Tire size can be confusing. Some numbers on the sidewall are listed in millimeters while others are inches. Plus, the right size for your car, truck, or trailer can differ depending on where and how you drive.
You can see your original equipment tire size in your owner’s manual or on the placard generally located on the driver’s side door jam. This is the sizing recommended by the vehicle manufacturer.
If you’re interested in switching out your tires for a different look or performance, a good place to start is the numbers and other indicators on your existing tires’ sidewall. Next, have a tire professional help you determine a tire size range that will fit your vehicle and driving needs.
Here’s what those numbers and indicators on the sidewall indicate and how to understand them:
A: TIRE TYPE The first letter in the code tells you what class of tire it is.
P stands for passenger vehicle tire. P-class tires include cars, SUVs, crossovers, minivans and smaller pickup trucks.
LT means light truck tire, designed for vehicles that are capable of carrying heavy loads, towing trailers, or for those looking for an extra heavy duty option. These are often equipped on three-quarter or 1 ton trucks and SUVs.
ST stands for Special Trailer. These tire sizes are meant for trailers, including fifth wheels and other travel trailers, as well as boat and utility trailers.
If there’s no letter before the first number, you have a metric tire most commonly referred to as European size. It’s also measured in millimeters but may have a different load capacity than a P or LT tire.
B: TIRE WIDTH The three-digit number following the letter is the tire’s width (from side to side, looking at the tire head on) in millimeters. This may also be referred to as the section width.
C: ASPECT RATIO The forward slash separates the tire width number from the two-digit aspect ratio. The bigger the aspect ratio, the higher/taller the tire’s sidewall, or “profile” as it’s sometimes called.
The aspect ratio is indicated on the tire sidewall as a percentage. It’s the height of the sidewall measured from wheel rim to top of the tread, expressed as a percentage of tire width.
In this example, the aspect ratio is 65, meaning the sidewall is 65 percent as high as the tire is wide. To get the sidewall height, take the tire width of 215 mm and convert it to inches (8.46). Then multiply this by 65% (.65). This gives you an answer of 5.5, the sidewall height in inches.
D: CONSTRUCTION TYPE This single letter tells you about the internal construction of the tire.
R is for radial tires, the industry standard for most tires today. They have better road grip, lower rolling resistance for better gas mileage, ride comfort and durability than previous generations of tires.
In a radial tire, the plies — layers of strong cords made of a blend of polyester, steel and fabric and coated with rubber — are laid perpendicular to the direction of travel.
D is for tires built with diagonal (crisscrossed) plies, called bias-constructed tires. They are also called conventional, x-ply, or cross-ply tires. Some motorcycle and trailer tires still use this internal construction.
Some run-flat tires are identified with an F followed by the type of internal construction.
E: WHEEL DIAMETER This two-digit number specifies wheel diameter in inches. It’s the distance between the two bead seat areas (where a tire gets tightly sealed onto the wheel).
F: LOAD INDEX The two-digit or three-digit number that follows the gap specifies tire load index. The load index symbol indicates how much weight a tire can support, based on the following standard chart. In our example, the load index is 89, which indicates the tire has a load capacity of 1,279 pounds, when inflated to the tire’s maximum air pressure rating.
G: SPEED RATING The last letter is the tire speed rating. This indicates the top speed it’s safe to travel at for a sustained amount of time. A tire with a higher speed rating can handle heat better and provide more control at faster speeds. The maximum operating speed of a vehicle is no more than the lowest speed rating of all tires mounted on the vehicle. (Of course, you should always abide by speed limits for safer driving.) Speed rating is usually, but not always, a single letter (see the chart).
Below you will find several charts that will help you understand tire sizing numbers, including a load index chart and speed rating chart.
A tire size calculator is a quick way to see whether the tire size you’re considering will likely fit your car, SUV, sports car, light truck or crossover.
But remember that is only an estimate. It’s important to stay within the sizing tolerances of your vehicle.
Tires that are the wrong size could cause some pull in the steering wheel, rub against the suspension or body of your vehicle, reduce clearance on hills, or result in a stiffer or noisier ride.
If you’re considering mounting a different tire size on your vehicle, check with a tire expert. Find out whether the tires and wheels you have your eye on are the right fit for your vehicle’s suspension, gearing, and bodywork. And ask how any differences in revolutions per mile, tire speed, load index, and speed rating will affect your ride quality and vehicle performance.
See how new tires and rims will look on your car or truck using our Virtual Wheels simulator, available at any Les Schwab.
Find Your Store
Most modern passenger tires bear a tire speed rating, a designation indicating the tire’s designed speed capability. In other words, it’s the fastest speed a tire can handle before it does not perform as designed.
Tire speed ratings do not imply that the vehicle may safely be driven at the maximum speed for which the tire is capable, particularly under adverse weather or road conditions.
Find Your Tire
If you’re wondering what tire speed rating your vehicle manufacturer recommends, simply look in the manual. You might also find it in the driver’s side door jamb, the gas tank hatch, or inside the glove box door – anywhere that lists the right tire code for your vehicle.
Speed rating is easy to locate because it’s usually the last item in the character sequence in the tire’s size code. For example in this tire code: “P205/60R16 82S,” S is the speed rating. To view the tire size code for your current tires, just look at the sidewall. Does the speed rating on each tire match what the manufacturer recommends? It should!
Also remember that the tire speed rating isn’t the same thing as a recommended travel speed. The rating will nearly always exceed maximum highway speed limits, but no tire or vehicle manufacturer advises driving faster than the law allows.
Speed ratings are the product of laboratory testing – with simulated speeds and loads. To receive any kind of rating, a tire must demonstrate that it’s capable of sustaining a particular speed. Industry standards govern the process of reaching and maintaining a given speed during a test.
However, it’s important to remember that the lab can’t simulate every conceivable condition. Think of your tire’s speed rating as an indicator of the product’s capability under controlled conditions (i.e. fully inflated, vehicle running properly, good weather conditions). Your tires’ actual speed capability may be less than its rated speed, since it is affected by factors such as inflation, wear, vehicle condition (including alignment), driving conditions and the duration at which speed is maintained. Speed ratings do not apply to tires that have been damaged, altered, under-inflated, overloaded or repaired.
Today’s speed rating system uses letters A through Z.
Each letter corresponds to a specific speed. In general, that speed goes up as the rating advances alphabetically. For example, a tire rated “L” is good for a lower maximum sustained speed than one rated “N.”
But the tire speed rating system isn’t without its quirks. For instance, the system’s European roots give it unusual mile per hour maximums. Another such quirk is that the letter “H” is out of place. Instead of appearing after “G,” it falls between “U” and “V” as does the speed to which it corresponds.
Additional speed rating “anomalies” include the following:
“I,” “O,” and “X” speed ratings don’t exist. Likewise, some speed rating charts don’t include the “P” rating.
Tires with the lowest speed ratings are usually listed as “A” followed by a number– for example, “A1,” “A2, “A3,” and so on.
Some tires carry “W” or “Y” speed ratings. Manufacturers may also insert “Z” into the size description (in the tire code data between aspect ratio and diameter) for these kinds of tires.
When the speed rating system was first developed, the highest speed rating was the unlimited “V” rating. This was for tires whose maximum sustained speed was 149 mph (240 kph) or more. Then, as more manufacturers came out with tires that could handle speeds in excess of 149 mph but still hit a maximum speed at some point, “V” became limited (149 mph instead of 149+ mph) and “W” and “Y” speed ratings were added to the chart.
Many tire speed rating charts also list the “Z” rating as anything over 149 mph. Some manufacturers will insert a “Z” in the middle of the tire size description (right after the aspect ratio) when the tire is rated at “W” or “Y.” And if a tire is rated in excess of 186 mph (300 kph), manufacturer’s usually will list a “Z” within the size description, per industry standards.
The following speed ratings are those you’re most likely to encounter for ordinary vehicles. They begin with a maximum speed of 118 mph (190 kph) and increase from there.
Indicated by a letter, each rating corresponds to a specific speed.
With a maximum speed of 118 mph, you usually find tires with speed rating “T” on family sedans and minivans.
If you recall from earlier, the “H” speed rating doesn’t appear after “G” but between “U” and “V.” It represents a maximum speed of 130 mph (210 kph) and is commonly found on sports sedans and coupes. In earlier incarnations of the speed rating system, “H” stood for “high performance,” which is why it maintains an unusual position in the speed rating spectrum today.
Once the highest speed rating a tire could have, “V” used to represent a maximum of 149 mph (240 kph) or more. Nowadays, it means 149 mph but no higher.
A relatively new addition to the speed rating chart, tires with speed rating “W” can achieve a maximum sustained speed of 168 mph (270 kph).
A “Z” rating can mean different things.
While it nearly always means a high performance tire for high-performing sports cars, “Z” may actually appear in the middle of a tire’s size information. When it does, it represents either a maximum speed of more than 149 mph (240 kph) or 186 mph (300 kph). Which of those speeds it refers to will depend on the specific tire. Contact the manufacturer to get details on any Z-rated tires. Sports car owners are more likely to encounter this speed rating than owners of typical family sedans.
Always choose the speed rating that corresponds to your vehicle manufacturer’s specifications, and be sure all four tires have the same rating. Speed ratings are based on laboratory tests under specific, controlled conditions. While these tests relate to performance on the road under those conditions, remember that real-life driving is rarely identical to test conditions.
Find Your 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.
195/65 R15 91 TXL
nine0002 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 take into account when choosing rubber that if you want to put tires with a size of 205/65 R15 instead of the size 195/65 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. nine0003
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 precisely 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. nine0003
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 - 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. nine0003
T - 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 markings for American tires. 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 (corresponding 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. nine0003
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).
All Season or AS all season tires. Aw (Any Weather) - Any weather. nine0003
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 pictogram (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. nine0003
RSC (RunFlat System Component) - RunFlat tires are tires on which you can continue to drive a car at a speed of no more than 80 km / h with a FULL drop in pressure in the tire (due to a 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..jpg)
Tubeless - tubeless tire. 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. nine0003
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 is a radial construction tire. 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.
nine0003
Temperature A, B, or C 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. The marking on the TWI wheel can also be with an arrow. Pointers are located evenly in eight or six places around the entire circumference of the tire and show the minimum allowable tread depth. The wear indicator is made in the form of a protrusion with a height of 1.6 mm (the minimum tread value for light vehicles) and is located in the tread recess (usually in the drainage grooves). nine0003
DOT - Manufacturer's coded address, tire size code, certificate, issue date (week/year).
Find tires / tire catalogPhoto: Shutterstock
adv.
rbc.ru
See also
Numbers and letters on a car tire provide all the necessary information about it. True, it is not easy to read them - here, even in the designation of one parameter, several measurement systems can be used simultaneously. In addition, many values are expressed in special indices. We decipher all important labels for the buyer. nine0003
adv.rbc.ru
A tire label is information about its properties printed on the outer rim. This is a huge amount of useful information. Here are the parameters of the tire that can be read from it itself:
The size designation is written in the form XXX/XX R XX. For example 225/65 R17.
The first three digits are the tire width in millimetres. In our case - 225 mm. nine0003
The second digit is the height, but not in millimeters, but as a percentage of the width. In our case, its height is 146.25 mm (225 * 0.65).
The third number after R is the outside diameter of the wheel or the inside diameter of the tire in inches. In our case, this is 17 inches or 43.18 cm. Do not confuse - this is the radius, not the diameter. The letter R itself stands for the radial design of the tire, which confuses many. Sometimes Radial can be written separately on the bus - the meaning is the same. In addition to the radial, there is also a diagonal design (D), but these are not found today. nine0003
Two numbers and a letter immediately follow the size.
These are the codes for the load capacity and speed limit of the tire.
Two digits - capacity or load index. This is a complex system of values, in which the larger the number, the greater the load, but the step size between the values is not constant. Therefore, it is easier to just know the most common of them:
The index value is the load on each wheel separately. To calculate the total load capacity, multiply by 4. This value can also be written elsewhere in a simpler form: Max load - xxx kg. nine0003
Photo: Shutterstock
The letter after the two digits of the load index is the index of the maximum speed for which the tire is designed. It starts with A, but the values relevant for modern machines start with the second half of the Latin alphabet:
This is not the limit, but the maximum "comfortable" value. In exceptional cases, you can even exceed it by 20-30%, but it is better to avoid this.
Another key parameter is the time the tire was produced. Usually it is indicated in a rounded rectangle, but may be without a frame. The first two digits are the week, and the second two are the year. nine0003
Also, three more parameters are usually indicated on the tire - wear resistance margin, grip quality class and temperature index.
The wear index is denoted by the word treadwear. Its unit is 480 km. Multiply the number next to that word by that value. If treadwear is 400, it means that under test conditions at the test site, such a tire has worn out after driving 192,000 km. Also, this parameter can be designated separately as the abbreviation TWI. nine0003
Traction is a measure of how well a tire grips on wet road surfaces. It has values from AA - the best level, to CC - the worst. Tires for regular passenger cars usually have class A, and the highest class is for sports and racing.
Temperature is the tire's ability to withstand heat when driving at a certain speed. There are three values here:
Tires of modern passenger cars most often have this index value - A.
Photo: Shutterstock
The letter E with a number indicates that the tire complies with the rules of the European Tire Standards Association (ETRTO) and has a corresponding certificate . The number indicates the country that issued it - but this does not matter, since the ETRTO requirements are the same. In this case, the tire can be produced anywhere.
The weather conditions in which this tire is allowed to be used are also usually indicated:
Winter tires must have a first, second or third designation. nine0003
On some tires you can find the designation of the type of car for which they are intended:
In addition, the tire may be marked:
