Take good care of your tyres

Nowadays car manufacturers themselves recommend the type of tyres to be used on their cars after a series of tests. For high speed driving, the manufacturers normally suggest radial tyres and that too rated tyres (Rated tyre means the maximum speed that it can achieve safely). For example, the figures - 195-65-15-91-H - in that order on a rated tyre represent the nominal width in millimetres, the aspect ratio, that is, the height, the diameter of the rim, the load carrying capacity of the tyre, and the last alphabet, the maximum speed the tyre can achieve. Cars that may be driven fast and have a capacity of being driven to a certain speed, say up to 200 kmph, will usually have tyres rated to be driven up to 240 kmph, almost 20 per cent more. The factory- approved radial-ply tyres are ideal for cars that provide the optimum road safety and the desired riding comfort.

The condition of tyres and the maintenance of specified tyre pressure influence not only the tyre life but also the road safety to a considerable extent. Incorrect tyre pressure often causes tyre problems which in turn have an effect on the road holding. For one's own safety, it is recommended to check the pressure on a regular basis - at least once in two weeks - especially when the load on the car is increased. Lower pressure will reduce stability and driving safety, because lateral locating forces are lower. The tyres will be less capable of withstanding high speed and will heat up more rapidly as a result of excessive flexing. The associated higher roll resistance will cause fuel consumption to deteriorate and can lead to tyre damage and accidents.If a tyre loses pressure considerably, one should have the cause investigated and rectified. Remember to check the spare wheel's pressure too, and keep this at about 0.3 bar (3-4 psi) higher than the specified value for heavier loads, so that the tyre can always be fitted without being inflated further. Higher tyre pressure reduces the comfort level in the car and leads to premature tread wear as well.

Inspect tyres frequently for damage, presence of foreign bodies, unusual wear and sufficient tread depth. Although the law in many countries calls only for a minimum tread depth of 1 mm (if indeed any minimum figure is laid down), it is, however, recommended to replace tyres for high speed driving, when the tread depth is down to 3 mm, or else the risk of aquaplaning even on shallow water will increase. As the danger of aquaplaning always increases with the car's road speed, this should be kept low if the road is wet and the tyres are known to be fairly well worn.

Recutting of tyre treads is not recommended because of the risk of the carcase being weakened. Retreading a tyre for high speed driving is a crime and should never be done. Drive with extreme care and at moderate speed on poor roads and over unavoidable obstacles such as kerbstones, so that the tyres do not suffer any damage. Usually, car manufacturers do an extensive study of the recommendation of the type of tyres (tubed or tubeless) to be used on their cars keeping in view the conditions of use and the service available to the user. Although a tubeless tyre is obviously more comfortable, economical and efficient to use the condition under which it is going to be used may not be favourable to the owner and hence is not recomended by the manufacturers. Uneven rim or a bent rim causes air leakage in a tubeless tyre. Do not drive too close to kerbs and avoid going fast on rough or stony roads. When parking or driving over loading ramps and workshop hoists make sure that the sides of the tyres are not damaged by violent contact with obstructions.

Warning

Avoid overloading the car. This can cause the tyres' load capacity limit to be exceeded, so that they overheat and cause internal damage at a rate that cannot be detected from outside, possibly leading to sudden pressure loss.

All forms of tyre damage (that can in the worst case lead to sudden and total loss of pressure) represent a risk of serious or even fatal injury to the occupants and other road users.

Never try to drive any further if a tyre goes flat. And never change a flat tyre while in the fast lane, which most of us do. To maintain the car's good road behaviour, always fit tyres of the same make and tread pattern to all wheels.

Tread wear patterns are different at the front and rear wheels. In the interests of safety and the best possible vehicle behaviour, it is advisable not to interchange only wheels after a period of running. If it is felt that the wheels should be interchanged for reasons of operating cost, please note the following precautions: Interchange the wheels on the same side of the car though the spare wheel can be included if desired. By doing this you can easily detect uneven tyre wear at an early stage and do some preventive maintenance, also you would have to change two tyres at a time as the driven tyres wear out less than the `drive' ones.

Do not use tyres that are more than ten years old for normal driving unless they have been used regularly in normal conditions. Failing this, they should be replaced. Spare tyres more than six years old should be reserved for genuine emergencies, that is, if the car's mobility cannot otherwise be maintained.

A tyre's date of manufacture is shown as part of the inscription on the tyre wall: DOT ... 258 means, for instance, the 25th week of 1988. On models with a top speed in excess of 240 kmph, certain tyre makes and sizes are compulsory. The correct choice is made easier if the meaning of the tyre markings is understood. Radial-ply tyres are marked as follows:

Nominale width in mm 195; Aspect ratio (in per cent) 65; Radial- ply construction code letter - R; Rim diameter (in inches) 15; Load capacity in figure (not on ZR tyres) 91; Speed code letter (ahead of the R on ZR tyres) - H

The speed code letter indicates the maximum permissible speed at which the tyre is to be operated.

On summer tyres: S = up to 180 km/h; T = up to 190 km/h; H = up to 210 km/h; V = up to 240 km/h; ZR = over 240 km/h.

On winter tyres: Q M+S = up to 160 km/h; T M+S = up to 190 km/h; H M+S = up to 210 km/h.

Marks on steel or light alloy wheels: Rim width (in inches) 6; Shoulder pattern code letter - J; Symbol for well-base rim - X; Rim diameter (in inches) 14; Hump on both rim shoulders - 2.

Prevent dirt from entering the tyre valves with screw-on dust caps. Dirt in the tyre valve can often lead to a gradual loss of air pressure.

For off-roading and snowy winters (M & S radial-ply), the same make and tread pattern should be used on all four wheels (preferably on the spare wheel as well) in the interest of good directional stability and steering response. Always note and comply with the maximum speed limit of your winter tyres. All four-wheel option vehicles should have the same make and size of tyres. Keep to the specified tyres and have the wheels and tyres rebalanced each time the wheels are changed, a puncture is fixed or new tyres are fitted.In case of puncture, the emergency- running characteristics of the tubeless type of tyres enables you to drive out of hazard zones such as bottlenecks, heavy urban traffic, tunnels or building sites without difficulty, even if the tyre is flat, so that the tyre can be changed in safety on a car park or at a filling station. This type of tyre, if flat, can be driven about 5 or 10 km if a particularly cautious approach is adopted, depending on the vehicle's load and the condition of the road. For a do it yourself `Quick Fix' for a tubeless tyre punctures, carry a tube of `Super Glue' (cyanoacrylate ester) and some round wooden tooth picks. Identify the place of puncture by inflating the tyre hard enough. Deflate the tyre completely by pushing the valve with a stub end of the tooth pick, put less than a drop of super glue on the identified puncture and shove the pointed end of the tooth pick to the full extent it can reach in one go, give it three to five minutes to set and break the end sticking out, re-inflate the tyre and you are ready to go.

TUTU DHAWAN

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