See Figure 1
The tires and wheels are an important part of any vehicle, because not only do they allow the power from the engine to be transmitted to the road, they also provide for a smooth ride, stable handling, and traction in harsh weather.
It is a good practice to perform regular wheel and tire inspection, as follows:
All tires today are equipped with built-in tread wear indicator bars that show up as 1 / 2 in. (12.7mm) wide smooth bands across the tire when 1 / 16 in. (1.5mm) 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 1 / 16 in. (1.5mm) of tread remaining.
You can check you own tread depth with an inexpensive tire depth gauge, or by using a Lincoln head penny. Push the base of the gauge down between two treads. Remove the gauge, and read the number at the top of the gauge. Most gauges record the measurement in both 1 / 16 in. (1.5mm) as well as 1 / 32 in. (0.80mm) increments. If the tire has less than 1 / 16 in. (1.5mm), the tire should be replaced.
To check tire depth using a penny, slip the penny into several tread grooves. If you can see the top of Lincoln's head in 2 adjacent grooves, the tires have less than 1 / 16 in. (1.5mm) 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 see the top of the Lincoln memorial, it's time to replace the snow tires.
See Figures 2 and 3
Up until, and including model year 1983, Ford did not recommend tire rotation. Instead, they recommended that tires be replaced in pairs as needed without rotation. But in 1984, Ford began suggesting in the their owners manuals a tire rotation interval as well as a pattern of rotation similar to the diagram in this section.
Tire wear can be equalized by switching the position of the tires about every 6,000 miles. Including a conventional spare in the rotation pattern can give up to 20% more tire life. The pattern of tire rotation you use will depend on whether or not your vehicle has a usable spare.
There are certain exceptions when rotating tires. These should be kept in mind when determining rotation patterns. For example, studded snow tires should never be rotated. This is because studded snow tires can ruin front wheel bearings if moved to the front of the car, as well as the studs potentially coming loose if the rotational direction is changed. Special attention should also be paid in rotating tires which are directional. Because these tires are designed to function only in one direction, particular attention must be paid to make sure the rotational direction is correctly maintained.
Because of the advances in tire technology, and especially radial tire technology, the belief that radial tires should not be cross-rotated no longer holds true.
Whenever tires are removed from the car, mark them, so you can maintain the same direction of rotation.
For maximum satisfaction, tires should be used in sets of five. Mixing of 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 sidewall. 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 the radial tire. Tread life is improved considerably over the conventional bias tire. The radial tire differs in construction, but instead of the carcass plies running at an angle of 90° to each other, they run at an angle of 90° to the bead. This gives the tread a great deal of rigidity and the sidewall a great deal of flexibility and accounts for the characteristic bulge associated with radial tires.
Remember that the tire sizes and wheel diameters should be selected to maintain ground clearance and tire load capacity equivalent to the minimum specified tire. Radial tires should always be used in sets of five, but in an emergency radial tires can be used with caution on the rear axle only. If this is done, both tires on the rear should be of radial design.
In addition the the advances in tire design, there have been improvements in tire construction, which has introduced a new consideration involved in tires. With the advances in tire construction, all tires including snow, all season, truck and car tires are given a speed rating which indicates the maximum speed at which a vehicle can be driven with those tires in normal weather conditions. This speed rating is given in the form of a letter which can be found on the side wall of a tire. At no time should a car be able to out-perform the tires which it equipped with. What this means, for example, is that a race car should not have tires that are meant to be driven at a maximum of 35 mph, when in fact it is capable of going 80 mph. In this case, the tires are unsafe.
When buying new tires, here are some additional points to consider, especially if you are considering a switch to larger tires or a different profile series;
- All 4 tires must be of the same construction type. This rule should not be violated, radial, bias and bias belted tires should 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 should be 80% or less of the tire (not tread) width.
- The height (mounted diameter) of the new tires can change the 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 operations, with any new tires.
- There should not be any body interference when loaded, on bumps or in turns.
Store the tires at proper inflation pressures, never over-inflated. All tires should be kept in a cool, dry place. If they are stored in the garage or basement, do not let them stand on a concrete floor; set them horizontally on strips of wood.
Tire inflation is the most ignored item of automotive maintenance. Gasoline mileage can drop as much as 0.8% for every 1 pound per square inch (psi) 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 many service station air hose is notoriously inaccurate.
The tire pressures recommended for you car can be found on a label attached to the door pillar or on the glove box inner cover or in the owner's manual.
Ideally, tire pressures should be checked when the tires are cool. When the air becomes heated it expands and the pressure increases. Every 10° rise (or drop) in temperature means a difference of 1 psi, which also explains why the tire appears to lose air on a very cold night. When it is impossible to check the ties cold, allow for pressure build-up due to heat. If the hot pressure exceeds the cold pressure by more than 15 psi, reduce you speed, lead 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 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
To clean aluminum wheels, wheel covers and wheel ornamentation, use a mild soap and water solution, rinsing thoroughly with clean water. Do not use steel wool, abrasive type cleaners or a strong detergents. Damage to the protective coating and discoloration may be result. Automatic car wash brushes may also damage aluminum and styled road wheel protective coatings. Before using such a service, be sure abrasive type brushes are not being used. If possible, try not to use these type wheels in winter weather. Road salt will eat away the finish. Even if clear-coated, salt will work it's way through the finish, and pit the surface.