Figure 3-14.—Mismatched tireskeeps dirt and moisture out of the valve body. Thescrewdriver cap has a forked tip that may be used toinstall or remove the valve core. The plain cap generallyis used on rubber-covered valves and has a skirt thatcontacts the rubber covering on the valve stem. Bothcaps are interchangeable with each other. Part of yourprestart operation is making sure that all valve stemshave valve caps.MismatchingFor longer tire life and more efficient performance,dual tires and tires on all-wheel drive vehicles must beof the same size, tread design, and tread wear.Improperly matched tires cause rapid uneven wear andcan also cause transfer case and differential failures.Accurate matching of tires is necessary, becausetires on axle-drive vehicles rotate at the same speedwhen all axles are engaged. Dual wheels turn at the samespeed, because they are locked together which meansthat tires on all driving wheels must be of the samecircumference and diameter. When one tire of a pair ofduals is worn considerably more than the other, the tirecannot carry its proper share of the load and will scrubthe road (fig. 3-14). The result is uneven and rapid wearon both tires and/or tire failure.Tires should be used in sets. Mixing different types(bias ply, fiber glass belted, radial ply) must be avoided.Snow tires should be of the same size and type ofconstruction as the front tires. Radial-ply tires shouldalways be used in sets.NOTE: Under no circumstances should radial-plytires be mixed with bias-ply tires, together or on thesame axle.The problems encountered when mixing tires on avehicle are loss of steering control, inadequate vehiclehandling, and potential mechanical damage. Theseproblems vary depending on the stability of the tiresused, differences in dimensions, differences in airpressure, and other operating conditions.RADIAL-PLY TIRES.— Radial-ply tires (fig. 3-15)are constructed with casing plies perpendicular to thetread direction, with several layers of tread-reinforcingplies (steel or fabric) just under the tread area. Thisconstruction permits flexing of the tire with a minimumof tread distortion, better traction, and a softer ride.Figure 3-15.—Radial-ply tire construction.3-9
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business