Tread wear indicator

Tire tread wear indicators are patterned ridges 1.6mm (0.0630in.) to 1.8mm (0.0709in.) higher than the rest of the tread surface, and are molded into the tread at four to six points along the circumference of the tire. As the tire tread wears in time, the depth of the ridges becomes less until they become flush with the surface of the tread. Tire tread wear indicators indicate the allowable limit of tire wear, showing when it is time to replace the tire. (3/5)

Unusual wear of a Tire

(1) Wear on tire shoulders or center If the tire inflation pressure is too low, the shoulders wear more faster than the center. Overloading produces the same effect. If the inflation pressure is too high, the center wear more faster than the shoulders.

(2) Inside or outside wear Cornering wear, shown in the left, is caused by cornering at excessive speeds. Deformation or excessive play in the suspension parts affects front wheel alignment, causing abnormal tire wear. If one side of the tire tread wears faster than the other, the main cause is probably incorrect camber.

(3) Toe-in or toe-out wear (Feathered wear) The main cause of feathered wear on the tire tread is defective toe-in adjustment. Excessive toe-in forces the tires to slip outwards and drags the tread’s contact surface inwards on the road surface, producing toe-in wear. The surface takes on a distinctive feather-like shape – shown in the illustration – that can be identified by running a finger across the tread from the inside to the outside of the tire. Excessive toe-out, on the other hand, producing the toe-out wear shown in the illustration.

(4) Toe-and-heel wear Toe-and-heel wear is partial wear that often appears on tires with lug and block tread patterns. Tires with a rib tread pattern wear to form wavelike patterns. Toe-and-heel wear tends to occur more easily when the tire is rotating and not being subjected to driving force or braking force. Therefore, toe-and-heel wear occurs most often in non-drive wheels that are not subjected to driving force. In the case of drive wheels, driving force causes tire wear in the direction opposite that of toe-and-heel wear. Braking force also produces similar results. As a result, there is normally little toe-and-heel wear in tires on drive wheels.

(5) Spot wear (Cupping) If the wheel bearings, ball joints, tie rod ends, etc. have excessive play, or if the spindle is bent, the tire will wobble at specific, points in its rotation at high speeds, applying strong friction of causing slippage, both of which lead to spot wear. A deformed or irregularly worn brake drum causes the brakes to be applied at regular intervals, leading to spot wear over a relatively wide area in the circumferential direction. HINT: A canvas patch applied to the tire tread to repair a puncture or a protrusion produced by separation will also lead to spot wear. Sudden starting, braking, and cornering may also lead to spot wear. An excessively unbalanced wheel assembly causes spot wear as well. (4/5)

5. Tire rotation

Because the load which is applied to the front and rear tires are different, and the level of wear also varies. Therefore tires should be rotated regularly so that they will wear uniformly. Tires which the rotational direction is determined must not be replaced at right and left. Tire which the tire size of front and rear are different must not be replaced at front and rear. As the recommended tire rotation method varies depending on model and region, refer to the Owner’s Manual.

Tire wear is the loss of or damage to tread and other rubber surfaces due to friction generated when the tire slips on the road. It varies with inflation pressure, load, vehicle speed, braking, road surface conditions, temperature, and other factors.

Inflation pressure

Insufficient inflation pressure accelerates tire wear by allowing the tread to flex excessively as it contacts the road.

Hard riding:

Higher inflation pressure means greater tire rigidity. If it is too high, however, the tire will fail to absorb shocks from the road surface, leading to hard riding. Each vehicle model has a recommended tire inflation pressure that is best suited for the intended load and

application. Installing tires that are more rigid will make the ride harder.

Hard steering:

Too low an inflation pressure makes the tread contact surface wider, increasing the resistance between the tire and the road surface and thus making the steering more sluggish.

Car pulls to one side during normal driving:

If the inflation pressures of the right and left tires differ, there will be a difference in the rolling resistances of the tires and the vehicle will tend to veer toward the right or left.

Tire uniformity refers to uniformity of weight, dimensions and rigidity. However, since uniformity of weight is ordinarily called “wheel balance”, and uniformity of dimensions (or rather, the lack thereof) is called “run-out”, uniformity alone usually refers to “uniformity of rigidity”. These greatly affect driving performance.

1. Wheel balance

It is necessary to balance the wheel assemblies properly in order to eliminate vibrations and this operation is what is called wheel balancing. Wheel balancing involves balancing the weight of the entire wheel assembly-that is, the disc wheel with the tire attached. Wheel balance can be divided into “static balance”( that when the wheel assembly is at rest) and “dynamic balance” (that when it is rotating). HINT: There are off-the-car balancers that balance the tires alone and on-the-car balancers that balance the tire with the rotating parts such as the disc brake rotor and axle hubs.

2. Run-out

Run-out is defined as the apparent change in a tire dimensions during rotation. Run-out is measured by holding a dial gauge against the surface of the tire, rotating the tire, and observing the fluctuations of the indicator needle on the gauge. There are two types of run-out: that in the tire’s radial direction (radial run-out), and that in the axial direction (lateral run-out).

3. Uniformity

The tire is subject to subtle fluctuations in the way it flexes as it rotates. These fluctuations introduce a periodic variation in the force which it receives from the road surface. This force can be resolved into three components:

Radial Force Variation (RFV) Fluctuation in the vertical force acting upwards toward the tire’s center. (parallel to the tire’s radius)

Lateral Force Variation (LFV) Fluctuation in the horizontal force acting parallel to the tire’s axis.

Tractive Force Variation (TFV) Fluctuation in the horizontal force acting parallel to the tire’s direction of motion.

SERVICE HINT:

Vibration Tire vibration problems are divided into body shake, steering flutter, and steering shimmy. Body shake is defined as vertical or lateral vibration of the vehicle body and steering wheel, along with vibration of the seats. Shimmy and flutter are defined as vibration in the steering wheel in its rotational direction.

There are various ways to classify tires. The type of tirea ccording to the road surface which is used is emphasized and the functions and characteristics of each type of tire are indicated.

1. Snow tires

The snow tire is designed to maintain maneuverability on muddy or snow-covered roads. This is done by providing a greater number of blocks in the tread pattern, and making these blocks deeper and further apart from each other. It combines the lug tread pattern,which effectively transmits driving force, and the rib pattern, which minimizes side-slipping.

Characteristics

Less side-slipping and better traction, and greater steering stability during braking.

Greater maneuverability when turning and changing lanes.

Easier escape from wheel ruts.

Smaller rolling resistance.

Less vibration and noise.

Since snow tire tread is less rigid than normal tire tread, on the other hand, it is less capable of stabilizing a vehicle traveling at a high speed on a dry road surface. Cornering especially suffers in this respect.

2. Spiked tires

Snow tires perform well on snow-covered roads, but have little road-hugging ability on icy roads. The spiked tire has been devised to provide greater driving stability under such conditions. It features snow tire tread, combined with metal spikes, which bite into the surface of the ice to transmit the vehicle’s driving and braking forces. Nevertheless, equipping the vehicle with the spiked tires alone does not ensure complete driving safety on snow-covered and icy roads. The

vehicle must still be operated with the utmost care. Also, use of spiked tires on road surfaces that are free of snow and ice must be avoided since this not only accelerates spike wear, but also could damage the road surface and pollute the air with concrete and asphalt particles. Authorities in some countries or localities restrict or prohibit the use of spiked tires and even tire chains for

these reasons.

3. Studless tires

In the past, spiked tires had primarily been used on ice and snow. However, since the use of spiked tires has recently been restricted or prohibited in many countries, studless tires have been developed to facilitate vehicle travel on icy roads without the use of spikes. Studless tires use a special tread rubber that, in addition to the capabilities of snow tires, also prevents loss of flexibility even at extremely low temperatures. This enables these tires to ensure sufficient contact with the surface of the road even when the road is covered with ice or snow. In addition, due to the provision of many small cuts in the tread surface, called “sipes”, or by other means, the tire is able to effectively dig up and throw off ice and snow, enabling it to obtain adequate driving force and braking force. However, there are cases in which the performance of studless tires cannot be sufficiently demonstrated under certain road conditions and with certain driving styles. It is therefore important to drive with caution on icy roads and use tire chains and so forth as necessary.

4. All-weather tires (All-season tires)

The all-weather tire is a regular tire that has been modified to enhance driving performance on sandy and snow-covered road surfaces. It is a multipurpose tire, which can be used throughout the year, because it features characteristics of both normal and snow tires. The graph in the left plots all-weather tire performance relative to that of an ordinary tire (the circle in the graph). The further the value falls outside the circle, the higher the corresponding performance. The all-weather tire has a steel-belted radial-ply carcass and a densely-siped block tread pattern to improve traction and resistance to side-slipping. The tread grooves of the all-weather tire are shallower than those of the snow tire but deeper than those of the ordinary tire. This means that they can stabilize the vehicle by digging deeply into the snow in order to get secure grip on the road.

(3) Rib-and-lug pattern

This pattern combines the rib and lug patterns to provide stable driving performance on both paved and unpaved roads.

The rib pattern running along the center of the tire stabilizes the vehicle by minimizing tire side-slipping, while the lug pattern on the edges of the tire enhances driving and braking performance. The lug portion of the pattern is more susceptible to uneven wear.

(4) Block pattern

In this pattern, the tread is divided into independent blocks. Used on most snow tires and studless tires, the block tread pattern is now coming to be used on radial-ply tires for passenger cars as well.

The block pattern provides better driving and braking performance.

The block pattern reduces slipping and skidding on muddy or snow-covered roads.

The tires tend to wear faster than those with the rib and lug patterns.

Rolling resistance is slightly greater.

The tread is susceptible to unusual wear, especially on hard surfaces.

Unidirectional Pattern Tires

These are tires with a tread pattern, which has directionality with respect to the direction of rotation. Lateral grooves in the tire tread are given directionality in order to improve performance on wet roads, making it easier for the tires to drain off water. The performance of these tires on wet roads worsens if they are mounted in the wrong direction.

2. Pattern noise

Pattern noise is the most distinctive operating sound of the tire. The tread grooves coming into contact with the road surface contain air, which is trapped and compressed between the grooves and the road surface. When the tread leaves the road surface, the compressed air bursts out of the grooves, generating noise. Pattern noise increase if tread design is such that air is more liable to be trapped in the grooves.

The block or lug tread pattern, for example, is more likely to generate noise than the rib pattern. The pitch (frequency) of the noise rises as the vehicle speed increases. Since pattern noise thus depends on tread pattern, the pattern can be designed to minimize this. What appears to be a simple repetitive lug and zigzag pattern, for example, may contain subtle variations in pattern spacing.

Tires are installed on the vehicle together with disc wheels. Vehicles ride on pneumatic tires filled with pressurized air. Tires are the only vehicle components that come into direct contact with the road surface. If the tire air pressure is improper, this can cause abnormal wear and lower the driving performance. Tires perform the following functions:

The tires support the overall weight of the vehicle.

The tires directly contact the road surface and therefore transmit the vehicle’s driving and braking forces to the road, thus controlling starting, acceleration, deceleration, stopping, and turning.

The tires attenuate (reduce) shock caused by irregularities in the road surface.

Outline Construction

Construction

(1) Tires The types of tires are tubed tires and tubeless tires. Also, there are radial tires and bias tires, both of which comprise the following parts.

<1>Tread

<2>Belt (rigid breaker)/Breaker

<3>Carcass (cross plies)

<4>Inner liner

<5>Bead wire There are also other types, such as compact spare tires (temporary tire types) used for punctures and other emergencies, and run-flat tires on which you can drive a certain distance even with a puncture.

(2)Tire size The size, performance, and the construction of the tire are indicated on the sidewall of a tire. The diagram on the left shows the names of the sizes of the various areas of a tire.

(3)Disc wheels

Tread Patterns

1. Types of tread patterns

A wide variety of patterns are molded into the tread both to help drain away water, and to cope with various factors dictated by the conditions of the road surface and the type of the vehicle being used.

(1)Rib pattern

The rib pattern consists of several parallel zigzag grooves that run along the circumference of the tire. This pattern is best suited for traveling on paved surfaces at high speeds and is used for a wide variety of automobiles, from passenger cars to buses and trucks.

The rib pattern minimizes the resistance of the tire to rolling.

Greater resistance to side-slipping provides good vehicle controllability.

Tire noise is reduced.

Traction is somewhat inferior to that of tires with the lug pattern.

(2) Lug pattern

The grooves in the lug pattern run at roughly right angles to the tire circumference. Frequently used on construction machinery and truck tires, this tread pattern is suited for driving on unpaved roads.

The lug pattern provides good traction.

Tire rolling resistance is somewhat high.

Resistance to side-slipping is smaller.

Tread in the lug area is susceptible to uneven wearing.