A tire ratings chart can be the best way for a consumer to determine which tires are right for their vehicle. Unfortunately, most drivers don’t have a great deal of experience reading such a chart, so they often purchase the wrong products for their vehicle or for the circumstances in which they typically drive. Through understanding the rating indicators on individual tire models, it is possible for consumers to buy a set of wheels that last longer and provide better performance no matter what type of car they drive.
Where Do the Numbers and Letters Come From?
Ratings for tires were established by the National Highway Traffic Safety Administration. The system is designed to ensure safety and provide enhanced fuel economy. Moreover, the ratings system also provides measurement of tread durability and gives information about recommended speed maximums and load capacities.
Where to Find Numbers and Letters for Tire Ratings
In the United States, federal law requires manufacturers to place these labels on the sidewalls of every product they sell. Tires that are suitable for passenger cars and trucks begin with a “P” indicator. The number directly following the P indicates the width of the tire measured in millimeters. Basically, a bigger number indicates a wider wheel. The next number indicates the height to width Aspect Ratio. Any number lower than 70 usually means a shorter sidewall that grants more responsive steering to the driver. For driving in dry weather, this is typically an ideal choice.
Next on the chart is a letter, which is typically an “R.” This designation indicates radial ply construction. This method of construction has been the accepted industry standard for approximately 20 years, so this indicator is found on nearly all tire manufacturer’s products. The Rim Diameter Code is next. This is a measurement in inches, and it’s important to be precise, particularly if the driver is purchasing new wheels.
The next number refers to the load index. Legally, manufacturers are not required to label this number on the sidewall. Drivers who are looking at tires on which the load index is not shown should refer to their vehicle owner’s manual and ask questions of sales personnel to ensure they are buying a product that is appropriate for their vehicle. The tire speed rating typically appears next. This is a letter that indicates performance capabilities on the vehicle.
Some tires also exhibit an M+S or M/S designation. These letters stand for mud and snow, and they may be of particular interest to drivers who drive off-road or frequently encounter adverse weather.
Drivers in Hot Conditions
Sometimes the label on the sidewall will also indicate information about heat resistance. Drivers who live in hot, dry climates may be particularly interested in this data. Heat resistance ratings are either “A,” “B” or “C.” Only 11% of tires receive the “C” rating, and these products are especially adept at handling exceptionally hot conditions. It’s advisable for drivers to look for tires with this “C” rating when they know they drive in very hot conditions on a regular basis.
Traction for Safety
Traction indicators of “AA,” “A,” “B” or “C” inform consumers about the car’s ability to stop on wet surfaces. “AA” is the highest rating, with most tires manufactured today receiving a rating of “A.” Only drivers dealing with unusually wet, treacherous roads need to be concerned with choosing tires rated at “AA.”
The Origin of Speed Indicators
One of the most important tire ratings numbers to understand is that which relates to speed. The concept behind this indicator originated with the German Autobahn where high-speed driving is the norm rather than the exception. An “A” indicates the lowest speed rating while “Y” corresponds to the highest. However, it’s important to realize that the list is not entirely in alphabetical order. As an example, the “H” rating falls between “U” and “V.” Also of note is the fact that, the speed letter indicators evolve as tire technology evolves. At one point, “Z” was the highest rating at 149 miles per hour or more. Now, “W” and “Y” indicators have been added to accommodate exotic car models that have extremely high performance.
The Speed Indicator Is Not Just About How Fast the Car Travels
The speed indicator does relate to the speed at which the vehicle typically travels. However, it also relates to the comfort of the ride. Additionally, cornering ability may be improved through a tire that has a higher speed rating. Wear is also a factor of the speed indicator. A higher level is likely to provide better stopping and a higher degree of gripping ability. On the downside, such a tire is also likely to wear out more quickly.
It’s important to know that consumers can also choose new tires that have a higher speed indicator than their current set. This typically improves performance. However, changing to tires with lower speed indicators will negatively impact vehicle performance with reduced speed and handling capabilities.
Understanding the Load Index
The load index is a two-digit number located to the left of the letter that indicates the speed rating. The load carrying capacity is indicated by the two digit number. For instance, a 97 demonstrates an ability to carry 1,609 pounds while a tire rating of 99 shows a capacity of 1,709 pounds. While it is always possible to choose new models that have a higher load index, it is never advisable to go the other way. A smaller two-digit number than the number on the existing model indicates an inability to cope with the vehicle’s weight, which can be a major safety concern. Numbers between 70 and 130 are common for passenger vehicles, and it’s important to check the current number before determining what is appropriate for the new tires.
Armed with the knowledge of how to read a tire ratings chart, any consumer can make a wise purchase. Having the right model on any vehicle helps to maximize fuel economy and assists to ensure the safety of the driver and his or her passengers. When consumers can identify the numbers and letters on the sidewalls, they can rest assured that their ride will always perform at its best.