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TRUCK & BUS WORLD



FAQ

Increasingly often tyres are appearing on the market with an arrow embossed on the sidewall. What’s it for?

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.


Do all valves have the same technical specifications?

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.


What do the letters FRT mean on some trailer tyres?

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.


Is it possible to trace the date of manufacture of a tyre?

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.


The treads on road trailer and semi-trailer tyres all seem to run lengthways around the tyre; is there a technical reason for this?

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.


Seeing the word “REGROOVABLE” written on the side of Commercial vehicle tyres is becoming more and more common. What does it mean?

“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.


What is the purpose of sipes in a tread pattern?

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.


Are there any “winter” tyres for heavyduty vehicles?

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.).


Can Tube Type tyres (e.g. with a 20” rim diameter) be mounted tubeless?

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).


Why is proper tyre pressure important and how often should it be checked?

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.


When should tyres be changed?

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..


Why do tyres sometimes wear irregularly?

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.


What components are essential when manufacturing a truck tyre?

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.


On the sides of some tyres for industrial vehicles, there’s a number followed by “PR”. What does this mean?

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.


Do all tyres homologated for sale in Europe have to include the E3 code imprinted on the sidewall?

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.


Is aspect ratio always indicated in the tyre code?

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%.


What is a 6x4 vehicle?

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.


What does “rolling resistance” for a tyre mean?

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.