Distribution: Winter Tire Tips
October 15, 2008
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Winter weather presents its own particular set of challenges because of unexpected weather changes and the hazards of driving in adverse conditions. As winter approaches, there are a number of things to consider when preparing your fleet and your drivers for this season.
Naturally, equipment should be winterized. This should encompass, among other things, making sure the engine is properly tuned and serviced, and that all vehicle systems are functioning as intended.
It is good practice to review with your drivers the importance of using extra caution when driving in winter weather conditions (see sidebar). Routers and dispatchers should also be reminded to allow extra time for traffic delays.
An area often overlooked in preparing equipment for winter is tires. Maintaining proper tire inflation pressure becomes more challenging during the winter. Because air is a gas, it contracts as the temperatures get colder, and low inflation adversely impacts tire life and performance.
For every 10-degree Fahrenheit change in temperature, a tire’s inflation pressure will change by about 1 psi — down with lower temperatures; up with higher temperatures.
Tire manufacturers advise that tire pressure be checked when a tire is “cold” — before a vehicle has been driven, or driven less than one mile. Once a vehicle has been driven, tires warm up and experience an increase in air pressure, resulting in an inaccurate inflation pressure reading.
A “hot” tire can take three or four hours to cool down after a vehicle is parked.
Tires on vehicles parked in a garage during the winter, especially one that is heated, “lose” air pressure when the vehicle is driven outside. If air pressure is checked while the vehicle is inside, about 1 psi of “cold” tire pressure should be added to the reading to compensate for each 10-degree temperature difference.
Valve caps should be installed on all valve stems and they need to be kept tight, say tire manufacturers. Metal valve caps are best, as they contain a rubber gasket to provide an airtight seal. Plastic caps do not.
Further, experts stress the importance of keeping air pressure even between mated dual tires. Inflation mismatches can cause tire diameters to differ enough that the larger tire will drag the “smaller” tire, causing rapid and irregular wear.
Tests by Bridgestone/Firestone found that a 5 psi difference in air pressure created a 5/16-inch difference in tire circumference on a set of dual tires. In just one mile, this small difference caused the smaller tire to be dragged 13 feet. Figuring 50,000 miles per year, this tire would be dragged 123 miles.
This same type of situation can occur if tread depth and design on dual tires are not properly matched. Dual assemblies should be matched within a tolerance of 3/4-inch in circumference and 1/4-inch in diameter.
Because tread depth has an impact on traction, tires need to be checked for tread depth. A tire with a lot of tread will have more traction than a tire with worn tread.
While many truck fleets remove tires with a worn tread depth of 4/32-inch in the spring and summer months, that is not a recommended practice in the winter, according to Goodyear. It recommends that tires be removed at 8/32-inch tread depth. These tires can be placed on trailers or put in racks until spring arrives and then put back onto vehicles.
Goodyear says having an “aggressive” drive-axle tread pattern is important for single drive-axle tractors and straight trucks during the winter. The reason being, a pattern with lots of lugs will dig into snow and provide better traction. On a tandem-axle rig, aggressive tread doubles the drive and traction.
Taking proper care of tires through all seasons, say tire manufacturers, optimizes tire performance for increased uptime, better fuel efficiency and longer tire life. BI
