Tread carefully

Autocar India
First Published: 12:54 IST(21/9/2012)
Last Updated: 19:07 IST(26/11/2012)
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Our detailed guide to buying, maintaining and extending the lifespan of your car’s tyres.

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The tyres are one of the most important parts of a car. You can do without leather upholstery or a sunroof, but you can’t do without the right set of rubber for your car. Unfortunately, tyres are often taken for granted by car owners. It’s only when it’s too late that any heed is paid, not to mention money spent. However, a little knowledge on the subject goes a long way in extracting the best performance from your tyres and having a safe and economical drive. On the following pages you will learn about the different kinds of tyres there are, and the different uses they can be put to. We will also tell you about how best to look after them and we’ll decipher the numbers and figures on the tyre side-wall for you so it doesn’t sound like Latin anymore.

What do you need?

Depending on what you intend to do with your car and where you want to go, you will need a specific tyre for your car. Before we tell you about the different types of tyres, it’s important to understand what tread is. Simply put, it is the pattern of grooves and bands on the tyre surface. Depending on the kind of tread on the tyre, things like road grip, tyre noise, the amount of rubber in contact with the road, and therefore its performance, will be affected.

For common everyday driving, a standard set of all-weather tyres should do. Most cars sold in the country are equipped with these as standard fitment. These are suited for most situations, are designed to have long lives and are usually made of a hard rubber compound. The tread pattern is such that it should work equally well in wet or dry conditions, but will not excel in either condition.

Then there are wet-weather tyres, which have tread specifically designed to disperse water. If the water isn’t channeled away from the contact patch, it can lead to aquaplaning and loss of grip and, consequently, loss of control over the car. It is a good habit to replace the stock tyres with a set of wet-weather tyres during the rainy season, especially if you live in places that are prone to heavy downpour. However, having a spare set of seasonal tyres may work out a bit too costly for most.

Most sports and luxury cars come with specially made performance tyres that forego long life in a bid to improve grip and cornering performance. They are usually made of a soft rubber compound and the tread is such that it works best in dry conditions. These also need to be replaced more quickly and cost considerably more in comparison.

Most SUVs sold in India come with multipurpose all-terrain tyres. These feature a ‘block’ pattern tread and have sturdy side-walls which don’t flex in tough conditions. These tyres are equally at home on tarmac or mud; a good thing, considering most SUVs don’t go off-road too often in our country. There are also specialised sand tyres, which have a thicker, more pronounced tread pattern that digs into the loose sand and aids off-roading.

Then there are different kinds of tread patterns on tyres. Most cars come with symmetrical tread pattern. This means that both the inner and outer halves of the tyre have the same tread design. These days though, you can get asymmetrical tyres, which have different designs for the inner and outer halves. The inner tread is designed to disperse water like a wet-weather tyre, while the outer-half tread is designed for better grip. It’s the best of both worlds.

When to buy

So you have decided to get yourself a new set of tyres. But do you really need a new set? A quick glance at the current set will tell all. We recommend an inspection at least once every couple of weeks, especially if you cover a lot of distance on a daily basis.

What you should look out for is the tread wearing out unevenly on the inner and outer halves of the tyres. This, apart from degrading the tyre, can also mean that your suspension is faulty. Also check for any damage to the tyre-wall – but more about these issues in a bit. The major factor influencing the ‘to buy or not to buy’ conundrum is the amount of tread depth left in the tyres.

To function reliably, a minimum tread depth of 2mm is recommended. Check the tread depth markers on the tyres or just use the tried and tested one-rupee coin trick. Stick the coin vertically inside the tread and if the word ‘rupiah’ is visible, it’s time to change the tyres.

The writing’s on the wall

Every piece of equipment you buy these days comes with its own manual and/or guide, which lists the specifications of the device and details on how to use it. Tyres too come with a manual, only it’s not on a piece of paper, but on the tyre itself. The words and figures on the side-wall can tell you all you need to know about that specific tyre.

At first glance, the inscription on the tyres may look like some sort of secret code that the manufacturer doesn’t want you to know, but don’t be put off. Yes, it is technical in nature, but is easily understood once you know what each of the symbols represents. The most important thing you should know about your car’s tyres is their size. Start by looking for something that reads along the lines of 175/70 R14. The first figure, 175, is the width of the tyre in millimetres. This is measured across and includes any raised lettering on the side-wall.

Number 70 represents the height of the side-wall – or the distance between the outer edge of the wheel rim and the outer edge of the tyre, in relation to the width of the tyre. It is also called the aspect ratio and is a percentage measure of the actual width. Therefore in this example, it’s 70 percent of 175, which is 122.5mm. The letter R signifies the kind of construction the tyre uses – R stands for ‘radial’ and is the most common kind these days. The number 14 is the diameter, in inches, of the wheel rim that the tyre is designed to fit. Trying to use a different wheel size than what’s prescribed will prove difficult and can be dangerous as well.

Next comes the load index. It is the amount of weight that a tyre can carry. A load index of 76, for example, means that the tyre is designed to carry a weight of 400kg safely. As you travel faster, the stress on the tyres increases, and a tyre with a higher load index is safer. Tyres are also rated for speeds they are designed for. This is called a speed rating and uses an alphabetic representation. A look at the table will give you the speeds in kilometres per hour the tyres are capable of traversing.

It’s best to buy tyres of a higher load index and speed rating than what the car is capable of. This ensures that the tyres will not undergo any more stress than they are designed for and will hence be safe. The tyres are also marked with the time of manufacture on the side-wall itself. 0710 for example tell you that the tyre was manufactured in the seventh week of the year 2010.

The buying process

Now that you know what kind of tyres there are and what the symbols on the tyre-wall mean, you are all ready to buy a new set. The first question you need to ask yourself is how much money you are willing to spend on them. A set of high-performance tyres just to go shopping doesn’t make sense given their relatively short life span.

We recommend buying the spec of tyre recommended by the vehicle’s manufacturer. This means when buying a new set, make sure it is of the same size, load index and speed rating. Changing any of these parameters too dramatically can have an adverse impact on the car’s mechanicals. We also recommend changing the full set instead of one or two at a time. This ensures that all the tyres on the car are of the same make and have the same capabilities. If the tyres are not replaced as a complete set then a minimum of two tyres should be changed, and both from the same axle. So at any given time the front tyres should be the same as each other, and the same goes for the rear.

Going up

A common practice we have seen among buyers is fitting wider tyres. Tyre upsizing, simply put, is increasing the width of the tyre and the diameter of the wheel rim while keeping the outer diameter of the tyre the same by reducing the aspect ratio. There are some advantages to this. For one, the tyre’s contact patch increases in size and therefore the handling and grip levels increase. A lower aspect ratio means that the side-wall is not as tall and doesn’t flex as much while cornering, providing better handling. Granted, wider tyres look good, but it’s easy to get carried away and this can impact the car’s performance.

Too wide and they foul with the wheel arches and put extra stress on the suspension parts, the turning circle decreases, fuel efficiency goes down given the increased road friction, and there are chances of the ABS not working properly. A shorter tyre-wall also means that on broken surfaces, more road anomalies are transmitted through the suspension and to the cabin. The lower the aspect ratio, the worse the ride quality gets and the more stress there is on the mechanicals. Therefore it’s best to stay within three percent of the original overall diameter of the wheel and tyre combined. If this is not adhered to, the speedometer and odometer will give you inaccurate readings. If your car’s stock wheels are 13 inches in diameter, don’t go over 14 inches in wheel size if upsizing so that these problems don’t occur.

Take care

Just like the rest of the car, tyres too need specific care to keep them in good shape so that that they last long and perform better. A brand new set of tyres needs to be run in and it’s best to drive sedately and not push the car to its limits for the first 200km. This is because, if the previous tyres were significantly worn, you would be used to the car behaving differently. Now, however, you too have to get used to different grip levels and braking distances.

Long tyre life is dependent on the amount and kind of wear that they go through. Even and gradual wear across all tyres is something that owners should strive for. The most important thing affecting tyre wear is the air pressure. Filling too much pressure in a bid to improve fuel economy leads to the centre of the tread wearing out faster than the sides. Under-inflating the tyres similarly can lead to the outside of the tyre wearing faster than the centre. Recommended pressure levels should be maintained. As mentioned before, a thorough look at the tyres once every two weeks is a must. Any uneven or peculiar tyre wear should be easy to spot.

If while driving, you notice the car swerving to one side, the alignment needs adjustment. Don’t ignore this for too long as it means the tyres are wearing out unevenly. Signs of this are the tread being deeper on one side than the other and bits of frayed rubber around the main tread itself. If the wear is irregular, it’s worth inspecting the suspension parts too; as prolonged irregular wear can increase the vibrations and damage the mechanicals. Check the side-wall for bulges. These are caused by a broken belt on the inside of the tyre and make it susceptible to punctures and blowouts. Replacement is the proper cure.

Rotating the tyres and getting the alignment fixed every 5,000km helps keep the wearing process even across the set. With most cars sold in India being front-wheel drive, the best rotation policy is to switch the right front tyre with the left rear. Similarly, the right rear should be switched with the front left. On rear-wheel-drive cars the rear tyres undergo more wear than the front. On these cars, the rear tyres should be put on the front axle, but swapped left and right. The front tyres should be placed at the rear, but on their original sides. On four-wheel-drive cars like SUVs, the rear tyres should go to the front but on the same sides. The front tyres, though, should switch sides when placed on the rear axle. If you car comes with directional tyres they can only be switched from the front to back on the same side of the car to maintain the direction of rotation.

As they wear out, the weight of the tyres also shifts from one side to the other. When the wheel rotates, this imbalance in weight causes movement, which can be felt as vibrations through the steering wheel. As practice, the wheels should also be balanced every time tyres are rotated. The wheel is mounted on the balancing machine which rotates it and calculates how much counter-balancing weight is required and the exact spot where it should be placed.

In a hole

Nobody likes a puncture, especially when they are in a hurry. If you have tubeless tyres installed on your car, carrying a puncture repair kit is a good idea. Repairing a puncture isn’t that hard either. Just remove the tyre, locate the puncture, remove the foreign object that has caused it and clean the puncture. After this, thread the needle tool with the supplied rubber plug and coat it with the silicon-based lubricant supplied.

Now place the needle on the puncture and push the rubber plug into the tyre with about a quarter of it still sticking out. Now rotate the needle and, with one swift tug, pull it out. This will ensure that the plug fills the puncture completely. There will be a small part of the plug still sticking out of the tyre which can be cut off with a blade.

We are sure after reading the past few pages, you would have learnt enough about tyres, tread patterns, upsizing, buying and looking after your tyres. Remember the tyres are the only contact between the car and the road. Always take good care of them.

WhatCar? tip

There are unidirectional tyres which are made to rotate in a given direction. These are common on performance cars and can only be spun in one direction – this means you can not switch left and right-hand-side tyres. The direction of rotation, and which side of the tyre is out and which is in, are well marked out.

Speed Rating

Rating                Max speed
                               (kph)
L                               120
M                              130
N                              140
P                               150
Q                              160
R                              170
S                              180
T                              190
U                              200
H                              210
V                              240
W                             270
Y                              300


WhatCar? tip

Tyres are also marked with the highest possible air pressure that can be filled in them. This figure is usually higher than the carmaker recommends. However, sticking to the carmaker’s figure is the best bet for optimum handling, ride quality and fuel efficiency, and is a figure achieved after a lot of testing and research.

The fifth Element

Some things are easily neglected. The spare tyre is one of them. It spends most of its time in the boot only to come out when you suffer the dreaded puncture. When buying new tyres, it’s best to change the spare as well to maintain a consistency of tyre performance.

Every time you get the air pressure checked, get the spare inflated as well. In case of a puncture, get the tyre fixed as soon as possible and put the spare back in the boot. Make sure the spare tyre is also a part of the tyre rotation process to ensure that all of them wear out evenly.

Being hands-on is helpful as well. Stuck with a puncture in the middle of nowhere without knowing how to change the spare is not a situation one wants to be in. Familiarise yourself with the tools and how to use them. It doesn’t take more than ten minutes to change a tyre and is something anyone can learn.

WhatCar? tip

Replacing worn-out tyres is a good policy, but replacing old tyres should also be considered. A tyre, even if not used much, undergoes wear thanks to the large variation in temperature and weather conditions in our country. Over a period, the constant exposure to hot and cold temperatures hampers the structure and tyres more than five years old should be replaced.


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