April 16, 2013

News & Features

ABCs of tires: The right ones can help your car get a grip

The Virginian-Pilot


If you find yourself in need of a new set of tires and don't know what all of those letters and numbers on the sides of tires mean, here's a handy guide to decode the sidewall and find the best tire for your vehicle.

Types of tires

All-season: Best for year-round traction, ride comfort and long tread life.
Performance all-season: Better handling than all-season, but a more comfortable ride than performance tires.

High-performance: Superior grip in wet or dry conditions, but usually has a shorter life span and harsher ride than other types. Not a good choice for snowy climes.

Winter: Great traction in snow and ice but less traction for other types of weather conditions.

Light truck: A good choice for all-around use.

All-terrain: Best for venturing off-road.

Size numbers

The tire size is expressed in a series of numbers and letters, such as P235/70R16.

P: Passenger car, but commonly seen on crossover utility vehicles and minivans. Other prefixes: "LT" for a light-truck tire and "T" for a temporary spare.

235: Width of the tire in millimeters.

70: Ratio of the sidewall height to the tires width, which is 70 percent. Sportier tires have a lower ratio.

R: Radial construction. A "D" indicates bias-ply construction.

16: Wheel's diameter in inches. Sizes range from 8 inches to 28 inches.

Load index and speed rating

Located after the tire size is a code such as 104S, which can contain any number between 71 and 110.

The number specifies the weight that can be safely carried.
71: 761 pounds
80: 992 pounds
90: 1,323 pounds
100: 1,764 pounds
104: 1,984 pounds
110: 2,337 pounds

The letter denotes maximum sustainable speed:
M: 81 mph
N: 87 mph
Q: 99 mph
R: 106 mph
S: 112 mph
T: 118 mph
H: 130 mph
V: 149 mph
Z: more than 149 mph

In addition, Z-rated tires will also have a letter diameter size to specify the tire's top speed:
W: 168 mph
Y: 186 mph

How good are they?

Tires have ratings on them, but they are manufacturer-supplied, so you can use them only to compare tires within the same brand.

Tread-wear rating runs from 300 to 540, describing the life of the tire. The higher the number, the better.

Traction and temperature scores range from AA (best) to C (worst) and rate foul-weather traction and temperature resistance, which can indicate a higher-quality tire.

Maximum pressure is listed for maximum safe pressure when hot, measured in pounds per square inch. This is not the recommended tire pressure. That is specified by the auto manufacturer and is located on a placard on the driver's-side door jamb.

Tire date

A tire marked 0412 was made in the fourth week of 2012. Make sure the tire you're buying is no more than two years old.


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