bias ply.

Radial tires are the most common on the road. Rodial construction simply means that internally the cords are orientated in a radial direction, from one bead over the others.

Speed Rating

The final figure is the speed rating which will be indicated by a letter. Just like your load index this corresponds to a particular speed capability.  Replacement tires need to have the same or a higher speed rating as the original tires in order to maintain the speed capability. If a tire has tires with a multiple different speed rating, it is the speed rating of the “slowest” tires that will dictate the vehicle’s top speed.


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