Tyre Care Tips

Tyres are expensive, and of all the consumables in motoring tyres come second only to fuel in terms of cost. As with fuel consumption, the way you drive can impact on your tyre consumption.

If a tyre does develop a problem, it is useful to be able to identify what that problem is, so that you can prevent it recurring. The main problems are wheel alignment and incorrect tyre pressure. Don't just assume that when you have had your alignment checked that it will be correct; keep an eye on your tyre wear. Similarly, air pressure needs to be checked, even on recently fitted tyres.

However, your driving habits may impact on your tyre wear. It has been said that high speed driving can overheat tyres and result in the degradation of the rubber, resulting in the breakdown of the tyre. This is true, but generally your car should be fitted with tyres with speed ratings above the maximum speed of the car itself. Also, that heat build-up usually only occurs when the tyre is under-inflated. So high speed driving alone is not usually the sole reason for tyre failure - or else our motorways would be littered with cars needing tyres replaced.

Tyre wear is accelerated under hard driving, so the heavy footed driver, both on the accelerator and brake is likely to see higher tyre wear. If he adds high speed cornering he can expect to increase tyre wear even more.

Harsh braking wears down tread quicker, and it can lead to flat spots, especially on older cars with oval brake drums or uneven discs.

Inflation is key to keeping tyres in good safe condition. The air in the tyres warms up very quickly, even on a cold day, and when the tyre starts rolling it generates some heat, which heats up the air in the tyre, which expands thus creating a higher air pressure. So, when you drive a mile to the garage to set your tyre pressures, and they are at 32lbs instead of 30lbs, and you drop them by 2lbs you have actually reduced the pressure from the correct 30lbs.

Tyre pressures should always be checked at cold before you move the car - which is why tyre pressure monitoring systems that function as soon as you put the key in the ignition are better than ABS fed systems. (Most cars sold in Europe with TPMS have electronic sensors in the wheels that check tyre pressure automatically).

Incorrect tyre pressures have various outcomes. Firstly too low a pressure can result in uneven wear on the shoulder of the tyre. It can lead to overheating and tyre breakdown. It makes the suspension feel softer, and can make the car's handling sluggish and slow to react to steering input.

Too high a pressure results in uneven wear around the centre of the tread. With less contact on the road it makes wheelspin and skidding more likely, accelerating wear in the high pressure contact area. The car will have very light steering and in some situations it will be over-responsive to steering input and have a propensity to skid.

There are very few circumstances where reducing tyre pressure on the road can be recommended. Not even in snow and ice. However, if towing, or running a heavily laden vehicle it may be a requirement that the tyres are inflated to a higher pressure - see your vehicle owners' handbook for details.

Balancing your wheels is important for several reasons. Firstly, an imbalance in the wheels, especially front, will be felt as a vibration through the steering at some or all speeds. It can increase noise levels and make the car uncomfortable to drive. On the short to long term it can increase mechanical component wear in the track rod ends, ball joints, steering rack and even the wheel bearings can fail. If you have your wheels balanced after a new tyre fit or a puncture repair, be wary of any detrimental changes to your car's "feel", it may need the wheels rebalancing.

Another area that causes increased tyre wear is that of road surfaces. There isn't a great deal that the driver can do, other than be aware that on some road surfaces - even those that appear smooth, there may be a multiplying factor on tyre wear. A worst case example would be that tyres that might do 30,000 miles in the UK, might, under similar driving conditions in some areas of Norway or Sweden only do 20,000 miles or less. This is because the Scandinavian road surfaces are built to offer better surface drainage and grip due to their adverse weather conditions.

Spotting the Faults

Tyre pressure is best checked with the tyres cold, in the morning. Tyres should be inflated to the vehicle manufacturer's recommendations. However, when you buy replacement tyres you should check that they need to be inflated to the same level - some tyres operate batter at slightly different pressures.

Balancing. Any feel of vibration should be investigated, and the first stop is wheel balancing. If you are not happy with the response from one tyre fitter, use another.

Alignment is one of the bugbears. Every tyre depot claims to do wheel alignment but many just don't get it right, and that includes some very big names. So watch for uneven tyre wear and at the first sign of poor alignment or you can feel your steering pulling to one side under normal driving on a flat road get your car in and have it checked. You will be told that you may have kerbed the car, hit a pothole or similar, but have it checked by someone you can trust and who lets you see quite clearly what they are doing. If your tyre fitter doesn't use laser alignment then take it somewhere that does, and ask to see the figures.

Accounting for general wear requires tyre rotation. Most owner's manuals show the proper cycle for rotation.

Punctures can sometimes be avoided by removing objects just stuck in the tyre. Beware however, or removing penetrations from inflated tyres. You may be able to drive to a tyre depot with a nail in the tyre. This is because radial tyres have a soft butyl liner that seals around small penetrations to prevent sudden air loss. This minimises the risk of high speed sudden loss of pressure, and it allows a get to safety option. If you remove a screw or nail, the tyre will deflate quickly and you will need a roadside tyre change - not always the best place to do the job.

Tread Depth Law and The Effect of Tread Depth on Tyre Performance

Current tread depth legislation requires that car tyres must have a minimum of 1.6mm of tread in a continuous band throughout the central ¾ of the tread width and over the whole circumference of the tyre.

However, despite the law, it is generally recognised in the tyre industry that the legal limit is an extreme. Many tyre manufacturers state that they design tyres to function as well at 1.6mm as they do at 9mm (the accepted normal tread depth when new). That is a surprising statement for any tyre company to make, but some have said just that.

So, if a tyre performs as well at 1.6mm as it does at 9mm, what happens at 1.5mm? Is there a sudden drop in performance? Actually there isn't, because industry testing has shown that when a tyre reaches around 3.5mm in tread depth, the level of performance in the wet, in particular, starts to deteriorate, as does its dry handling characteristics.

The recommended point for change is accepted Europe-wide as being 3mm. So much so that ministerial cars in the UK have their tyres changed at, you guessed it, 3mm.

Why then the current legal limit of 1.6mm? There are several arguments against the change, some of which you may question. One is that the sudden change from 1.6mm to 3mm would have a serious impact on the pockets of hundreds of thousands of motorists who are already struggling to keep their cars on the road. Another is that it would require changing all the tyre moulds in use to increase the tyre wear indicator depth to 3mm. And of course Europe plays a part, as there would not be universal implementation of 3mm tread depth, requiring double standards in production and possibly in policing.

The reality is that since tyres are now a global commodity it would almost require a global adoption of 3mm as a minimum. It doesn't take an Einstein to counter the arguments against 3mm, but until the legislation is in place you can make up your own mind, scrape by on 1.6mm, or be safe on 3mm. Your choice.

But before you make that choice, it might be worth your while having a look at the video indicated at the bottom of this article. It might make you change your mind.

Truck tyres currently have a 1mm legal minimum tread depth - which many are trying to drive up to 1.6mm - for exactly the same reasons as they want to see 3mm for car tyres.

Incidentally - you may wonder why the normal new tread depth is generally around 9mm. This is to do with the slip, ie distortion in a tyre block, and its level of hysteresis. If you take an eraser and holding it vertically, draw it across a desk, you will see that it distorts before it loses grip - that is what we call "slip". If you increase or decrease the length of rubber you are flexing, the slip increases or decreases. It becomes obvious that too much slip would make a vehicle unstable. Remember that the compound is a compromise too and the ratio of slip to tread block and the compound used is all finely tuned. The industry norm is for car, van and SUV treads, 9mm.

The Impact of Tread Depth on Tyre Safety

The braking and grip performance of tyres in wet weather deteriorates considerably once the tread depth reduces below 3mm. This is because the main function of the tread pattern of a tyre is to evacuate water. As the tread depth decreases it gradually loses the ability to evacuate all water from the road surface under the tyre and the car will eventually aquaplane.

Many tyre tests have shown that the wet braking distances of a new tyre compared with a tyre with only 1.6mm of tread left on it are huge and can be the difference between life and death.

Tyre Rotation

Tyre wear rates differ depending on the axle on which the tyres are fitted and whether the vehicle is front or rear wheel drive. To extend the life of your tyres it is advisable to change tyre positions on a regular basis. Different tyre manufacturers may recommend different rotation periods, ranging from 2-6,000 miles. It is advisable to switch tyres from left to right periodically as well as from the back to the front of the vehicle.Certain high performance tyres are position specific and should not be rotated. If in doubt, contact a specialist tyre dealer.

There is some dispute over the fitting of a pair of new tyres to a car. Simple logic suggests that the car needs most traction at the drive axle. In some cases that would be true, for instance if you were constantly driving in muddy conditions and needed the grip to keep you moving. However, irrespective of the vehicle, front or rear wheel drive, or even 4x4, the typical vehicle is designed to understeer in skid conditions. That is, it ploughs forwards.Generally, backing off the power and the brakes will recover the vehicle from the skid, though not always.

By putting the grippier tyres on a front wheel drive car, it increases grip at the front, but equally increases the difference in traction/grip between the front and the rear tyres, so the rear tyres lose grip early and as a consequence the car is at risk of going into oversteer. For the average motorist oversteer usually means ending up rear end first into the field (if they are lucky). That argument can also apply to rear wheel drive vehicles, it is not about getting the power down on the tarmac, it is about keeping the rear end of the car in contact with the road.

With four wheel drive vehicles, rotation of tyres is much more important and all four tyres, ideally, should be replaced at the same time. So, location should not be an issue. If it is, the same rule applies, newer tyres to the rear.

When a Tyre Stops Working

A tyre is designed to keep your vehicle in contact with the road. When it stops doing that it is no longer working and your vehicle develops a skid. The dynamics of skidding are for another website; here we briefly look at why your tyre stops working.

The micro detail of a tyre would show its micro irregularities in its tread surface interacting with similar micro irregularities in the road surface. Rather like a lizard climbing a sheet of glass, its microscopic hairs on its feet clinging to microscopic roughness on the glass.

When the car is sitting still, the tyre is sitting still and there are no dynamic changes in that interface between two surfaces. When the tyre begins to roll though those micro interfaces create a resistance that results in grip. Close examination of the tread block will show that as force is applied by accelerating (or cornering) the tread block distorts allowing the tyre casing to shift slightly in relation to the tread interface with the road. This distortion of the tread block is called "slip". The amount of slip in the tread block is determined by its size and its compound. A small block will have more slip than a large block, a deeper block more than a shallow block. And the amount of "slip" is also determined by how much the compound will allow itself to be distorted.

Whatever the compound and the tread depth, once the slip has reached its maximum level, the tyre casing then distorts, this happens both in acceleration and deceleration and also in cornering.

When the tyre casing reaches the limits of its distortion, the tyre has nothing left to give and, suspension settings accounted for, the tyre loses its grip at the point of micro interface with the road and the tyre skids across the tarmac.

It is highly unlikely that any normal driver would ever notice the tyre actually deforming. However most drivers will experience from time to time what happens when the tyre stops working: The skid.

There is one area where this is of critical importance in tyre choice. Most car drivers select tyres that suit their vehicle and its everyday use. There is one exception. The SUV/4x4 driver. There is a propensity amongst some 4x4 drivers to opt for the biggest, chunkiest tyres they can find. If they actually spend a great time of their driving off the road and in conditions that require those chunky tyres then there is no problem with that selection. However, when the vehicle is on the road for the majority of its life there are safety issues to be considered.

Those big chunky mud-plugging tyres may work well in the mud, and may even give comfort in snow, but, they offer a false sense of security on asphalt in the wet, and can add metres to the stopping distance, even in the dry. Not really important unless that extra metre or so happens to be occupied by another vehicle, or a pedestrian.

Those issues on stopping distances also apply to car and van tyres. Though the visual differences are not always so obvious. In tyre tests there can be varied results, tyres can be good in one area of measurement and not in another. So, when making your tyre choice do listen to the experts, read any tyre reports you can find. Most reputable tyre fitters have copies of test reports lying around. And remember, the most important metre in your braking distance is the very last one.

Tread Patterns and Profiles

Most people don't realise it but tyres are fashion accessories. No, you won't get away with giving your wife or girlfriend a pair of 255/35R16 as a set of earrings, but, when a car is designed, an integral element in the designing of a car is to include the tyre width, profile, diameter and pattern as a core factor in the design.

Whilst the tyre will always be required to do its job, of providing grip, traction, adhesion and being an element of the car's suspension, it nowadays also has to look good. It has to look good on the car and in the showroom. That makes the car tyre a fashion item.

It is impossible to tell from looking at one tyre tread whether it works better than another tyre of a similar style. It used to be pretty simple, a question of bars and lugs, and blocks. Now we have a different approach to tyres and how they work, and that means that things can get very confusing for the tyre buyer: Though they need not be.

Back to Basics

Very early on it was realised that tyres worked better if they had a tread pattern. Designs were arbitrary and Dunlop actually produced a tread pattern that left an imprint of the brand name Dunlop as it ran over soft surfaces.

There is a history of tread design that can be followed through the years. But essentially, there was the bar or lug type tread with solid lugs across the tyre tread traction. Then there was the circumferential channel pattern that gave lateral grip. A combination of the two basic patterns led to the block type tread pattern that survives in many tyre patterns today.

Interestingly, all three early type patterns are still available for specific uses today. However, modern motoring's focus has changed slightly, and whilst grip and traction are still core values, today we are more focussed on wet and dry handling and braking ability.

The best tyre on dry, level road surfaces is a slick. However, road surfaces are rarely dry, and the roads that we drive on every day - even the smoothest of them, are a far cry from racetrack surfaces, and as a consequence the road tyre needs to be harder wearing, so it has a firmer compound (generally), it has to have grip and traction, and it also needs to resist aquaplaning.

The tread on a modern car tyre is considered to be a water pump, designed to express water from between the contact patch and the road surface. How it manages to do that is the subject of many millions of pounds of investment for each of the leading tyre manufacturers.

For the tyre buyer, generally speaking, the greater the number of channels in your tyre's tread the greater its ability to pump water away. However, the design of those channels may make the tyre more or less efficient. A wide tyre may require a different approach to water dispersal than a narrow tyre. So that trendy looking tread you find on a Porsche tyre, may not be suitable on a narrow tyre fitted to the family saloon - and vice versa.

A recent trend has been the development of high performance tyres with circumferential grooves and tread bands that offer different characteristics across the tread of a tyre - these tend to be asymmetric and directional. Another trend is for the "single tread" where the tread pattern is such that the "land" area of the tyre never breaks contact with the road and the "sea" area (the troughs) channel water away from under the tyre. Both these tyre patterns are claimed to be quieter than block type tread patterns.

Noise Travels

Tyre noise is a big issue nowadays. Cars have become so quiet that often the loudest bypass noise comes from the induction system and the tyres. Tyre pattern can make a great deal of impact on the noise a tyre makes. The noise actually comes from the leading edge of the tyre block making contact with the road surface, and the trailing edge snapping back as it breaks contact with the road. So, the more blocky a tyre is, the noisier it will be: Perhaps something to consider if road noise is intrusive in your car. Winter tyres are always going to be louder than their all season counterparts because they are blockier and have many more sipes (thin slices in the tread block) to give better grip and pump more water away.

Noise is a comfort issue and comfort is a big issue for vehicle manufacturers and tyre makers. The tyre is an integral part of your vehicle's suspension. It absorbs the first and all minor impacts with variations in the road surface. It softens the ride and suspension settings at the point of vehicle design and manufacture take into account the Original Equipment (OE) tyre design. So, when replacing your car's tyres it is always a good idea to buy, at least with the first replacement, the same tyre as is fitted OE. By the time your car needs its second or third change of tyres the original specification of the suspension will have been diminished by wear and tear and it becomes feasible to fit non-OE tyres without any real impact on the car's feel since it will rarely feel like new by that stage anyway.

Comfort Profile

Comfort is also impacted by profile. Now this is where we are all becoming fashion victims. Cars are coming with ever larger wheels and lower profile tyres. The technical reason is that the larger wheels allow the manufacturers to fit larger brakes, and therefore make the braking of the car more efficient. In utilising larger wheels the car requires thinner, lower profile tyres to stay within the style and design characteristics of the vehicle, and also within the ability of the tyre industry to produce suitable tyres, and the aftermarket to deal with them. A vehicle that leaves the factory with 18 inch rims and 20 profile tyres will have had its suspension designed to deal with the harsher ride created by the low profile tyres. However, if a car comes with 70 series on a 15 inch rim and the owner changes to 18 inch and 20 profile (as an example), he will definitely have a harsher riding car as the lower profile tyre has a stiffer, less supple sidewall and will absorb far less of the surface undulations than the car fitted with the 70 profile.

So, unless you drive on excellent road surfaces for most of the time the low profile tyre is potentially harsher. If you fit low profiles to a car not designed for them, you will gain in looks (perhaps) but suffer in the ride. Your handling on smooth roads will improve, but on poor roads and potholed surfaces your handling will only be of use to you as you dodge the rim smashing voids in the asphalt.

If you want to know more about tread design then you will be best served reading the product news and the tread descriptions.

Low Profile Tyres - Performance Characteristics

Compared to conventional passenger car tyres, low profile car tyres have greater width ratio to cope with the demands of higher performance vehicles.

The key performance advantages are:

• Improved handling and grip
• More traction and braking power

Disadvantages are:

• Increased road noise
• A harsher ride
• Less resistance to aquaplaning due to the amount of rubber on the road

Run Flat Tyres

All the latest technology brings the modern motorist the run flat tyre - by whatever name you wish to call it - a tyre that you can drive on when the pressure has dropped.

Actually, it isn't new technology at all, just more modern interpretations of old ideas using modern materials. The first patent for a pneumatic tyre was taken out by Robert W. Thomson in 1846. Thomson called it the Aerial Wheel, and one of his patents included a tyre with multiple inner tubes - another of his suggestions was to fill the tyre cavity with horsehair or sponge to support the tyre and prevent it collapsing onto the rim. In essence both these methods are in practice today in one form of run flat tyre or another.

If that isn't enough to convince that run flat technology isn't new, then let's go back to a small conflict in Europe in the middle of the last century. The War Office supported research into self supporting tyres. In one version the air in the tyre was replaced by a rubber ring with voids in it - This was the PT Support tyre and it was expensive and heavy, but it worked. In one report a raid on enemy lines was subjected to three hours of air attack. Three of the vehicles were set alight, and one put out of action by gunfire. The remaining three all drove 70 miles back to safety with punctures in every tyre.

There was also a run flat that used thick sidewall construction and a rim filler to retain the beads in place. This was revisited in the 1960's with the Tyron band - still available and selling well around the world.

Today's modern run flat tyres are essentially designed around those original principles - though perhaps the tyre manufacturers might disagree.

There is the Goodyear Run-on Flat - this is a tyre which is designed with stiffer than normal sidewalls, which use a temperature resistant compound to fend of destruction by heat generated by running flat.

There is the Michelin Pax system, which uses a well filler and support system to keep the tyre on the wheel and prevent the tyre from being destroyed by the rim in the event of a flat tyre.

Continental has the integrated wheel system, IWS, a stiffer sidewalled tyre combined with a rim and bead system that retains the tyre on the wheel.

And in truck tyres there is the Greatec system which has a tube inside the tyre that when the tubeless tyre is punctured, the tube fills the void and supports the tyre in a "get-to-safety" role.

The key aim in all of these systems is to keep the tyre on the rim for as long as possible and to delay the destruction of the tyre, allowing the driver to make his way to a place of safety.

The one thing all these tyres have in common is the need for a tyre pressure monitoring system (TPMS).

TPMS is essentially a method of monitoring the level of pressure in a tyre and alerting the driver if there is a loss of pressure. Allowing him to reinflate the tyre or have the tyre swapped (usually a professional job as TPMS and run flat tyre equipped cars rarely have a spare tyre.

There are two basic types of TPMS, one is fed data by the vehicle ABS and traction control system which can identify a differential in wheel rotation - a flat tyre turns more slowly than an inflated tyre, so that differential can be used to flag up a pressure difference. The disadvantage of this system is that the vehicle needs to be moving for it to operate.

The other system uses chips in the wheel well of the wheel and tyre assembly to monitor pressure and report to the on board computer. This gives an instant pressure reading and can even be used to limit the speed of the vehicle. The minus point here is that these sensors mean that extra care has to be taken when fitting tyres, possibly even special equipment. They are also expensive to replace if damaged.

Most European vehicles with TPMS are manufactured with wheel mounted version.

Tyre Choice by Season

Summer Tyres The main characteristic of the summer tyre is excellent driving and braking performance on both dry and wet roads, in temperatures above freezing throughout the spring, summer, autumn and winter. A simple block-shape tread pattern ensures the tyre's contact area remains as rigid as possible, ensuring maximium grip at all times by optimising friction with the road surface. If the tyre has any special indication on it, it means this tyre is for summer usage.

Winter Tyres This type of tyre is suitable for snow and ice covered roads. The tread pattern features a heavily siped, fine-block design with grooves that are deep and wide, providing excellent driving traction and braking performance on winter road surfaces. The tread rubber used in winter tyres provides good friction characteristics and suppleness even in low temperatures. At present, winter tyre design is focused toward braking performance and driving control on icy roads. Recent developments in tyre pattern design and rubber technology have greatly improved winter tyre performance.

All-season Tyres These tyres are designed to be used all year round to save having to change the tyres to suit the season. All-season tyre patterns are more complicated than those of the summer tyre because of the longer block-edge for winter usage. More sipes appear in the all-season tyre than summer tyre to improve the braking and driving performance by maximising the effect of edge. It is important to remember that in regions where winter temperatures are very low and heavy snow falls are frequent, braking performance will rarely be 100 percent so it is safer to use winter tyres. All-season tread designs will provide good all-around traction for varing road conditions, but still provide good treadwear and tyre noise characteristics.

Information courtesy of Kumho.

Tyre Ageing

All tyres undergo an "ageing process" due to exposure to the environment even if they have never been used or have only been used occasionally.

This phenomenon is caused by a number of factors including:

• the process of aftercuring, whereby the tyre continues to culcanise very slowly. This is caused by factors such as light, heat and movement and makes the tyre become stiffer and more brittle.
• oxidation involving oxygen and ozone from the atomosphere causing hardening of the rubber and reduced elasticity
• plasticisers drifting from the tread area to other parts of the tyre, resulting in increased hardness.

Tyre ageing can be minimised by proper storage in a cool, dry environment, away from direct sunlight and away from electric motors (such as air conditioning units) or other sources of ozone.

Interestingly, tyres, which are infrequently used or not used at all, age and crack quicker than tyres, which are in regular use. For this reason tyre manufactureres tend to recommend including the spare tyre in any tyre rotation process. Spare tyres, which are old should be used with caution. If in doubt, get the tyre checked by a tyre expert.

Caravan tyres or tyres on other vehicles that are parked for long periods are particularly subject to ageing and owners of these vehicles are generally advised to jack the weight off the tyres and cover them so that they are not exposed to sunlight.

How long before tyres become too old?

This is rather like asking "how long can a piece of food be kept before it goes off?" and therefore it is something on which the tyre manufacturers have some difficulty in agreeing. No expert can definitively say how long a tyre will last as a tyre's life depends on many factors such as the type of rubber compounds used, temperature, usage, humidity etc.

However, Bridgestone's website points out that many tyre companies, including Bridgestone, offer manufacturing warranties on tyres for 5 years from the date of manufacture, which has resulted in many vehicle manufacturers advising against the use of tyres that are more than six years old.

The British tyre industry has not been able to agree on a definitive statement relating to tyre ageing. As a result of this the National Tyre Distributors Association is understood to be preparing a members' advice document for release in early 2008, which is said to be based on a similar leaflet produced by the German tyre dealers association (BRV)

The BRV's advice on the subject is, in fact, based on a joint statement dating back to 2001 and prepared in conjunction with Bridgestone, Continental, Dunlop, Goodyear, Michelin and Pirelli, which advises dealers to make sure tyres are not sold, which have a production date that lies more than 5 years in the past.

In terms of tyres already fitted to vehicles the BRV advises a maximum age of 10 years for car tyres and 6 years for tyres fitted to caravans, trailers of other vehicles likely to be standing around for long periods.

How do I check the age of my tyres?

All tyres are marked with a serial tyre identification number. The last three digits (for tyres made before 2000) or the last four digits (for tyres manufactured after 2000) denote the week and year of manufacture. For example, a tyre carrying the number 3506 denotes a tyre manufactured in the 35th week of 2006.

Wheel and Tyre Fitting Check List

Before fitting tyres on aftermarket wheels check:

1. that the stud/bolt hole pattern is correct. 2. that the wheel fits freely onto the hub without interference and that there are no screws, rivets or retaining clips which may interfere with a firm, flat location of the hub against the wheel mounting face. 3. that the wheel rotates freely and truly on both front and ear hubs

4. when fastened to the hub, that no part of the wheel can make contact with the brake drums or calipers or any other part of the steering or suspensionCheck nuts and bolts. Correct fitting is vital. Be sure1. that the thread form is correct (fit nuts without wheels).2. that the nut/bolt seating is correct.3. that the stud length is adequate for minimum thread penetration of approximately 1 x stud diameter and not too long as to permit "bottoming" of the stud in the nut.4. that the threads are rust free and not over-lubricated5. when sleeve nuts are used, that the shank diameter is correct and that the bearing washers are always used.When fitting the tyre

1. make sure that the rim size is compatible with tyre size. 2. be wary of scratching the protective lacquer coating (on aluminium wheels and some chrome wheels). Aluminium corrodes very easily once exposed to atmosphere, water or chemicals. 3. where possible always use the adhesive type of balance weight, as these help to avoid scratching of the wheel finish.

Finally Check

1. that the wheel and tyre assembly does not contact any part of the suspension or body work by carrying out full 'bump' and lock to lock tests before driving the vehicle away from the fitting bay.Do not take risks. Wheel security is vital. Check with experts if you have any doubt.

(Editorial supplied courtesy of Wheelwright Ltd)

Torqueing Nuts

If people give little consideration to their tyres, apart from price, then how much less attention do they give to their wheel nuts/bolts? Most people will just be happy if their wheel nuts are tight enough to keep the wheel on the car - and those nuts simple cannot be over-tight, can they?

Well, yes they can.

The issue of a loose wheel nut is pretty self- evident. If one wheel nut on a set is loose, then it puts additional strain on the remaining wheel nuts. Now, for some reason, that additional strain only very rarely causes a wheel nut to tighten itself.

It usually results in a loosening. For most drivers that becomes a very obvious danger as the loose wheel vibrating on the hub transmits that vibration and possibly impacts on handling and steering control, so the driver will usually identify a problem and have it fixed. 

With an over tight nut there is no evidence of a problem until things go wrong, and go wrong they can. 

The first problem with over tightening a wheel nut is that the chances are they will all be over tightened, so on a wet and windy night when you get a puncture you can't get the wheel off and you have to wait for the AA or the RAC or whoever to come and sort a flat tyre. A repair most folks could do in less than the time it takes the fitter to arrive. That though is a minor problem. 

The next issue is that when a nut tightens on a stud it can, if over tightened, stretch the stud. In itself not an issue, but the stretching of the stud weakens it. It is unlikely that it will weaken it below its breaking point, but repeated over tightening can do. The stud in the process work hardens and can shear.

If one goes, so too might a second; that increases the likelihood of a third or fourth coming off. If you think that unlikely, then consider that trucks from time to time lose wheels from trailers when all the studs shear at the same time!

Alloy wheels are not quite as forgiving as steel wheels, and over tightening the wheel nuts can cause damage to the wheel centres, creating stress points that can lead to fracturing at worst, damaged wheel nut facings at best.

If your car uses wheel bolts rather than nuts, then you still have the same issues, plus the over tightening of the hardened bolts in the hub may strip the threads or even crack the hub. 

Every tyre shop should have a reference chart to which they can refer for wheel torque settings. If the fitter runs the wheel nuts/bolts on with an air gun and hands you your car back, ask him to check the torque settings.

However, remember that if the air wrench has set the torque higher than it should be, using a torque wrench will not identify that the nuts are over tight.

Torqueing Nuts - The Trade Side

The issue of the correct torque settings for wheel nuts raises its head from time to time. One popular motoring magazine suggested that a majority of tyre depots did not correctly torque wheel nuts and that this created, at best, a nuisance for drivers, at worst a safety issue.

To be fair torque setting is not just an issue for the tyre trade: it is an issue throughout the motor trade and is exacerbated by the increasing use of air wrenches for every nut and bolt task. The issue is less one of training, but rather one of monitoring. Companies may train their staff all they wish, but at the end of the training many staff go back to their depots and carry on doing it the same old way. We have all been sitting in on training sessions and said, or heard said, "That's all very well in theory, but in practice..." 

Question?

How can the tyre trade improve its performance in this field, monitoring the effectiveness of the training, and ensuring that the lessons taught in the classroom are followed up in reality? That applies equally to jacking up cars, repairs, fitting, balancing as well as torque setting the wheel nuts.

It is worth noting that in the caravan sector many of the specialist service centres will mount wheels on the caravan and manually tighten the wheel nuts, but will not release the caravan to its owner until he/she has personally tightened the wheel nuts. Thus relieving the service centre of liability should the wheels then fall off! 

Is there a need for industry backed performance monitoring?

Mystery shoppers are all well and good, but if the customer doesn't know that the quality of the work being done is inadequate, how can he tell? How can the mystery shopper tell? If a nut is over-torqued by the air wrench in the first place, checking with a torque wrench afterwards will only give a minimum reading. The wheel nut could be 10-15-20 Nm over tight, checking with a torque wrench will not readily show that. 

Dave Smith, Chief Training Officer at Michelin's Stoke Training Centre agreed that it was his job to train to the highest standards in the classroom, but out in the field it becomes an operational management issue. Asked how checks could be run at depots he suggested that following the policy of one particular chain the fitter who mounted the wheels would set the torque and fit the wheels but the job had to be signed off by a senior technician or depot manager. 

James Bailey handled our enquiry at Hi-Q and he agreed that monitoring was difficult but added, " Hi-Q has a national policy of checking torque settings but always recommend that the motorist checks the wheel nut torque setting after a few hundred miles." 

On the truck-side Hi-Q use a Torque Right gauge to ensure that wheel nuts are tightened to the correct setting. It is something that could be looked at for the car market too. 

ATS Euromaster, as one might expect, train staff to the highest standards, but once again when the staff leave the classroom how do the standards get monitored? 

At the depots wheel nuts are run-on with an air wrench and the torque settings, taken from a wall chart guide, are set by torque wrench. It is policy at ATS Euromaster that the senior technician at the depot should check the torque setting of the wheel nuts on every vehicle before it leaves the depot.

However, in reality it may well be that this ideal is not always attained. There is though a further check in place. There are quarterly competency checks run by the depot managers on all staff in all areas of skill application. For truck fitters there is a specialist five day training course designed to ensure that they are fully competent in mounting tyres and wheels to commercial vehicles under all conditions. 

National told Tyres Online, "National Tyres and Autocare has strict procedures in place to ensure that any work carried out, including tyre fitting, is performed to the highest standard. Any branches or individuals identified as not following these procedures could face disciplinary proceedings." 

All the fast fit people we spoke to were adamant that they were doing their best to check settings. However, the one question that no-one could adequately answer was, if the settings are too tight, how can the supervisor be aware of this? Also, if the nuts have already been over-torqued by as much as 50 per cent the threads will already have been damaged and the studs stretched. Will the retailer then replace the studs and nuts free of charge? Will they offer redress for potential damage to alloy wheels? 

In any event, how does the client know what the correct torque setting for the wheel nut should be? It isn't in any owner's Hand Book Tyres Online has seen. One suggestion is that the torque setting for the wheel nuts should be displayed on a sticker on the door pillar alongside the tyre pressures guide. Then again, would that not just be another piece of information for the motorist or the mechanic to ignore?

There is no denying that this is a tricky question. It is also a wider subject than just wheel nuts. If the tyre trade can find a workable monitoring system to ensure that the correct standards are being met then it may well be taking a lead for other automotive servicing sectors to follow.

Sidewall Markings

On the sidewall of a tyre you will find various codes and markings. The list below aims to simplify the coding system and allow you, the user, to understand the valuable information imprinted on the sidewall.

Tyre Sizes

Tyre sizes are made up of a number of different numbers and letters. For example tyre size 175/70 R 13 82 T is made up of the following information:

175	The tyre section width in millimetres (That is the width of the tyre tread)
70	The aspect ratio in % (the height of the sidewall divided by the tyre's width)
R	Denotes the tyre's construction type - in this case it's a radial
13	Rim diameter in inches
82	Load Index
T	Speed Rating

Tyre Age

Tyres carry a three digit age code on the sidewall indicating the month and year of manufacture. For example 129 means the tyre was manufactured in December 1999.

Other Markings

M&S - Identifies Mud and Snow tyres

DOT Codes - Coding satisfying the requirements of the US Department of Transportation contain a mixture of letters and numbers such as DOT DVDE MTA 129. These identify the place of manufacture.

E-Marks - Tyres for sale in the European Community must carry an E -Mark in accordance with ECE Reg 30 - eg E4 027550.

Load Indices

Drivers should be aware that these ratings exist to protect the public from the possible outcome of overloading a tyre. Also, that these load ratings apply to a properly inflated tyre.

Overloading a tyre - either by carrying more weight than it is designed to carry, or by running at a lower than specified pressure, can cause heat build up that can destroy the tyre. Even at low speeds a blow out can be fatal.

It is a breach of Construction and Use Regulations to run on overloaded tyres or tyres with the wrong load rating. The load-index figure imprinted on the sidewall of the tyre denotes the maximum load capacity of a tyre when driven at maximum speed.

A list of load indices and maximum weights is give below:

Li	kg	Li	kg
65	290	94	670
66	300	95	690
67	307	96	710
68	315	97	730
69	325	98	750
70	335	99	775
71	345	100	800
72	355	101	825
73	365	102	850
74	375	103	875
75	387	104	900
76	400	105	925
77	412	106	950
78	425	107	975
79	237	108	1000
80	450	109	1030
81	462	110	1060
82	475	111	1090
83	487	112	1120
84	500	113	1150
85	515	114	1180
86	530	115	1215
87	545	116	1250
88	560	117	1285
89	580	118	1320
90	600	119	1360
91	615
92	630
93	650

Speed Ratings

All tyres carry a speed symbol in the form of a letter indicating the maximum speed for which the tyre is intended. The table below shows which speed goes with each letter.

Speed symbol	Maximum speed km/h	mph
N	140	87
P	150	93
Q	160	99
R	170	106
S	180	112
T	190	118
H	210	130
V	240	149
W	270	168
Y	300	186

It should be noted that these ratings are important in that it is a breach of Construction and Use regulations to run on tyres that are below the specified Load Index, it may also be dangerous.

Additionally, if your car is fitted with W-rated tyres, and you tow a trailer, then in the UK that trailer may have T-rated tyres (if applicable), but in France your trailer tyres' rating should match that of the tow vehicle.

Aspect Ratio

Aspect ratio is the ratio of a tyre's width to it's height. A 70 series tyre, therefore, is a tyre whose height is equal to 70% of its width. Lower Profile Tyres hence have lower series numbers.

People upsizing to lower profile tyres should be aware that they will change the nature of their vehicle's handling and comfort.