Roll into winter weather with caution Published Oct. 16, 2007 By Master Sgt. Theresa Lex 52nd Fighter Wing Safety Office SPANGDAHLEM AIR BASE, Germany -- In addition to maintaining proper tire pressure, here are tips for making sure vehicles are ready for upcoming winter weather. * Install four snow tires -- To help maintain control and stability of vehicles in slippery conditions, snow tires must be installed in sets of four. * Watch tread -- As a tire wears, snow traction is reduced. Tires that are worn close to the tread-wear indicators have reduced traction and should not be used on snow-covered roads or in severe snow conditions. * No mixing -- Avoid mixing tires with different tread patterns, internal construction and size. This degrades the stability of the vehicle. The following are some differences between all-season and weather tires. Winter tires have treads specifically designed to improve snow and ice traction. * Wider and frequently "zigzagged" grooves enhance winter traction by providing more efficient drainage of water and snow. * Unlike older snow tires, smaller shoulder grooves increase snow and ice traction without sacrificing handling on dry roads or on the highway. * Special lug and groove shapes allow more snow to be packed into the tread and expelled as the tire rotates for better deep snow traction. * Sophisticated, high-density sipe designs (sipes are the little slits in the tread surface) help cut through water and slush so the tread compound can make better contact with snow and ice. * Rounder casing designs add traction by cutting into the snow's surface. All-season tires do not include these features and still deliver the wear and high temperature traction that is required for driving during other times of the year. * Shoulder blocks and groove designs are a "compromise" that must meet cornering, wear and all-season traction requirements. * Less aggressive tread designs deliver more highway ride comfort, but tend to pack and not expel snow as effectively as winter tires. * Less siping is used. * Flatter tread designs enhance dry traction but do not cut into snow effectively. To help in selecting a winter tire that improves the margin of safety, the Rubber Manufacturers Association designates winter tires that meet the new severe snow standard with a symbol. Any tire is a compromise because no one tire can be the fastest on the track, most controllable in the snow and longest wearing. The ultra high performance tire that grips the track with tread temperatures of 200 degrees is useless in winter as its tread compound becomes like hard plastic at temperatures below 32 degrees.