Merityre Article Archive

It’s that time of year again, the one when we awake to the merry sound of sparrows shivering. Temperatures are down thermostats are up. We have the occasional benefit of a pretty, snow clad landscape and the road conditions that put us and our car tyres under stress.

Luckily, car tyres are made to cope with harsh conditions, which they are perfectly capable of doing, with a little help from their friends, i.e. you, their owners. None of the following little maintenance tasks are particularly difficult, time-consuming or even expensive. Carry them out and your car – and its tyres will carry you around reliably, in most conditions.

The first idea to take on board is that there isn’t a road tyre made that will provide grip on sheet ice. On such a surface, a car tyre might as well be a ‘slick’ with no tread at all. However, on snow, slush and in the wet, tread matters. Officers of the law will have something to say if you don’t have the regulation 1.6 mm of tread around three quarters of all your tyres and this is a worst case scenario. In practice, letting tyres this worn meet winter conditions is folly.

How can you maximise grip? Among the car tyres on the market are numerous ‘Winter Tyres’. These are made of a softer than usual compound and offer superior grip in winter. But are they worth it? If you do a lot of driving in cold, disagreeable conditions, the answer is ‘yes’.

Then there are grip aids for car tyres. In some countries, snow chains are a legal requirement in winter conditions. This is not so in the UK but there are ‘snow socks’, tough, net covers that enhance grip in the short term at low speeds. Are these worth it? Assuming conditions are seriously bad, the answer is a qualified ‘yes’. Bear in mind that snow chains do tarmac a power of no good, while tarmac will soon put paid to snow socks. Think of these things as emergency equipment.

Naturally, car tyres should be at the correct pressure. Checking this is any easy job that should be repeated regularly throughout the winter. Bear in mind that temperature and tyre pressure are irrevocably interlinked, so head for the tyre inflation facility soon after the ice appears.

While up close and personal with them, run a hand over your tyres’ carcasses to check for bulges, lumps, cuts or the evidence of misalignment. Remember also that you have a spare tyre that you might need in a hurry. Check first that you can access it, particularly if it lives beneath the car. Finding out that the spare is shredded and corroded firmly into place mid-snow storm is undesirable at best.

There are a number of bits and pieces that warrant checking as much as car tyres. Screen wash fluid needs to be kept up to strength as well as up to level. The same goes for your car’s coolant, as well as its oil. A car battery rarely has to be checked these days but if yours is marginal, a cold snap will probably kill it off completely.

Your car tyres can’t carry you safely if you can’t see where you’re going. This is reason enough to regularly check every last bulb and LED on your car. Also, pensionable windscreen wipers merely tend to move snow and rain around on your screen. For deicing, a proprietary spray is worth having, as is the more paint friendly and economical

‘Ice Plane’. You can tackle frozen-up doors using cold water but be quick – it re-freezes. Hot or boiling water is a great way to crack cold glass. Remember that setting off peering through a ‘porthole’ that represents the total extent of your demisting is an offence.

Finally, what should you take on a winter journey? This depends on the conditions. For example, you might need a torch, reflective waistcoat or jacket and a warning triangle, and some extra screen wash fluid for normal journeys. Whether you need boots, gloves, a shovel and a thermos of tea depends on where you’re headed. The last, some bars of chocolate and heavy clothing are for when conditions are despicable. In any event, a functional, well-charged mobile phone can be a life saver.

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Merityre.co.uk are one of the  leading UK independent suppliers of car tyres. Why not visit their website for an online tyre quote or contact your nearest fitting centre.

All car tyres wear – they are, after all, consumable items. However, some car tyres wear faster than others. Let’s take a look at eight aspects that affect car tyre life.

1. Wheel Alignment

When your car’s wheel alignment is correct, the tyres can run true on the road. This means that a balance exists between the car tyre’s drag and the amount of compliance in the car’s suspension.  Incorrect alignment spells increased wear, and can affect your rear wheels as well as the front ones.

2. Speed

Continuous high-speed driving accelerates car tyre wear. If you doubt this, just take a look at Formula One – pit stops aren’t to give the driver a rest while the tyres are changed!

3. Driving Style

If you drive sympathetically, your car tyres will last longer. Drive aggressively and you’ll pay for it through having to replace your car tyres sooner. An aggressive driving style will raise car tyre flexing and running temperature, and increase tread wear.

4. Car Tyre Placement

On a rear-wheel drive car, the front tyres must cope with steering and braking while the rear tyres offer traction as well as grip. On a front-wheel-drive car, the front tyres have still more to do, consequently wearing faster.

5. Vehicle Weight

Heavier vehicles wear our car tyres faster than lighter ones. There are, of course, heavier duty car tyres to compensate for this to some extent. However, the basic principle remains.

6. Car Tyre Type

Car tyres are constructed to meet particular needs. A performance tyre will give superior grip but will wear out sooner, as it has a softer rubber compound. Conversely, a harder, long life tyre will offer a longer life, at the cost of lesser grip and increased noise. There are tyre types that offer a compromise between the various demands on car tyres.

7. Tyre Pressure

An underinflated car tyre flexes more, runs hotter and wears faster than a correctly inflated one. Underinflation also increases fuel consumption, by creating additional tyre drag. Overinflation is nearly as bad, causing strange wear patterns and reducing grip.

8. The Passage of Time

This is the one aspect affecting tyre life that can’t be avoided. Ultra violet light causes rubber to degrade, as do chemical spills on the road. The usual giveaway is the appearance of cracked sidewalls…themselves indicative of a car tyre that is old. A car that is garaged will receive better car tyre life than a car that lives outside.

As is now clear, the factors affecting car tyre life – and performance – are many and varied. Mechanical sympathy and assiduous car maintenance positively affect tyre life. Conversely, it isn’t really surprising that bad habits can affect tyre life negatively.

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Merityre.co.uk are one of the  leading UK independent suppliers of car tyres. Why not visit their website for an online tyre quote or contact your nearest fitting centre.

Car tyres are often taken for granted. You turn the steering wheel, your car takes the corner, you press the brake, your car stops. This is fine but knowing how car tyres work and the characteristics they generate in terms of handling and roadholding is both interesting and potentially helpful to your driving.

Every car tyre has an area of tread, about the size of an adult’s footprint, in contact with the road surface. This is called, somewhat predictably, its contact patch.  Imagine the tyres’ four contact patches travelling along a road in a straight line. These four areas of tread are what keep your car on the road, allowing you to accelerate, steer and brake with confidence.

Now, what happens to car tyres in corners? Imagine the wheels following the arc that the corner represents. The wheels will be following the arc faithfully, but there’s a hidden force at work. Imagine you’re Superman and have X-ray vision. Looking down at the top of a wheel and tyre combination, you’d see that the contact patch will be following a tighter curve than the wheel is following.

So, what’s happening? Why the difference? It’s there because sideways force put on the tyre by the weight of the car is deforming the car tyre’s carcass. Now, imagine a straight line drawn through the centre of the wheel and another drawn through the centre of the contact patch. There will be a difference between the two – this difference is called the slip angle.

As slip angles increase, the car tyre’s grip increases, up to a point. When the forces involved head towards the maximum level of grip the car tyres offer, one of three states will apply. Say the slip angles are equal at both ends of the car. In this case, the grip at each end of the car will be the same. When the grip level’s limit is reached, the car will go into a classic, four-wheel drift. The car’s handling will be ‘neutral’. Racing cars are set up to give neutral handling.

Supposing the slip angles of the car tyres at the front are greater than those at the rear. Then, the driver will need to apply more steering input to make the car follow the chosen curve. This is called ‘understeer’.

When it reaches the limit of effective grip of its car tyres, an understeering car will slide off the track forwards – it simply won’t be able to corner tightly enough. In practice, most road cars understeer. Why? Because understeer is a generally controllable condition –  it’ll help scrub off excess speed when a corner is taken too enthusiastically.

The third state occurs when the rear car tyres’ slip angles are greater than those of the front tyres. The rear tyres will be giving less grip than the front ones. At the limit, the car’s tail will slide towards the outside of the curve. When you see a Formula One car or Touring Car spin off a track, it’s gone beyond oversteer.

This explanation is necessarily basic. In fact, very many parameters affect how car tyres respond to the forces imposed upon them. However, the physics are just as basic, and give car designers benchmarks from which to work.

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Merityre.co.uk are one of the  leading UK independent suppliers of car tyres. Why not visit their website for an online tyre quote or contact your nearest fitting centre.

‘If in doubt, blame the computer’ is an office standby. When it comes to car tyres, there are plenty of instances when it would be appropriate to say, ‘Thank the computer’. Several computer-controlled systems optimize car tyre performance these days. Let’s pick our way through the acronyms and look at some such systems.

ABS a.k.a. the Anti-Lock Braking System has its roots in aircraft technology. Gabriel Voisin, a French aeronautical and automotive engineer came up with it as far back as 1929. Forty-two years later, ‘Sure Brake’ appeared on the 1971 Chrysler Imperial. It’s now hard to find a single car tyre whose stopping power isn’t maximised by ABS. Here’s how it works.

Enter the ECU, or Electronic Control Unit, which is what is in charge of ABS. Imagine a car tyre is rotating more slowly than its fellows. A wheel speed sensor detects this, and tells the ECU. The ECU, in turn, opens a hydraulic valve to divert brake fluid pressure away from the locking wheel, until the tyre in question speeds up again. The system can do this at up to 20 times per second. The result? On a wheel that isn’t quite locking, the car tyre is gripping at maximum efficiency. A locked wheel offers virtually no grip, while a wheel nearly at locking point can still offer steering and braking force.

EBD (or EBFD) is a refinement of ABS. This acronym stands for Electronic Brake Force Distribution. On the old, ‘classic’ Mini, for example, there used to be a mechanical inertia valve, which would reduce braking force to stop the rear tyres locking under heavy braking. EBD does the same thing, far faster, far more accurately and in relation to each car tyre simultaneously.

Strange as it may sound, ABS can help a car tyre achieve maximum traction under acceleration. TCS – the Traction Control System – uses the ABS’s wheel speed sensors to detect if a car tyre on a driven wheel is spinning (i.e. not gripping). The TCS applies braking force to the spinning wheel for a few milliseconds. In more sophisticated TCS systems, the throttle can be cut briefly, preventing wheel spin.

Speaking of sophisticated systems, we can now look at ESC (Electronic Stability Control). This again is ABS-related. In ESC (or DSC – Dynamic Stability Control), two further sensors play a role. One detects the angle of the steering wheel, while its gyroscopic stablemate checks this angle against the car’s direction of travel. Should the figures not add up, the system applies braking force to individual wheels. Once again, each car tyre is maintained at its optimum level of efficiency in any given circumstance, by the application of very short pulses of braking pressure, and/or throttle input, as appropriate.

Here’s where further refinement steps in, and where we become awash with acronyms. It’s probably best to think of the refinements under the ACC (Adaptive Chassis Control) banner. Often using a button, with markings such as ‘Comfort’, ‘Sport’ and even ‘Race’, a car driver can dial in all manner of changes to how his car responds. While the stiffness of physical springs can’t be changed electronically, the firmness of the suspension can, by the actuation of electronic tweaks to suspension damper rates. While the car tyres don’t change, that which controls them can. It’s possible for driving force to be distributed according to car tyre grip across an axle and, in some cases, between the front and rear wheels.

The bottom line about these immensely clever, capable systems is that they use car tyre grip as a benchmark. When the car tyres are offering optimum grip, tyre performance – and therefore the performance of the car – is necessarily optimized.

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Merityre.co.uk are one of the leading UK independent suppliers of car tyres. Why not visit their website for an online tyre quote or contact your nearest fitting centre.

The usual seasonal symptoms are back again. In the UK, winter presents a series of tough tests for car tyres. As well as your tyres, it is you who are on test – drivers, rather than cars, generally cause accidents. Here are some salient points about winter driving…

Snow and Ice

A mountain climber’s crampons, the tracks on a Caterpillar tractor, the toothed drive belt on a snowmobile…certain things are made to grip on snow and ice. Since (with some exceptions) you can’t fit such things on your car, you have to cope, using the tyres your car usually wears. There is, however an option. When the temperature drops, your usual tyres will lose flexibility. Winter car tyres are designed to retain their flexibility at lower temperatures, so it makes sense to invest in a set. Motorists are discovering that such car tyres really do offer significantly enhanced grip and control, and using them on a set of  (preferably steel) ‘winter wheels’ will preserve your usual alloy wheels from the ravages of salt and grit.

What are the exceptions? Countries with permafrost can be home to car tyres with studs. In the UK, seriously bad conditions can trigger the use of snow chains. A new item occupies the middle ground. Snow socks are car tyre covers made of a tough, woven material. Easier to fit and quieter than chains, they can be useful when drivers are caught out by unexpected snowfalls. Bear in mind that they will wear out in no time on tarmac.

Rain

When it isn’t quite cold enough to snow, rain and sleet present car tyre challenges of their own. Reduced visibility is a foregone conclusion but don’t forget that wet weather compromises grip. Your car tyres will move surface water but a wet surface remains relatively slippery. Remember to leave more room between you and the vehicle in front, to allow for increased braking distances.

Flooding

Lots of rain can lead to flooding. Standing water can be dangerous. When your car tyres hit it, you’ll feel the steering wheel pulling in response. At worst, your tyres may aquaplane. When the tyres ride on the surface of the water, suspiciously light steering signals radically reduced grip. If you feel this, lift off the throttle and slow down until the grip returns.

If you encounter a flood, remember that negotiating it requires care. Keep to the crown of the road, where the water will be shallower, and look out for the white line. This will help you gauge the depth of the water. While you can trust your tyres, remember that your engine, if it sucks in water, will be wrecked. Keep the engine revs up to help stop the exhaust inhaling water. However, if you are in any doubt whatsoever about the depth of the water, use another route.

Fog

In thick fog, you’re bound to suffer loss of visibility. Your car tyres won’t suddenly offer greater grip just because you notice that you’re hurtling towards the back of stationary truck. So drive as fast as you can see, and no faster. Remember to use your windscreen wipers and washers often in fog; your screen can collect water and grime surprisingly quickly, further reducing visibility.

In winter, the watchword is caution. Even on winter car tyres, grip will be compromised to some extent by bad weather. Should the visibility and grip be truly awful, simply put your feet up by the fire and live to drive another day.

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Merityre.co.uk are one of the leading UK independent suppliers of car tyres. Why not visit their website for an online tyre quote or contact your nearest fitting centre.

Here are a few sobering figures. When you’re driving, the grip of your car tyres ultimately determines how quickly it can stop. At 30mph, the tonne or more of moving metal you’re piloting is travelling at 45 feet per second; every second equals 2.8 car lengths. At 70mph, every second’s travel is 105 feet. In ideal conditions, a car travelling at 30 mph takes 75 feet to stop; at 70mph, it’s 105 feet. In wet conditions, the 30mph stopping distance jumps to 120 feet and at 70mph, it’s a whopping 560 feet – that’s 35 car lengths. The strategies for coping when driving in poor conditions aren’t all obvious but the need for them will become so. Read on and learn.

It’s clear that when driving in rain, we need to leave more stopping space, to give your car tyres room to work with their reduced grip. Reducing your speed is a good idea too.

Car tyres have more to deal with than just surface water. If it rains after a long dry spell, the road surfaces’ build up of dirt and diesel, plus water, makes for near skid-pan conditions. Moreover, it isn’t just car tyres that are affected by rain. It’s a fact that vision is compromised on many levels by rain. First, a rain-sodden windscreen isn’t the same as a dry one, regardless of how efficient windscreen wipers have become. Furthermore, any car has areas of unwiped glass. Second, clammier conditions lead to misting up. This can be cleared by demisters and heated windows, but this is rarely instant and it obviously affects vision. Third, heavy rain and the resultant spray compromises vision yet more. Fourth and last, pedestrians tend to shy away from the rain and are unlikely to keep as sharp a lookout as they might.

Apart from attending to the elements of speed, distance and grip, you need to take further care in wet weather. A flood, for example, can cause major problems. Drive into one too fast and your engine could inhale a measure of water. This could do anything from causing it to stop to doing irreparable damage. What’s more, even if you negotiate a flood successfully, you’ll have wet brakes. Apply your brakes lightly until you feel them start to work properly or they won’t be there when you need them. Also, remember that anti-lock brakes let you steer when skidding but won’t necessarily reduce stopping distance as much as you might think. In fact, a June 1999 National Highway Traffic Safety Administration (NHTSA) study found that ABS increased stopping distances on loose gravel by an average of 22 percent.

What about the still worse conditions of ice and snow, and fog. The former requires gentle, intelligent control inputs – you’ll soon find out how gentle you must be. Fog driving is all about vision. Some clearly feel they have magic tyres but the bottom line is if you can’t see or are following too close, you can’t stop in time, period. Remember to use your wipers when the fog droplets build up on your windscreen.

Lastly, it may seem odd to include ideal conditions, i.e. sunny, dry and bright, under defensive driving. If it does, try this. Picture yourself driving west, late in the day. The level sun is in your eyes, your windscreen’s grimy and your view of the road isn’t at all clear. This would be a good time to stop and clean your screen.

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