SHOCK ABSORBERS

Springs alone cannot meet the requirements for a light vehicle suspension system. A stiff spring gives a hard ride, because it does not flex and rebound when the vehicle passes over a bump. On the other hand, too flexible a spring rebounds too much, and the vehicle rides rough. For these reasons, shock absorbers are needed to smooth the ride of the vehicle. They do so by keeping the vehicle from jolting too much, by balancing spring stiffness and flexibility, and by allowing the springs to return to rest after they are compressed. Although single-acting shock absorbers check only spring rebound, double-acting shock absorbers check spring compression and spring rebound to permit the use of the more flexible springs.

Figure 3-9.-Coil spring mounting.

FRONT AXLE SUSPENSION

Most passenger car front wheels are individually supported with independent suspension systems. The ones you are likely to see are the coil spring and the torsion bar suspension systems used with independent front axles and shock absorbers.

REAR AXLE SUSPENSION

Driving wheels are mounted on a live-driving axle suspended by springs attached to the axle housing. Leaf springs generally suspend live axles using the Hotchkiss drive, as shown in figure 3-10. Coil springs are used on a number of passenger cars with independent suspension.

TIRES

Because tires are expensive, they require proper care and maintenance. While natural wear and tear affects tire life, premature tire failure can be caused by abuse and neglect. Proper maintenance of tires results in better performance and longer service and prevents a hazardous tire failure that can cause loss of life and equipment.

TIRE INSPECTION

Tires are cut by sharp objects, bruised by bad roads and stones, and injured by road shocks in general. To drive with a seriously damaged tire is dangerous, because it may blow out and cause the driver to lose control of the vehicle.

Carefully inspect your vehicle tires during prestart and post operations. Remove glass, nails, stones, and other foreign materials embedded in tires. Tires give longer mileage and safer driving when damages are repaired immediately.

Inflation

Correct air pressure is the basis for reliable tire performance. Tires are designed to operate at specified air pressures for given loads and inflated to the prescribed air pressure for your driving condition. When

Figure 3-10.-Hotchkiss drive.

checking air pressure, use an accurate gauge and check the valve cores for leaks.

NOTE: Reduce the tire pressure when driving in soft sand and over dunes. This increases the amount of tire surface in contact with the sand to provide better flotation (support). However, never reduce the tire pressure so much that the tire slips on the rim. On some equipment, the air pressure for normal conditions and off-road conditions is listed on a data plate on the dashboard or in the operator's manual. When operating with reduced tire pressure, drive at low speed. Inflate the tires to normal pressure as soon as the situation permits.

PROPERLY INFLATED.- A properly inflated tire, as shown in figure 3-11, view A, shows proper contact with the road.

Figure 3-11.-Proper and improper tire inflation.

Figure ^3-12.-Valve cores.

UNDERINFLATED.- An underinflated tire is shown in figure 3-11, view B. This tire does not contain enough air for its size and the load it must carry. It flexes excessively in all directions and gets hot. In time, the heat weakens the cords in the tire, and it blows out. Underinflation also causes tread edges to scuff the road that puts uneven wear on the tread and shortens tire life. Never run a tire flat, or nearly flat, unless the tactical situation in combat requires it. When run flat for even a short distance or almost flat for a long distance, the tire may be ruined beyond repair.

OVERINFLATED.- An overinflated tire is shown in figure 3-11, view C. Too much air pressure also causes tire failure. Excessive pressure prevents the tire from flexing enough and causes it to be constantly subjected to hard jolts. When an overinflated tire hits a stone or rut, the cords may snap and cause a break in the cord body. The center of the tread wears more rapidly and does not permit equal wear across the entire tread. Hard riding from too much air pressure also increases wear and tear on the vehicle.