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Because they accelerate the wear of road surfaces, not all states permit the use of studs in tires. Refer to the following list for a summary.

Permitted: CO, KY, NH, NM, NC, VT and WY; soft type only in FL and TX; rubber only in AL; projection limited in SC.
Calendar restriction: AK, AZ, AR, CA, CT, DE, DC, ID, IN, IA, KS, ME, MD (western counties only), MA, MO, MT, NE, NV, NJ, NY, ND, OH, OK, OR, PA, RI, SD, TN, VA, WV; soft only in MI and UT.
Prohibited: GA, HI, IL, LA, WS, WI.

THE NUMBERS

Nearly all passenger car tires sold today are sized and described by a string of numbers in both metric and American units. The accompanying illustration portrays a standard tire description, but a few explanations are likely in order. The first letter describes the use, typically "P" for passenger or "T" for temporary spare. The three-digit number that follows is the width in millimeters at the widest point. Following the slash comes the two-digit aspect ratio or profile, which is the percentage of height to width. A 50 profile tire is half as high as it is wide. Next comes the speed rating, either "S" (up to 112 mph), "H" (up to 130 mph), "V" (up to 149 mph) and, believe it or not, "Z" (anything goes). Following that is a letter describing the car cass construction: "R" for radial, "B" for belted-bias or "D" for bias-ply. Finally comes the rim diameter. It's usually in inches, but some companies, such as Michelin on their TRX series, are now using metric rims.

Elsewhere on the tire's sidewall you'll find a set of Department of Transportation (DOT) required tire ratings. First comes tread wear, expressed as a three-digit number that can be multiplied by 300 to estimate life expectancy in miles. Don't take these figures too seriously, though. Driving style and road surface can make big differences, and DOT's authority to enforce the ratings is essentially toothless. Right after tread wear, you'll find traction and heat resistance ratings, expressed as "A," "B" or "C," with "A" being the best. A decent tire should rate at least "B" in both categories.

WHAT'S IN A NAME?

Ever wonder whether department stores actually go to the trouble to make their own tires? Hardly. Tire manufacturing is a complex and exacting business, one where it pays to keep equipment busy by engraving other companies' names in sidewalls (or even applying different treads) and selling wholesale. At present, there are about 15 domestic and 15 foreign tire manufacturers, and each of them has a set of identifying letters that must be a part of the DOT-required serial number.

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