How to Read Tire Size

Installing the correctly tires on your vehicle is all-important to the overall performance and safety of your vehicle. Your tire option should reflect the conditions in which you drive and your preferences for vehicle reception and handling. To make the most inform decision, though, you must understand how to read run down size when it ‘s time to buy tires.
thankfully, determining the correct run down size for your fomite is relatively childlike. All the information you need is immediately available either in your owner ‘s manual or somewhere on the vehicle itself. already know how to read run down size numbers ? Skip the explanation and find the correct Bridgestone bore for your vehicle on-line or by visiting a Bridgestone tire dealer near you.

While actual, physical measurements like width and diameter are factors in finding the right run down size, there are extra details to consider. Knowing how to read car tire sizes besides means understand terms like load index and travel rapidly rat that affect your vehicle ‘s overall capabilities.


No matter what vehicle you drive, finding the manufacturer-recommended tire size should be easy. The best place to start looking is the owner ‘s manual .
Do n’t worry if you ca n’t locate the manual ; you may besides find a bore burst scout in these locations :

  • The driver’s side door jamb
  • Inside your glove box door
  • Within your gas tank hatch

You can besides find bore size data on the sidewall of your current tires ( assuming they ‘re the proper size ). however, no count where you find your tire size, you will have to decipher a sequence of numbers and letters. Do n’t worry if it looks confusing at first base — every letter and number has a straightforward think of. Let ‘s break down how to read car run down size .
Find Your Tire Size Information Image


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


Tire Sidewall Information Image
For most vehicles, you ‘ll see the letter “ P ” before the number sequence begins : P225/70R16 91S. The “ P ” is light for “ P-metric, ” which is a appointment by the Tire and Rim Association for a “ passenger car ” run down type. A “ P ” signifies the tire was designed to chiefly be used on passenger vehicles, which can include cars, minivans, SUV ‘s and other light-duty pickup trucks .
If you see “ LT ” rather of “ P, ” it ‘s because you need “ luminosity hand truck ” tires – “ LT ” is short for “ LT-metric, ” which is a appellation by the Tire and Rim Association for a “ lightly hand truck ” type bore. light truck tires are designed to be used on vehicles capable of carrying dense cargo or pulling trailers .
similarly, “ T ” stands for “ irregular ” and is for your spare tire. If you see “ ST, ” that means “ special dawdler. ” A special trailer tire is never installed on the drive or steer wheels. It ‘s only intended for use on dawdler axles .


The first act to appear in your tire size information is the width, in millimeters, of the decline tires for your vehicle : P225/70R16 91S .
Tire width constantly refers to the measurement from one sidewall to another. thus, a tire with the measurement “ P225 ” is for a passenger fomite and has a nominal width of 225 millimeters .


After the flog crisscross, the adjacent number you see is for the tire ‘s view proportion, which basically tells you how tall your tire ‘s profile is : P225/70R16 91S. aspect ratios are delivered in percentages. tire makers calculate the aspect ratio by dividing a tire ‘s sidewall altitude by its width. If a tire has an aspect ratio of 70, it means the run down ‘s acme is 70 % of its width .
Lower aspect ratio tires, such as a 60 series, by and large offer vehicle handling performance advantages over higher view ratio tires, such as a 75 series .


After the aspect ratio comes a letter to indicate the bore ‘s structure : P225/70R16 91S. “ R ” refers to the internal structure of your tire and gives you a general estimate of its constancy .
There are two types of construction that you may see on the sidewall of a tire

  • R – Radial 
  • D – Diagonal or Bias Ply

“ Bias-ply ” tires were used on automobiles and light trucks until the ’70s, ” reports the classical car site, Hemmings. But radial tires represent the huge majority of tires on the road in the United States today. In fact, you will about always see the letter “ R ” on tires as radial tires have been the diligence standard for over 40 years. radial construction means the tire ‘s internal ply cords are oriented in a radial direction ( at 90 degrees to the centerline of the tread ) .


The future count is the wheel ’ sulfur diameter. For model, a tire with the P225/70R16 91S would fit a rim with a 16-inch diameter .
Take note : if you decide to change your rims ‘ size, you will besides need to get new tires that are compatible with the change in size. Tires designed to fit a 16-inch rack diameter will not stretch to fit on newly 18-inch rims .
position other Common Diameter Sizes :

14-Inch Diameter Tires

15-Inch Diameter Tires
17-Inch Diameter Tires
18-Inch Diameter Tires
19-Inch Diameter Tires
20-Inch Diameter Tires
21-Inch Diameter Tires
22-Inch Diameter Tires


The next figure needed to read tire size numbers is your bore ‘s load index. The load index tells us how much weight, in pounds, the bore can support when amply inflated : P225/70R16 91S .
It is called the load “ index ” because the design does n’t tell us the accurate number of pounds the tire can support, at least not by itself. rather, the total corresponds to a particular load capacity listed in an index. Beginning with one and ending with 150, numbers in the load index present carrying capacities of 99 to 7385 pound .
additionally, you may not find this number present on all tires. This is because the warhead index is not required by law to be printed on tires. If there is no load index measurement on your tires, check the owner ‘s manual or contact your local anesthetic Bridgestone run down dealer for more information .


The final examination name in a tire size sequence is the accelerate rating indicated by a letter : P225/70R16 91S. merely as your load exponent count corresponds to a detail lode, your rush evaluation letter corresponds to a specific speed capability based on a standardized testing ground trial .
For model, a tire with a amphetamine rate “ S ” is rated for improving to 112 miles per hour, while a tire rated “ R ” is up to 106 miles per hour. Remember that this is n’t a recommend cruise speed, but rather the maximal accelerate that tire type can withstand. Of course, you should constantly follow legal rush limits on roadways .
hera are the most common letters for travel rapidly ratings and their corresponding maximum speeds :

  • Q: 99 mph
  • R: 106 mph
  • S: 112 mph
  • T: 118 mph
  • U: 124 mph
  • H: 130 mph
  • V: 149 mph
  • W: 168 mph
  • Y: 186 mph
  • ZR: 186+ mph

Tires with higher speed ratings tend to offer increase handle performance. surrogate tires must have the same or higher amphetamine rate to maintain fomite speed capability. If a vehicle has tires with different speed ratings, the focal ratio rate of the “ slowest ” tire dictates the fomite ‘s top speed .
Like the load index, the travel rapidly rating is not required by law to be listed on all tires. If your tires do not have the speed rat listed, your owner ‘s manual of arms will have the relevant information for your model ‘s stock bore type .


You may find “ M+S ” or “ M/S ” after the main bore size sequence on some tires. This indicates that the tire has some capacitance to handle snow and mud conditions. This indication is coarse on most radial or “ R ” type tires .


You may notice another set of letters and numbers on your tire ‘s sidewall begin with “ DOT. ” This is not an indication of bore size, but rather that the tire complies with Federal Motor Vehicle Safety Standards. The “ DOT ” stands for Department of Transportation and is followed by the tire designation act.

The first two letters or numbers after DOT refer to the manufacture plant where the bore was produced and the concluding four numbers indicate the workweek and class the tire was made. The numbers 4318, for exemplify, indicate that the tire was manufactured during the 43rd workweek of 2018 .


While it ‘s surely possible to upgrade your tires ‘ size, it ‘s normally best to stick to your manufacturer-recommended bore size for optimum performance. Increasing the size of your tires may give your car more ground headroom, but it may besides affect handle, drivetrain performance and fuel economy. Keep in heed the changes to key figures mentioned above, such as load index and speed denounce, and how they may affect your vehicle ‘s capabilities if you decide to increase tire size .


once you know how to read the numbers on tires, you can explore tires by size and narrow down your bore options cursorily. Compare tire sizes online or visit a Bridgestone run down dealer near you for assistant .

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