TYRE BASICS
Cars rely on four small contact patches on their tyres to provide traction through turns, accelerating and braking. People push their cars to the limit, driving in extreme conditions and the tyres need to be able to grip through whatever is thrown at them. The importance of having the right type of tyre for your usage is paramount to getting the most out of your vehicle.
What are the differences in tyre tread designs and type?
All Season Tyres – These tyres provide great all-weather performance with a lot of channels for water to pass through, providing excellent aquaplaning resistance. They are also able to tackle light snow and ice too. Their performance is not as good in the dry as with high performance tyres, but the all-weather ability of them makes them the choice of tyre for many that drive in areas with changing conditions. All-season tyres usually last longer than high performance tyres due to a harder compound.
4x4 Tyres – These tyres come with chunkier tread blocks designed to be able to grip through whatever comes their way, be it road, mud, dirt, rock. They come in different categories (Highway Terrain, All Terrain and Mud Terrain) depending on the level of usage and off-road capability that you require. Highway Terrain (H/T) is more road focussed, designed for 90% road and 10% off-road use. They are quieter and have longer tread life, but with less aggressive tread blocks making them not as capable off-road as All Terrain and Mud Terrain tyres. All Terrain (A/T) tyres are designed for 60% road and 40% off-road use. They have larger, wider tread blocks with larger gaps between them, allowing for better grip on loose surfaces in comparison to Highway Terrain. Mud Terrain (M/T) is designed for 15% road and 85% off-road use. The tread blocks are very aggressive and wrap around to the sidewall. This is particularly beneficial with very low air pressures as the wider contact patch makes full use of the tread blocks on the sidewall. These tyres will be able to take you to places not possible with H/T or A/T tyres.
High Performance Tyres – These tyres are road legal but with an emphasis on dry performance. Modern tyre technology has come a long way and the traction available from tyres in this category is incredible. They are still very capable in the wet. Tyres in this category are far more durable than racetrack tyres, however all-season tyres are still far ahead in this respect.
Racetrack Tyres – These tyres are for competition and serious track junkies. They offer levels of grip in the dry that is beyond what is possible with a road tyre. The compound of the tyre is soft and they have a few shallow grooves. This means that they do not last very long and are not very capable in the wet, aquaplaning easily. Most tyres in this category are not road legal.
How to Maintain your Tyres
Correct inflation of tyres is imperative to getting the most out of your tyres and improving the life of them.
Indicators of tyre wear:
Alignment – tyres go through many small and large bumps over the course of even a short trip to the shops. Wheels go through significant load and can become misaligned. Toe (turn of the tyre) and camber (tilt of the tyre) alter slightly as a result and a wheel alignment will correct this so the tyres are facing straight (toe) and they are not tilted (camber).
Over-inflation – over-inflating your tyres reduces your contact patch with the road, as the tyre deforms. The tyre will wear out more in the middle and will have less available grip.
Under-inflation – under-inflating your tyres will provide better traction when off-road and is commonly done by 4x4 owners. On the road however, under-inflated tyres will not contact the ground correctly as the tyres were designed to, and will lead to increase wear on the shoulders of the tyre. Fuel use will also increase as rolling resistance is much higher.
TYRE SIZES
What is a Tyre Size and Where can I find it?
Every vehicle requires a specific size for your tyres. Your tyre size can be found on the side wall of the current tyres you would like to have replaced. You can also search your vehicle for the manufacturers placard to find a suggested tyre size and a minimum tyre size, load rating and weight rating. This is usually found on the drivers door, under the bonnet, or in the glove box, but locations vary between manufacturers and models.
Tyre Code
The tyre size comes in a code molded on sidewall rubber of your tyre. It provides the driver with valuable information about the tyre’s intended purpose, dimensions, load capacity and speed durability.
Tyre Width
The first set of numbers are the three-digit numeric measurement (such as “205”)which represents the tyre’s ‘Section Width’, (or cross section), in millimeters. The width of a tyre is measured directly across from the outermost point of the sidewall of the tyre to the outermost point of the opposite sidewall of the tyre.
Next and divided by a forward slash from the three digits identifying the tyre’s width is a two-digit number (such as “65”)which identifies the tyre’s profile or aspect ratio.
This measurement is of the tyre’s section height. This measurement is of the height of the sidewall of the tyre and is registered as a percentage of the width of the tyre. So a sidewall height that is 65% of the width of a tyre is written as 65.
Diameter / Rim
The next part of the tyre code is the tyre diameter or wheel size which is measured in inches (such as “15”). To know the range of tyre sizes you can safely fit to your vehicle you need to consult the manufacturer’s guide as there is no rule of thumb. When considering changing the wheel and/or tyre size on your car, you have to remember you need to keep the diameter as close as possible to its original size.
This is because the speedometers, traction control and the gear settings of your car are based on the time/distance taken for a tyre’s full revolution. This is directly related to the outside diameter of your tyre.
When changing the size of your wheel and tyre, your tyre diameter has to remain the same. However, this it isn’t always as straightforward as you might think as tyre sizes are most commonly measured by the inside diameter of the tyre rather than the tyre’s total diameter. There are tyre size calculators available to help you arrive at the right measurement however.
TYRE LOAD RATINGS
What is a Tyre Load Rating?
The rating determines the load capacity or maximum weight a tyre can carry and are represented by a numerical value. The higher the tyre’s load index number, the greater its load carrying capacity. The load rating information can be found on the sidewall of your tyre.
On some light trucks the load index is broken up into two ratings divided by a forward slash. Here is an example: 104/101. This is because the light trucks these ratings are used for often have dual tyres on their rear axle. The first number indicates the load carrying capacity if the tyre is for a single-wheel rear axle, and the second number applies to a dual rear axle.
The reason the second load index number is less even though it is supported by a second pair of tyres, is to maintain reserve capacity if one of the tyres fail. Were this to happen, it would leave the sole remaining tyre the load supposed to be supported by two tyres.
TYRE SPEED RATING
What is a Tyre Speed Rating?
The speed rating of a tyre outlines the maximum speed your tyre is capable of maintaining on the road. Speed ratings are based on engineer tests run to find out what speed can be safely maintained at length. The speed rating is displayed on the sidewall of your tyre within the tyre code and is represented by a letter of the alphabet.