How to Read Tire Size?

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Tire Size:

Installing the correct tires on your vehicle is vital to the general performance and safety of your vehicle. Your tire choice should reflect the conditions within which you drive and your preferences for vehicle response and handling. You must understand what tire size is correct for your vehicle to be able to make the proper choice when it is time to shop for tires.

Thankfully, determining the right tire size for your vehicle is fairly simple. All the knowledge you wish is straight away available either within the owner’s manual for your vehicle or somewhere within the vehicle itself.

While actual, physical measurements like width and diameter are factors that find the correct tire size, there are additional details you ought to consider. Things like load index and speed rating are integral to finding the proper tires.



No matter what vehicle you drive, finding the manufacturer-recommended tire size should be easy. The simplest place to begin looking is that the owner’s manual.

Don’t worry if you can’t locate the manual; you’ll also find a tire fit guide in these locations:
  1. The driver’s side doorjamb
  2. Inside your glove box door
  3. Within your tank hatch

Assuming they’re the right size, you’ll find tire size data on the sidewall of your current tires. However, irrespective of where you discover your tire size, you may decipher a sequence of numbers and letters.



Let’s take a glance at what each number or letter stands for, one by one, within the order, they seem in your tire size data. We’ll be using this tire size as an example: P225/70R16 91S



For most vehicles, you’ll see the letter “P” before the amount sequence begins: P225/70R16 91S. The “P” is brief for “P-metric” which may be a designation by the Tire and Rim Association for a “passenger car” tire type. This signifies the tire was designed to primarily be used on passenger vehicles, which may include cars, minivans, SUVs, and other light-duty pickup trucks. If you see “LT” rather than “P,” it’s because you wish “light truck” tires – “LT” is brief for “LT-metric” which could be a designation by the Tire and Rim Association for a “light truck” type tire. Light truck tires are designed to be used on vehicles capable of carrying heavy cargo or pulling trailers.

Similarly, “T” stands for “temporary” and is for your adipose tissue. If you see “ST,” meaning “special trailer.”



The first number to seem in your tire size information is that the width, in millimeters, of the right tires for your vehicle: P225/70R16 91S.

Tire width always refers to the measurement from one sidewall to a different. Thus, a tire with the measurement “P225” is for a passenger vehicle and encompasses a nominal width of 225 millimeters.



After the slash mark, the following number you see is for the tire’s ratio, which essentially tells you the way tall your tire’s profile is: P225/70R16 91S. Aspect ratios are delivered in percentages. Tire makers calculate the ratio by dividing a tire’s height off the rim by its width. If a tire has a side ratio of 70, it means the tire’s height is 70% of its width.
Lower ratio tires, like a 60 series, generally offer vehicle handling performance advantages over higher ratio tires, like a 75 series.



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

There are two kinds of construction that you just might even see on the sidewall of a tire:

  1. R – Radial
  2. D – Diagonal or Bias Ply

Radial tires represent the overwhelming majority of tires on the road today; thus “R” will usually be shown within the tire size designation. Radial construction means the tire’s internal ply cords are oriented during a radial direction, from one bead over to the opposite, essentially perpendicular to the axis of rotation.



The next number is that the diameter code, in inches, of the rim onto which the tire is mounted. As an example, a tire with the P225/70R16 91S would fit a rim with a 16-inch diameter.

View Other Common Diameter Sizes:

  1. 14-Inch Diameter
  2. 15-Inch Diameter
  3. 17-Inch Diameter
  4. 18-Inch Diameter
  5. 19-Inch Diameter
  6. 20-Inch Diameter
  7. 21-Inch Diameter
  8. 22-Inch Diameter



The next figure within the sequence is your tire’s load index, which tells us what proportion weight, in pounds, the tire can support when fully inflated: P225/70R16 91S

We call it the load “index” because the quantity doesn’t tell us the precise number of pounds the tire can carry, a minimum of not by itself. However, the quantity does correspond to a particular load capacity listed in an index. Beginning with 1 and ending with 150, numbers within the load index represent carrying capacities of 99 to 7385 lbs.



The final figure in a very tire size sequence is that the speed rating, which is indicated by a letter: P225/70R16 91S. Even as your load indicator corresponds to a selected load, your speed rating letter corresponds to a selected speed capability supported a consistent laboratory test.

For example, a tire with speed rating “S” is rated for up to 112 mph, while a tire rated “R” is up to 106 mph. Remember that this isn’t a recommended cruising speed. Of course, you must always follow legal speed limits on roadways.

Tires with higher speed ratings, tend to supply increasing handling performance. Replacement tires must have an identical or higher speed rating to take care of vehicle speed capability. If a vehicle has tires with different speed ratings, it’s the speed rating of the “slowest” tire that dictates the vehicle’s top speed.

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