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  • Tire Tech 102: Numbers and Ratings

    In the previous course -- Tire Tech 101: Dimensions -- we explained what some of the most common information printed on a tire's sidewall meant.  Now that you've aced that class and are ready to graduate to the big leagues, we're going to look at some of the smaller print on your tires, and also chat a little about tire designations you might see on various websites or in the stores.

    But first, a minor digression:

    Uniform Tire Quality Grading System, or UTQGS

    The United States government established the UTQGS (Uniform Tire Quality Grading System) to assist consumers in understanding -- at least at a basic level -- the quality of the tires they can buy.  It looks at three areas:

    • Treadwear
    • Traction
    • Temperature

    These three areas are graded during safety and inspection tests, and are printed both on the tire's sidewall and on the paper labels affixed to each tire's tread when they are to be sold to consumers, so that you can easily find the information.

    So, digression over, here's where Tire Tech 102 truly begins:

    Tire Ratings

    Tire Ratings

    Treadwear

    This is a comparative rating -- usually within brands -- of the useful life of a tire's treads under controlled conditions.  Because one manufacturer may grade something as a 400 (which means it will last twice as long as a tire graded 200) and another manufacturer might grade essentially the same tire as 300 (lasts twice as long as a 150 grade wheel), it's not very useful when comparing tires made by different companies.  And you have to take into account that you probably won't be driving in scientifically controlled conditions, so who knows what kind of elements might reduce tread performance.

    Tread Depth

    Tread Depth

    Traction

    Graded AA, A, B, or C (from highest to lowest, respectively), this is a measure of the tire's stopping ability on wet pavement.  This doesn't take into account turning performance or any vehicle-based stopping performance, and is yet another test done under scientifically controlled situations, so it's really just a comparison rating.

    Temperature Resistance

    Resistance to heat and ability to dissipate heat are important  because tires are constantly under friction (which, as any physicist knows, creates heat), and surrounded by even more friction (brakes on wheels, for instance).  The grades from highest to lowest are A, B, and C, with C being the minimum required performance under federal safety standards.

    Other Designations

    There are several other designations, some of which can be found on the tire, others which might not be.  These include:

    • Service Designation: A designation of "M&S" somewhere on the tire means it is rated by the manufacturer as suitable for use in mud and snow, with guidelines set by the Rubber Manufacturers Association (RMA) in the U.S.
    • All-Season Designation: This is basically saying that the tires meet the "M&S" service designation (above) without the drawbacks of noise or rolling resistance that comes with some winter tires.  Passenger and light trucks might also meet criteria that provide superior snow performance, usually designated by a mountain/snowflake symbol on the tire.
    • D.O.T. or DOT Code: This is a numeric code (sometimes alphanumeric) that indicates the manufacturer, plant where the tire was produced, tire line, tire size, and the week/year of manufacture.
    • Maximum Pressure / Load: All tires are marked on the sidewalls with the maximum load capacity in pounds, as well as the maximum inflation pressure (just look for "P.S.I.").  Truck tires have dual and single application recommended pressure for maximum loads.

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