Monday, November 30, 2009

Tire Speed Ratings Are Easier to Understand Than You Think

What are tire speed ratings and why are they so important? Many tire buyers have asked this question and understanding the answer can help you the next time you buy a set of replacement tires for your car or truck.

The importance of tire speed ratings can be summed up quite simply. Tires are manufactured to a wide variety of specifications that meet, or exceed, certain levels of performance. The standard tires that will perform best on a Ford Focus, will not get the job done on a Chevrolet Corvette. Conversely, a Corvette tire will far exceed the needs of a Focus.

If you look closely enough you will notice there is a fair amount of information imprinted onto the side of your tire. Among this information is the speed rating, which is generally listed by a letter that follows the tire size and load index. For example, your tire may include this set of numbers and letters: P205/55R-15 88V. The P means passenger tire, 205/55 is the width and aspect ratio of the tire and the R designates this as a radial tire. The number 15 indicates that this tire fits 15 inch diameter wheels, 88 is the load index and V is the speed index. All tire manufacturers in the world adhere to a universal system of rating.

The whole idea of a speed rating may seem unnecessary in the United States, where our "legal" speed limits max out at 70mph, but in truth speed ratings were born overseas in Europe to meet the needs of the infamous German autobahn. Here posted speeds are not listed as maximum limits, but minimum requirements for the lane you choose to occupy. As vehicles became capable of higher and higher speeds, tire manufacturers realized that different tire grades were necessary to avoid catastrophic high-speed blowouts.

Speed ratings are determined through lab testing. Essentially, it involves pressing a tire at its appropriate load against a large, high-speed metal drum, and then gradually increasing running speed until the required speed rating has been reached. The chart below lists the tire speed ratings and the maximum speed for that rating:

M: 81mph (130 km/h)
N: 87 mph (140 km/h)
P: 93 mph (150 km/h)
Q: 99 mph (160 km/h)
R: 106 mph (170 km/h)
S: 112 mph (180 km/h)
T: 118 mph (190 km/h)
U: 124 mph (200 km/h)
H: 130 mph (210 km/h)
V: 149 mph (240 km/h)
W: 168 mph (270 km/h)
Y: 186 mph (300 km/h)
(Y): 186+ mph (300 km/h)

As you can probably guess, the speed ratings were originally created in kilometers-per-hour, thus the odd miles-per-hour increments. Also, there are two Y ratings; the Y rating enclosed in parentheses (Y) indicates that it has been tested in excess of 186 mph.

When you shop for replacement tires make sure you select a speed rated tire that meets your driving requirements. Naturally, you must be careful when driving not to exceed the rated speed of your tires. And also keep in mind that even though tire manufacturers market and sell tires capable of high speeds, they do not condone the use of their products in excess of legal speed limits. Don't try explaining to the officer that pulls you over for speeding that you thought you were allowed to go faster because your tires were capable of such excessive speeds.

Speed ratings are only effective when tires have not been damaged, altered in some fashion, are not overloaded and are properly inflated. Even if a tire has been repaired due to a puncture or other damage, it no longer retains the original speed rating because the manufacturer cannot control the quality of the repair.

Finally, although speed ratings do not indicate tire handling capabilities, a higher speed rating may translate to different handling characteristics. This is important to note if you buy a new set of tires with a lower speed rating. Make sure you are familiar with the handling characteristics of your car or truck and make the necessary driving adjustments to allow for the lower speed rating.

About Belle Tire
Allen Park, Mich.-based Belle Tire was founded in 1922 when it opened the first Belle Tire location in Detroit, Mich. Today, the company has expanded to 80 locations across Michigan and Ohio. Belle Tire offers discount tires and variety of car care needs, ranging from auto glass repair, auto glass replacement, brakes, alignments, batteries, shocks and struts, exhaust system repair, batteries, and oil changes. For more information about Belle Tire, visit Join the Belle Tire Advantage today,

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