See Figure 1
Tire rotation is the moving of the tires from wheel-to-wheel position in order to even wear. Tire rotation is recommended every 6000 miles (10,000 km), and then every 15,000 miles (25,000 km) there after to obtain maximum tire wear. The pattern you use depends on whether or not your car has a usable spare. Radial tires can be cross-switched (from one side of the car to the other). Be careful though if you have directional tires on your car, they can not be cross-switched. Snow tires sometimes have directional arrows molded into the side of the carcass. The arrow shows the direction of rotation. They will wear very rapidly if the rotation is reversed. Studded tires will lose their studs if their rotational direction is reversed.
Mark the wheel position or direction of rotation on radial tires or studded snow tires before removing them.
See Figures 2 and 3
For maximum satisfaction, tires should be used in sets of five. Mixing different types (radial, bias-belted, fiberglass belted) should be avoided. Conventional bias tires are constructed so that the cords run bead to bead at an angle. Alternate plies run at an opposite angle. This type of construction gives rigidity to both tread and side wall. Bias belted tires are similar in construction to conventional bias ply tires. Belts run at an angle and also at a 90° angle to the bead, as in radial tires. Tread life is improved considerably over the conventional bias tire. The radial tire differs in construction, but instead of the carcass running at an angle of 90° at each other they run at an angle of 90° to the bead. This gives the tread a great deal of rigidity and the side wall a great deal of flexibility (which accounts for the characteristic bulge associated with radial tires).
Store the tires at the proper inflation pressure if they are mounted on wheels. Keep them in a cool dry place, on their sides. If the tires are stored in the garage or basement, do not let them stand on a concrete floor, and make sure there is no danger of water collecting inside them. Set them on strips of wood. Keep tires away from sources of heat and ozone such as hot pipes and electric generators. Be sure tires surfaces on which the tires are stored are clean and free from grease, gasoline or other substances which could deteriorate the rubber.
See Figures 4 and 5
Tire inflation is the most ignored item of auto maintenance. Gasoline mileage can drop as much as 0.8% for every 1 pound per square inch (6.9 kPa) of under inflation.
Two items should be a permanent fixture in every glove compartment: a tire pressure gauge and a tread depth gauge. Check the tire air pressure (including the spare) regularly with a pocket type gauge. Kicking the tires won't tell you a thing, and the gauge on the service station air hose is notoriously inaccurate. General Motors recommends checking your tire inflation once a month.
The tire pressures recommended for your car are usually found on the left door or in the owner's manual. Ideally, inflation pressure should be checked when the tires are cool. When the air becomes heated it expands and the pressure increases. Every 10°F (rise (or drop) in temperature means a difference of 1 psi (6.9 kPa), which also explains why the tire appears to lose air on a very cold night. When it is impossible to check the tires cold, allow for pressure build-up due to heat. If the hot pressure exceeds the cold pressure by more than 15 psi (103.4 kPa), reduce your speed, load or both. Otherwise internal heat is created in the tire. When the heat approaches the temperature at which the tire was cured, during manufacture, the tread can separate from the body.
Before starting a long trip with lots of luggage, you can add about 2-4 psi (13.8-27.6 kPa) to the tires to make them run cooler, but never exceed the maximum inflation pressure on the side of the tire.
CARE OF SPECIAL WHEELS
See Figure 6
If you have invested money in magnesium, aluminum alloy or sport wheels, special precautions should be taken to make sure your investment is not wasted, and that your special wheels look good for the lifetime of the car.
Special wheels are easily scratched and/or damaged. Occasionally check the rim for cracks, damage or air leaks. If any of these conditions are found, replace the wheel. In order to prevent this type of damage, and the costly replacement of a special wheel, observe the following precautions:
See Figures 7, 8 and 9
All tires made since 1968, have 7 built-in tread wear indicator bars that show up as 1 / 2 in. (13mm) wide smooth bands across the tire when 1 / 2 in. (0.8mm) of tread remains. The appearance of tread wear indicators means that the tires should be replaced. In fact, many states have laws prohibiting the use of tires with less than 13 / 32 in. (0.8mm) tread.
You can check your own tread depth with an inexpensive gauge or by using a Lincoln head penny. Slip the Lincoln penny into several tread grooves. If you can see the top of Lincoln's head in 2 adjacent grooves, the tires have less than 13 / 32 in. (0.8mm) tread left and should be replaced. You can measure snow tires in the same manner by using the tails side of the Lincoln penny. If you can see the top of the Lincoln memorial, it's time to replace the snow tires.
BUYING NEW TIRES
When buying new tires, give some thought to the following points, especially if you are considering a switch to larger tires or a different profile series:
- All four tires must be of the same construction type. This rule cannot be violated. Radial, bias, and bias-belted tires must not be mixed.
- The wheels should be the correct width for the tire. Tire dealers have charts of tire and rim compatibility. A mismatch will cause sloppy handling and rapid tire wear. The tread width should match the rim width (inside bead to inside bead) within an inch. For radial tires, the rim width should be 80% or less of the tire (not tread) width.
- The height (mounted diameter) of the new tires can change speedometer accuracy, engine speed at a given road speed, fuel mileage, acceleration, and ground clearance. Tire manufacturers furnish full measurement specifications.
- The spare tire should be usable, at least for short distance and low speed operation, with the new tires.
- There shouldn't be any body interference when loaded, on bumps, or in turns.