Tire Basics

Balancing  

Why Balancing Is Important
Balancing means compensating for both the weight of the tire and wheel after the tire is mounted. A wheel is out of balance when one area is heavier or lighter than the rest. This can cause eccentric treadwear, vibration, and increase the stress on the front-end parts and may cause them to wear prematurely.

When to Balance
You should have your wheels balanced whenever a tire is replaced, when a balance weight is moved or removed, and whenever you purchase new tires. Of course, at the first sign of vibration or irregular treadwear, your car should be thoroughly checked for wheel balance and alignment, and for worn or broken mechanical parts.

How a Wheel Is Balanced
To balance the wheel, your mechanic will use a balancing machine to determine where the heavy spots are. Weights are then attached to the exterior or interior of the wheel to counteract centrifugal forces acting on the heavy areas when the wheel is turning. This will eliminate vertical bouncing (static balance) and side-to-side wobble (dynamic balance).
 

Rotation tips
Regular rotation helps extend the life of your tires, saving time and money in the long run. For rotation, each tire and wheel is removed from your vehicle and moved to a different position. This ensures that all of the tires wear evenly and last longer. If no period is specified in your vehicle owners manual, tires should be rotated every 6,000 to 8,000 miles. If you have a full-size spare, it should be included in the rotation process.

Alignment  
Why Alignment Is Important
Alignment generally refers to the adjustment of a vehicle's front and rear suspension parts. Proper alignment ensures that your vehicle handles correctly and will help increase the life and performance of your tires.

When to Check Alignment
The alignment of your vehicle can be knocked out of adjustment from daily impacts such as potholes and railroad crossings or by more severe accidents. You should have the alignment checked if:

You know you have hit something.
You see a wear pattern developing on the shoulders of the tires.
You notice a difference in your vehicle's handling.

How Wheels Are Aligned
Alignment involves adjusting the angles of the wheels so that they are parallel to each other and perpendicular to the ground. The three main adjustments made in alignment are Camber, Caster, and Toe.

Camber
Camber is the angle of the wheel, in degrees, when viewed from the front of the vehicle. Positive camber is when the top of the wheel is leaning out from the center of the car. Negative camber is when the top of the wheel is leaning into the car. If the wheel leans too far from the center, uneven wear will occur. The camber angle is designed and adjusted per vehicle to keep the tires on the outside of a curve flat on the ground during a turn. If you have too much positive camber, your tires will wear on the outside. Too much negative camber will wear them on the inside. If there is too much of a difference between the camber settings on the front wheels, the vehicle will tend to pull sharply to one side.

Caster
Caster is the forward or rearward tilt of the steering axis, measured from the top of the tire as viewed from the side. The axis is formed by extending an imaginary line through the upper and lower steering knuckles. The line extends through the upper and lower ball joints on vehicles with front control arms, and through the lower ball joint to the center of the strut mount on cars with struts.

If the angle is towards the rear of the vehicle, the wheel has positive caster. If the angle is too far to the front of the vehicle, the wheel has negative caster.

Caster is set so that your car will tend to go straight ahead. Positive caster has the effect of making your front wheels act as if your car was being pulled from the front so that they will line up behind the point of pull, like a child's pull toy.

Another example is the caster wheel found on furniture or on some shopping carts. When you push a shopping cart equipped with caster wheels, it tends to roll in a straight line because the wheels line up or trail behind the point of pull. The greater the trail distance, the greater the tendency to roll straight ahead. The caster setting on a vehicle is adjustable in order to increase or decrease the effective trail distance.

Caster affects your vehicle's low-speed steering, high-speed stability as well as how well your vehicle drives in a straight line (on-center feel). Too little caster will cause your car to "wander" and make it feel unstable at high speeds. Too much caster causes hard steering and can also result in excessive road shock and shimmy. Caster does not affect tire wear.

Toe
Toe is the difference in the distance between the front of the tires and the back of the tires. Usually, tires are set so that they are parallel with each other. If the fronts of the tires are closer, the wheels are toe-in. If the rears of the tires are closer, the wheels are toe-out.

Toe settings affect the handling characteristics of a vehicle in turns. Toe-in introduces Understeer going into a curve and may make the vehicle feel like the back end is trying to come around to the front end. Toe-out introduces Oversteer in a curve and makes the vehicle feel like it is "diving" into the turn too sharply.

If the tires are toed-in too much, the tread will be "worn" off, starting from the outside edges. If they are toed-out, the wear will start from the inside. This type of wear is called "feathering" and can be felt by running your hands across the tread of the tire.
 


Inflation Pressure  
Keeping your tires properly inflated is essential for the proper performance and longevity of the tire. Not to mention, the ride quality and safety of your vehicle. Your tires carry the entire weight of your vehicle. When underinflated or overinflated, they cannot do their job properly. Operating your tires underinflated can also result in sudden tire failure.


How Often
We recommend checking air pressure once a month, and before a long trip. Whether you have a full-sized or mini-spare, make sure that it is properly inflated as well.

Recommended Pressure
Always inflate your tires to the recommended pressure listed by your vehicle's manufacturer. This information can be found in the owner's manual and often on a placard located in the vehicle's door jamb, inside the fuel hatch, or on the glove compartment door.

The Best Time to Inflate
Air expands when it's hot and contracts when it's cold. For accurate pressure, always check the pressure when the tires are "cold" - at least three hours after the vehicle has been stopped and before it has been driven one mile. It's best to inflate your tires in the morning before the day's heat.

For example, it is possible for a passenger tire initially inflated to 35 psi to lose 1/2 psi per month. A substantial, seasonal temperature change can also affect inflation pressure, with cold ambient temperatures causing effectively lower air pressure.

Valves and Valve Caps
The tire's valve is a very important maintenance item in terms of keeping the inflation air in your tires. These valves are ordinarily rubber, can deteriorate over time, and should be replaced when you buy new tires. At high speeds, a cracked, deteriorated rubber valve stem can bend from centrifugal force and allow air loss.

The valve cap is likewise an important item. Buy some good quality valve caps that can contain the inflation air should the core of the valve fail for any reason. Valve caps also keep out moisture, which could freeze and in turn depress the valve core, causing loss of air. The cap also keeps out dust and dirt particles, which could also interfere with the proper operation of the valve core and cause loss of air.

Inflation Tips
Purchase a good pressure gauge and check it for accuracy with your tire dealer.

Beware of public gauges at the gas station. They are often abused and unreliable.
 

 


The final decision to install a tire on a vehicle will be made by the Costco tire center manager or supervisor. The tire must meet all vehicle manufacturers’ safety standards and specifications.

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