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Once you have determined it’s time to buy tires, you’ll need to know what size tires are correct for your vehicle. Depending on what you drive, you may be interested in how to find the right tire for your…
This information is usually inside your car’s doorjamb, in your owner’s manual. To ensure your current tire or a replacement tire you may be looking at matches your vehicle’s requirements, it will be good for you to understand how tire sizing works. You may have never paid attention to the string of numbers and letters on every tire, but it’s a gold mine of information.
If you’re unsure of how to read tire measurements from your tire walls, the information and graphics below will tell you how to read tire size, understand and interpret it. If you decide you want to substitute a new size or tire type, consult an authorized tire retailer who can expertly advise you, because many optional tire sizes may have different load capacities and could require wheels of a different rim width or diameter and different inflation pressure.
Not sure you need new tires? Our Tire Replacement Guidance article will help you determine whether it’s time to retire your tires.
Most passenger cars, SUVs and light pickups (1/2 ton and smaller) will come with tires that are either P-Metric or Euro-Metric. For P-Metric tires, you’ll see the letter “P” before the number sequence begins: P225/70R16 97H. P-metric is a designation standardized by the Tire and Rim Association for a “passenger car” tire type. For Euro-Metric there will be no preceding letter before the number sequence begins: 225/70R16 98H. Euro-Metric is a designation standardized by the European Tyre and Rim Technical Organization for a “passenger car” tire type.
Both P-Metric and Euro-Metric size tires are designed to primarily be used on passenger vehicles, which can include cars, minivans, SUVs, and other light duty pickup trucks.
If your vehicle is an SUV, Pickup truck or van, you might see a different type of size designation on your placard that is specific for heavy duty light trucks and vans, especially common on ¾ ton and larger pickup trucks and vans. There are two common size types in this category, LT-Metric and Euro-Metric Commercial (aka C-type). Both size types are metric and so use the same structure as P-Metric and Euro-Metric but have some different characters in the size that differentiate them from their passenger car cousins. LT-Metric tires will have the letters “LT” before the size number sequence: LT245/75R17 119/116R Load Range E. Notice that there are two load index numbers and a Load Range, see the section on Load Index for more info. LT-Metric is a designation standardized by the Tire and Rim Association for a “light truck” type tire.
Euro-Metric Commercial or C-Type tires will look very similar to a passenger Euro-Metric size except that there will be a “C” right after the rim size: 23/65R16C 121/119R. Notice that the C-type tires also have two load index numbers. Euro-Metric Commercial, or C-Type is a designation standardized by the European Tyre and Rim Technical Organization for a light truck type tire. Light truck tires are designed to be used on vehicles capable of carrying heavy cargo and are usually only specified by a vehicle manufacturer on vehicles exceeding a certain load capacity.
Other types of tires that fall into the Metric sizing type are Temporary Spares, they start with “T”. If you see a size that starts with “ST,” that means “special trailer” and is only for use on a trailer.
Regardless of whether you are looking at a P-Metric, Euro-Metric, LT-Metric, Euro-Metric Commercial, T or ST tire the numbers in the size mean the same thing.
The first number to appear in your tire size information is the width, in millimeters, of the correct tires for your vehicle: P225/70R16 91S.
Tire width always 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 slash mark, the next number you see is for the tire’s aspect ratio, which essentially 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 height off the rim by its width. If a tire has an aspect ratio of 70, it means the tire’s height 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, but a typical trade off can be ride harshness.
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:
Radial tires are the most common tires on the road in the United States today; thus “R” will usually be shown in the tire size designation. Radial construction means the tire’s internal ply cords are oriented in a radial direction, from one bead over to the other, essentially perpendicular to the direction of rotation. You may also occasionally see RF indicating a run flat tire or ZR indicating a tire that is a speed rating higher than V.
The next number is the diameter code, in inches, of the rim onto which the tire can be mounted. For example, a tire with the P225/70R16 91S would fit a rim with a 16-inch diameter.
Load index can be a confusing subject because there are so many different caveats, but we will try to explain everything here.
The next figure after the rim size in the sequence is your tire’s load index, which tells us how much weight, in pounds, the tire can support when fully inflated: P225/70R16 91S
We call it the load “index” because the number doesn’t tell us the precise number of pounds the tire can carry, at least not by itself. However, the number does correspond to a specific load capacity listed in an index. Beginning with 1 and ending with 150, numbers in the load index represent carrying capacities of 99 to 7385 lbs.
There are two types of load types for passenger tires though, Standard Load and Extra Load. If a tire is Standard Load there will be no markings indicating it but if it is Extra Load the letters XL will appear after the size and load index.
Standard Load Euro-Metric: 215/55R17 94V
Extra Load Euro-Metric: 215/55R17 98V XL
Passenger car tires like P-Metric and Euro-Metric will only have one load index number where LT-Metric and Euro-Metric Commercial (C-Type) will have two numbers separated by a slash.
The first number is the load index if the tire is used in a single application, the second number is the load index if the tire is used in a dual application. Passenger type tires cannot be used in a dual application. Light truck tires will also have a Load Range that is indicated by a letter, such as Load Range E. Load Range is an older term that is still commonly used in the industry so you may hear your tire dealer reference it but the load index numbers are the best way to ensure you have the proper tire.
One important but often misunderstood facet about load index is that the load index numbers between standards organizations (P-Metric vs Euro-Metric) are not necessarily on the same scale. Meaning that two tires in the two different systems that have the same load index number could have different maximum load capacities. This is why it’s important to not only look at the load index number but also verify the actual load capacity.
The final figure in a tire size sequence is the speed rating, which is indicated by a letter: P225/70R16 91S.
Just as your load index number corresponds to a specific load, your speed rating letter corresponds to a particular speed capability based on a standardized 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 should always follow legal speed limits on roadways.
Replacement tires must have the same or higher speed rating as the vehicle’s Original Equipment to maintain vehicle speed capability. If a vehicle has tires with different speed ratings, it is the speed rating of the “slowest” tire that dictates the vehicle top speed.
There is one last sizing type that you should know about, especially if you are in the market for off road tires for a light truck or SUV. It’s called a Flotation size and the numbers in this sizing format are very different from the Metric formats.
Flotation sized tires are similar to LT-Metric tires in application except for a few important points. Number one, they cannot be used in dual applications and number two, an equivalent size tire may have different load capacity than its LT-Metric counterpart.
The first number in the Flotation tire size is the overall diameter in inches. Pretty straight forward.
The second number is the section width (sidewall to sidewall) measurement in inches. Again, fairly simple.
After the section width comes a letter that indicates the type of internal construction: 33X12.50R17LT 120Q.
This is the same as is found in the metric sizing systems.
There are two types of construction that you may see on the sidewall of a tire:
Radial tires are the most common tires on the road in the United States today; thus “R” will usually be shown in the tire size designation.
Radial construction means the tire’s internal ply cords are oriented in a radial direction, from one bead over to the other, essentially perpendicular to the direction of rotation.
The next number is the diameter code, in inches, of the rim onto which the tire can be mounted. For example, a tire with the 33X12.50R17LT 120Q would fit a rim with a 17-inch diameter.
The letters LT will be after the Rim Diameter indicating that this tire type is intended for Light Truck vehicles similar to the LT-Metric and Euro-Metric Commercial (C-Type) tires.
Load Index and Speed Rating have the same meaning and format as the tires using the metric sizing system. Note that since flotation tires cannot be used in a dual application there will be only one load index number instead of two.
Another group of stamping on certain types of tires is the Uniform Tire Quality Grading or UTQG. This grading and stamping is required for passenger car tires (i.e. P-metric and Euro-metric) in the all season and summer categories. Dedicated winter tires, Light Truck (LT-Metric, Euro-Metric Commercial, Flotation) and Motorcycle tires are excluded from this requirement.
Quality grading is designed to make the tire purchase decision easier for you. Ideally, the system is intended to provide simple, comparative data so you can make an intelligent buying decision. However, the ratings are based upon test results achieved under special conditions. This means it’s possible to misinterpret the comparative data as it relates to your individual driving habits, conditions, etc. You should still rely on your service or tire professional for assistance.
Quality grading designates the comparative performance levels of a tire based on government-specified tests but commissioned by the individual tire manufacturers.
All tire manufacturers are required to grade regular and all-season passenger tires in three categories:
UTQG
Treadwear
The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test course for 6,000 miles (9,600 km). For example, a tire graded 150 would wear one and a half times as well on the government course as a tire graded 100. However actual tire performance depends on driving habits, road characteristics, service practices, and other factors that can influence the outcome.
Traction Grades AA, A, B and C
The traction grades from highest to lowest are AA (the highest), A, B and C. They represent how well tires stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. C-rated tires will have the lowest traction performance.
WARNING: THE TRACTION GRADE ASSIGNED IS BASED ON A WET BRAKING (STRAIGHT AHEAD) TRACTION TEST AND DOES NOT INCLUDE CORNERING (TURNING) TRACTION.
Temperature Grades A, B and C
The temperature grades A, B, and C represent the tire's resistance to the generation of heat and its ability to dissipate heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustained high temperature can cause the tire’s material to degenerate and reduce tire life, and excessive temperature can lead to sudden tire failure. The grade C corresponds to a performance level all passenger car tires must meet under the Federal Motor Vehicle Safety Standard No. 109. Grades A and B represent higher levels of performance on the laboratory test wheel than the minimum required by law.
WARNING: THE TEMPERATURE GRADE IS ESTABLISHED FOR A TIRE THAT IS PROPERLY INFLATED AND NOT OVERLOADED. EXCESSIVE SPEED, UNDER INFLATION, OR EXCESSIVE LOADING, EITHER SEPARATELY OR IN COMBINATION, CAN CAUSE HEAT BUILDUP AND POSSIBLE TIRE FAILURE.
DOT Quality Grades
All passenger car tires must conform to other federal requirements in addition to these grades.
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Installing the right tires on your vehicle is essential to the overall performance and safety of your vehicle. Your tire choice should reflect the conditions in which you drive and your preferences for vehicle response and handling. To make the most informed decision, though, you must understand how to read tire size when it's time to buy tires.
Thankfully, determining the correct tire size for your vehicle is relatively simple. 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 right Bridgestone tire for your vehicle online or by visiting a Bridgestone tire dealer near you.
While actual, physical measurements like width and diameter are factors in finding the right tire size, there are additional details to consider. Knowing how to read car tire sizes also means understanding terms like load index and speed rating 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.
Don't worry if you can't locate the manual; you may also find a tire fit guide in these locations:
You can also find tire size data on the sidewall of your current tires (assuming they're the proper size). However, no matter where you find your tire size, you will have to decipher a sequence of numbers and letters. Don't worry if it looks confusing at first — every letter and number has a straightforward meaning.
Let's break down how to read car tire size.
Let's take a look at what each number or letter stands for, one by one, in the order they appear 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 number sequence begins: P225/70R16 91S. The "P" is short for "P-metric," which is a designation by the Tire and Rim Association for a "passenger car" tire type. A "P" signifies the tire 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" instead of "P," it's because you need "light truck" tires – "LT" is short for "LT-metric," which is 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 spare tire.
If you see "ST," that means "special trailer." A special trailer tire is never installed on the drive or steer wheels. It's only intended for use on trailer axles.
The first number to appear in your tire size information is the width, in millimeters, of the correct tires for your vehicle: P225/70R16 91S.
Tire width always 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 slash mark, the next number you see is for the tire's aspect ratio, which essentially 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 height by its width. If a tire has an aspect ratio of 70, it means the tire's height 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 tire and gives you a general idea of its stability.
There are two types of construction that you may see on the sidewall of a tire
"Bias-ply" tires were used on automobiles and light trucks until the '70s," reports the classic car site, Hemmings. But radial tires represent the vast majority of tires on the road in the United States today. In fact, you will almost always see the letter "R" on tires as radial tires have been the industry 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 next number is the wheel’s diameter. For example, 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 also need to get new tires that are compatible with the change in size.
Tires designed to fit a 16-inch wheel diameter will not stretch to fit on new 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 next figure needed to read tire size numbers is your tire's load index. The load index tells us how much weight, in pounds, the tire can support when fully inflated: P225/70R16 91S.
It is called the load "index" because the figure doesn't tell us the precise number of pounds the tire can support, at least not by itself. Instead, the number corresponds to a specific load capacity listed in an index. Beginning with one and ending with 150, numbers in the load index represent carrying capacities of 99 to 7385 lbs.
Additionally, you may not find this number present on all tires. This is because the load 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 Bridgestone tire dealer for more information.
The final figure in a tire size sequence is the speed rating indicated by a letter: P225/70R16 91S. Just as your load index number corresponds to a particular load, your speed rating letter corresponds to a specific speed capability based on a standardized laboratory test.
For example, a tire with a 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, but rather the maximum speed that tire type can withstand. Of course, you should always follow legal speed limits on roadways.
Here are the most common letters for speed ratings and their corresponding maximum speeds:
Tires with higher speed ratings tend to offer increased handling performance.
Replacement tires must have the same or higher speed rating to maintain vehicle speed capability. If a vehicle has tires with different speed ratings, the speed rating of the "slowest" tire dictates the vehicle's top speed.
Like the load index, the speed rating is not required by law to be listed on all tires. If your tires do not have the speed rating 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 main tire size sequence on some tires. This indicates that the tire has some capacity to handle snow and mud conditions. This indication is common on most radial or "R" type tires.
You may notice another set of letters and numbers on your tire's sidewall beginning with "DOT." This is not an indication of tire 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 identification number.
The first two letters or numbers after DOT refer to the manufacturing plant where the tire was produced and the last four numbers indicate the week and year the tire was made. The numbers 4318, for instance, indicate that the tire was manufactured during the 43rd week of 2018.
While it's certainly possible to upgrade your tires' size, it's usually best to stick to your manufacturer-recommended tire size for optimal performance. Increasing the size of your tires may give your car more ground clearance, but it may also affect handling, drivetrain performance and fuel economy. Keep in mind the changes to key figures mentioned above, such as load index and speed rating, 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 tire options quickly. Compare tire sizes online or visit a Bridgestone tire dealer near you for help.
Author: Sochi Auto Remont
Heading: Tips for a car enthusiast
First of all, we find the exact size of the wheel diameter, and then we go to buy the appropriate tires. How correctly you do this, how correctly and steadily your car will behave on the road. The diameter of the wheel is a composite value, which is why care is required in the calculations. How to determine the diameter of the wheel is our topic today. nine0003
Determining the diameter and choosing the right tires!
Step-by-step instructions on how to determine the diameter of a wheel
How to determine the diameter of a wheel
Step 1. The simplest formula is used for calculations: it is necessary to add the sum of two tire profile heights to the diameter of the wheel. This method is applicable only when calculating for passenger cars.
Step 2. Take a tape measure for the usual way of measuring the diameter of the wheel.
Each parameter taken from the formula must be measured separately. The values that you get must be converted to inches (since the unit of measurement for the diameter of a car wheel is an inch). We translate into inches as follows: divide each number obtained by 2.54. Then you need to add together the values obtained as a result of the measurement. The resulting number is the diameter of your wheel. nine0003
Step 3. You don't have to do mathematical calculations, just apply an even simpler calculation formula. How to determine the diameter of the wheel using the second formula - you need to take the number that indicates the width of the rim, and add 20% to it, so you get the full width of your wheel. If the tire width is narrow, then the difference between the total width of the wheels and the width of the rim will be 15%.
Step 4. Experts do not recommend making the wheel diameter larger than the allowable limits. The permissible norm is to increase the diameter of the wheel by a maximum of several centimeters.
A wheel size that exceeds the allowable values will have a bad effect on the chassis of the car, as well as touch the wheel arches. It will be necessary to change the alignment of the car, which will then affect fuel consumption. nine0003
Step 5. When maximizing the diameter of the rim, choose an appropriately low profile tire compared to the standard tyre. Do not forget that low-profile tires do not have the same margin of safety as a standard tire. It is necessary to maintain a balance between the overall diameter of the wheel and disk. Plus, low-profile tires, along with the maximum diameter of the disk, deprives you of the usual comfort, and also affects the chassis.
Step 6. Wheel rim diameter is an important part of a car wheel. You need to know and remember that wheel parameters in terms of rim diameter can vary from 10 to 23 inches. The parameters of small indicators refer to motorcycles and mopeds. Large indicators are used among powerful vehicles. nine0003
Useful tips for car owners.
If you have doubts about your calculations, you can always turn to specialists. How to determine the diameter of the wheel - experienced specialists at a glance can give you accurate information on your wheels. To do this, you can drive to any auto service or car service station. There you will receive the exact information you are interested in.
We told you how to determine the diameter of the wheel, try it! nine0003
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Valery Leonidov
31 August 2017 11:21
A large number of manufacturers, shapes, sizes, patterns and other indicators of car tires are shocking for an inexperienced car owner. The right choice is the key not only to a long service life of the wheels, but also to safety while driving, since the appropriately selected rubber tread is responsible for the car's grip on the road.
For the right choice, you need to take into account some subtleties, determine the priority characteristics that rubber should have. nine0003
Today there are a lot of options to get the necessary information. For example, you can consult online, on the site, but in any case you should know what to ask. If you are changing tires or rims from smaller to larger and vice versa, you need to know a thing or two about sizing and other intricacies of selection. As a rule, cars are produced with factory wheels, which are somewhat smaller than we might like. Such a replacement carries more aesthetic meaning, but it still has practicality. nine0003
Larger wheels up to 18 inches have a positive effect on cornering, traction, braking performance, ride comfort and steering feel, while negatively affecting acceleration and fuel economy due to the greater weight of the wheels themselves. In 19 inches and up, tests have shown that the positive improvements have disappeared, and acceleration and fuel economy have deteriorated.
So the large diameter of the wheels and tires, apart from beauty, does not carry anything in itself. Car owners usually set a smaller radius if they have a second set of tires, such as winter tires that they install every winter. Winter tires tend to get a lot more expensive at sizes over 17 inches. In addition, the wider the tire, the more effective it is on snow and ice. nine0003
So if you have 18" or 19" wheels and want an extra set of wheels for winter tires, it's a good idea to go down to 17" or 16" wheels. These diameters are not only cheaper, easier to find, but also have better grip than other sizes.
Speedometer, odometer, traction control, torque and gear settings are based on the distance your tire travels in one full revolution, which is determined by the outside diameter of the tire and wheel combined. A tire with a different outer diameter will travel a different distance compared to one revolution with different torque. When changing the diameter of your rims, you must make sure that the new wheels in the assembly have the same overall diameter as the old one or your speedometer, otherwise the readings of these gauges will not be correct.
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The outer diameter of a tire is its height. To keep the same outer diameter, you need to take a smaller tire height with large rims and vice versa. It takes a bit of math to figure out the right size. nine0003
To get the standing height of the tire, multiply the aspect height by two for the top and bottom sidewalls and add the 16-inch inner diameter of the tire.
After converting from millimeters to inches, this gives a height of about 25.74 inches. Once you have the standing height of the old tire, you will calculate the size of the new tire.
