Round Black Things - Motors' Guide to Tyres

Always buy the best you can afford. Remember to look after your tyres and they will look after you.

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Four tyres are all that connect your car to the road. By simply generating friction with the road surface, tyres enable cars to accelerate, brake and go around corners. To most people they are nothing more than round black things that are a pain to change when they get a puncture! Tyre technology is complex and very impressive, but the differences in performance between high end and cheap tyres can be alarming.

Tyres are the most important element in a car's performance and too often overlooked. When it comes time to replace the 'round black things' we often search out the cheapest option without fully understanding the potential impact a budget tyre will have on a car's performance and safety. Often, too, the open market can reveal a wide price gap for the exact same tyre so, of course, shopping around is vital. A little research and knowledge can help you make a more informed choice.

What is Tyre Pressure?
Thanks to Mr Dunlop, tyres are filed with compressed air and as a result provide additional suspension for the car, thus helping the ride quality. The correct tyre pressure depends on the tyre size and type, the car itself and the weight of cargo carried. So if you are heading off on the holidays with a loaded car, the tyres generally will need more air in them to help support the additional weight and also to maintain the correct operating temperature during the journey.

A metal plate with the correct tyre pressures is often found inside the doorframe, or more recently carmakers put an information plate inside the fuel filler cap (the car's manual will also have them). While all four wheels may have the same recommended tyre pressure figure, often they don't (with the front wheels generally having a little more). It is critical that the two front tyres have the same pressure and, likewise, the two rear tyres. Underinflated tyres use more fuel, wear quicker, corner poorly and can overheat. Overinflated tyres (think they're great – sorry, couldn't resist) provide less grip – especially when cornering and again will wear out quickly. Drift car drivers overinflate their rear tyres to get the back to spin out more easily.

What do the letters and numbers on a tyre mean?
The three main numbers found on the side of a tyre, e.g. '195/70/R15 H' refer to the tyre's footprint on the road, i.e. section width 195mm, and then its sidewall/profile or aspect ratio, i.e. 70 series. The letter R stands for 'radial' structure of the tyre, while '15' denotes the rim's size in inches, i.e. the metal wheel is 15 inches in diameter. At the end of the sequence there is the letter 'H': it represents the tyre's specific speed rating.

High performance cars need expensive tyres with far more ability than your average 'Runabout' – the engineering allows for a higher heat cycle and greater friction for the demands the car can place on it. The alpha range goes from the letters N-Z. Generally, the further down the alphabet the higher the speed rating, e.g. 'Z' for cars that can do up to 295kph. Always replace your tyres with the same numbers and correct speed rating, or if in doubt check your car's manual.

What is an E mark?
This letter is embossed on the sidewall of the tyre and lets you know the tyre meets European standards. If it is not present you are not legal. This letter was brought in as a reaction to extremely poor tyres coming into Europe from Asia that fell far short of the safety standard required here.

What are Low Rolling Resistance tyres?
These are designed to maximise a car's fuel economy. They are made of special compounds that reduce friction with the road – which sounds contrary to what we want our tyres to do! It is a balancing act between a trade-off for grip, cornering and braking performance and the ability to reduce fuel consumption by making it easier for the engine to push the car along. In normal driving it can be hard to notice a fall-off in grip but, with more demanding driving - particularly in the wet - it can be easy to reach limits. Inferior low rolling resistance tyres can be very poor.

What are Summer Tyres?
Ireland has a temperate climate, so unlike Europe we do not require by law the fitting of special winter tyres. Irish cars are as standard fitted with what Europeans call a 'Summer Tyre'. This tyre type works well in our climate but on the rare occasion when we get extreme winter weather the compound and groove patterns do not provide enough grip, especially in rear-wheel drive cars.

What are Winter Tyres?
These tyres grip more in cold weather but in hot weather the reverse is true. Winter tyres use a special type of rubber - tyre compounds have more ingredients like Silica but let's keep it simple for now. The rubber used is more resistant to freezing up and going brittle at temperatures below 7 degrees Celsius. The tread pattern used is also different from normal tyres. It has a greater number of tiny grooves in it to help put the biggest footprint on the surface to gain friction and grip. Unlike summer tyres (our normal tyre in Ireland), winter tyres go off from about 4mm in tread depth as the tiny grooves wear away. The tyres should be replaced at 4mm but will still be legal. Winter tyres should be considered if you live in a remote or hilly area, or if you have a rear-wheel drive car and need to get about in all weathers.

Is there an All Weather Tyre?
Yes. A one-stop solution for those fearful of very cold weather is to fit 'All Weather' tyres. These are a new type of tyre and certified as a winter tyre in Europe but they still manage to work as well as your average summer tyre in warmer weather. Having driven on all three types of tyres in temperatures of -24C near the Arctic Circle I feel the all weather tyre is the best solution for rear wheel drive car owners in Ireland as there is no need to switch tyres and rims for winter/summer use. They are a little more expensive at the moment than a standard tyre but will give that needed peace of mind.

No matter what tyres are fitted to your car, they cannot perform miracles and turn you into a rally driving legend, especially in the snow - even on full winter tyres.

Always buy the best you can afford. Remember to look after your tyres and they will look after you.

Michael Sheridan


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