Tyres

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Tyre Construction

To the casual observer all tyres look the same. But if you look carefully, you'll find modern tyre construction offers a degree of handling, ride comfort, traction, tread-wear and fuel economy that far exceeds tyres built just a few years ago

Today there are tyre designs that contain up to 200 raw materials as well as a complex architecture of steel belts, textile plies and computer designed tread patterns. Tyre manufacturers strive to deliver the most competitive designs in terms of performance and wear.

In 1946 the tyre industry was revolutionized by the introduction of the radial tyre. A cross section of the radial design is shown above. Today, virtually all tyres sold are radials due to their benefits of superior handling, ride quality and wear.

The benefits of radial construction are attributed to the design of the tyre's casing — the part of the tyre underneath the tread that forms the foundation of the tyre. The casing is made up of a series of cords (most typically polyester) which are combined to form layers or plies. In a radial tyre, these plies are positioned so the cords run alongside each other in a series of circular bands across the tread of the tyre. Radial construction allows the tyre to better flex and absorb the irregularities of the road surface. The radial design also produces much less friction resulting in much longer tread life. The top layer of the radial casing usually consists of steel belts made up of woven strands of steel cord. Steel belts provide a stable foundation for better tread wear and traction, and also protect the casing against impacts and punctures. Other components may include bead chaffers and cap plies – usually built into performance tyres to enhance cornering and stability at high speeds.

The outermost part of the tyre, the tread, usually attracts the most attention. The material used is referred to as tread compound, which varies from one tyre design to the next. A winter tyre, for example, has a compound that provides maximum traction in cold weather. Competition tyres, at the other extreme, use a compound designed for very high temperature ranges. The great majority of tyres are built with an all season compound that delivers traction in the broad middle range of every day driving conditions. In addition, this compound must deliver good wear; this dual goal of traction and wear remains one of the most challenging design parameters for tyre manufacturers.

While tread designs vary tremendously, the elements of the tread are consistent in their use. The tread block provides traction at its leading and trailing edge. Within the block, sipes are often moulded or cut to provide additional traction. Groves are built into tread designs for channelling away water. Shoulder designs provide protection as well as additional traction during hard cornering.

Tyre Dimensions

Rim WIDTH

The WIDTH between the flanges of the wheel (the part the bead of the tire touches).

Section WIDTH

The linear distance between the outside of the sidewalls of an inflated tyre without any load on it (this does not include any sidewall decorations).

Section Height

This is also known as the Aspect Ratio. This is figured on a percentage of the section WIDTH. A tire size of 205/60R15 would have a section WIDTH of 205 millimetres and a section height of 60 percent of 205 millimeters.

SPEED RATING
RATING DESCRIPTION
Q Up to 100mph
S Up to 112mph
T Up to 118mph
U Up to 124mph
H Up to 130mph
V Up to 149mph
W Up to 168mph
Y Up to 186mph
Z 149mph and over

Speed Ratings

Two important notes when considering speed rating:

We do not recommend downgrading the speed rating of your tyres. This may result in poor handling and unpredictable steering. However, if you want better cornering response, there is no problem installing a higher speed rated tire on your vehicle. Never mix and match tyres with different speed ratings on your vehicle. This will cause serious problems with the handling of your vehicle.

Below is a list of speed ratings along with the corresponding speeds they represent. Remember, the speeds are test speeds, not recommended speeds.

Sidewall Reading

The graphic shows what each letter and number on the sidewall of a tire indicates. Many of the items on the sidewall have further explanations and have links at the bottom of this page. The following is a breakdown of the components of the size of the tire (shown in top, centre of tire graphic).

P

Passenger car tire. If there is no P before the size it would indicate it is a European metric tire. An LT before the size would designate a light truck tire.

205

This is the Section WIDTH in millimetres. This measurement is taken from sidewall to sidewall.

65

This number refers to the height of the sidewall, or the Aspect Ratio. It is a percentage of the section WIDTH. In this example, you would take 65 percent of 205 millimetres and this would give you the sidewall height.

R

Radial tire construction.

15

Wheel diameter in inches.

Tyre Balancing

Maintaining the tire balance on your vehicle is critical to receiving satisfactory service from your tire investment. In addition to a providing a smooth ride, balancing is a key component in tire wear. The focus of this article is to help you understand the balancing process and to know why it is important to keep your tyres balanced throughout their tread life.

For those of you who may think that tire balancing isn't that important, consider some industry trends—they may help you rethink the issue. Perhaps the most compelling argument for precision balancing comes from an obvious fact…vehicles are being made lighter and lighter. The heavier cars of yesterday actually helped smooth-out the ride by dampening many vibrations before they could be felt by the driver. The softer suspensions also had the same effect.

The second factor is tire technology; generally, more responsive tyres with lower profiles (which send more road feedback to the driver) are being used in today's style and performance oriented market. By the way, lower profile tyres do provide lower rolling resistance, which helps fuel economy. As a result, the slightest imbalance (as little as half an ounce) can be felt in most modern vehicles; this is significantly less than the average of ten years ago. For those of you who have plus-sized your tyres and wheels, balancing is even more critical.

The Balancing Act Perhaps the best way to begin is to discuss the lack of balance. When a tire is mounted onto the wheel, two slightly imperfect units are joined to form an assembly weighing forty pounds (this is the average for cars). The chances of this assembly having absolutely precise weight distribution about its radial and lateral centres are virtually impossible. Remember that all it takes is half an ounce of uneven weight distribution for a vibration to be felt. The illustration below shows how an imbalance creates vibration.

Static Imbalance

Occurs when there is a heavy or light spot in the tire so that the tire won't roll evenly and the tire and wheel undergoes an up-and-down motion. The static imbalance creates a hop or vertical vibration.

Dynamic Imbalance

Occurs when there is unequal weight on one or both sides of the tire/wheel assembly's lateral centreline, thus creating a side-to-side wobble or wheel shimmy The dynamic imbalance creates a side-to-side or wobbling vibration.

Most assemblies have both types of imbalance, and require dynamic balancing (commonly referred to as spin balancing) to create even weight distribution. The balancing system directs a technician to place counter weights on the rim's outer surface to offset the imbalance. When the balancing system tests for virtually perfect weight distribution, the assembly is in balance and will not vibrate. Your tyres will ride smoothly and wear evenly (with regard to balance).

Keeping Your Tyres Balanced For sake of example, assume you have driven your tyres 5,000 miles since their purchase and it's time to rotate. Over the miles, turning left and right, hitting bumps and holes you could not see or avoid, and driving down uneven road surfaces have led to uneven tread wear on your tyres. Perhaps a pothole has knocked-out your vehicle's alignment (this creates uneven tire wear). Well, besides rotating the tyres and getting an alignment to set things right, you should also rebalance the tyres. Even if you can't feel vibrations, they are present. The uneven tread wear has created an imbalance that generates excessive heat and wear on your tyres! Considering the hundreds of dollars you spent on your tyres, a rebalance is a wise expenditure. If you live near one of our Discount Tire stores, you should ask about the Lifetime Balancing program. For a nominal, one-time charge you can have your tyres balanced at every rotation.

Other Sources of Vibration

Very often the wheel/tire assemblies on a vehicle may be in balance but you still feel a vibration! Here are some of the other causes of vibration:

  • Bent wheel Tire out of round (radial or lateral runout)
  • Wheel to axle mounting error Inconsistent tire sidewall stiffness (force variation)
  • Brake component wear or failure
  • Drive train or engine component wear or failure
  • Suspension wear or failure
  • Wheel bearing wear or failure
  • Wheel alignment is out

Tyre Rotation

Rotating your tyres periodically is an essential part of tire maintenance. The main purpose of regularly rotating tyres is to achieve more uniform wear for all tyres on the vehicle. If no rotation period or pattern is to be found in your owner's documentation, rotate your tyres at least every 6,000 miles.

However, rotate your tyres earlier if irregular or uneven wear develops, and check with a qualified tire dealer or alignment shop to determine the cause of the wear problem. Remember that a hard impact such as hitting a pothole can cause misalignment, which then causes uneven tire wear.