THE THREE KEY MOMENTS IN THE CHOICE OF TYRES FOR A COMMERCIAL VEHICLE
Generally the choice of a tyre by the client may take place at three different moments; they are analysed separately below.

PURCHASE OF A NEW VEHICLE
When the client intends purchasing a new vehicle or a new trailer he has to select the product that best responds to his requirements. His choice will be made on the future use of the vehicle.
The type of journeys made and the type of load are the two variable that usually have most influence over the final purchase.

The O. E. (Original Equipment) is defined according to the technical specifications of the vehicle.
Our technical support is, however, important as the fleet manager must be actively involved in order to ensure the choice of the most appropriate tyre sizes and tread patterns from the possible range specified by the manufacturer.

INCREASED PERFORMANCE
Should the fleet manager wish to improve the performance of his vehicles he will make his choice of tyre on the basis of the experience gained with the O. E. tyres or those fitted by the previous owner.

When the time comes to replace the tyres (due to damage or variations in the type of use to which the vehicle is normally put) the fleet manager may feel a need to improve the performance of his vehicle in terms of mileage, manoeuvrability and general performance.

The fleet manager may also wish to up-date the performance of his vehicle (whilst respecting current legislation) by responding to the technical evolution of the products available on the market.

REPLACEMENT OF WORN TYRES
When the tyres fitted to a vehicle reach the end of their useful life the fleet manager turns to a tyre distributor to replace them: if his vehicle is to continue to perform the same tasks he will normally see no need to fit a different size or type of tyres.

However, it may be that the fleet manager has heard of new products capable of providing superior all-round performance and has decided to take them into consideration as an alternative to his old type of tyre.

A third opportunity to assist the fleet manager in his choice occurs when, with winter approaching, he needs to replace his standard tyres with winter tyres.

Externally tubeless tyres are similar to traditional tyres fitted with inner-tubes (Tube Type).
From a constructional point of view the tubeless tyres are distinguished by a special air-tight internal layer of rubber named liner, making the inner-tube superfluous, and by beads with inclined bases allowing easy fitting and a perfect airtight seal.

ADVANTAGES
Tubeless tyres provide users with a number of advantages. These can be summed up as follows:

SAFETY
> In the case of punctures the tyre deflates very slowly and only through the hole in the tyre, allowing control over the vehicle to be maintained.
> They provide reliable braking thanks to improved cooling of the brake components.

ECONOMY
> Tubeless are more durable and resistant to accidental failure because they are less prone to overheating, thanks to lower rolling resistance, improved heat dispersal due to the absence of the inner-tube and flap and the larger space between the brake drums and the bead area due to the different wheel design.
> The lower overall weight of the tyre/wheel assembly allows a greater payload to be carried.
> Ease of fitting and removal: the fitting/removal operations can be performed manually, very quickly and by a single operator.
> The elimination of the risk of damage to the inner-tube during removal of the tyre and of subsequent problems with the tube or flap.
> Lower costs of the Tubeless rim and tyre set in comparison to Tube Type.

COMFORT
Improved balance. The lack of an inner-tube, flap and movable wheel components reduces the likelihood of vibration due to out of round or unbalanced wheels.

RIMS
The tubeless well-type wheel rims are constructed in one piece with bead seats inclined at 15° and lowered flanges, rather than complicated multipiece tube type rims.

Increasing numbers of high powered vehicles means a growing demand for high performance tyres which are designed to provide these vehicles with increased stability, excellent roadholding in corners and under braking and improved handling. All these advantages can be achieved by fitting low profile tyres.

These tyres also provide a lower loading platform facilitating easier loading and unloading operations and providing a greater useful loading volume whilst remaining within the dimensional restrictions and the loads specified by local legislation.

When fitted to buses these tyres lower the platform height of the vehicle facilitating passenger access to and from the vehicle. Appropriate further benefits can be obtained with the ultra low profile series (/60, /70).

Changing from one size of tyre to another is a relatively complex operation and is not always possible.
Itmust conformto the vehicles manufacturer’s recommendations and the local regulations.

For this reason we have listed below a series of fleet managers considerations to help our technical and commercial personnel advise clients on the compatibility of tyre sizes.

Before changing the size of tyre fitted the following points regarding both the tyre and the vehicle should be checked:

LOAD CAPACITY
The load capacity of the replacement tyre should not be inferior to that of the original tyre, or at least it should be compatible with the maximum loads homologated for the vehicle in question.

SPEED
The speed code of the replacement tyre must correspond to the maximum speed of the vehicle.
In some countries it is sufficient to respect the maximum speed imposed by the governor.

EXTERNAL DIAMETER OF TYRE
Every vehicle is designed for a certain tyre size.
In order not to impare the performance of the vehicle the tyre sizes should only vary within certain limits.

The increase or decrease in the diameter of the tyre leads to a corresponding variation in the rolling circumference, which can affect both the vehicle height and vehicle speedometer and tachograph.
The permitted variation is of ± 5%.

WHEEL RIMS
Check that the new tyre can be fitted to the existing wheel rims (consult the “Technical Data” booklet). If not, replace the rims.

SIZE
It is important to check that the tyre and the wheel do not foul any part of the bodywork or the mechanical components of the vehicle at full articulation of the wheel. Furthermore, the tyre must not protrude from the vehicle, or exceed local vehicle width regulations.
The minimum clearances that should in general be respected are as follows:

> vertical space, that is the distance between the top of the tyre and the wheelarch, this must be for a fully laden vehicle = 70/80 mm.

> lateral space, that is, the distance between the sidewalls of the tyre and the closest part of the vehicle:

fixed components (springs, spring hangers, brake arms), in this case the minimum distance should be 15 mm.

mobile components (coachwork, mudguards, steering arms), in this case the minimum distance should be 50 mm.

The steering wheels should be checked on full lock.

> wheel to brake drum space, that is the distance separating the wheel and the brake drum.

The wheel must revolve freely and allow the brake drum to be ventilated.
The minimum distance should be at least 15 mm.

> dual spacing for twinned tyres, that is the distance separating the mid-points of twin tyres.

The technical tables in the “Technical data” booklet should be checked for this information.

The distance between the twinned tyres should be such that:

> it allows heat to be dispersed

> it avoids the trapping of foreign bodies between the tyres which may cause damage.

This section contains tables showing compatible loads for different tyre sizes (at given axle loads).

It should be remembered that any change of tyre size must respect all current legislation and the homologation specifications of the vehicle in question.

COMPATIBILITY IS CALCULATED ON THE BASIS OF THE LOADING CAPACITY.
It is important to choose tyres in relation to the use to which they will be put.
For long-distance transport low profile tyres (/80 series) are advised whilst ultra-low profile tyres (/70, /60 series) are suggested for volume transport.

In bad weather conditions, unloading at the time of receipt must be carried out in a covered area; in any event, if water is found inside the tyres, this must be removed immediately.

Unloading must not be carried out by dropping the tyres or by any other method which could damage the quality or visual aspect of the tyres.

Tyres must not be moved by inserting the forks of a fork lift truck through the center of a tyre which could damage the bead area.

Tyres must be stored inside a clean, dry and ventilated area, protected from direct sunlight or other source of artificial light (illumination must be realized with lamps of low ultraviolet and infrared emission).

In the case of temporary external storage, the tyres must be covered (eg. with an impermeable opaque material) and protected from contact with water and humidity.

The storage temperature must be less than 35°C and preferably less than 25°C. A temperature greater than 50°C, especially if stock rotation is not sufficient, can result in accelerated forms of deterioration, such as to reduce the duration in use of the tyre.
Avoid contact with heaters and radiators.

Very low temperatures in the storage area are not in themselves damaging, but can provoke rigidity of the tyre. In this case, they must not be deformed during movement or fitting.

If they are destined to be used immediately they are released from storage, it is necessary to keep them for a few hours in an area with a temperature of approximately 20°C.

Appliances which generate ozone must not be introduced into the storage area, also gas and vapors from combustion which can generate ozone via photo-chemical processes must be excluded from the area. Neither the area or the equipment in the storage location must present traces of solvents, inflammable materials, lubricants, chemical products, acids, disinfectants, rubber solutions, etc. which could prejudice not only the visual aspect but also the characteristics of the product.

Tyres must not be submitted to any deformation due to tension or compression.

Storage for long periods

The best method for storage is vertically in rows of one tyre high, on racks, positioned at least 10 cm from ground level, with the sidewalls positioned vertically, so that the profile is not altered (fig.1).
The vicinity or stacking of other racking or pallets must not deform the profile of the tyres.
The number of tyres per row must be such as to not compromise the sidewalls.
Agricultural tyres with a width greater than 12.4" (315 mm), with the exception of those tubeless, must be stored in stacks.
The position of the tread lugs must be such that they correspond (one on top of the other, fig.2) in order to limit deformation to the sidewalls.
As a general indication a stack should not exceed 5 tyres.



Short term storage

Up to 4 weeks, tyres can be stored in stacks, one on top of the other, preferably on a fixed rack or on stackable pallets, reforming the stack inverting the order of the tyres on a weekly basis.
In all cases when tyres are stored in stacks, it is necessary to ensure that there is no partial misplacement from the vertical plane, in order to avoid any permanent deformation of the lower tyres in the stack.
The maximum height of the stack must not exceed 1.2m and the tyres in the stack must all be of the same dimension.



The following tyres cannot be stacked for storage:

• Motorbike and scooter
• Earthmoving
• Tubeless agricultural
• Tube type agricultural with width £ 12.4"
• Agricultural with x-ply nylon carcass
 

Whether inner tubes are supplied by the producer in single boxes, large boxes or wrapped in plastic film, it is always preferable to maintain the original packaging.
In alternative they can be stored also slightly inflated, inserted within the tyre, or piled deflated, up to a maximum height of 50 cm, on racking shelves with a closed base, accurately avoiding that the valve can damage the surface of the tube when squashed under the pressure of their own weight.

Ensure that the tubes do not overlap the edge of the plane on which they are stored to avoid accidental laceration.
It is not recommended to store on slatted pallets because the pressure applied to the tubes will not be uniform.
Do not hang inner tubes during storage. Valves should be stored in their packaging in a clean, well ventilated and dry location.

Flaps should preferably be placed within the tyre together with the inner tube. If they are stored separately, they should be placed horizontally, in a pile on a shelf, protected from dust, grease, humidity, ozone and direct sunlight. To avoid deformation and stretching they must not be hung up in any way.

The storage location must be organized in such a way as to guarantee constant stock rotation, limiting to the minimum the storage period of the tyres. Products which enter storage first must be the first to leave. First in, first out.

In the last few years products have been marketed with this characteristic.

These are specific tyres for drive axles and the arrow indicates the preferred direction of rotation. On mounting the tyre, therefore, make sure to check whether there is such a mark, and if so, take this into account and follow the manufacturer’s instructions.

In this way, the designers have tried to optimize performance.

Setting a preferred direction of rotation makes it possible to improve the features of quietness, traction, resistance to slippage and regularity of wear.

In practice, if these instructions are not followed, the tyre “works” under non-optimal conditions and the characteristics mentioned above may be adversely affected.

It must first be said that there are many types of valve on the market and each has been designed for a specific use.

The first thing to do is to check the category mark normally found on the stem or at the base of the valve. If the code starts with V3 then the valve is specific for use on commercial vehicles.

V1 identifies valves for bicycles and motorcycles and V2 for cars.

There are, however, particular cases in which valves of different categories are used (normally if special inflation pressures are required).

For heavy commercial vehicles, there are valves with essentially 2 maximum pressure levels (1050 kPa and 1400 kPa) depending on the size of the tyre, rim and valve hole.

It is important to check regularly that the valves are working correctly. The easiest way to do this it to wet the tip and base of the valve with soap and water.

If bubbles are formed it may be necessary to tighten the valve mechanism (with a special instrument) or to check that the valve is tightened on the ring with the correct torque.

If the air leak persists, it is advisable to have the valve checked by a specialist.

To be able to check the pressure of tyres correctly we recommend the use of specific extensions (for the internal tyres of twin axles) and to protect the valve mechanism from dirt and dust we recommend fitting valve caps.

The letters FRT (Free Roling Tyre) are present on most products specifically for use on trailers/ semi-trailers.
Legally the FRT mark indicates products which must not be fitted on drive axles and front steering axles of vehicles, but can be mounted on all axles of trailers/ semi-trailers and on any additional axles of a vehicle.
These are very robust products (the load index is normally higher than normal products) specially designed to withstand strong stresses in the use of trailers such as: sliding, lateral pressure and high loads.
For this reason, driving performance features have been sacrificed and the speed code is also limited to use on trailers. Mounting FRT products on drive axles or front steering axles of vehicles is, therefore, technically inadvisable as well as being illegal.

There is a code that shows the product’s “date of birth”.
By law, situated on the lower part of the tyre sidewall, i.e. the part closest to the rim.
At the end of a series of codes, must display a four digit code (for tyres made after 2000); the first two digits indicate the week of manufacture, while the final two show the year.
Therefore for the number 2009, the tyre was made in the 20th week of the year 2009.

Tyres on trailers/semi-trailers require different levels of performance than products mounted on drive axles.
For this reason, tyres are often designed according to both size and application.

Tread design has specific characteristics and is designed to enhance performance in terms of mileage, wear uniformity, rolling resistance and braking.
The most frequent conditions affecting trailers/semi-trailers are largely influenced by lateral forces that cause high levels of contact friction with the ground.

Manufacturers have therefore deemed a tread design which runs around the circumference of a tyre the most suitable for achieving the required performance goals.
We must take into account that tractor+semi-trailer or tractor+trailer systems are designed to ensure distributed braking, whereby the towed unit brakes slightly in advance.

If transverse treads were used, when braking on a rough surface (e.g. due to a manhole in the road), the tyre would be tugged back with a risk of tearing the tread.

“REGROOVABLE” means that the tyre has been specifically designed to be regrooved.
Regrooving must always be performed by a specialist who restores a used tyre’s tread by re-cutting the tread grooves using special equipment.
Tyre manufacturers provide instructions on recommended groove width and the maximum depth of rubber to be removed from the base of the tread.

All tyres that could possibly undergo this procedure must be inspected. Regrooving is not advisable if the tread shows signs of lacerations, cuts or cracking.
Tyre tread regrooving safely allows the user to optimise tyre mileage, and particularly in road application does not jeopardise the tyres remoulding potential.

The sipes cut into the tyre tread are very important to obtaining proper tyre performance.
For this reason, a large part of the time that Pirelli dedicates to tread patterns concerns the study of these sipes. Sipes have at least 3 functions in particular:

1) sipes to improve consistency in tyre wear are designed to optimize the tyre’s contact patch and to better distribute the pressures applied to this area.
They are normally positioned where it is necessary to reduce the rigidity of the blocks or ribs.
In addition, by increasing the tread’s local mobility, they help to better reduce the forces applied;

2) sipes to increase traction in wet conditions create additional “edges” in order to increase lateral grip and/or tyre traction/ braking.
Of course, it’s necessary to find the proper balance in the number of sipes used, which depends on the use of the tyre and the physical and mechanical characteristics of the tread compound used.
For example, in “on/off” tread patterns, there should be no sipes, or as few as possible, in order to avoid worsening the cut resistance of the tyre.
Sipes also play an essential role in the rain in that they “break” the layer of water that forms on the asphalt.
In snowy conditions, the sipes capture the snow, through snow-on-snow contact, in order to reduce sliding;

3) sipes for acoustic/ style purposes are an element that distinguishes the tyre in the eyes of the future user by providing the performance and other particular features desired.
But their function is not purely one of style.
In recent times, they have taken on greater importance with the introduction of noise-reduction regulations.
Indeed, sipes are also used in order to alter the frequency of the sounds made by new tyres in order to reduce the noise that can be disturbing to the human ear.

Current legislation allows for “standard” tyres to be differentiated from “winter” tyres using the M+S label (or also MS, M&S, M/S or M-S), which stands for mud and snow.
In fact, European regulations have established that tyres with the M+S label are equivalent to chains.
The best tyre manufacturers for medium/ heavy-duty tyres do have specific products for those who often find themselves driving in temperatures below -5°C and in heavy snow.

In such cases, each manufacturer has different methods for labelling the specific features of their products, but it is common for there to be a snowflake on the side of the tyre.

The tread pattern of such a specific purpose tyre is easily recognizable because it features a dense system of sipes, whereas the width of the tyre will depend on the type of tyre design (e. g. for fresh snow, compact snow, mixed conditions, etc.).

It is very much not recommended to mount a Tube Type tyre without an inner tube.
This type of tyre does not have a suitable liner compound or liner thickness to ensure that it won’t let air pass through it and, consequently, through the tyre’s carcass, which could cause serious problems.

However, there are tyres with a 20” or 24” rim diameter that can be used tubeless.
Such products are intended for niche markets (e.g. military use) and have been designed specifically for use with run-flat/bead-lock systems that cannot be used with an inner tube.

Should you not need these accessories, it is normally possible to mount the tyre with a tube (following the manufacturer’s instructions) using a specific fixed-valve modular rim with seal (either round or triangular).

Tyre pressure does not remain constant over time, but rather tends to diminish due to a number of factors.
Proper tyre pressure is key to tyre safety, performance and durability.
Tyre pressure that is too low leads to overheating and consequently to tyre damage.
reduced driving safety and irregular tyre wear. These shorten tyre life.
Excessive pressure, on the other hand, lowers performance by reducing the tyre’s contact patch with the road, lowering driving comfort and shortening tyre life.
Pressure of the tyres, including the spare, should be checked at least once a month while the tyres are cold and corrected when necessary.

Driving safety, especially in unfavourable weather conditions, depends on a great many factors with the depth of the tyre tread playing an essential role.
Performance in the wet diminishes in proportion to tread depth.
Tread depth should never be less than the prevailing legal limit (e.g. 1.6mm in Europe), which is why tyres bear a tread wear indicator (or TWI) to warn when this limit has been reached. However, for safety reasons, we recommend replacing tyres when tread depth approaches 3mm..

Irregular tyre wear can be the result of one or more mechanical or geometric characteristics of the vehicle that are beyond tolerance levels (alignment, camber, worn shock absorbers, air leaks, etc.) and/or of incorrect tyre pressure.
Once it has started, it’s diff cult to correct, but it is possible to reduce the rate at which the irregular wear progresses by restoring the vehicle to its optimal condition.
There is also a type of treadwear that is typical of the drive axis (high power/ torque or use of a retarder system) that is seen with high tread depths and which tends to regress proportionately with tread wear.

The basis of the compounds used is definitely natural rubber.
There are various kinds, and only certain types have the physical and mechanical characteristics for use in tyres.
The natural rubber is then “reinforced” mainly with carbon black.

Here, too, depending on the number and size of the particles (i.e. how fine the grain is), various types of performance can be achieved.
For example, some types of carbon blacks are used to increase tyre life in terms of distance travelled, while others significantly increase stress resistance.
For this reason, some 15 different compounds can be used in a tyre, depending on their function and where they are used within the tyre.

Nowadays, the structural part of a truck tyre is based on steel cord (of various diameters) that form the “frame” of the tyre to which the compounds are then applied, encompassing the frame. In a truck tyre, steel can account for more than 20% of its total weight.

This indicator is now obsolete in Europe and relates to the old standards for “conventional” tyre carcasses, which were based on multiple overlapping textile fabrics.
“PR” stands for ply rating (number of layers) and is an indicator of the tyre’s load capacity or resistance, but is entirely unrelated to the current load index system.

In Latin America or in Africa, where these conventional tyres are still in use, this labelling is required even for steel radial tyres (and is usually located next to the load index), which is why tyre manufacturers still tend to include it in their lettering.

However, even when it’s not indicated, it’s possible to find it by checking the DOT code for the North American market (if found).

This lettering includes an indicator for load range (LR) on a scale from A to N, and a conversion table can then be used to convert load range to ply rating. For example, LR G corresponds to 14 PR.

The number following the “E” indicates the country in which the tyre was homologated. For example, E3 simply indicates the tyre was homologated in Italy, but a tyre can just as easily bear other country codes. For example, E4 indicates the Netherlands, and E1 is for Germany.

Normally, for the latest generation of tyre sizes, i .e . with a nominal tyre width expressed in millimetres, the aspect ratio appears after the “/” (e .g . 315/80 R 22 .5).
This number is a percentage and represents the ratio of the total width of the inflated tyre (or its “chord”) and the sidewall height (the distance from the base of the bead to the highest point of the tread).

In certain standardised sizes, which tyre width is still expressed in inches, the aspect ratio is not always clearly indicated.
In the size 12 . 00 R 20, the number 12 is the nominal chord, while 00 indicates the aspect ratio, which is normally recognised as having an aspect ratio of 100 (more accurately, for radial tyres the ratio is closer to 98%).

Another example of a size in inches is 13 R 22.5, where the aspect ratio is not indicated at all.
In such cases, it is normally considered to be an aspect ratio of 90, although technically the ratio is more like 85%.

In 6x4, the first number indicates the total number of hubs on a motor vehicle (i .e . the ends of the axles on which the wheels are mounted), whereas the second number indicates how many of these hubs transmit power.

In this way, we can easily identify all-wheel drive vehicles as 4x4, 6x6, 8x8, 10x10, etc. , whereas in the case of 6x4, we have a vehicle with three axles (and 6 hubs), with only 2 drive axles (for 4 hubs).

With this type of classification, it is not possible to know if the configuration of the vehicle calls for the use of twin tyres or how many steering axles the vehicle has.

There are forces in nature that oppose the movement of a vehicle.
One of these is the tendency for a tyre to resist rolling by losing shape and absorbing energy, which is dissipated in the form of heat.
Tyre deformation is caused by a number of factors, including: pressure, load applied, type of structure, size (diameter and tread width), and the quantity and characteristics of the materials used (particularly the compounds).

All of these parameters are optimised when a given tyre is designed based on the performance required, but the end user is responsible for ensuring proper tyre pressure and load.

Rolling resistance is often mentioned when talking about fuel consumption.
Indeed, for an industrial vehicle moving in a straight line at the highest speed allowed by law, the tyres can account for up to one-third of the fuel consumed.