How to Read Tire Size

Installing the right tires on your vehicle is essential to the overall performance and condom of your fomite. Your tire choice should reflect the conditions in which you drive and your preferences for vehicle response and cover. To make the most inform decisiveness, though, you must understand how to read tire size when it ‘s time to buy tires.
thankfully, determining the right tire size for your vehicle is relatively dim-witted. 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 tire size numbers ? Skip the explanation and find the good Bridgestone tire for your vehicle on-line or by visiting a Bridgestone run down trader near you.

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


No matter what vehicle you drive, finding the manufacturer-recommended bore 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 run down fit guidebook in these locations :

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

You can besides find run down 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 inaugural — every letter and numeral has a square mean. Let ‘s break down how to read cable car bore size .
Find Your Tire Size Information Image


Let ‘s take a spirit at what each number or letter stands for, one by one, in the order they appear in your run down size data. We ‘ll be using this tire size as an exemplar : 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 brusque for “ P-metric, ” which is a appellation by the Tire and Rim Association for a “ passenger car ” bore character. A “ P ” signifies the run down was designed to primarily 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 “ lighter hand truck ” tires – “ LT ” is short-circuit for “ LT-metric, ” which is a appointment by the Tire and Rim Association for a “ light truck ” type bore. light truck tires are designed to be used on vehicles able of carrying heavy cargo or pulling trailers .
similarly, “ T ” stands for “ irregular ” and is for your plain tire. If you see “ ST, ” that means “ special trailer. ” A extra dawdler tire is never installed on the drive or steer wheels. It ‘s only intended for use on dawdler axles .


The first gear number to appear in your bore size information is the width, in millimeters, of the discipline 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 vehicle and has a nominal width of 225 millimeters .


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


After the aspect ratio comes a letter to indicate the tire ‘s construction : P225/70R16 91S. “ R ” refers to the internal structure of your bore and gives you a general idea 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 classic car locate, 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 following number is the rack ’ sulfur diameter. For example, a tire with the P225/70R16 91S would fit a rim with a 16-inch diameter .
Take notice : if you decide to change your rims ‘ size, you will besides need to get newfangled tires that are compatible with the deepen in size. Tires designed to fit a 16-inch wheel diameter will not stretch to fit on modern 18-inch rims .
view 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 adjacent figure needed to read tire size numbers is your tire ‘s load index. The load index tells us how much slant, in pounds, the tire can support when fully inflated : P225/70R16 91S .
It is called the lode “ index ” because the figure does n’t tell us the precise numeral of pounds the tire can support, at least not by itself. alternatively, the number corresponds to a specific load capacity listed in an index. Beginning with one and ending with 150, numbers in the load exponent represent carrying capacities of 99 to 7385 pound .
additionally, you may not find this number portray on all tires. This is because the lode index is not required by jurisprudence to be printed on tires. If there is no load index measurement on your tires, check the owner ‘s manual or contact your local Bridgestone bore principal for more information .


The concluding figure in a bore size sequence is the rush denounce indicated by a letter : P225/70R16 91S. merely as your cargo index number corresponds to a particular load, your speed rate letter corresponds to a specific focal ratio capability based on a standardize testing ground test .
For model, a bore with a accelerate evaluation “ S ” is rated for up to 112 miles per hour, while a tire rated “ R ” is astir to 106 miles per hour. Remember that this is n’t a recommend cruise rush, but preferably the maximal accelerate that tire type can withstand. Of naturally, you should constantly follow legal accelerate limits on roadways .
here are the most coarse letters for travel rapidly ratings and their match utmost 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 handling performance. successor tires must have the lapp or higher accelerate rat to maintain vehicle travel rapidly capability. If a vehicle has tires with different amphetamine ratings, the speed fink of the “ slowest ” bore dictates the vehicle ‘s peak accelerate .
Like the load index, the accelerate evaluation is not required by law to be listed on all tires. If your tires do not have the amphetamine rat listed, your owner ‘s manual will have the relevant information for your model ‘s stock tire type .


You may find “ M+S ” or “ M/S ” after the chief tire size sequence on some tires. This indicates that the tire has some capacity to handle snow and mud conditions. This reading is common on most radial or “ R ” type tires .


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

The beginning two letters or numbers after DOT refer to the fabrication implant where the tire was produced and the last four numbers indicate the workweek and year the tire was made. The numbers 4318, for example, indicate that the tire was manufactured during the 43rd week of 2018 .


While it ‘s surely possible to upgrade your tires ‘ size, it ‘s normally best to stick to your manufacturer-recommended tire size for optimum performance. Increasing the size of your tires may give your car more establish clearance, but it may besides affect wield, drivetrain performance and fuel economy. Keep in take care the changes to key figures mentioned above, such as load index and focal ratio evaluation, and how they may affect your vehicle ‘s capabilities if you decide to increase run down size .


once you know how to read the numbers on tires, you can explore tires by size and narrow down your tire options quickly. Compare tire sizes online or visit a Bridgestone tire principal near you for help .

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