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.
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.
Tubeless tyres provide users with a number of advantages. These can be summed up as follows:
> 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.
> 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.
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.
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:
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.
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%.
Check that the new tyre can be fitted to the existing wheel rims (consult the “Technical Data” booklet). If not, replace the rims.
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.