How to Buy Tires

Phil Ramsey
Tags: automotive

The rationing of gasoline in World War II was not to save gasoline, because we had enough to wage the war, but it was designed to save tires. Tires back then were made primarily from natural rubber, and the Japanese had captured most of those supplies. The rubber plants in South America were not enough to keep up with U.S. civilian and military needs. So by limiting the public consumption of gas, we conserved rubber needed for military uses.

As a mechanic, I should be awed by metal things, but today’s tires, in my opinion, are the most amazing parts of a car. They are subjected to centrifugal forces of a ton or more as the tire rotates at 90 mph or faster. The tire shape changes for an instant as it strikes the pavement, then resumes its original shape as it continues rotating. It carries the whole weight of the car and absorbs tremendous shocks as the tire strikes the uneven part of the pavement. Tires grip in rain, ice, desert temperatures, and still last for thousands of miles, or hundreds of thousands of revolutions, on a surface that will peel off your skin if you are dragged across it. In those car-chase scenes on TV cop shows, what happens when the tires blow? A shower of sparks and the rim soon wears off.

After a few years, tires must be replaced. In shopping for new tires, do you simply go to the tire dealer and buy the latest sale item? No way. Do you buy one tire, or three? No again. So, how does one buy tires?

To start with, buy a pair of tires to be placed on the same axle, or buy four new tires. A new tire across from an old worn tire of the same size has a definite size-difference disadvantage. Two or four is the number to buy. Buying odd numbers of tires places tremendous strain on the differential gears in a transmission or transaxle. Repairing those can cost a fortune, far more than three sets of tires. Buy in pairs only.

Are “on sale” tires a great bargain? Not necessarily. Buy tires according to use and cost vs. quality.

I drive very little, but I drive in an area where it is hot and rains a lot. My tires must perform well in high temperatures and on rain-slick roads. For me, the service mileage is not all that important. It will take me about four years to wear out a set of tires. How do I determine what tire to buy?

Our government has given us yet another acronym, UTQGS, or uniform tire quality grading system. Using this grading system wisely and making a few notes on your next tire-buying trip will save you money and make life a little safer. Modern tires are graded in three areas. Treadwear, traction and temperature. These ratings numbers, peculiar to each tire, are molded into the sidewalls of every tire sold in the United States. A label with these ratings must be placed on every tire.

Treadwear is numbered from 60 to 500 in increments of 20. The higher the number, the longer the tire should last. A treadwear of 300 should last twice as long as a treadwear of 150. Theoretically it should cost twice as much; any less makes it a bargain in longevity.

There is one little secret about tread wear numbers: They are not comparable from one manufacturer to the other. Those tread wear numbers are valid only when comparing apples to apples. Each tire manufacturer sets his own numbers. One manufacturer may rate a 400 tire as comparable to another manufacturer’s 300 tire. Tires are not government tested and regulated. Tread wear is used only as a comparative between the tires of the same manufacturer. So use the tread wear number within the same product line.

Traction ratings are a measure of a tire’s ability to stop in straight-ahead braking on both wet and dry surfaces. It is measured on both concrete and asphalt. It does not measure acceleration, traction or cornering. The tires are graded from AA, A, B and C, with AA having the best traction for braking.

Temperature is rated from A to C. C-rated tires run hotter at the same speeds and weather conditions, and C is the minimum allowed by the U.S. Department of Transportation. Do not buy a C-rated tire.

Great tires can be bought, mounted and balanced for about $300 for a set of four. Use the treadwear numbers to determine the best bargain, and use the temperature and traction ratings to suit your local driving conditions.

It is not so common to find a tire A-rated for both temperature and traction. These are usually trade-offs, but they can be found. Begin looking for a treadwear 300, temperature B, and traction A. Go from there and read those sidewalls. Base your price deliberations on treadwear numbers and nothing else. Temperature and traction are determined by where you drive. Also worth noting, blackwall tires last longer than whitewall tires.

Tires that are sold with mileage guarantees are most likely being sold as return-customer potential. Suppose you buy a 75,000-mile tire and it lasts only 54,000 miles. As you return for warranty adjustment, you will find out that the adjustment is based on the retail price of the tire. The adjustment price, when prorated against the retail price, is often the same you paid for the tire when you bought it “on sale”.

It has been known for customers to pay the same price for an “adjusted” tire, that failed after it was prorated against the retail price, with half the tread still usable. You will be credited for the remaining tread based on the full retail price, not the sale price you originally paid. You could also be convinced that alignment, balance or chassis problems caused the wear, thus negating the warranty. Then you will be approached about buying some new tires which will be on sale. Do not let mileage warranties affect your buying decision.

What are all those little numbers on the side of the tire? (P185/60R15 87S.) P stands for passenger; LT denotes a light truck. 185 is the width of the tire in millimeters. The 60 is the aspect ratio, or the height of the rubber of the tire from the rim to the outside edge, often called the sidewall, divided by the width of the tire times 100. A P185/60 tire should have a sidewall of about 111 mm. R means it is a radial tire and the 15 means it is a 15-inch rim diameter. The 87 tells the load capacity of the tire in pounds. The number is a key number on a chart located on the Internet at: http://www.tirerack.com/tires/tiretech/general/speed.htm

Our tire can support 1,201 pounds according to this chart, or 4 X 1,201 = 4,804 total load capacity for our set of four tires. The last number (or S) is the maximum speed rating; 112 mph in our tire example. These numbers range from Q (100 mph) to Z (149 mph or more). Recently introduced ratings of W and Y carry 168 mph and 186 mph, respectively.

Keep your tires inflated for maximum wear and safety. Have your tires rotated every 5,000 miles and inspected for alignment problems about every 10,000 miles.

Motorcycle Tire Speed Ratings


Motorcycle tires, like car tires, must handle acceleration, braking and cornering. Unlike their automobile counterparts, however, motorcycle tires must perform these chores while sometimes operating at extremely lean angles. Motorcycles, with only two tires, use much less rubber on the ground than the wider footprint of four car tires.

Today’s motorcycles are available in many styles to accommodate a wide range of riding activities. Lightweight commuting cycles require tires that provide average overall performance and mileage. Dual-purpose cycles require tires that can provide the necessary performance for the pavement, yet still offer an aggressive tread for off-road use. Most dual-purpose tires approved for street use by the U.S. Department of Transportation are usually designed more for the pavement than for off-road riding. A modern sport cycle requires tires that can provide maximum traction while being ridden aggressively at extremely lean angles. These tires must also be able to transmit power from the engine to the ground without losing traction - no small feat considering that a common engine delivers 100+ horsepower for a machine weighing 350 to 450 pounds. Sport-riding tires generally have a short life span because of their softer rubber composition. Touring cycles require tires that must be able to carry a heavy load while staying cool during extended miles touring across Death Valley - sometimes pulling a trailer with the kitchen sink in it. However, that same tire must still perform in the cool, twisty terrain of Colorado. Heavy load capacity and mileage are key issues here. Some tire manufacturers offer tires with a harder compound rubber in the center tread area of the tire for longer mileage on straight-up riding and a softer compound on the outside tread areas for increased grip when leaning the motorcycle.

Motorcycle tires are rated by load capacity and a maximum sustained speed rating. The latest addition to the speed rating chart is the “Y” rating, designated for 186 mph sustained. Motorcycle tires are of course primarily built for tubeless use; however the motorcycle industry still widely uses tube-type wheels. Nonradial or bias-ply tires are used in tube applications. The use of inner tubes in radial tires generates extra heat in the tire and affects the handling characteristics of the tire. Manufacturers warn of these adverse effects. Because of some of the aforementioned special requirements expected from motorcycle tires, they can cost two to three times more than an automobile tire.

Motorcycle Tire Speed Ratings
by Donny Meador, The Kinetic Playground
www.kineticplayground.com


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