Merityre Article Archive

Back in the mists of time, motorists used to change their own tyres – by hand. No doubt there are diehard enthusiasts who still do this but for us mere mortals, there are car tyre bays. Here’s how a car tyre is changed – by machine.

To be attended to on a tyre machine, the car wheel with the tyre to be replaced must be taken off. Enter the trolley jack and powered wheel nut wrench. Almost without exception a key or adaptor to cope with the locking wheel nut is needed now. Soon enough, the errant car tyre will be detached from the car, complete with wheel.

Now the fun begins! We’re contemplating separating a big, tough rubber ring from the big, heavy metal wheel it’s been embracing, probably for many miles. The tyre fitter can unscrew the tyre valve and let the air out, but he can’t make any impression on the car tyre/wheel combination without mechanical assistance. This is why the tyre machine has powerful, compressed air-powered jaws, better known as the bead breaker. With the deflated car tyre placed correctly, all the fitter need do is press on a pedal. The jaws seize the tyre and separate the bead from the wheel rim.

The failed car tyre now has to go up in the world. More accurately, it has to lie flat on the tyre machine, with the wheel clamped firmly in place. More compressed air is used to let the machine seize the wheel firmly. Then, the fitter will place the hooked head of the tyre machine by the car tyre’s bead. Lifting the broken bead carefully over the wheel rim with a tyre lever, the fitter will flip it over the machine’s head. Another press of a pedal releases compressed air, causing the wheel to rotate. The tyre machine’s head peels the upper bead of the car tyre up and off the wheel rim. Repeat the process for the lower bead and that’s it – the old car tyre is off.

Now for a spot of wheel preparation. The old tyre valve’s inner fitting is sawn off and the valve is drawn out. The old balance weights will be peeled off or unclipped and, in some instances, the fitter will use a hand wire brush to clean corrosion off the wheel rim. Then, after having replaced the tyre valve, the fitter will apply a special compound to the wheel rim and the new car tyre. This stuff is a lubricant that will make fitting the new tyre easier.  However, where there has been an air leak between the old tyre and the wheel, the fitter will brush on a special sealant.

The tyre machine comes into play again now. Once cleaned, lubed (or sealed) and re-valved, the wheel is ready to accept the new car tyre. The machine is simply used in reverse order, the push the new tyre over the wheel rim, bead by bead. Using a compressed air line, the fitter will then inflate the new car tyre. Sometimes, the tyre/wheel will need encouragement to seal but the tyre will eventually seat itself   – sometimes with a loud bang – when air pressure builds up.  Throughout the car tyre-fitting process, the tyre machine has done most of the heavy work, while the tyre fitter carried out the intelligent tasks.

So, are we finished? Not quite – the wheel and car tyre combination need to be balanced. There’s another machine for this. Having placed the wheel on the tyre-balancing machine and clamped it on firmly, the fitter will close a safety guard and start the machine. The machine spins the wheel up to a given speed, which is usually about 200 revolutions per minute. Now it’s the balancing machine’s turn to be clever. Using its sensors and electronics, the machine will tell the fitter how heavy the balance weights need to be and exactly where they must go. Using the machine’s recommendations, wheel weights will be fitted and the newly balanced wheel taken up to speed again. Fine-tuning can be done but it’s rarely needed.

What used to be done manually, and could lead to sore hands and backache has been done quickly and efficiently. Should you watch from the comfort of the waiting area, you’ll know exactly what the fitter was doing at each stage of the tyre change…and why!

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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.

A car tyre must be inflated to work properly. Should you suffer a puncture, you can change the wheel concerned. Here’s how to do so in safety…

When

When to change a wheel becomes pretty obvious. A heavy pulling at the steering wheel and/or squirmy handling with assorted noises is usually sufficient to let you know a car tyre has deflated.

Where

Where to undertake a tyre change may seem obvious but this isn’t necessarily so. The first and most important rule is to never, ever try to change a car tyre by a busy carriageway, be it a on a motorway hard shoulder or at the side of an A-road. Why? Quite simply, it is hugely unsafe.

So, what if you’re caught out, on a busy road? Sometimes, it’s possible to coax your car to a quieter location. Bear in mind that you’ll need to find a level, firm surface to work on. If the car tyre has deflated fully, just pull up and call out the cavalry. The breakdown service will do the rest, after your mobile phone, or a roadside phone, has done its lifesaving bit.

How to prepare

A spot of preparation makes changing a flat car tyre much easier.  Pull up in your chosen spot, apply the car’s handbrake, put the car into gear (or ‘park’), switch on the hazard lights and set up the car’s warning triangle. This should be placed 45 metres (147 feet) behind the car.

The next stage in dealing with a flat car tyre is to have any passengers leave the car and stand well away from it, and from passing traffic. Then, it’s time to extract the spare wheel, jack and tools – your car’s handbook will tell you where they are to be found.

Jacking the Car

This step in the proceedings involves safety procedures, to which you must pay attention. First, you have to chock the wheel diagonally opposite to the one with the flat car tyre. No chock to hand? Then find a stone, brick or any other piece of debris that’ll do the job.

Time for your car to go up in the world. There’ll be a specific place under which the car jack must be placed. Once again, the handbook will tell you where this is. Do not improvise; only the proper jacking point will do. With the jack placed correctly, wind it up until it’s bearing enough of the car’s weight to not move.

Loosening the wheel nuts or bolts holding the wheel with the flat tyre comes next. These are always undone anticlockwise, with the wheelbrace that is in the toolkit. You may have to undo a locking wheel nut too – there’s a key device for that.

Now, wheel fastenings can be very tight. Use the wheel brace so you’ll be applying downward pressure (far less injurious if the tool slips). Loosen the fastenings first; the wheel can’t turn because it’s still on the ground.

Now, you can jack the car up. Do this steadily, until there is daylight between the flat car tyre and the roadside surface.

Changing the Wheel

Unscrew the fastenings completely one by one, removing the uppermost one last. You may need to ‘persuade’ the offending wheel to come off but be careful – over enthusiasm could cause the car to fall. For this reason, never let any part of you go between the car and the ground.

A car tyre and wheel combination can be heavy. Make sure that when lifting one, you’re on a firm footing with a straight back. Fit the spare wheel, securing it with the topmost fastening. Then, refit the remaining fastenings, tightening them only enough to seat the wheel firmly on the hub. Lower the car until the tyre is on the ground, and tighten the fastenings in a diagonal pattern. Now, you can stow the deflated wheel and tyre, put your tools away and continue your journey.

Finished?

Not quite, there are a couple of post-wheel change necessities. You need to get to a tyre bay, to have the wheel tightened to a specific torque – a repair on the flat car tyre is often possible. If you need to continue on the spare, you have to be sure that the car tyre on the spare wheel you’ve used is at the correct pressure. Finally, if the spare tyre is a space saver, there’ll be limitations concerning speed and distance. The car handbook will show you what applies.

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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.

Car tyre forensics seems like an odd concept. However, in many instances, a ‘dead’ tyre can give you as much information as a corpse in the hands of a police pathologist. Information? Yes, tell-tale signs that can tell you what caused the tyre’s untimely demise. Such information is useful because in indicating possible faults, it can tell you what might require fixing to give your replacement car tyres or tyre the maximum possible life.

Let’s start with the basics. The type of tyre wear pattern that’s to be expected is straightforward, and is characterised by the tread’s having been worn away to the extent that the tyres’ tread wear indicators are at or near level with the surface of the tread. So, the tyre has nearly finished its useful service life. Is this the end of the story? Not necessarily. The suspension geometry on some cars can mean that the tyres’ treads don’t necessarily wear completely evenly.

Other car tyre tread wear patterns tell a different tale. What must be borne in mind is that they don’t necessarily tell it quickly – some wear conditions take a while to show that something is awry. For example, what does feathering on both outer edges of the tyre tread suggest? This pattern is the most likely indicator that the tyre has been consistently run at too low a pressure. Conversely, a strip worn around the centre of the tread indicates a tyre having been run at too high a pressure.

What about feathering on one edge of the car tyre tread? Should such wear be on the outer edge of the tyre, it suggests that the car’s steering is misaligned, having too much toe-in. Similarly, feathering on the tread’s inner edge indicates that there is too much toe-out. This kind of wear usually appears on both front tyres, as the steering will generally attempt to run straight and true. The fact that the steering tries to compensate for misalignment by effectively evening out the wear on each side of the car is no compensation in itself. However, it does advise you to have the wheel alignment checked before your new tyres suffer.

It’s worth noting that feathering on one side of a car tyre tread occurring only on one side of the car indicates something other than misaligned wheels. In this instance, one-sided feathering is more suggestive of wear in the car’s suspension joints, its springs and/or its wheel bearings. This pattern can also occur when the wheel’s camber, its position in relation to the vertical plane, is incorrect. Camber change of this kind can be caused by wear in the aforementioned areas; damage to the suspension can cause the same problem.

‘Cupping’ is also a phenomenon that can show you something is amiss on your car. A tread with cupping (also called ‘dipping’ or ‘scalloping’) has patches of wear across its tread’s surface. This can look almost like the tread surface has softened in places, or has been scooped away. Cupping indicates one of two problems or a combination of them. Wheels significantly out of balance can suffer cupping, as can car tyres under the control of worn shock absorbers. Cupping can affect rear tyres but it’s more commonly seen on a car’s front tyres.

As you can see, car tyre tread wear can be the result of maladjustment but wear and damage can give similar results. In the interests of your wallet, if not your life, pay attention to what your car tyres are telling you.

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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 don’t generally ask too much of you. However, neglecting them can prove expensive and, in some circumstances, dangerous. These ten tips will enhance car tyre life, reduce your spending and perhaps save your life.

1. The wrong car tyre pressure is costly. Running on overinflated tyres accelerates wear and reduces both grip and ride comfort. Underinflated tyres also wear more quickly, and can worsen fuel economy by as much as ten percent. Check your tyre pressures regularly.

2. Cuts in car tyres are obvious. Lumps or bulges may be less so but they tend to indicate damage inside the car tyre’s carcass. Check for any such damage while correcting tyre pressures. If in any doubt, avoid the risk of a blowout by having a tyre specialist examine the damage.

3. A spare wheel with a flat tyre is worse than useless. Check the spare tyre pressure regularly, unless you have run flat tyres or an onboard tyre pump and repair kit. Remember that space saver spare tyres generally have speed and distance restrictions.

4. If, at car tyre checking time, you find a stone embedded in a tyre tread, you can lever it out before it causes damage. However, if you find a nail in a tyre, leave it alone. The nail will be temporarily keeping the air in – have a tyre specialist take a look. He may be able to repair the tyre.

5. While using the tyre inflator at a garage, or a tyre pump at home, look after the tyre valve dust caps. They keep dirt and grit away from the delicate valves, and are a line of defence against tyre pressure loss. Always put them back carefully.

6. Potholes can damage more than your car tyres. Hit a large one hard enough and you could be facing a bill for the repair or replacement of one or more wheels. Should you be unlucky enough to encounter a big pothole and suspect damage has occurred, stop and examine the affected wheel(s) and tyre(s).

7. Never straddle a speed bump. Instead, let the wheels on one side of your car pass over the bump. This will prevent damage to your car’s tyres, steering and suspension. When negotiating speed bumps and road-width speed pads, slow down or face the cost of repairs.

8. When you’re manoeuvering, curb your enthusiasm so you don’t kerb your car tyres. Kerb impacts can wreck not only tyres, they can scratch, chip and even dent your car’s wheels. Steering misalignment can also result from kerbing.

9. Keep your car in a garage, if you can. Car tyres suffer from prolonged exposure to ultra violet light. This leads to cracking and crazing of the car tyre sidewalls’ structure.

10. When the time to buy replacement tyres rolls around, think about replacing all four. Should this be too costly, always have new tyres fitted in pairs. It’s accepted that the new tyres should be fitted to the rear wheels.

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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.

Wheel alignment? Surely your car’s wheels are in line all the time? In fact, they aren’t necessarily. Speed bumps, kerbing, speed pads and general wear and tear on a car’s suspension and steering can put the wheels out of alignment. Misalignment may be felt as pulling to one side or another, and/or strange steering. In the longer term, your car tyres will suffer – bad wheel alignment can radically reduce tyre life.

So, how do you fix poor wheel alignment, thus making your car steer and brake better, as well as achieving maximum car tyre life? The good news is that car manufacturers provide a means of adjusting wheel alignment. The not so bad news is that you can’t correct poor alignment yourself.

Cue a visit to your local friendly tyre man. Good tyre bays (and garages) have the equipment to check and adjust wheel alignment. All you have to do is watch (or not, depending on your preference) and pay for the work. Then, drive away secure in the knowledge that your car is shipshape in the wheel alignment department.

What happens in a wheel alignment session? Generally, three things are checked, and adjusted as necessary. The first check establishes that the car tyres are vertical, as viewed from the front or rear. Sometimes, the tyres may not be truly vertical. Some cars’ tyres sit at a slight angle from the perpendicular. This is the camber angle, which can be adjusted to meet the car maker’s specification.

The second check involves another angle, the castor angle. Does your car run on castors? Technically, yes, the castor angle permits the wheels and tyres to return to straight ahead when the car is rolling with no steering input.  As you know, your front wheels turn from side to side in response to your turning the steering wheel. No matter how the wheels and tyres pivot, a line drawn through the centre of the axis on which they pivot won’t be vertical. The line has to lean backwards slightly and if it doesn’t, the steering will feel very odd. Again, this can be cured by adjustment.

The last check is on a figure called the ‘toe’. All car suspension has a small degree of flexibility built into it. So, if the car tyres are parallel at rest, the drag between them and the road as the car moves would cause this flexibility to allow the wheels to splay very slightly. You wouldn’t see this but your tyres would soon tell you all about it, by wearing out the inner edges of their treads. So, the wheels are usually set to ‘toe-in’, so they run parallel. If the tyres toe out, if the toe-in is too much or if the toe angle varies from side to side, the car tyres will wear out prematurely. Curing this is again a matter of adjustment.

Wheel alignment used to be checked with a special gauge that used a mirror and lens system. Nowadays, it’s common for car tyre bays and garages to measure the angles involved using laser equipment. Yes, accurate measurement is necessary. In some instances, worn suspension or steering components mean that a problem can’t be adjusted away. Then, the tyre man in question will tell you what needs repairing or replacing for accurate alignment to be achieved.  It’s also the case, especially on a car with independent rear suspension, for the rear wheels and tyres to be misaligned. Once again, adjustment is usually possible.

Is it possible to stop your car’s wheels becoming misaligned and making the tyres suffer? In a word, yes. Don’t kerb your car tyres. Avoid potholes and traverse speed pads carefully. Above all, always negotiate speed bumps with the tyres on one side of your car. Straddling speed bumps is a major cause of both wheel misalignment and tyre carcass damage. You have been warned!

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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.

Last night’s frost warning was a harbinger of the approach of winter. Here in the UK, we should be used to harsh conditions. However, give us an inch (of snow) and the miles aren’t covered…the country tends to come to a grinding halt. Is there a solution? Well, the increasingly popular winter car tyres may help.

This begs a question: are winter tyres genuinely useful or are they just a way of extracting more money from we motorists? Let’s see.

Recommended in Andorra, Italy, Norway and Switzerland, winter tyres are compulsory in Austria, Germany and Sweden and mandatory in Finland. These rules naturally apply on snow-covered roads and/or during the snow season. Often, there is the distinction that the tyres must be marked ‘M&S’ (no, not Marks and Spencer, the marking stands for ‘Mud and Snow’.) Newer snow tyres may have a symbol of a snowflake in front of a mountain. Currently, the distinction between winter and snow tyres is a touch unclear. A good tyre bay will advise you of the exact designation and specification.

In fact, specification is what winter tyres are all about. Car tyres in general are made in much the same way but the rubber compounds used and the tread patterns vary. Winter tyres are made with a high silica content. The probable tread pattern has two tricks up its sleeve. One is a more aggressive tread pattern than ‘summer’ car tyres. This is present to enhance grip.

The winter car tyre tread’s second line of defence involves a winter tyre key word, flexibility. When ordinary tyres have to work in temperatures below 7 degrees centigrade, they stiffen up in the cold conditions. In winter tyres, the compound and tread pattern both improve flexibility.

The benefit of winter tyres is that they give better grip in cold conditions, in rain as well as when snow and ice are about. There are plenty of subjective reports concerning car tyres and most of those concerning winter tyres are favourable. In some cases, cars found to be pretty hopeless in snow are transformed!

Are winter tyres the car tyres for all seasons? Their name offers a huge clue here. Summer tyres will outperform winter ones on dry roads and in reasonable temperatures, and winter tyres, having a softer compound, will naturally wear faster. This suggests following the lead of many continental drivers. They have two sets of tyres, one for winter, one for summer.

This brings us, in turn, to a potentially superior arrangement, which is also popular on the continent and in some cases is a legal requirement. Generally speaking, car tyres can handle most road conditions. However, in the depths of winter, the environment down at road level can be especially harsh. Car tyres may be able to cope with the salt and grit that gives some winter grip but our alloy wheels can suffer. Many popular cars have base models that wear steel wheels. One solution is to have a set of winter tyres on these. A set of steel wheels, with winter tyres, balanced and ready to roll can be fitted when the thermometer starts to plummet. With these ‘winter wheels’ fitted, your car can take on whatever the season has to throw at it, while your pristine summer wheels can live in cool, dark storage, ready for Spring. Bear in mind that suitable wheel nuts/bolts will have to be factored into the equation.

What’s the bottom line? Assuming you need to use your car in the off season, winter car tyres are worth the investment.

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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.