DAMAGE CONTROL
Understanding and tracking tyre damage can help you save money
EXTRA LIFE
Make your tyres last longer by ďŹ ghting the causes of irregular wear
ISSUE 3 AUGUST 2009
Bridgestone Environmental Mission Statement To help ensure a healthy environment for current and future generations... We, the Bridgestone group, are committed to achieving ever higher levels of society’s trust and employee pride. We consider the environment and health and safety matters to be integral and important parts of all our business activities, as we work towards a sustainable society.
Environmental Perspective 3 Areas of Environmental Progress, 2 Core Strategies for Growth Products and Services We help our customers conserve natural resources through our continual improvement of products and services.
Community Activities
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Products and Services
Community Activities
TEAMS TEAMS (Total Environmental Advanced Management System) is designed to function as Bridgestone’s Global System and the basis of all of our activities to ensure continual environmental improvement throughout the world.
Operations Our concern for the environment in material selection, production processes and logistics continually improves our environmental performance.
Operations
Environmental Communication
Environmental Communication
TEAMS
We communicate openly and honestly about our shared environment.
BRIDGESTONE
| president's message
president’s message Undoubtedly, the situation surrounding us has changed drastically since our last issue. The financial crisis that originated in the US and Europe has had a significant impact on the global economy. Under these circumstances we believe that the best approach is to reemphasise the importance of business basics and principles. Since the business environment keeps changing, we strive to incorporate those changes into an enhanced management system. In October 2006, we established our strategic business unit for the Middle East & Africa to be closer to our customers in the region. This has enabled us to react quickly to changes in the market and customer requirements, with superior quality products and services. Despite the challenging conditions, we see this as an opportunity to further strengthen our services and support to you, as one of our valued customers. We realise that tyres form a major part of your
operating expenses; this magazine tries to help you to use and maintain tyres in the correct manner, thereby extending their service life and reducing your down time and operating expenses. At the same time, our efforts in achieving those objectives are complemented by our commitment to corporate social responsibility. We consider environmental, health and safety matters to be integral to our business activities. I hope that you enjoy reading this issue and that you are able to utilise the information within.
Shoichi Sakuma President Bridgestone Middle East & Africa FZE
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BRIDGESTONE
| contents
6
14
18
22
contents Helping tyres last longer
6
Understanding and fighting the causes of irregular wear DAMAGE CONTROL
Understanding and tracking tyre damage can help you save money
EXTRA LIFE
Make your tyres last longer by fighting the causes of irregular wear
ISSUE 3 AUGUST 2009
real QUESTIONS real ANSWERS Bridgestone Middle East & Africa FZE P.O. Box 16813, Jebel Ali Free Zone Dubai, UAE For correspondence with this publication please write to us through our postal address or by email to realanswers@bridgestone.ae. An electronic version of this publication is available at www.bridgestone-mea.com
Cutting down on carbon
10
Fuel economy can help to save money and the environment
Cracking the code
14
Demystifying the codes on a tyre’s sidewall
Damage control
18
Why it is important to identify and track tyre damage
Mechanical care: prolonging tyre life
22
Leaf suspension and brakes can affect tyre life Nicholas Publishing International FZ-LLC
P.O. Box 500573, Office 704 Executive Heights, Dubai, UAE Tel: +9714 4243600 Fax: +9714 3908022 For editorial enquiries, contact Oliver Ephgrave, Editor oliver.ephgrave@npimedia.com Tel: +9714 4243600
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august 2009 real questions real answers
Fit to last
26
How properly mounted tyres will last longer
Feeling tyred Doctor’s advice on how to combat driver fatigue
30
BRIDGESTONE
| foreword
26
22
FOREWORD In these challenging times, every type of business is looking to save money. Fleets are no different. For this reason, we decided to make ‘economy’ the subject of our third issue of Real Questions Real Answers. We believe that it is important for every fleet to go back to basics and follow the fundamental steps to make tyres last as long as possible. We have tried to cover the main cost-related issues that are relevant to our readers in the Middle East and Africa. Our opening article explains how to prolong tyre life by reducing the effects of irregular wear. This is followed by a piece which illustrates how reducing fuel consumption will benefit your bank balance and the environment. Also contained within the issue is an article which demystifies the various tyre codes, a piece
on the main forms of tyre damage, as well as a feature on how suspension (leaf spring) and brakes can affect tyre life. Our final two articles cover the importance of proper tyre mounting and ways to combat driver fatigue. As always, we welcome your feedback and questions. This magazine is a mouthpiece for the industry, so please send your queries to realanswers@ bridgestone.ae and we will try to cover them in our forthcoming issues. Needless to say, many of you will be facing tough questions at the moment and I hope that this issue provides some Real Answers.
Hiroshi Nakanishi, Director Technical Service & Commercial Tyre Marketing, Bridgestone Middle East & Africa FZE
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AUGUST 2009 real questions real answers
| irregular wear
BRIDGESTONE
| IRREGULAR WEAR
HELPING TYRES LAST LONGER A fleet that prolongs the life of its vehicle’s tyres will enjoy substantial savings. The key is in understanding and reducing the effects of irregular wear. WHAT IS MEANT BY IRREGULAR WEAR? The tread area of a tyre gets worn due to friction with the road surface. If the tread is worn evenly then this is known as ‘regular’ wear; if it is worn in an uneven manner then it is suffering from ‘irregular’ wear. Technically, there is no such thing as regular wear as a degree of irregular wear exists in every tyre. However, a tyre that has been worn in a comparatively regular fashion will cover far more kilometres than an irregularly worn tyre. Therefore, a tyre that has been irregularly worn will increase the purchase cost for the customer. TREAD
real QUESTIONS real ANSWERS AUGUST 2009
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BRIDGESTONE
WHY DOES AN IRREGULARLY WORN TYRE INCREASE THE PURCHASE COST? First of all, if the tread is significantly worn it will compromise road safety and will need to be removed and replaced. Bridgestone recommends a tread depth of 3.2mm as the safe removal limit for truck and bus tyres. However, in the case of a retread tyre, the removal limit may vary depending upon the operating conditions. Therefore, if a tyre has to be removed at an earlier stage because some portions have worn to 3.2mm or below at a faster rate than other areas, then the customer will have lost some usable tread. Every millimetre of tread that is lost is significant in terms of cost.
REGULAR AND IRREGULAR WEAR COMPARISON
HOW SO? It depends on the nature of a fleet’s operations and maintenance but generally speaking, each millimetre of tread will last for thousands of kilometres. Let’s look at an example (above right). If a tyre that has been removed due to irregular wear has an average of 6mm remaining tread depth, then the customer has only utilised 8mm of a possible 10.8mm; this means that 2.8mm of tyre life has been wasted. In other words, the customer has lost 26 percent of the tyre’s lifespan, and the potential to save 26 percent of the total tyre purchases.
POTENTIAL SOURCES OF IRREGULAR WEAR
SO IT IS IMPORTANT TO ASSESS THE TYRE AFTER IT HAS BEEN REMOVED? Yes, it is important to assess and analyse your tyres at the removal stage so that the appropriate action can be taken to rectify the cause of irregular wear. In addition, preventive maintenance of the vehicle and tyres is crucial for limiting irregular wear in the first place. HOW SHOULD A TYRE BE ASSESSED AFTER REMOVAL? The most accurate method is to measure the average amount of wear on the tread. But for control purposes on irregularly worn tyres, we would suggest that you measure the average amount of wear on the portions that do not have irregular wear. This is not an accurate method to determine how much tread depth has been utilised or unutilised. However, it is useful from a broader perspective, in order to assess whether there is scope for prolonging tyre life by reducing the effects of irregular wear. It should be noted that the control limit for tread depths (the ideal limit for removal) will vary depending on the operations of the vehicle. The limit can be optimised over time once the preventive measures against irregular wear, for the vehicle and tyres, have been put into place.
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| IRREGULAR WEAR
AUGUST 2009 real QUESTIONS real ANSWERS
CUSTOMER DATA
IDEAL CASE
IRREGULAR WEAR CASE
A
TREAD DEPTH OF NEW TYRE
14mm
14mm
B
USABLE TREAD IN AN IDEAL SITUATION
10.8mm
10.8mm
C
TREAD DEPTH AT REMOVAL STAGE
3.2 mm
6mm
D
UTILISED TREAD (A - C)
10.8 mm
8mm
E
UTILISED TREAD INDEX [D / B]
100%
74%
ROAD HAZARDS
ALIGNMENT
Rib Tear
EQUIPMENT
Thrust Angle-Drive
Tread Cut
Spread Axles
Thrust Angle-Trailer
Stone Retentions
Camber
Brake Lock
Component Placement Trade Contour Tread Pattern Uniformity
MANUFACTURING
Worn Parts
Ackerman Angle
Equipment Damage Missing Sipes
Worn Shocks
Toe
Brake Chip
Tread Splice
Misadjusted Air Bags
Bent Parts
Tandem Scrub
Set Back Axles
Inflation Pressure
Road Crown
Dual Matching
Road Surface
Uniform Mount
Operation
Balance Tyre Rotation 5th Wheel Position
MAINTENANCE
WHAT CAUSES IRREGULAR WEAR? A lot of factors contribute to irregular wear, some of which are controllable and others which are not. Irregular wear can be caused by vehicle layout or defects, operating conditions, vehicle alignment issues, improper maintenance, road hazards and manufacturing-related problems. A comprehensive overview of the causes is contained in the chart above.
Weather Loads Terrain
I R R E G U L A R W E A R
CONDITIONS
TYRE FOOTPRINT
Unloaded
WHY DO THESE SOURCES RESULT IN IRREGULAR WEAR? Any change to a tyre's optimum footprint (right) will affect the way it is worn. Modern radial tyres are designed to distribute an equal load across the portion of the tread which is in contact with the road surface, providing the tyre is correctly inflated. In an ideal scenario, if a tyre is rolling in a uniform manner then it will wear evenly. However, the factors outlined in the chart can result in a tyre rolling in an abnormal manner;
Loaded
specifically, the tyre may drag, slip, bounce or skip. Every time the tyre surface makes contact with the road, the abnormalities in the footprint will gradually result in irregular wear. Let's put this in perspective. A typical 1200R24 tyre rotates around 274 times in one kilometre. If a tyre travels 100,000 kilometres, then any part of the tread will hit the road 27.4 million times!
BRIDGESTONE
| IRREGULAR WEAR
THEORETICAL CALCULATION FOR ROTATION 27.4 million rotations 274 rotations
1 km 100,000 kms
HOW CAN IRREGULAR WEAR BE PREVENTED? It is extremely difficult to completely eliminate irregular wear, as there are so many different causes. However, it is possible for fleets to limit the impact of irregular wear by taking preventative measures. Fleets should pay attention to their vehicles’ alignment, suspension and rotating parts, and ensure that tyres are mounted correctly. Drivers should avoid rash driving, and try to make longer turns. Inflation pressure is of paramount importance since it is one of the major causes of irregular wear and other tyrerelated damages. Maintaining the correct level of inflation pressure is the easiest, cheapest and most effective measure for reducing irregular wear and ensuring maximum tyre life. Unfortunately, this simple procedure is often overlooked or neglected.
Tyre life
Long
Short Under inflated
Properly inflated
Over inflated
Irregular wear tends to be more noticeable in less severe operations where the tyre lasts for a long time; for example, if a tyre is run continuously on highways. In operations such as city usage, which involve a lot of turning and braking, the tyre may wear out so quickly that irregular wear will not be as obvious.
WHAT SHOULD BE DONE IF A TYRE DEVELOPS IRREGULAR WEAR? Once a tyre develops irregular wear it cannot be reversed, but it may be possible to prolong its life by rotating the positions of the tyres. Rotation as a routine preventive maintenance practice can reduce the typical irregular wear patterns that are found on different axles. There are a few golden rules to follow when rotating. Firstly, the tyres should be rotated so that they roll in the opposite direction (except in the case of unidirectional tyres). You can rotate between front or free-rolling and drive axles. It’s worth noting that a tyre should be rotated more frequently in the initial periods of wear. This is because there is a higher degree of tread squirm and irregular wear when the tread depth is greater. ARE THERE DIFFERENT WAYS TO ROTATE TYRES? Yes. The most common form of rotation is the cross rotation pattern. This involves swapping tyres from one side of the vehicle to the other. Tyres on tandems are also swapped between axles. Another rotation pattern is called ‘move back’. This is applicable to fleets that use very deep drive radials, like the Bridgestone M718/ M729. This method can also be used for all-position tyres such as the G582. Once the drive tyres are worn down to a certain tread depth, they can be moved back to the trailer positions. The move back pattern can get many more useful miles out of the tyres.
Cross rotation
Move back rotation
CAN ROTATION HELP TO WEED OUT IRREGULAR WEAR CAUSED BY MECHANICAL PROBLEMS OF VEHICLES? If the irregular wear is caused by a mechanical defect such as a misalignment, loose bearing or suspension issue, then there is not much that can be done, other than rectifying the cause of the irregular wear. Of course, each situation needs to be judged individually. Sometimes it may be necessary to adopt a temporary countermeasure, if major irregular wear damage to the tyre has occurred. For example, if the left portion of the tyre is being worn at a faster rate that the right portion, then reversing the direction of rolling in that same defective position will transfer the irregular wear to the right portion. The irregular wear forces will still be present, but the overall wear may be equalised. This may prolong the life of the tyre, rather than having to remove it quickly due to one-side wear. AREN’T TYRES DESIGNED TO BE RESISTANT TO IRREGULAR WEAR? A lot of technology goes into the making of a modern tyre to reduce the likelihood of irregular wear. Many of the sipes, rib edges, grooves, rubber compounds, and even the internal construction, help to combat irregular wear, as well as fulfilling functional requirements. However, tyre construction only plays a part in the prevention of irregular wear.
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Gallo/Getty
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AUGUST 2009 real questions real answers
| FUEL ECONOMY
BRIDGESTONE
| FUEL ECONOMY
Cutting down on carbon Road vehicles are the main cause of global warming but a fleet can become more environmentally-friendly by reducing fuel consumption. Real Answers takes a look at the main factors that influence fuel economy and how tyres play a part. Why should fleets save fuel? As well as saving money, cutting down on fuel will have substantial environmental benefits; fuel emissions from road vehicles are the number one cause of global warming. For this reason, the operators of any vehicle – whether it’s a car, van, truck or bus – should try to conserve fuel wherever possible. How do fuel emissions cause global warming? Global warming is caused by the emission of greenhouse gases. These gases trap heat in the Earth’s atmosphere and result in the ‘greenhouse effect’, essentially the warming of the Earth’s surface. Carbon dioxide (CO2) accounts for over 70 percent of the emitted greenhouse gases, and is created by burning fossil fuels such as oil, natural gas, petrol and diesel. The emissions of CO2 have dramatically increased within the last 50 years, and are said to be increasing by almost three percent each year. Of course, trucks use diesel fuel and this affects global warming in a different way to gasoline. Does diesel fuel cause more global warming than petrol? It depends on your viewpoint. Studies have shown that diesel causes more global warming than petrol
in the first decade after emission into the atmosphere, while petrol causes more warming after that period. From the perspective of shortterm climate change or the rate of warming, diesel is worse than petrol. However, when the emphasis is on long-term climate change, diesel is better due to lower CO2 emissions per kilometre driven. Yet, aside from global warming, it should be noted that diesel emissions are more pollutant than petrol emissions. How so? Diesel-powered vehicles pump out more local pollutants such as particulates and carbon monoxide. Both can aggravate respiratory and coronary problems in humans. Furthermore, Nitrous Oxide (N2O) emissions are higher with diesel-powered vehicles, and this is linked to allergic reactions and acid rain. These are some more reasons why fleets should make an effort to reduce fuel consumption. How does a truck consume fuel? Fuel is the energy source for a truck. The fuel in the tank accounts for all the energy produced or utilised by the vehicle. Even the headlights, the sound of the engines and the air-conditioning are the result of diesel fuel being converted into energy.
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WHAT CAN FLEETS DO TO REDUCE FUEL ECONOMY? As there are so many factors that contribute to fuel economy, it is impossible to accurately predict the effect of changing them, aside from real world testing. To complicate matters, the contributing factors keep changing and also interact with each other. For instance, a new engine may not consume the same amount of fuel as an old engine, while air resistance will play a bigger role in fuel economy at higher speeds than at lower speeds. Therefore, fleets need to assess their current levels of consumption, and address the factors that will noticeably reduce consumption in a cost-effective manner. WHAT ARE THE FACTORS THAT AFFECT FUEL ECONOMY FOR A FLEET? Fuel economy is affected by many factors such as the vehicle, operations, environment, drivers, tyres and how records are documented and analysed.
| FUEL ECONOMY
The shape of this truck is not optimised for aerodynamic performance
A roof faring and smaller cab-trailer gap will improve aerodynamics
FACTORS AFFECTING FUEL ECONOMY IN THE REAL WORLD TYRES
DRIVER
Pattern Compounding Type/Size Percent Wear Inflation Pressure Tread Depth Retreading
VEHICLE
Attitude Compensation Education Consistency Idle Time Engine Brake Use Habits
Alignment Transmission Configuration Paracitic Loads Aerodynamics Maintenance
FUEL ECONOMY On-Board Computer Odometer Test Method Measurement Fuel Receipts Analysing Results DOCUMENTATION
Traffic Terrain Road Surfaces Weather Temperature Manoeuvering ENVIRONMENT
Long Haul ¥ P&D Regional ¥ Load Speed Fuel Quality Percent Loaded Miles Route OPERATIONS
WHAT IS THE BIGGEST FACTOR IN FUEL ECONOMY? Speed is the biggest factor. Moving a truck down the road requires the engine, drive train and tyres to push against several different resistances that consume fuel, such as air resistance and tyre rolling resistance. Air resistance is practically non-existent if a truck is moving very slowly, but increases rapidly with speed to become a major part of fuel consumption. The impact of air resistance explains why truck manufacturers make a big effort to optimise the aerodynamic performance of vehicles. HOW CAN TRUCKS BE MADE MORE AERODYNAMIC? The shape of the trucks can influence aerodynamics. For example, a roof faring can reduce the drag for frontal wind. Also, reducing the gap between the back of the tractor cab and the front of the trailor will reduce drag if the vehicle encounters crosswind (yawn wind) conditions. Rounded vertical edges can also reduce air resistance by maintaining airflow along the trailer side.
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AUGUST 2009 real QUESTIONS real ANSWERS
Rounded vertical edges can improve the aerodynamic performance WHAT IS TYRE ROLLING RESISTANCE AND HOW IS IT INFLUENCED BY SPEED? Tyre rolling resistance is the amount of drag created by the tyres as a vehicle moves along the road. The tyre is constantly flexing and un-flexing as it rolls, and part of the rolling resistance comes from this. Even though tyre rolling resistance doesn’t increase as much as air resistance increases with speed, it is present and is a major factor at much lower speeds. Just as with air resistance, the amount of rolling resistance is influenced by many factors including load, speed, inflation pressure and tread pattern, among others. IS IT MORE BENEFICIAL FOR TRUCKS TO TRAVEL AT LOWER SPEEDS? From an environmental perspective, it's better for trucks to travel at lower speeds. Yet, from a cost viewpoint, it’s important to find the right balance; reducing speed will save fuel but will, of course, increase journey times. However, if your drivers can still meet delivery schedules, cutting speed can be an effective way to save money. It’s also worth noting that excessive speed can increase maintenance costs for engines, while damaging or decreasing tyre life. AFTER SPEED, WHAT IS THE NEXT BIGGEST FACTOR IN FUEL ECONOMY? Load is the second most important factor. Reducing the load can have a positive impact on fuel economy and should be considered. However, it is not always practical for trucks to reduce load because maximum payload is usually the primary goal. DOES THE CHOICE OF TYRE HAVE AN IMPACT ON FUEL ECONOMY? Tyres aren’t the largest factor in fuel economy; tyre rolling resistance is just one of the forces holding back a truck and is often overshadowed by the combined effects of air resistance and other factors. Yet it’s still worth looking at tyres. Radial tyres are one of the most significant improvements in tyre technology and in tyre fuel economy. In tests, Bridgestone found that converting from bias-ply tyres to radials improved fuel economy by over 10 percent (a 30-40 percent decrease in rolling resistance).
BRIDGESTONE
| FUEL ECONOMY
HOW DOES THE DESIGN AND CONSTRUCTION OF A TYRE CONTRIBUTE TO ROLLING RESISTANCE AND FUEL ECONOMY? The different parts of a radial tyre make different contributions to rolling resistance and fuel efficiency. Much of the rolling resistance (around 35-50 percent) comes from the tread. Therefore, many manufacturers focus on fuel-efficient tread compounding.
CONTRIBUTION OF TYRE COMPONENTS TO ROLLING RESISTANCE 35-50% TREAD COMPOUND CAP BASE
50-65% CASING
HOW CAN A TREAD BE MANUFACTURED TO BE MORE FUEL-EFFICIENT? Some compounds, especially those incorporating silica – or those that combine natural and engineered structure synthetic rubber – can reduce tyre rolling resistance. In some cases, a fuel-efficient ‘cap-base’ tread can be used. A cap and base compound can lower the overall tyre temperature which means lower rolling resistance and improved fuel economy. The cap compound, which is nearest the road, is chosen for high resistance to abrasion, long tread life and high traction on wet roads. Since compounds with these characteristics tend to generate more heat, a base layer – between the cap and the casing – contains a cooler running compound. This protects the casing from heat build-up. Similarly, shallow treads tend to be more fuel-efficient than deep ones, while rib designs tend to be more fuel-efficient than lug or block designs. Therefore, in theory, shallow-tread rib designs are the most fuel-efficient tyres. Yet there are exceptions to this rule. EFFECT OF TREAD DEPTH ON FUEL CONSUMPTION new
30% worn = 2% savings
IS FUEL ECONOMY AFFECTED BY TREAD DEPTH? Absolutely – as a tread wears, the fuel economy usually increases. This is partly due to the fact that less tread means less weight, and also because a shallower tread is less susceptible to energy-wasting squirm. The general rule is that just about every tyre is fuel-efficient during the last half of its useful tread life.
50% worn = 4.5% savings
DOES THE CASING OF A TYRE CONTRIBUTE TO FUEL ECONOMY? Very much so. Casings (including belts) contribute around 50 to 65 percent of tyre rolling resistance. Bridgestone uses supercomputer simulations and finite element analysis to create new casing designs and shapes that minimise rolling resistance without reducing casing durability. By optimising the distribution of stresses in the casing, fuel economy is maximised. That is why inflation pressure is critical. 80% worn = 6.5% savings
WHY IS INFLATION PRESSURE SO IMPORTANT? It is the air inside the tyre, not the tyre itself, that supports the load and keeps the casing in the right shape. Maintaining a tyre at the correct air pressure is critical for optimum stress distribution in the tyre. Proper inflation optimises the amount of
flexing and balances heat generation; less heat means less fuel consumed. Generally, tyres which are under-inflated by 10 PSI result in a one percent reduction in fuel economy. Maintaining proper inflation pressure is probably the easiest and most effective tyre-related measure to improve fuel economy. FINALLY, DO DRIVERS PLAY AN IMPORTANT ROLE? Of course. Educating drivers can be one of the most effective measures for improving large truck fuel economy. According to the American Truck Association’s Technology and Maintenance Council, the most skilful drivers will use 35 percent less fuel than the least skilled drivers. Reducing speed and idle time, avoiding frequent braking and turning, and careful journey planning are some of the ways in which drivers can contribute to improving fuel economy.
TRUCK FUEL CONSUMPTION – AN EXPERT’S VIEW Truck fleet managers should implement effective measures to check the efficiency of their trucking units and reduce overall fuel consumption. Diesel fuel emissions contribute a significant portion of overall green house gas emissions. In fact, part of this emission is not even directly related to the transport of freight or commodities. Many trucks run idle for hours during stopovers, causing truck engines to work and burn fuel while not in motion. It is common sense that larger engines require more fuel to operate, and heavy loads mean more work for engines and consequently more fuel consumption. Trucks should be maintained to a higher degree than small cars for health, safety and environmental reasons. Simultaneously, there should be an education programme to raise awareness of truck drivers on environmental issues. Many growing cities have confronted big challenges on the traffic, pollution and even safety considerations brought by passing trucks. The operation of trucks should also be considered in the overall planning of the city; for example, roads dedicated to trucks, truck stopover stations, and more efficient border controls. People should make crucial choices that are proenvironment and encourage others to do the same. We should always balance our needs and wants. By reducing our demands, we lessen the pressure from the environment to sustain us and provide time for it to regenerate. This is the best way to create a positive wave of change for the environment. Habiba Al Marashi, Chairperson of Emirates Environmental Group (EEG), Board Member, UN Global Compact
real QUESTIONS real ANSWERS AUGUST 2009
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BRIDGESTONE
| TYRE CODING
Cracking the code Although they may appear puzzling, the markings on a tyre’s sidewall hold vital information. What do the tyre codes mean? Every tyre can have different sets of codes moulded onto its sidewall. Each digit will have a purpose and meaning. The codes may denote the size of the tyre, its construction, manufacturing date, load capacity, ply rating, and other information which shows that the manufacturer certifies the tyre meets various industry standards and government regulations.
load and speed index Contains a load rating for single and dual assemblies.
DOT CODE
Contains manufacturing information and signifies that the tyre meets or exceeds the safety standards of the US Department of Transportation.
tyre size
Contains the specifications for section width, aspect ratio, construction and rim diameter.
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AUGUST 2009 real questions real answers
BRIDGESTONE
| TYRE CODING
SAFETY WARNING
Explains how injuries can occur if the correct procedures are not followed.
WHAT DOES THE ‘TYRE SIZE’ CODE MEAN? The example below is a 315/80R22.5 tubeless tyre. SECTION WIDTH This is the width of a new tyre when mounted on the tyre’s measuring rim, including normal sidewalls but not including protective side ribs, bars, raised letters, or decorations. On tubeless tyres with an aspect ratio of 80 or below (as shown here), section width will usually be displayed in millimetres, such as 315. On tube type tyres, the section width is generally displayed in inches, as in the ‘12’ in 12.00R24.
ASPECT RATIO This describes the shape of the cross-section of the tyre. It is the section height divided by the section width multiplied by 100. Generally, truck and bus tube type tyres have 100 as the aspect ratio and are not separately mentioned; for example, 12.00R24.
Section width
Section height
Rim diameter
CONSTRUCTION The letter ‘R’ indicates radial construction. Bias ply construction is indicated by a dash (-).
RIM DIAMETER This is the distance, in inches, from one bead base to the other (approximately the diameter of the hole that you see in the tyre). In this case, the rim diameter is 22.5 inches.
real QUESTIONS real ANSWERS AUGUST 2009
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BRIDGESTONE
| TYRE CODING
WHAT IS A DOT CODE?
DOT This signifies that the tyre meets or exceeds the US Department of Transportation’s safety standards. MANUFACTURING CODES Digits 1 and 2 indicate the manufacturer and plant. Digits 3 and 4 are a tyre size code. Digits 5, 6, 7 are for optional use. MANUFACTURING DATE (WEEK) Digits 8 and 9 designate the week (1-52) of the year, in this case, the 1st. MANUFACTURING DATE (YEAR) Digits 10 and 11 represent the last digits of the year of manufacturing, in this case, 2009.
WHAT INSTRUCTIONS ARE CONTAINED IN THE SAFETY WARNING? Serious injury may result from: • Tyre failure due to under-inflation/overloading - follow owner's manual or tyre placard in vehicle. • Explosion of tyre/rim assembly due to improper mounting - use safety cage and clip-on extension of air hose. Only specially trained persons should mount tyres.
WHAT IS THE LOAD AND SPEED INDEX?
LOAD INDEX The load index indicates the maximum weight that a tyre can hold vertically at the given PSI (pounds per square inch). Load indexes are determined using an applied vertical force against a tyre under laboratory conditions. The speed rating for the tyre can affect the maximum load the tyre can handle at a given temperature. The load index is often displayed as a combination of load and speed, such as 154/150M. This indicates that the tyre is rated for 3,750kg at a maximum of 130kmph (note speed symbol below). Usually there are two components to the load index – a rating for single tyre and wheel assemblies, and a rating for duals (two tyres bolted together). For this tyre, 154 is the single tyre load index and 150 is the dual tyre load index. SPEED SYMBOL The speed symbol is a letter code that indicates the maximum speed a properly inflated tyre will withstand for a determined amount of time on an indoor test drum. The speed symbol denotes the maximum speed capacity of the tyre under properly controlled conditions. They are not applicable if the tyres are under inflated, overloaded, worn out, damaged or altered. Tyre speed ratings do not imply that the vehicle may be safely driven at the maximum speed for which the tyre is capable, particularly under adverse weather or road conditions. In this example, M stands for 130km/hr.
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AUGUST 2009 real QUESTIONS real ANSWERS
BRIDGESTONE
WHY IS THE LOAD INDEX LOWER FOR DUAL ASSEMBLIES?
| TYRE CODING
Table indicating relations between load index and actual load
Dual load ratings are lower than single ratings to compensate for typical mismatching of inflation pressure, as well as momentary overloading if the tyres encounter an uneven road surface.
IS THERE ANY OTHER LOADRELATED INFORMATION ON A TYRE? Certain tyres will contain a ply rating Ð this identifies the tyre’s strength and ability to contain air pressure; the stronger the tyre, the greater its capacity for holding air pressure and hence the higher the load it can carry. It should also be noted that the ply rating is dependent upon size i.e. 18PR on a 1200R20 tyre size and 18PR on a 1200R24 tyre size will have different load carrying capacities.
CAN YOU EXCEED THE LOAD CAPACITY? It is important not to exceed the maximum load capacity or maximum inflation pressure of the tyre unless recommended by the tyre manufacturer. Lower inflation pressures may be used, but only with lighter loads. More detail will be provided in the load/inflation pressure relationship tables that are published by tyre standard organisations such as JATMA (The Japanese Automobile Tyre Manufacturers Association), ETRTO (The European Tyre and Rim Technical Organisation) and TRA (The Tyre and Rim Association).
LOAD Index
LOAD (kg)
LOAD Index
LOAD (kg)
LOAD Index
LOAD (kg)
LOAD Index
LOAD (kg)
120
1400
130
1900
140
2500
150
3350
121
1450
131
1950
141
2575
151
3450
122
1500
132
2000
142
2650
152
3550
123
1550
133
2060
143
2725
153
3650
124
1600
134
2120
144
2800
154
3750
125
1650
135
2180
145
2900
155
3875
126
1700
136
2240
146
3000
156
4000
127
1750
137
2300
147
3075
157
4125
128
1800
138
2360
148
3150
158
4250
129
1850
139
2430
149
3250
159
4375
SPEED Symbol
SPEED (km/h)
SPEED Symbol
SPEED (km/h)
SPEED Symbol
SPEED (km/h)
SPEED Symbol
SPEED (km/h)
A1
5
A8
40
J
100
R
170
A2
10
B
50
K
110
S
180
A3
15
C
60
L
120
T
190
A4
20
D
65
M
130
U
200
A5
25
E
70
N
140
H
210
A6
30
F
80
P
150
V
240
A7
35
G
90
Q
160
W
270
Speed symbol
Load/Inflation pressure table from JATMA standards Inflation pressure
TYRE DESIGNATION
kPa
500
525
550
575
600
625
650
675
700
725
750
775
kgf/cm2
5.00
5.25
5.50
5.75
6.00
6.25
6.50
6.75
7.00
7.25
7.50
7.75
S
1315
1360
1400
1440
1480
1500
1560
1595
1635
1650 (12)
1705
1750 (14)
D
1240
1280
1320
1360
1395
1450
1470
1505
1540
1550 (12)
1610
1650 (14)
Fitment
7.50 R 18
In this case, 14 indicates the ply rating. 1650 is the maximum load a 7.50 R 18 tyre with a 14 ply rating tyre can carry at 775 KPA (113 PSI).
real QUESTIONS real ANSWERS AUGUST 2009
17
BRIDGESTONE
| TYRE ANALYSIS
DAMAGE CONTROL Fleet managers can reduce their operating costs by assessing and analysing tyre damage and taking preventive measures to ensure that tyres are not removed prematurely.
WHY IS IT IMPORTANT TO ASSESS A DAMAGED TYRE? Tyre damage could be due to a specific problem. In many cases, if the problem is not rectified then it will reoccur in time. Yet fleets can save money and improve safety if they examine the tyres that are removed due to damage. SHOULD EVERY TYRE BE CHECKED FOLLOWING REMOVAL? Damage assessment is an essential part of recordkeeping and it is best practice to note the type of damage for every tyre that is removed. The data collected can be analysed on a periodic basis. WHY SHOULD THE RECORDS BE ANALYSED? The purpose of analysing the records is to spot damage trends. This will enable fleet managers to pinpoint specific problems and to put remedial measures into place. For instance, if several tyres need to be removed due to tread chipping then this could mean that the vehicles require a different specification of tyres. Likewise, if several tyres have to be removed due to sidewall cuts from rough driving, then it could be beneficial to train drivers about the importance of driving style. If a fleet records tyre history then this will enable deeper analysis and could help to identify the causes of damage that are less obvious. For example, tyre damage could be specific to certain vehicle models, axle positions or even operating routes.
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AUGUST 2009 real QUESTIONS real ANSWERS
DOES IDENTIFYING TYRE DAMAGE REQUIRE A HIGH LEVEL OF EXPERTISE? It might not be necessary to have an intricate knowledge of the technicalities, but an understanding of the common damage forms and causes will help you prevent damages from reoccurring. Bridgestone representatives can help you analyse damages and train your staff if required. 'Deformed' state
WHAT ARE THE MAIN CAUSES OF TYRE DAMAGE? The tyre consists of different parts (tread, belts, sidewall, bead etc.) and materials such as steel and rubber that are cured together with heat and pressure to function together as a whole unit. However, a tyre will have a tolerance limit beyond which it can disintegrate and separate. Heat generated inside the tyres and stress on the tyre components can weaken the belt package, rubber to steel bonding, as well as cords, leading to separations and breakage of cords. Furthermore, external factors such as an impact with rough road surfaces, nails, sharp stones or road curbs can also cause tyre damages such as tread cuts, chipping, tread penetration, etc. WHAT CAUSES HEAT AND STRESS? When a vehicle is moving, a tyre’s point of contact with the road surface changes as the tyre rolls. Therefore the tyre is constantly in a state of deformation and release (see diagram, right). This causes internal friction and deflection
'Released' state
of different body components. If the amount of deflection is excessive, it causes stress on the steel cords and adhesion between different components of the tyre. WHAT CAUSES AN EXCESSIVE AMOUNT OF DEFLECTION? If the load is increased then this increases the amount of deflection. Similarly if the pressure is too low for the load that the tyre is carrying, then this causes an increase in the amount of deflection. A faster rate of deflection gets converted into thermal energy i.e. heat. WHAT CAUSES A FASTER RATE OF DEFLECTION? An increase in the speed of the vehicle increases the speed of the deflection on tyres. It has to be noted that speed will produce more heat and stress if the amount of deflection is increased (i.e. if the vehicle is overloaded or the tyres are underinflated).
BRIDGESTONE
| TYRE ANALYSIS
real QUESTIONS real ANSWERS AUGUST 2009
19
BRIDGESTONE
| TYRE ANALYSIS
WHAT ARE SOME OF THE TYPICAL DAMAGES ASSOCIATED WITH HEAT AND STRESS?
1. CORD BREAK-UP Cord break-up is the result of deflection caused by low inflation pressure or overloading. The stress from the deflection concentrates on one spot of the tyre, and this continuous action causes the ply-cords to rupture. In the case of trucks and buses with dual assemblies, if one of the tyres has extremely low inflation pressure, a large deflection will occur and the inner sidewalls of the two tyres will rub, causing heat and stress which leads to cord break-up. Similar to a low pressure situation, if the rim offset is small, then dual tyres will rub together even if the inflation pressure is correct. Bridgestone recommends that the correct level of inflation pressure is maintained, that overloading is avoided, and that the proper rim size is used.
3. PLY-END SEPARATION (PES) Low inflation pressure and overloading will make a tyre deflect more severely in the sidewall-to-bead area. The stress from this deflection concentrates on the ply-end. Continuous stress leads to the ply-end separating from the rubber compound. Furthermore, if a narrow rim-width is used then this will cause a deflection which excessively compresses the section from the bead to the sidewall. The stress on the plyend from this deflection may result in PES.
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AUGUST 2009 real QUESTIONS real ANSWERS
2. RUN-FLAT If a tyre is continuously run after air loss Ð or under very low inflation pressure Ð then this will result in a break-up of the ply cords. This is because low inflation pressure causes an increase in deflection which Ð coupled with speed Ð leads to heat and stress on the ply cords. Further, in the event of extreme deflection, the rim can cut into the ply cords or sidewall. Several measures need to be taken in order to prevent a run-flat. In addition to maintaining air pressure, it is recommended that the rim is checked for cracking and to make sure there is a valve cap. The fitting condition of a tyre on a rim should be clear of debris to prevent tube puncturing and air leakage, while the proper tubes and flaps must be used. If a tyre receives a puncture, the vehicle should be stopped and attended to.
Excessive speed and/or braking will generate heat which gets transferred to the wheel and also to the tyre bead. This heat deteriorates the quality of the rubber compound in the bead, thus increasing the chance of separation. In order to prevent ply-end separation, it is recommended that the correct inflation pressure is maintained, that care is taken to avoid overloading, excessive speed and braking, and that the proper rim size is used.
4. BELT LEAVING BELT (BLB) Often you will see bits of tread by the road, and this can be caused by belt separations. Running tyres with low inflation pressure and overloading makes tyres deflect largely and generate heat and/or stress, especially between the opposing belts within the belt package Ð this causes the weakening of the adhesion between them and leads to separation. We therefore recommend that air pressure is maintained and that overloading and excessive speeds are avoided.
BRIDGESTONE
| TYRE ANALYSIS
WHAT ARE SOME OF THE MAIN DAMAGES DUE TO EXTERNAL FORCES? 1. TREAD CUT-BURST A cut-burst is literally when a tyre bursts as a result of a cut in the tread. If a tyre is overinflated or overloaded, the high tension will make it more likely to burst from a small cut than a properly inflated tyre. Usually belts are blasted outwards due to the high pressure escaping from the tube or tyre after the cut. High speeds will increase the likelihood of a cut-burst, since the impact on the tyre will be stronger. Therefore, it is recommended that tyres are maintained at the correct inflation pressure, that rough driving is avoided, and that any cuts to the tread are repaired immediately. 2. TREAD CUT CHIPPING Tread cut chipping occurs if the truck or bus is driven continuously on rough surfaces with sharp stones, which creates small cut-chipping on the tread. Chipping is far more likely to occur if a vehicle is driven off-road without the suitable specification of tyres. Therefore, it is critical that the road surface conditions are taken into consideration during the tyre selection process. Just like cut and shock-bursts, a tyre is more susceptible to chipping if it is over-inflated or overloaded, or if the vehicle is driven at high speeds off-road. 3. TREAD CUT PENETRATION Tread cut penetration can result from driving on roads which contain objects such as sharp stones, rocks, glass, nails, bolts or steel bars, etc. Rough driving increases the chance of an object penetrating the tread, so it’s important that drivers are careful on the road. Tyres should be inspected frequently; stones, rocks, nail and other objects should be removed to prevent them from penetrating deeper into the tyre. If cuts are spotted early, then it may be possible to repair the tyre.
TREAD BELT PACKAGE
INNER LINER CASING PLY PLY-END
SIDEWALL
BEAD
SO THE MAINTENANCE OF A TYRE IS A VERY IMPORTANT PROCESS? Absolutely. You should also note that a well maintained tyre is a stronger tyre. A tyre that is not properly maintained becomes weak after prolonged use. It is more susceptible to damages from heat, stress and road hazards. Even retread tyres with improperly maintained casing may suffer from premature removal due to damages. IN A NUTSHELL, WHAT IS THE KEY TO PREVENTING DAMAGE? Treating your tyre well! If the correct tyre is selected, and care is given to tyre maintenance and usage – such as avoiding excessive speed, sudden braking, and harsh turning – then this will ensure that your tyre lasts a long time.
real QUESTIONS real ANSWERS AUGUST 2009
21
BRIDGESTONE
22
AUGUST 2009 real questions real answers
| suspension and brake maintenance
BRIDGESTONE
| SUSPENSION AND BRAKE MAINTENANCE
MECHANICAL CARE: PROLONGING TYRE LIFE Tyre damage and irregular wear can be due to mechanical issues, such as defective leaf suspension parts and brakes. Regular inspection will help to spot mechanical defects before they cause tyre-related problems.
HOW CAN LEAF SPRING SUSPENSION BECOME DEFECTIVE? A leaf spring can become fatigued from repeated exing due to load, road conditions, brake conditions, and others factors which may eventually lead to failure. A leaf spring and its parts, which include u-bolts and clips, should be regularly inspected and maintained. Aside from safety and damage issues for a driver and vehicle, they can also affect the life of a tyre.
HOW CAN LEAF SPRINGS AFFECT TYRE LIFE? A misaligned, worn or broken leaf spring will make the vehicle pull to one side (wheels out of track). This will cause irregular wear, usually in the form of shoulder wear, feather wear and other types. A broken or subsided spring can cause tyres on one side to support more load than the other, which may cause tyre failure or reduce tyre life. HOW CAN LEAF SPRING U-BOLTS AFFECT TYRE LIFE? If a u-bolt is loose then the centre bolt area will absorb the greatest stress and this can cause leaf rupture. A loose u-bolt or centre bolt will create a length-wise and width-wise shifting of the leaves. The resulting movement may cause tyre wobbling, creating vibration and leading to wavy wear and other forms of irregular wear. Wavy wear is characterised by localised areas of fast wear creating a scalloped appearance around the tyre.
HOW CAN SPRING CLIPS AFFECT TYRES? Spring clips are installed to assist the leaf spring suspension when exposed to shock and rebound loads, and prevent spreading or fanning out of the leaves. A missing clip may cause excessive stress on the master leaf which leads to irregular wear and damages. It is also important that clip bolts are assembled with the head of the bolt away from the tyre. This is to prevent the tyre from being cut if the nut loosens and the clip bolt becomes partially protruded.
real QUESTIONS real ANSWERS AUGUST 2009
23
BRIDGESTONE
24
AUGUST 2009 real questions real answers
| suspension and brake maintenance
rELAY VALVE AND SLACK ADJUSTER
BRAKE CHAMBER
BRAKE SHOEs
BRAKE DRUM
BRIDGESTONE
HOW CAN BRAKES AFFECT TYRE LIFE? Brakes convert the energy of motion into heat, but tyre-related problems will occur if they generate an excessive amount of heat. The heat produced is absorbed by the metal brake drums, and then dissipated into the atmosphere. During this dissipation, heat is also transmitted to the wheel and tyre. Most of the tyre damages due to overheating brakes are located in the bead area, as this is close to the heat source. The inner tyres are often more affected due to their closer position to the drum. Damages such as burnt, cracked or burst beads and bead area separation are due to this excessive heat. The shoe lining, brake drum, wheel, tube, flap, and valve are all affected by excessive heat and may also show signs of heat failure. WHAT CAN CAUSE BRAKES TO OVERHEAT? Operating conditions – such as speed, load, traffic and terrain – can cause overheating. HOW CAN SPEED AND LOAD CAUSE BRAKES TO OVERHEAT? If speed is doubled, the brake requires four times as much force to stop the vehicle. Likewise, if the customer is operating with overloaded conditions, the tyres will receive a lot more heat during braking. HOW CAN TRAFFIC CAUSE BRAKES TO OVERHEAT? Driving in urban areas requires a more frequent use of the brakes than highway driving, as there will be lots of stopping and starting due to traffic and signals, etc. It’s worth bearing in mind that tyres will receive even more heat if the driver does not maintain the minimum recommended distance from the vehicle in front, as this requires an even more frequent use of the service brakes. WHAT ABOUT THE TERRAIN? If a vehicle has to travel downhill, the driver has to press harder on the pedal, and this causes the drum to overheat and move away from the shoes. If the curvature of the brake shoes fails to match the curvature of the brake drum, a total loss of braking power can occur. When driving downhill, drivers should use a low gear in order to utilise engine braking to slow the vehicle down. ARE THERE ANY OTHER FACTORS THAT CAUSE BRAKES TO OVERHEAT, AND THEREFORE SHORTEN TYRE LIFE? Yes, brakes may overheat if the brake shoes are in constant contact with the drum/rotor. This effect is called brake drag – the failure of one or more brakes to release immediately or completely after a driver removes his foot from the brake pedal.
| SUSPENSION AND BRAKE MAINTENANCE
WHAT ARE THE MAIN CAUSES OF A DRAGGING BRAKE? 1
1. OVER-ADJUSTED SLACK ADJUSTER This can be due to an improper adjustment by the person in charge, or because of an automatic slack adjuster that does not have the ability to back-off or increase slack.
2
2. LOOSE OR BROKEN RETURN SPRING With repeated usage the shoe return springs lose their tension. Eventually they may allow constant contact of the brake shoes with the drum. The brakes will drag causing excessive and unnecessary heat. It is important to use a high quality return spring and it is also recommended practice that return springs are replaced at each brake reline.
3
3. LEAKING AIR LINES Air passes through hoses that are connected to the brake chamber. Should the inner tube of a brake hose rupture, considerable braking capability will be lost immediately. The inner tube can even collapse and prevent a return spring from releasing, resulting in dragging and overheated brakes.
WHAT KIND OF IRREGULAR WEAR IS RELATED TO DRAGGING BRAKES? Dragging brakes can lead to irregular wear such as fast wear, spot wear (a localised spot of excessive wear across the face of the tread) and diagonal wear (diagonal flat spots across the face of the tread which may repeat around the circumference of the tyre). The surface texture may show circumferential abrasion marks from the tread sliding on the road surface. Flat spots and diagonal wear are usually exhibited on both tyres in a dual assembly.
WHAT ACTION SHOULD BE TAKEN IF A TYRE HAS FLAT-SPOT WEAR? If the condition is mild, dual tyres can be rematched to position the flat spots 180 degrees from each other after making the necessary adjustments to brakes. If the wear is more extensive, but the belt is not damaged, then the tyre can be repaired or retreaded. If the damage is severe then the tyre may need to be scrapped. This is obviously costly for a fleet – the key is to catch the problem before it develops.
real QUESTIONS real ANSWERS AUGUST 2009
25
BRIDGESTONE
| tyre mounting
fit to last Careful tyre mounting is in the interests of both fleet managers and drivers as tyres that are mounted in the correct manner will have a longer tyre life and provide a more comfortable journey.
26
AUGUST 2009 real questions real answers
BRIDGESTONE
1a CORRECT
Seating both beads correctly should minimise mounting-related bouncing or wobbling
1b offcentre
If the wheel is off-centre with respect to the tyre, there may be bouncing-like ride disturbance, and eventually irregular wear
1c crooked
If the wheel is crooked with respect to the tyre, there may be a vibration-like ride disturbance, together with rapid wear, irregular wear, or all three
| tyre mounting
Why is it important to mount a tyre correctly? For truck and bus drivers, it’s crucial to feel comfortable on the road, particularly on longdistance trips. However, badly mounted tyres will affect the smoothness of the ride, making journeys far more uncomfortable. Also, from the perspective of the fleet manager, it’s not cost-effective to have badly mounted tyres as they will suffer from irregular or rapid wear and will need to be replaced sooner than correctly mounted tyres. What is the correct way to mount a tyre? When tyres are mounted, the centre of the wheel should be in exactly the same place as the centre of the tyre mounted on it. This is known as ‘concentric’ mounting (see 1a). What happens if a tyre is not mounted concentrically? If the wheel is non-concentric (off-centre) in relation to the tyre then this may cause a bouncing-like ride disturbance (see 1b) which will affect driver comfort. The condition is likely to cause severe irregular wear, if left untreated, and will result in the need to replace the tyre.
If a wheel is crooked in relation to the tyre, there may be a vibration-like ride disturbance (see 1c). The tyre will vibrate or wobble, and this will reduce the driver’s comfort. This can also cause irregular wear, rapid wear, or both. What has to be done to make sure that a tyre is mounted correctly? Unfortunately, the mounting process does not automatically make tyres and wheels concentric. Before mounting the tyre, it is important to ensure that the wheel and tyre are correctly prepared. This must be done by a professional that has the proper training and equipment. What is involved in the preparation stage before mounting? Firstly, the wheel and tyre should be carefully inspected. On the wheel, bent or dented flanges, rust build-up, dirt or damage will result in the tyre’s bead not seating properly. If the bead can’t seat properly, the mount will probably be non-concentric. Finally, before mounting, both the wheel and the tyre bead need to be properly lubricated.
real questions real answers AUGUST 2009
27
BRIDGESTONE
| TYRE MOUNTING
RIM WIDTH
RIM DIAMETER
WHY IS IT NECESSARY TO LUBRICATE THE WHEEL AND TYRE? Proper lubrication will reduce bead damage, enable easier mounting, and will help the bead fit into its proper position on the rim bead seat.
BEAD SEAT
BEAD FLANGE
WILL ANY TYPE OF LUBRICATION SUFFICE? No. Water-based lubricants can cause wheels to rust and moisture will penetrate and deteriorate the inside of the tyre, while petroleum-based lubricants can destroy rubber over time. Bridgestone recommends using a high-quality, vegetable oilbased lubricant for truck and bus tyre mounting.
DOES THE RIM WIDTH MATTER IN RELATION TO THE TYRE SIZE? It is important to ensure that a tyre is fitted on the recommended rim width. The specifications for a tyre can be found on the tyre standards – if necessary, ask the manufacturer for clarification – while the rim width is displayed on the rim itself (see left). For example, a 295/80R22.5 tyre can be fitted on a rim width of either 9.00 or 8.25 inches. TYRE SIZE 295/80R22.5
Rim width measurement
28
AUGUST 2009 real QUESTIONS real ANSWERS
Rim width
RECOMMENDED RIM WIDTH APPROVED RIM WIDTH 9.00 inches
8.25 inches
BRIDGESTONE
| TYRE MOUNTING
ONCE THE TYRE IS FITTED, HOW CAN I CHECK THAT IT IS MOUNTED CORRECTLY? You can check a tyre for concentricity by using the tiny rib, called the ‘rim line’, which is moulded into the tyre sidewall, near the bead. The rim line should be the same distance from the flange in all locations. You should check at least four locations, 90 degrees apart, on both sides of the tyre. If you can spot a difference then the tyre is not concentrically mounted.
MEASURE THIS DISTANCE
Check the assembly for concentricity by using the tiny ring moulded into the tyre sidewall, observing its distance from the wheel flange
WHAT SHOULD I DO IF A TYRE IS NOT MOUNTED CORRECTLY? If you discover that a tyre is not concentrically mounted then it should be re-fitted. Deflate the tyre, release the beads, re-lubricate and re-fit once again. This should rectify most cases of incorrect mounting. THE TYRE HAS BEEN RE-FITTED IN THE CORRECT MANNER BUT IT IS STILL NONCONCENTRIC. WHAT SHOULD I DO NOW? If the tyre is still non-concentric, deflate, rotate 180 degrees in relation to the wheel, re-lubricate and inflate the tyre to seat the beads. Check the rim line once again and if the problem persists then a new wheel or tyre should be fitted.
If the tyre has been re-fitted but is still non-concentric you should rotate it 180 degrees but keep the rim in the same position
real QUESTIONS real ANSWERS AUGUST 2009
29
BRIDGESTONE
| DOCTOR'S OPINION
FEELING TYRED With the need to travel long distances on a regular basis, truck and bus drivers are particularly susceptible to fatigue, which can result in serious accidents. Dr Jim Mathew, specialist in internal medicine at Dubai’s Welcare Hospital, explains the effects and dangers of driver fatigue, while providing advice on preventing and combating tiredness.
IS FATIGUE A BIG ISSUE FOR TRUCK AND BUS DRIVERS? Driver fatigue is a serious problem which results in many accidents every year. Young male drivers, truck drivers, company car drivers and shift workers are most at risk of falling asleep while driving. But any driver travelling a long distance, or driving when tired, is at risk of causing a sleeprelated accident. HOW DOES FATIGUE AFFECT A DRIVER’S PERFORMANCE? Fatigue reduces alertness, delays reaction time, as well as inducing memory problems, poor psychometric coordination and less efficient information processing. Tiredness will impair a driver’s interaction with his surroundings and his decision making ability. A tired driver will experience a progressive withdrawal of attention from the road and traffic demands, leading to an impaired performance behind the wheel. WHAT IS THE LEVEL OF IMPAIRMENT? Research by the European Road Safety Observatory found that a person who drives after
30
AUGUST 2009 real QUESTIONS real ANSWERS
being awake for 17 hours has impaired driving skills comparable to someone with a blood alcohol level of 0.05. A person who has been without sleep for 24 hours has impaired driving skills comparable to someone with an illegal high blood alcohol content of 0.1 g/l.
HOW SERIOUS ARE MOST FATIGUE-RELATED ACCIDENTS? Sleep-related accidents tend to be severe, possibly because of the high speed and the fact that the driver is unable to react to situations that arise.
ARE MOST DRIVERS AWARE OF THE DANGERS OF FATIGUE? Even people who drive on a daily basis fail to recognise the silent dangers of driver fatigue. Many drivers are often prepared to disregard the onset of fatigue whilst driving in order to reach their destination, and a large percentage of the population are unaware that driving whilst tired can be as dangerous as driving a vehicle after having consumed alcohol.
WHAT’S THE BEST WAY TO PREVENT FATIGUE? The safest option for drivers is to avoid travelling when tired, and to take overnight stops during long distance trips wherever possible. For truck and bus drivers, it is important to feel well rested and hydrated before starting a journey. Drivers should also bear in mind that some medications impair alertness, and they should check with a doctor if in any doubt. Drivers should wear clothing which is comfortable but suitable for driving, and the seat should be adjusted to an upright position. A good way for a driver to check the seat is by testing that his wrists can make contact with the top of the steering wheel. Drivers should also plan the journey to include regular rest breaks (at least 15 minutes every two hours).
WHERE AND WHEN ARE FATIGUE-RELATED ACCIDENTS MOST LIKELY TO HAPPEN? The early hours of the morning and the middle of the afternoon are the peak times for fatigue-related accidents. Long journeys on monotonous roads, such as motorways, present the highest risk.
BRIDGESTONE
WHAT SHOULD A DRIVER DO IF HE FEELS SLEEPY WHILE ON THE ROAD? Most of the things that drivers do to try to keep themselves awake and alert when travelling are ineffective; they should only be regarded as emergency measures to allow the driver time to find somewhere safe to stop and rest. For example, drivers can wind the windows down and let in some fresh air, turn up the radio, pull over and go for a short walk, drink caffeine or take a nap for about 15 minutes. Yet these are only temporary solutions; sleepiness will return if the driver does not stop travelling within a fairly short period of time. Drivers should not attempt to drive through fatigue. However, if they need to take a break, the hard shoulder of the motorway should never be used. CAN FATIGUE BE DETECTED BY OTHERS? In many countries, police are trialling roadside tests which may detect sleepy drivers, as well as drivers affected by alcohol, drugs or medications. Some vehicles are now being equipped with devices to detect driver fatigue
| DOCTOR'S OPINION
and provide warnings, or even take control of them. But these devices are few and far between; moreover the driver should be responsible for detecting fatigue and taking corrective measures rather than relying on such devices.
Fitting the fleet vehicles with tachographs would enable driving and rest times to be reviewed, and would help enforce driver hours rules. Employers must understand that fatigue is physiological and that the body and mind need rest.
IS DRIVER FATIGUE SIMPLY THE RESPONSIBILITY OF THE DRIVERS THEMSELVES? No. Employers must play a major role in reducing the risk of their employees who drive for work purposes, such as truck and bus drivers. Many of the fatigue-related accidents involve vocational drivers who often disregard the safety standards to meet the job demands. Safety standards should be implemented and followed as in any other skilled job. HOW CAN EMPLOYERS HELP? As part of their health and safety policies, employers should adopt and implement the principles to reduce occupational road risk and reduce the likelihood of their employees being involved in a sleep-related driving accident. They can ensure that journey schedules enable drivers to stay within the law and have sufficient time and facility for rest.
Dr Jim Mathew, Specialist in internal medicine at Dubai’s Welcare Hospital
real QUESTIONS real ANSWERS AUGUST 2009
31
PASSION for EXCELLENCE