You’re our first priority.
Every time.
Swain Automotive is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate we earn from qualifying purchases. Read more
The tire dimension can be complex. Some numbers on the sidewall are detailed in statistics while others remain in inches. And also, the right dimension for your car and truck, truck, or trailer can vary relying on tire use and also your driving habits.
You can see your initial equipment tire size in your owner's guidebook. This is the sizing recommended by the lorry manufacturer.
If you have an interest in switching over your tires for various look or efficiency needs, an excellent location to begin is to check out the codes on your existing tires' sidewall. After that have a tire professional assist you identify a tire dimension array that will fit your lorry as well as driving goals.
Below's an explainer of what all the sidewall numbers and letters indicate.
Finding Your Tire Size
Tire Dimension Definitions
A: TIRE TYPE
The very first letter in the code informs you what class of tire it is.
- P represents traveler lorry tire.- P-class tires consist of cars and trucks, SUVs, crossovers, minivans, and smaller pickup trucks.
- LT implies light vehicle tires,- made for vehicles that are towing trailers or have 3/4- as well as 1-ton lots capability.
- ST -stands for Unique Trailer. These tire dimensions are meant for trailers, including fifth wheels and also other traveling trailers, boat trailers, and also energy trailers.
If there's no letter before the first number, you have a statistics tire most commonly referred to as the European dimension. It's also measured in millimeters yet may have various load abilities than a P or LT tire.
B: TIRE SIZE
The three-digit number adhering to the letter is the tire's width (from side to side, checking out the tire head-on) in millimeters. Likewise called the area width, this measurement is taken from the external sidewall to the inner sidewall.
C: FACET PROPORTION
The onward slash separates the tire width number from the two-digit aspect proportion. The bigger the aspect proportion, the higher/taller the tire's sidewall, or "account" as it's in some cases called.
The element proportion is a portion. It's the height of the sidewall determined from wheel rim to top of the walk, expressed as a percent of tire width. To put it simply, it's sidewall height divided by tire width.
In this instance, the element ratio is 65, implying the sidewall is 65 percent as high as the tire is large. To get the sidewall elevation, take the tire width of 215 mm as well as transform it to inches (8.46 ). Then increase this by.65 as well as you obtain 5.5 inches, the sidewall height in inches.
D: CONSTRUCTION KIND
This solitary letter tells you about the interior construction of the tire.
R is for radial tires, the market standard for a lot of tires today. They have better road grip, and reduced rolling resistance for much better gas mileage, trip convenience, and also sturdiness than previous generations of tires. In a radial tire, the plies-- layers of strong cords constructed from a mix of polyester, steel as well as fabric as well as coated with rubber-- are laid vertical to the instructions of travel.
D is for tires constructed with angled (crisscrossed) plies, called bias-constructed tires. They are also called standard, x-ply, or cross-ply tires. Some bike and trailer tires still use this inner building.
E: WHEEL SIZE
This two-digit number defines wheel diameter in inches, just how vast the wheel is throughout the center. It's the range between both grain seat locations (where a tire gets slotted and also tightly secured onto the wheel).
F: LOAD INDEX
The two-digit or three-digit number that follows the space specifies the tire tons index. The tons index symbol indicates just how much weight a tire can support, based upon adhering to a common chart. In our example, the tons index is 89, which indicates the tire has a lot capacity of 1,279 extra pounds.
G: RATE RANKING
The last letter is the rating score, which informs you of the top speed it's safe to travel at for a continual quantity of time. A tire with a higher speed rating can handle warmth far better and also supply even more control at faster rates. The maximum operating speed of an automobile disappears than the most affordable speed ranking of all tires placed on the lorry.
(Naturally, you ought to constantly follow rate restrictions for more secure driving.) Speed score is normally, but not constantly, a solitary letter (see the graph).
DETERMINING TIRE DIMENSION
Just how to identify tire dimension.
Once you have determined it's time to buy tires, you'll need to recognize what size tires are right for your vehicle. This information is generally inside your car's doorjamb, in your proprietor's manual. To guarantee your present tire or a replacement tire you might be looking at suits your lorry's requirements, it will certainly be good for your to recognize how tire sizing works. You may have never focused on the string of numbers and also letters on every tire, yet it's a gold mine of info.
If you're uncertain of exactly how to review tire dimensions from your tire walls, the information and graphics below will inform you just how to check out tire dimension, and understand as well as interpret it. If you choose you to want to substitute a new dimension or tire type, consult an authorized tire seller who can adeptly suggest you since several optional tire dimensions might have different lots abilities and also could require wheels of a different edge size or diameter as well as various inflation pressure.
Metric Sizing
A lot of passenger cars, SUVs, and also light pick-ups (1/2 heap and smaller sized) will include tires that are either P-Metric or Euro-Metric. For P-Metric tires, you'll see the letter "P" prior to the number sequence starting P225/70R16 97H. P-metric is a designation standardized by the Tire and also Edge Association for an "auto" tire type.
For Euro-Metric there will certainly be no preceding letter prior to the number sequence starting 225/70R16 98H. Euro-Metric is a classification standard by the European Tire and Edge Technical Company for a "passenger car" tire kind. Both P-Metric and Euro-Metric size tires are developed to primarily be utilized on guest cars, which can consist of cars, minivans, SUVs, and also other light obligation pickup trucks.
If your vehicle is an SUV, Pickup truck, or van, you may see various sort of dimension classification on your placard that specifies sturdy light trucks and also vans, specifically common on 3/4 load and larger pickup as well as vans. There are two typical dimensions enter this category, LT-Metric as well as Euro-Metric Commercial (aka C-type).
Both size types are statistics and therefore utilize the very same framework as P-Metric and Euro-Metric yet have some different characteristics in the dimension that distinguish them from their automobile relatives. LT-Metric tires will have the letters "LT" before the dimension number series: LT245/75R17 119/116R Lots Variety E.
Notice that there are 2 load index numbers and a Tons Array, see the section on Tons Index for more details. LT-Metric is a classification standardized by the Tire and Edge Association for a "light truck" kind of tire. Euro-Metric Commercial or C-Type tires will certainly look extremely comparable to a guest Euro-Metric dimension except that there will be a "C" right after the edge dimension: 23/65R16C 121/119R. Notification that the C-type tires likewise have two tons index numbers.
Euro-Metric Commercial or C-Type is a classification standardized by the European Tire as well as Rim Technical Organization for a light vehicle type tire. Light truck tires are made to be utilized on lorries with the ability to lug hefty freight as well as are usually just specified by an automobile supplier on automobiles going beyond a certain load ability.
Other kinds of tires that fall into the Metric sizing type are Short-lived Spares, which start with "T". If you see a dimension that starts with "ST," that means "unique trailer" as well as is just for use on a trailer.
Regardless of whether you are taking a look at a P-Metric, Euro-Metric, LT-Metric, Euro-Metric Commercial, T or ST tire the numbers in the size mean the same point.
Size
The first number to appear in your tire size information is the width, in millimeters, of the right tires for your car: P225/70R16 91S.
Tire width constantly refers to the measurement from one sidewall to an additional. Therefore, a tire with the measurement "P225" is for a guest car and also has a small size of 225 millimeters.
Element Ratio
After the lower mark, the following number you see is for the tire's element proportion, which basically tells you just how tall your tire's account is: P225/70R16 91S. Facet ratios are delivered in percentages. Tire makers compute the aspect ratio by dividing a tire's height off the rim by its size. If a tire has an element proportion of 70, it means the tire's height is 70% of its width.
Reduced aspect ratio tires, such as a 60 series, typically supply lorry managing efficiency advantages over higher element proportion tires, such as a 75 collection, however, a normal trade-off can be flight violence.
Building
After the element ratio comes a letter that shows the type of inner construction keeping your tire's security: P225/70R16 91S.
There are two kinds of construction that you might see on the sidewall of a tire:
- R-- Radial.
- D or "B" or "-"-- Diagonal or Bias Ply.
Radial tires are one of the most typical tires on the road in the United States today; thus "R" will typically be received the tire dimension designation. Radial building means the tire's internal ply cords are oriented in radial instructions, from one grain over to the other, essentially perpendicular to the instructions of rotation. You might likewise occasionally see RF suggesting a run blowout or ZR indicating a tire that is a rate ranking more than V.
Lots Index
Lots index can be a confusing subject because there are so many different caveats, however, we will attempt to discuss everything here.
The next figure after the rim dimension in the series is your tire's load index, which tells us how much weight, in pounds, the tire can sustain when totally blown up: P225/70R16 91S.
We call it the lots "index" due to the fact that the number doesn't inform us the specific number of pounds the tire can lug, at least not by itself. Nevertheless, the number does represent a detailed lot capability detailed in an index. Starting with 1 and also finishing with 150, numbers in the load index stand for lugging abilities of 99 to 7385 lbs.
There are 2 sorts of tons kinds of traveler tires though, Requirement Lots as well as Additional Lots. If a tire is Standard Load there will certainly be no markings showing it but if it is Additional Load the letters XL will show up after the dimension and lots index.
- Criterion Tons Euro-Metric: 215/55R17 94V.
- Extra Lots Euro-Metric: 215/55R17 98V XL.
Auto tires like P-Metric and also Euro-Metric will only have a one-ton index number whereas LT-Metric, as well as Euro-Metric Commercial (C-Type), will have two numbers divided by a slash. The first number is the tons index if the tire is utilized in a solitary application, and the 2nd number is the load index if the tire is utilized in a dual application. Traveler kind tires can not be used in a double application.
Light truck tires will certainly additionally have a Tons Array that is suggested by a letter, such as Lots Variety E. Tons Variety is an older term that is still frequently used in the industry so you may hear your tire dealer recommendation it yet the lots index numbers are the most effective means to guarantee you have the correct tire.
One important however commonly misinterpreted aspect of load index is that the load index numbers between criteria organizations (P-Metric vs Euro-Metric) are not always in the same range. This implies that 2 tires in both different systems that have the same lots index number can have various maximum load abilities. This is why it's important to not only consider the lots index number but additionally verify the reallots capability.
Rate Ranking
The last figure in a tire size sequence is the speed rating, which is shown by a letter: P225/70R16 91S. Equally, as your lots index number represents detailed lots, your rate score letter corresponds to a certain rate capability based upon a standardized lab examination.
As an example, a tire with a rating score of "S" is ranked for up to 112 mph, while a tire rated "R" depends on 106 miles per hour. Keep in mind that this isn't a recommended traveling speed. Obviously, you must always adhere to legal rate restrictions on roadways.
Substitute tires must have the very same or higher rate ranking as the car's Original Devices to preserve car rate capability. If an automobile has tires with various speed scores, it is the speed ranking of the "slowest" tire that determines the automobile's full throttle.
Flotation protection Sizing
There is one last sizing kind that you need to learn about, especially if you are in the market for off-roadway tires for a light truck or SUV. It's called a Flotation dimension as well as the numbers in this sizing format are really different from the Metric formats. Flotation-sized tires are similar to LT-Metric tires in the application besides a couple of vital factors. Leading, they can not be used in double applications and number two, an equivalent size tire might have various lots capacity than its LT-Metric counterpart.
- Total Size.-- The very first number in the Flotation protection tire size is the general diameter in inches. Pretty simple.
- Section Size.-- The second number is the area width (sidewall to sidewall) measurement in inches. Again, rather easy.
- Construction.-- After the section size comes a letter that suggests the type of interior construction: 33X12.50 R17LT 120Q.
This is the same as is found in the statistics sizing systems.
There are 2 kinds of building and construction that you might see on the sidewall of a tire:
- R-- Radial.
- D or "B" or "-"-- Angled or Bias Ply.
Radial tires are the most typical tires on the road in the United States today; hence "R" will generally be received the tire dimension classification. Radial construction means the tire's interior ply cords are oriented in a radial direction, from one grain over to the various other, basically perpendicular to the direction of rotation.
Rim Diameter
The following number is the diameter code, in inches, of the rim onto which the tire can be installed. For example, a tire with the 33X12.50 R17LT 120Q would fit a rim with a 17-inch diameter.
LT kind.-- The letters LT will certainly desire the Edge Diameter suggesting that this tire type is meant for Light Vehicle cars comparable to the LT-Metric and Euro-Metric Commercial (C-Type) tires.
Tons Index and also Speed Score.
Tons Index, as well as Speed Ranking, have the same significance and also layout as the tires using the statistics sizing system. Note that because flotation tires can not be made use of in a dual application there will be only one lot index number rather than 2.
Attire Tire Top Quality Grading
Another group of stamping on specific kinds of tires is the Attire Tire High-Quality Grading or UTQG. This grading and marking is needed for passenger car tires (i.e. P-metric and also Euro-metric) in the all-season and also summertime groups. Committed wintertime tires, Light Vehicle (LT-Metric, Euro-Metric Commercial, Flotation Protection), and Motorcycle tires are left out of this need.
Quality grading is developed to make the tire purchase choice less complicated for you. Preferably, the system is intended to provide simple, relative information so you can make an intelligent buying choice. Nonetheless, the ratings are based upon test results achieved under unique conditions. This suggests it's possible to misinterpret the comparative data as it associates with your specific driving habits, conditions, and so on. You need to still depend on your service or tire specialist for support.
Quality grading designates the comparative performance degrees of a tire based upon government-specified tests however appointed by the private tire producers. All tire producers are needed to quality normal as well as all-season guest tires in 3 categories:
UTQG
1. Treadwear.
2. Grip.
3. Temperature.
Treadwear
The treadwear quality is a comparative rating based on the wear rate of the tire when evaluated under regulated conditions on a given federal government test program for 6,000 miles (9,600 kilometers). For example, a tire graded 150 would wear one and a half times as well on the government program as a tire graded 100. Nevertheless, real tire performance depends on driving habits, roadway attributes, service methods, as well as other variables that can affect the result.
Traction Grades AA, A, B, and also C
The traction qualities from greatest to least expensive are AA (the greatest), A, B as well as C. They stand for how well tires quit on wet pavement as gauged under controlled conditions on given federal government test surface areas of asphalt and also concrete. C-rated tires will have the lowest grip efficiency.
WARNING: THE TRACTION QUALITY ASSIGNED IS BASED ON A WET BRAKING (STRAIGHT AHEAD) GRIP TEST As Well As DOES NOT CONSIST OF CORNERING (TRANSFORMING) GRIP.
Temperature Grades A, B as well as C
The temperature level qualities A, B, and C stand for the tire's resistance to the generation of warmth and its capacity to dissipate heat when checked under controlled conditions on a defined interior lab test wheel. Sustained high temperatures can cause the tire's material to deteriorate and reduce tire life, as well as excessive temperature can bring about sudden tire failure.
Grade C represents an efficiency level all auto tires should fulfill under the Federal Car Safety And Security Requirement No. 109. Qualities An, as well as B, represent greater degrees of performance on the research laboratory examination wheel than the minimum needed by law.
CAUTION: THE TEMPERATURE LEVEL QUALITY IS ESTABLISHED FOR A TIRE THAT IS APPROPRIATELY INFLATED AND ALSO NOT OVERLOADED. EXCESSIVE RATE, UNDER INFLATION, OR EXCESSIVE LOADING, EITHER INDIVIDUALLY OR IN MIX, CAN REASON HEAT ACCUMULATION As Well As FEASIBLE TIRE FAILURE.
DOT Top Quality Grades.
All passenger car tires have to conform to various other federal requirements along with these qualities.
