All tires are not created equal — make sure that you select the right tire for your car with clear understanding of Tire Speed Rating, which is very important to handle the overall performance of your vehicle.
Biggest mistake we make when replacing tires is not considering the correct speed ratings of the tire. The speed rating indicates the maximum allowable speed that the tire can continue for a 10 minute endurance with no danger. It’s wrong to mix tires with different speed ratings. More than the maximum speed rating of your tire could result in tire failure or damage, putting you and others in danger. Also, the tire with the lowest speed rating will limit the actual tire-related speed. Moreover, keep in mind that fitting lower speed rated Tyres in vehicle may invalidate your insurance. So, care should be taken that tyres with the correct speed rating are fitted to your vehicle. No, it’s not so difficult to make out Speed Rating of the tire, just have a simple look on a Tyre Markings that is clearly molded into the sidewall of the tire. This is filled with vital information that tells you everything you should know about your tire like tire’s construction (e.g. radial), its size, its load-carrying capacity along with its speed rating. Tire Marking carries an important information, but it’s all in code. Code language is very hard to understand. That’s why, many owners are not concerned this Tyre marking.
Don’t do so, here we give the best way to understand tire markings, by breaking down the code example and figure out it bit by bit. Just go through, and put all dangers far away!
Little about Speed Rating:
The speed rating system was set in Europe to control the safe performance of tires at regular speeds. Tire speed ratings range from A ( for the lowest) to Y ( for the highest) from 5 km/h (3mph) to above 300 km/h (186 mph) respectively, however the chart is not in alphabetical order totally. For ex., H is between U and V, following common perception that H stood for “high performance”. Later on, as manufacturers continue to add speed to their vehicles, Z was the highest rated speed at 149+one time, then W & Y were used to match the higher speeds. This rating system describes the top speed for which a tire is certified. Note that it does not point to the total performance capability of a tire.
As said, tires reveal a set of code printed on their sidewalls. This code is known as the ISO Metric tire code, which is a set of numbers and letters and may be printed in any of three ways. For ex.: P205/45ZR17 88W or 205/45ZR17 or 205/45R17 88ZW. Keep in mind that before 1991, tire speed ratings were placed inside the tire size, ahead of the “R” character as in 205/45ZR17, however some tire manufacturers carry on to use this format. Speed ratings only relevant to tyres that have not been damaged, altered, under-inflated or overloaded because cut or punctured tire no longer holds the original speed rating even after being repaired.
Each tire has a distinct speed rating. On replacing a tire, make sure that the new tire’s speed rating should be equal to the speed rating of the existing tire. If tires with different speed ratings are fitted on the single vehicle, the lowest speed rated tire dictates the highest vehicle speed. For the best performance of the vehicle, it is suggested that use the same size and type of tire for all four wheel positions.
Speed ratings are based on tests, wherein engineers run the tyre at 6.2 mph steps, in 10 minute increments, awaiting the requisite speed has been met. In the U.S., these ratings are derived from tire testing in laboratory , by meeting minimum industry standards for reaching and sustaining a specified speed. The ISO (International Standard Organization) system presently serves as a international standard for tire markings. A tire gets its speed rating from the U.S. Government, but tire manufacturers test their own tires and allot their own speed ratings considering type of that vehicle.
To select the right replacement tire, you have to know what the numbers and letters on your tire marking mean:
Take a sample code: P205/55R16 89H M+S
P: Here, P indicates that it is a passenger-car tire. Thus, first letter represents the intended use or vehicle class for the tire. Other options are:
- P: Passenger Car
- LT: Light Truck
- ST: Special Trailer
- T: Temporary (which is primarily used for small spare tires.)
In case, a tire does not have any letter in front of the numbers, it is considered to be a “Euro-metric” tire, which match to the European tire specifications, and often carries a dissimilar load index than a comparably sized P-metric tire.
205 (the first number): This number indicates the tire’s width in millimeters or distance from sidewall edge to sidewall edge (in millimeters) when calculated up and over the tire’s tread. It is obvious that the larger this number, the wider the tire will be.
/: Slash character for separating characters.
55 (2 or 3 digit number following the slash): This number is the tire’s aspect ratio, which is measured by comparing section height to section width of the tire. In this example, the section (or sidewall) height is 55 percent of the section width, which is 205 mm. This number is very useful for indicating tire’s purpose. For ex, sporty tire with shorter sidewalls are considered as lower-series tire while off-road tires tend to be higher-series, intended to absorb the impact from rough surfaces. Lower-series, like 55 or less, signify a short sidewall for superior steering response and improved overall handling. And, when the number is larger than 200, it means this is the diameter of the whole tire in millimeters.
R (Internal Construction): Here are optional letters, which indicate construction of the fabric carcass of the tire. Like,
- B: bias belt (where the sidewalls are the same material as the tread, leading to a stiff ride)
- D: diagonal
- R: radial
If none of these, then it would be a cross ply tire.
In the sample code, “R” refers to tire with radial construction, which is considered to be the industry standard in passenger-car tires for more than 20 years. Before radial tires, the majority cars came with bias-ply tires, having crude construction that prepared for poor handling. Bias-ply tires are still used for certain truck applications.
16 (the last number): This number indicates the rim or wheel diameter in inches, for which the tire was sized. This number is very useful if you plan to upgrade your wheel size. If you change wheel diameter, you’ll have to buy a new set of tires that matches this new diameter. So, be careful about this number.
89H: This is the service description, which is separated from the main code. It represents the tire’s load index along with speed ratings.
Load index is one of the most important numbers on your tire, measuring how much weight every tire is intended to support. If the number is larger, the tire has higher load capacity. Here 89 load index represents 1,279 pounds (per tire), based on a Load-Carrying Capacity Per Tire chart. Remember that it is per tire, and to get the total capacity for a complete set of tires, you have to multiply by four.
In some cases, load index on the tires is much higher than a standard-load tire, known as “XL” tires . Here “XL” tires don’t mean that they’re extra large, however they are extra-load tires. It is necessary to replace an XL tire with another XL tire.
“P-metric” and “Euro-metric sizing” create confusion. P-metric tires have one or two points lower load index than related Euro-metric tires. It means don’t replace Euro-metric tires with P-metric tires. The load index is mainly important when shopping for a tire online, because many retailers do not mention whether a tire is P-metric or not.
H (Speed rating): This is the most important part of the whole tyre marking, here H indicates speed rating. It is a measurement of the speed, at which the tire is intended to run for extended periods. An “H” speed rating indicates that this tire can be run safely at speeds of up to 130 mph for extended periods. In the U.S., where the speed limits are lower even the lowest speed rating (N, or 87 mph), speed rating is less important. In other countries, people are acknowledged to drive 100 mph and above.
You can find different tire speed ratings along with their associated letters in the following list:
M+S: This is optional part. It stands for mud and snow, that indicates tire as an all-season tire. There aren’t other designations for summer and winter tires. Summer tires obviously lack the M+S, it means winter tires are labeled with M+S and comes with icon of a mountain plastered with a giant snowflake.
It is good to Drive as per the speed rating of you car’s tyres. Once you make out your Tyre speed rating, you can know what is the maximum speed your Tyre is capable of maintaining.
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