What do the numbers mean on the sidewall of your tire? At first glance, you look at your tire sidewall and think, “’Do I need a super secret decoder ring to read this?” In addition to the model name of the tire there is a series of numbers that at first, you don’t deem important. However, these numbers are extremely helpful, especially when it’s time to replace your tires. Here’s a quick breakdown to help you decipher one of the best kept secrets in the automotive world: How do you read tire sizes?
TIRE SIZE
Example: P225/50/R17 98H
P identifies your tire as a Passenger Tire. The P stands for PMetric. If your tire size starts with LT rather than a P than it identifies the tire as a Light Truck tire.
225 identifies the tire section width, which is the measurement of the tire from sidewall to sidewall in millimeters. This measurement varies depending on the rim to which it is fitted.
(There are 25.4 millimeters per 1 inch.)
50 is the two-figure aspect ratio. This percentage compares the tire's section height with the tire's section width. For example, this aspect ratio of 50 means that the tire's section height is 50% of the tire's section width.
R indicates the construction used within the tires casing. R stands for radial construction. B means belted bias and D stands for diagonal bias construction.
17 The last dimension listed in the size is the diameter of the wheel rim, which is most often measured in inches.
LOAD INDEX AND SPEED RATING
Example: P225/50/R17 98H
The load index and speed rating, or service description, are the numbers that follow the tire size.
The load index tells you how much weight the tire can support when properly inflated. Load indices range from 75 - 105 for passenger tires, with each numeric value corresponding to a certain carrying capacity.
The carrying capacity for each value can be found on a load index chart. On each U.S. passenger car tire, the load limit is listed in pounds. European tires have the load limit listed in kilograms and sometimes pounds.
H Speed ratings are represented by letters ranging from A to Z. Each letter coincides to the maximum speed a tire can sustain under its recommended load capacity. For instance, S is equivalent to a maximum speed of 112 mph. Even though a tire can perform at this speed, Continental Tire does not advocate exceeding legal speed limits.
Rating | Maximum Speed |
Q | 100 MPH |
S | 112 MPH |
T | 118 MPH |
U | 124 MPH |
H | 130 MPH |
V | 149 MPH |
W | 168 MPH |
Y | 186 MPH |
Z | Over 149 MPH |
DOT Serial Number
The "DOT" symbol certifies the tire manufacturer's compliance with the U.
S. Department of Transportation (DOT) tire safety standards. Tires made in the United States have the DOT serial number located on the inside sidewall near the rim.
Below is a description of the serial number. Starting with the year 2000, four numbers are used for the Date of Manufacture, the first two numbers identify the week and the last two numbers identify the year of manufacture. This identifies how old a tire is.
Prior to year 2000 three numbers are used for the date of manufacture, first two numbers identify the week and the last number identifies the year of manufacture. To identify tires manufactured in the 90s, a decade symbol (a triangle on its side) is located at the end of the DOT serial number.
See those markings on the tire sidewall? They are shorthand for a veritable wealth of information.
The tire model name is present and correct, obviously, but that’s just the start. There’s also a sequence of numbers detailing the load index, speed rating, tire size, construction, and much more besides.
Why exactly are these markings so important? This information is necessary when the time comes to fit your wheels with replacement tires. Every driver wants to maintain optimal safety and performance when buying new tires; understanding the sidewall markings is an effective way of achieving exactly that.
Follow our tire expert Nels explaining the tire sidewall markings:Let’s start with the following sequence of tire markings as an example: 225/45 R 18 95 H
The first number to appear in the sequence is “225.” This number is the nominal width of the tire (in millimeters) from one sidewall to the other.
Following the slash, the next number in the sequence is “45.
” This number is the tire’s aspect ratio – essentially the height of the tire’s profile outward from the rim represented as a percentage of the tire’s width. We calculate this number by dividing the tire’s section height by the tire’s section width. So, if a tire has an aspect ratio of 45, that means the tire’s height is 45% of its width.
Next in our series of tire markings is a letter instead of a number. This letter indicates the type of construction used within the casing of the tire, which in our example is “R” for Radial construction. Other examples are “B” for Bias-ply or “D” for Diagonal construction.
Radial tires are the most common tires on the road today. They’re called radial because the tire’s internal ply cords are orientated in a radial direction, from one bead over to the other, at right angles to the direction of the tire’s rotation.
The number “18” in our example represents the diameter of the wheel rim in inches.
The number after the rim diameter represents the load index. In our example, “95” is a code for the maximum load a tire can support when fully inflated. Passenger tires have load indices spanning from 75 to 105, where each numeric value corresponds to a specific load capacity. The carrying capacity for each value is described in a load index chart in your vehicle or tire documentation. More information on the load index.
Last in our sequence, we come to the speed rating. Letters ranging from A to Z represent the speed rating. Each letter denotes the maximum speed a tire can sustain under its recommended load capacity. In our example, “H” is equivalent to a maximum speed of 209 kph (130 mph). Even though a tire is capable of performing at this speed, drivers should not exceed legal speed limits. Read our guide to speed ratings.
After this sequence of information, other letters and symbols may also be present on the sidewall.
In our example, they denote the following:
| 7 | Self-Supporting Run-flat tire |
| 8 | Mercedes Original Equipment key |
| 9 | Suitable for mud and snow conditions |
| 10 | Compliant with US Department of Transportation motor vehicle safety standards |
| 11 | Week of manufacture |
| 12 | Year of manufacture |
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The sidewall of a tire has all the information you need to know about it. Below you will find a small guide to deciphering all these numbers and letters.
Tire width from side to side in mm.
Ratio of the section height of a tire to its width, expressed as a percentage. For example, a profile height of 65 means that the height of the tire is 65% of its width
Wheel diameter (height) in inches.
The maximum load per tire (in kg) depends on the load index. The load index value is printed on the sidewall of the tire to the right of the diameter value.
For example, for a tire with a load index of 91, the maximum load is 615 kg.
When buying new tires, consider the load and speed indexes in combination. In addition, you should always follow the recommendations of your vehicle manufacturer.
The Speed Index is the maximum allowable speed at which a properly inflated tire can be driven under load. The speed index, indicated by a letter, is located after the load index on the sidewall of the tire.
For example, for a tire with a speed index of V, the maximum speed is 240 km/h.
When buying new tires, it is important to consider that their speed rating matches the vehicle's speed capabilities.
Your vehicle may be compatible with tires with load and speed ratings that differ from those specified in the manufacturer's documentation.
However, it is always worth checking first whether the vehicle manufacturer allows the installation of such tires and whether their operation is permitted by the current legislation. Always comply with all legal requirements in your country regarding the characteristics of the tires used, and also take into account the recommendations of the vehicle manufacturer regarding speed and load. If necessary, consult your dealer before purchasing or installing tires.
Is it possible to use tires with higher speed ratings than those recommended by the car manufacturer?
Yes, you can.
However, it is always worth checking first whether the vehicle manufacturer allows the installation of such tires.
Can tires with higher load indexes be used than those recommended by the car manufacturer?
Yes, you can. However, it is always worth checking first whether the vehicle manufacturer allows the installation of such tires.
Can tires with higher speed and load ratings be used than recommended by the car manufacturer?
Yes, you can. However, it is always worth checking first whether the vehicle manufacturer allows the installation of such tires.
Can tires with lower speed ratings be used than those recommended by the car manufacturer?
Yes, it is possible. These can be all-season or winter (M+S) tires with a lower speed index, if: a) a sticker indicating the maximum speed limit is in the driver's field of vision; b) the driver does not exceed the specified maximum speed limit. However, it is always worth checking first whether the vehicle manufacturer allows the installation of such tires and whether their operation is permitted by the current legislation.
Can tires with higher load indexes and lower speed indexes be used than recommended by the car manufacturer?
Yes, it is possible. These can be all-season or winter (M+S) tires with a lower speed index, if:
a) a sticker indicating the maximum speed limit is in the driver's field of vision;
b) the driver does not exceed the specified maximum speed limit. However, it is always worth checking first whether the vehicle manufacturer allows the installation of such tires and whether their operation is permitted by the current legislation.
Refer to the vehicle owner's manual for load limits. Overloading a vehicle puts unnecessary stress on its tires and other structural elements. This can result in poor handling, increased fuel consumption and tire damage. Tires may develop large cracks, defects or tears.
The presence of the letter "P" or the absence of letters indicates that this is a tire for a passenger car.
The letter "R" stands for radial construction. Most tires manufactured today are radial.
This mark indicates that the tire meets the United Nations Economic Commission for Europe (UNECE) standards for pneumatic tyres.
This is the maximum pressure for your tire. Check your vehicle's owner's manual for recommended tire pressures, which affect your vehicle's handling, cornering and braking behavior, and fuel consumption.
The letters "TWI" indicate the location of the tire tread wear indicators. You should regularly pay attention to them in order to monitor the degree of tread wear. In most European and Customs Union countries, the minimum permitted tread depth is 1.6mm.
The four-digit code indicates the week and year of manufacture of the tire.
Do you want to choose a tire for your car, but do not understand tire markings well? It's not a problem! In this section, we will help you figure out what tire parameters are, what they mean, and which tire is right for your car.
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195/65 R15 91 T XL
195 is the tire width in mm.
65 - Proportionality, i.e. profile height to width ratio. In our case, it is equal to 65%. Simply put, with the same width, the larger this indicator, the higher the tire will be and vice versa. Usually this value is simply called “profile”.
Since the tire profile is a relative value, it is important to consider when choosing rubber that if you instead of size 195/65 R15, if you want to put tires with a size of 205/65 R15, then not only the width of the tire will increase, but also the height! Which in most cases is unacceptable! (except when both of these sizes are indicated in the car's operating book). You can calculate the exact data on changing the outer dimensions of the wheel in a special tire calculator.
If this ratio is not specified (for example, 185/R14C), then it is equal to 80-82% and the tire is called full profile.
Reinforced tires with this marking are usually used on minibuses and light trucks, where a large maximum wheel load is very important.
R - means a tire with a radial cord (in fact, almost all tires are made this way now).
Many mistakenly believe that R- means the radius of the tire, but this is the radial design of the tire. There is also a diagonal design (indicated by the letter D), but recently it has practically not been produced, since its performance is noticeably worse.
15 - wheel (rim) diameter in inches. (It is the diameter, not the radius! This is also a common mistake). This is the “landing” diameter of the tire on the disk, i.e. is the inside size of the tire or the outside of the rim.
91 is the load index. This is the level of maximum permissible load on one wheel. For passenger cars, it is usually done with a margin and is not a decisive factor when choosing tires (in our case, IN - 91 - 670 kg.
). For minibuses and small trucks, this parameter is very important and must be observed.
T is the tire speed index. The larger it is, the faster you can ride on this tire (in our case, IS - H - up to 210 km / h). Speaking about the tire speed index, I would like to note that with this parameter, the tire manufacturer guarantees the normal operation of the rubber when the car is constantly moving at the specified speed for several hours.
There are two different American tire markings. The first one is very similar to the European one, only the letters “P” (Passanger - for a passenger car) or “LT” (Light Truck - light truck) are placed before the size. For example: P 195/60 R 14 or LT 235/75 R15. And another tire marking, which is fundamentally different from the European one.
Example: 31x10.5 R15 (corresponds to European size 265/75 R15)
31 is the outside diameter of the tire in inches.
10.5 is tire width in inches.
R - a tire with a radial design (older tire models were with a diagonal design).
15 is the inner diameter of the tire in inches.
Generally speaking, except for inches that are unusual for us, the American tire marking is logical and more understandable, unlike the European one, where the height of the tire profile is not constant and depends on the width of the tire. And here everything is simple with decoding: the first digit of the standard size is the outer diameter, the second is the width, the third is the inner diameter.
XL or Extra Load is a reinforced tire, the load index of which is 3 units higher than that of conventional tires of the same size. In other words, if a given tire has a load index of 91 marked XL or Extra Load, then this means that with this index, the tire is able to withstand a maximum load of 670 kg instead of 615 kg (see the table of tire load indices).
M+S or tire marking M&S (Mud + Snow) - mud plus snow and means that the tires are all-season or winter. Many summer tires for SUVs are labeled M&S. However, these tires must not be used in winter, as winter tires have a completely different rubber compound and tread pattern, and the M&S badge indicates good flotation performance.
All Season or AS all season tires. Aw (Any Weather) - Any weather.
Pictogram * (snowflake) — rubber is designed for use in harsh winter conditions. If this marking is not on the sidewall of the tire, then this tire is intended for use only in summer conditions.
Aquatred, Aquacontact, Rain, Water, Aqua or icon (umbrella) Special rain tires.
Outside and Inside ; asymmetric tires, i.e. It is important not to confuse which side is the outside and which is the inside. When installing, the Outside inscription must be on the outside of the car, and Inside on the inside.
RSC (RunFlat System Component) - RunFlat tires are tires that allow you to continue driving at a maximum speed of 80 km/h with a FULL tire pressure drop (puncture or cut). On these tires, depending on the manufacturer's recommendations, you can drive from 50 to 150 km. Different tire manufacturers use different designations for RSC technology. For example: Bridgestone RFT, Continental SSR, Goodyear RunOnFlat, Nokian Run Flat, Michelin ZP etc.
Rotation or arrow This marking on the tire sidewall indicates a directional tire. When installing the tire, you must strictly observe the direction of rotation of the wheel, indicated by the arrow.
Tubeless - tubeless tyre. In the absence of this inscription, the tire can only be used with a camera. Tube Type - indicates that this tire must be used only with a tube.
Max Pressure ; maximum allowable tire pressure. Max Load - the maximum allowable load on each wheel of the car, in kg.
Reinforced or the letters RF in the size (for example 195/70 R15RF) means that this is a reinforced tire (6 layers). The letter C at the end of the size (for example 195/70 R15C) indicates a truck tire (8 layers).
Radial this marking on the rubber in the standard size means that this tire is a radial design. Steel means that there is a metal cord in the tire structure.
Letter E (in a circle) - the tire meets the European requirements of ECE (Economic Commission for Europe). DOT (Department of Transportation - US Department of Transportation) is an American quality standard.
Temperature A, B, or C The temperature resistance of the tire at high speeds on the test bench (A is best).
Traction A, B, or C Tire wet braking capability.
Treadwear ; relative expected mileage compared to a specific US standard test.
TWI (Tread Wear Indiration) - tire tread wear indicators.
