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How To
Sidewall Graffiti: How to Read Your Tire
By Karl Brauer, Editor in Chief, Edmunds.com
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Have you ever taken a close look at your tires? Not a "hey, they're still pretty shiny" glance but a really close look? If you have, you probably noticed that they're covered with all sorts of strange letters and numbers. You might have even thought they displayed some kind of secret code that only the "Tire People" know how to read. They do this after disembarking from their black helicopters and rummaging through your trash at 3 a.m.
The truth of the matter is that anyone, with a little knowledge and a printed copy of this article, can decode these rubberized hieroglyphics. I'm going to spend the next few paragraphs telling you how so you won't have to live in fear of your sidewall graffiti anymore. I'd still watch what you put in your trash, however.
The best way to understand tire markings is to take an example and break it down, bit by bit. We'll start with the most important numbers found on a sidewall. For our example these numbers are:
205/55R 16 89V
205
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The first number in this series refers to the tire's section width, or distance from sidewall edge to sidewall edge (in millimeters) when measured up and over the tire's tread. Generally speaking, the larger this number is, the taller and/or wider the tire will be.
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55
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This number is the tire's aspect ratio, or its section height compared to its section width. In this case, the section (or sidewall) height is 55 percent of the section width. This number can be very indicative of a tire's purpose. Lower numbers, like 55 or less, mean a short sidewall for improved steering response and better overall handling.
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R
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The "R" refers to radial construction, which has been the industry standard in passenger car tires for more than twenty years. Prior to radial tires, most cars came with bias-ply tires which had a crude construction that made for poor handling. Bias-ply tires are still used for certain truck applications.
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16
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This is the rim diameter, in inches, for which the tire was sized. Pay particular attention to this number if you plan on upgrading your wheel size. If your wheel diameter changes, you'll have to purchase a new set of tires that match this new diameter.
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89
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A tire's load index is a measurement of how much weight each tire is designed to support. To find out what "89" means, it must be looked up on the official Maximum Load-Carrying Capacity Per Tire chart. In this case, 89 indicates a maximum weight of 1,260 pounds. Remember that this is per tire, which means you have to multiply by four to get the total capacity for a complete set of tires.
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V
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The speed rating is a measurement of what speed the tire is designed to run at for extended periods. A "V" speed rating signifies that this tire can be run safely at speeds of up to 149 mph for extended periods. Will it explode if it goes to 155? No, not immediately. But it might if it is run at that speed for several minutes.
Here is a complete list of the various tire speed ratings, and their associated letters:
S 112 mph
T 118 mph
U 124 mph
H 130 mph
V 149 mph
*W 168 mph
*Y 186 mph
* For tires having a maximum speed capability of more than 149 mph, a ZR may appear in the size designation. For tires having a maximum speed capability greater than 186 mph, a ZR must appear in the size designation.
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In addition to these basic tire specifications, you might find a DOT number that is used by the Department of Transportation to track tire production. No, this isn't more black helicopter stuff; the DOT uses this information for recall purposes. If a certain tire produced by a certain manufacturer on a certain day at a certain plant proves to be defective, this number helps keep track of where these tires ended up so that buyers can be notified of the problem.
There is also a traction rating found on the sidewall of all modern tires that can be represented as an A, B, or C. This is a rating of a tire's traction when tested for straight line braking on a wet surface. For this rating A signifies the best traction performance and C indicates the worst.
Finally, you might find the word TREADWEAR on the sidewall followed by a number like 120 or 180. This is a rating of the tread's durability, as tested against an industry standard. The reference number is 100 so a tire with a treadwear rating of 180 has an 80 percent longer predicted tread life while a rating of 80 means a predicted tread life only 80 percent as long as the industry standard.
There's also a newer version of the treadwear rating that ranges from 20 to 620. Once again, the higher the number, the longer a tire's useable tread life will be.
This should give you a basic understanding of what you'll find on a tire's sidewall. You can find out more about tires and wheels at www.discounttires.com if you're really interested in what keeps your vehicle rolling.
I could go into further detail about things like tire construction or speed ratings but those subjects require an article of their own.
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