Tires: Description and Operation
DESCRIPTIONTIRES
Tires are designed and engineered for each specific vehicle. They provide the best overall performance for normal operation. The ride and handling characteristics match the vehicle's requirements. With proper care they will give excellent reliability, traction, skid resistance, and tread life.
Driving habits have more effect on tire life than any other factor. Careful drivers will obtain in most cases, much greater mileage than severe use or careless drivers. A few of the driving habits which will shorten the life of any tire are:
- Rapid acceleration
- Severe brake applications
- High speed driving
- Excessive speeds on turns
- Striking curbs and other obstacles
Radial-ply tires are more prone to irregular tread wear. It is important to follow the tire rotation interval. This will help to achieve a greater tread life.
TIRE IDENTIFICATION
Tire type, size, aspect ratio and speed rating are encoded in the letters and numbers imprinted on the side wall of the tire.
In a metric sire size as P185/80R13. The first letter of the tire size tells if the tire is used for passenger (P), temporary (T), or commercial (C) use. The second designation tells the section width (1) of the tire. The section width is the distance in millimeters from one side of the tire to the other when it is inflated normally. The third designation tells the aspect ratio (2). The aspect ratio (2) is found by dividing the section height (2) by the section width (1). The aspect ratio means the tire's height is 80% of the width. This is called the profile of the tire. Lower profile tires make the vehicle closer to the road and reduce wind drag underneath the vehicle body. The next designation tells the construction type. R means radial tire, B means belted, and D means diagonal (bias). The last designation gives the wheel rim in inches. The most common car rim sizes are 13, 14, 15. Some rims are as large as 20 inches in diameter.
Performance tires have a speed rating letter after the aspect ratio number. The speed rating is not always printed on the tire sidewall. These ratings are:
- Q up to 100 mph
- S up to 112 mph
- T up to 118 mph
- U up to 124 mph
- H up to 130 mph
- V up to 149 mph
- Z more than 149 mph (consult the tire manufacturer for the specific speed rating)
An All Season type tire will have either M + S, M & S or M - S (indicating mud and snow traction) imprinted on the side wall.
RADIAL PLY TIRES
Radial-ply tires improve handling, tread life and ride quality, and decrease rolling resistance.
Radial-ply tires must always be used in sets of four. Under no circumstances should they be used on the front only. They may be mixed with temporary spare tires when necessary.
Radial-ply tires have the same load-carrying capacity as other types of tires of the same size. They also use the same recommended inflation pressures.
The use of tires from different manufacture's on the same vehicle is NOT recommended. The proper tire pressure should be maintained on all four tires.
Z-rated tires are optimized for performance driving and may provide slightly reduced ride comfort, increased tire noise and substantially increased tread wear compared to all-season tires.
TIRE INFLATION PRESSURES
WARNING: OVER- OR UNDER-INFLATED TIRES CAN AFFECT VEHICLE HANDLING AND TREAD WEAR. THIS MAY CAUSE THE TIRE TO FAIL SUDDENLY, RESULTING IN LOSS OF VEHICLE CONTROL.
Under-inflation will cause rapid shoulder wear (1), tire flexing, and possible tire failure.
Over-inflation will cause rapid center wear (1) and loss of the tire's ability to cushion shocks.
Improper inflation can cause:
- Uneven wear patterns
- Reduced tread life
- Reduced fuel economy
- Unsatisfactory ride
- Vehicle drift
For proper tire pressure specification refer to the Tire Inflation Pressure Chart provided with the vehicle's Owner's Manual. A Certification Label on the driver's side door pillar provides the minimum tire and rim size for the vehicle. The label also lists the cold inflation pressure for these tires at full load operation.
Tire pressures have been chosen to provide safe operation, vehicle stability, and a smooth ride. Tire pressure should be checked cold once a month. Tire pressure decreases as the ambient temperature drops. Check tire pressure frequently when ambient temperature varies widely.
Tire inflation pressures are cold inflation pressure. The vehicle must sit for at least 3 hours to obtain the correct cold inflation pressure reading, or be driven less than one mile after sitting for 3 hours. Tire inflation pressures may increase from 2 to 6 pounds per square inch (psi) during operation. Do not reduce this normal pressure build-up.
TIRE PRESSURE FOR HIGH SPEED
Where speed limits allow the vehicle to be driven at high speeds, correct tire inflation pressure is very important. For speeds up to and including 120 km/h (75 mph), tires must be inflated to the pressures shown on the tire placard. For continuous speeds in excess of 120 km/h (75 mph), tires must be inflated to the maximum pressure specified on the tire sidewall.
Vehicles loaded to the maximum capacity should not be driven at continuous speeds above 75 mph (120 km/h).
For emergency vehicles that are driven at speeds over 90 mph (144 km/h), special high speed tires must be used. Consult tire manufacturer for correct inflation pressure recommendations.
REPLACEMENT TIRES
WARNING: FAILURE TO EQUIP THE VEHICLE WITH TIRES HAVING ADEQUATE SPEED CAPABILITY CAN RESULT IN SUDDEN TIRE FAILURE.
The original equipment tires provide a proper balance of many characteristics such as:
- Ride
- Noise
- Handling
- Durability
- Tread life
- Traction
- Rolling resistance
- Speed capability
It is recommended that tires equivalent to the original equipment tires be used when replacement is needed.
Failure to use equivalent replacement tires may adversely affect the safety and handling of the vehicle.