66 Tire and Wheel Bearing FundamentalsII (1)

© Goodheart-Willcox Co., Inc.


Tires perform two basic functions: act as a soft cushion between the road

and the metal wheel provide adequate traction (friction) with

the road surface


Tire Types Pneumatic

filled with air internal air pressure pushes out on the

inside of the tire to support the vehicle Tubeless tire

does not use an inner tube tire and wheel form an airtight unit

Tube-type tire uses an inner tube to hold air pressure


Bias Ply Tire Plies run on an angle from bead to

bead Angle is reversed from ply to ply Does not use belts Body of the tire flexes easily Provides a smooth ride Plies and tread are weakest

reduces traction at high speeds increases rolling resistance


Bias Ply Tire


Radial Ply Tire Plies run straight across from bead to

bead Stabilizer belts lie beneath the tread Belts can be made of steel, flexten,

fiberglass, or other materials


Radial Ply Tire Uses a very flexible sidewall with a stiff

tread provides a very stiff footprint improves safety, cornering, braking, and

wear may produce a harsher ride at low speeds


Radial Ply Tire


Tire Sidewall Markings


Tire Size

Alpha-Numeric–Uses letters and numbers to denote tire size in inches and its load-

carrying capacity in pounds


Tire Size

P= passenger LT=Light Truck ST= Special Trailer T= Temporary C= Commercial


Points of Measurement


Aspect Ratio

Height-to-width ratio of a tire. Comparison of a tire’s height and width


Tread Plies Number of plies and ply rating:

2-ply 2-ply with a 4-ply rating 4-ply

Ply rating doesn’t mean how many plies the tire has Plies are made of different materials today


Maximum Load Rating Amount of weight the tire can carry at

the recommended inflation pressure Printed on the sidewall P-metric:

given in kilograms and pounds Alpha-numeric:

indicated by a letter such as B, C, or D


Maximum Inflation Pressure

Highest air pressure that should be pumped into the tire

Many tires have a maximum recommended pressure of 32 to 40 psi (220 to 275 kPa)


Checking Tire Inflation Pressure

Check the manufactures recommended tire pressure In Door Jam In owners manual

Compare to max inflation and inflate to proper inflation

Many of today's cars have to be inflated to manufactures specs


Tire Inflation Pressure


DOT Serial Number Identifies the manufacturer, plant,

location, construction, and date of manufacture

Stamped into the sidewall Department of Transportation rating

means the tire has passed prescribed safety tests


Speed Rating Maximum allowable sustained road

speed a tire can safely withstand without failure


Traction Rating Traction rating is a letter based on a

straight-line wet surface braking test AA- (Best) A B C- (Worst)


Tread Wear Higher the number the better the tread

wear Tread wear rating 200 will last 2 times as

long as a 100

Can not compare different manufactures tread wear ratings


Heat Rating A- Best (coolest running tire)

B-

C- Least able to dissipate heat


Wear Bars

When too much tread has worn

away, solid rubber bars will show up across the tread


Tread Depth Checking tread depth

Min depth allowed is 2/32”


Rotating Tires Ensures maximum tire life Front and rear tires wear differently Rotation helps even out tire wear Tires are rotated at intervals such as

every 3000 miles (5000 km)


Rotation Patterns


Tire Rotation Dually


Today’s Preferred Pattern

This Pattern is used today because of radial tire memory!


Compact Spare Tire

This is a high pressure spare, requiring60 psi (415 kPa)


Self-Sealing Tire Action

A. Nail punctures tireB. Nail is pulled outC. Sealing compound

flows into the hole


Run-Flat Tires Use extremely stiff sidewall

construction Still usable with a loss of air pressure Tire will still retain most of its shape

because the sidewall is strong enough to support vehicle weight


Run-Flat Tires


Retreads Used tires that have had a new tread

vulcanized to the old carcass, or body Large truck tires are often recapped

because of the high cost of new truck tires


Tire Inflation Monitoring System

Often used with run-flat tires Pressure sensors are mounted on each

wheel If tire pressure is not correct, the wheel

sensor produces a radio signal Signal is received by a module that

turns on a dash warning light


Pressure Sensor


System Operation


ABS Tire Monitoring Wheel speed is

measured using ABS sensors

Different wheel speeds equals uneven tire pressures


Dimensions of a Wheel


Valve Stem Assembly

Valve stem snaps into the holein the wheel

Press fit forms an airtight seal

Valve core screws into the

valve stem body


Lug Nut and Stud

Stud is pressed into the hub or

axle flange

If metric or left-hand threads are used,

markings will normally be given


Torquing Lug Nuts Torque is very important, especially on

vehicles with mag wheels and lightweight hubs

Overtorquing can cause wheel and hub distortion, or brake pulsation

Undertorquing might allow the lug nuts to loosen and the wheel to fall off


Wheel Cover Removal

Pry between the wheel and coverat four alternating points


Wheel Cover Installation

Hold the wheel cover in place with the valve stem sticking through the cover


Tire Impact Damage

Typical damage found on used tires


Causes of Tire

Vibration


Wheel balance is a common cause of tire and steering wheel vibration

When one side of a tire is heavier than the other, centrifugal force tries to throw the heavy side outward when the tire is rotating


Tapered Roller Bearing

Lubricated with high-temperature grease


Hub and Wheel Bearing

(Nondriving Wheels)


Bearing Inspection


Ball Bearing

Balls allow parts to rotate with a minimum amount of friction and wear



(Driving Wheels)



(Four-Wheel Drive)

Front axle, brakes, hub, and wheel bearing assembly


Wheel Bearing Noise Produced by a dry, worn wheel bearing When balls or rollers are damaged from

lack of lubrication, they may emit a humming or growling sound

Checking the bearings: raise the vehicle on a lift rotate the tire by hand feel and listen for bearing roughness wiggle the tire to check for looseness


Inspecting the Tires

Wiggle the tire to check for dry, rough, or loose wheel bearings

Documents

66 Tire and Wheel Bearing FundamentalsII (1)