The markings that appears on the side of the tyres also tells us the basic size of the tyre, the rim diameter and the width of the rim.
We will illustrate how to read two different types of branding that may appear on the side of the rally tyres.
C: Nominal section width expressed in mm - 225
D: Nominal external diameter expressed in mm - 600
d: Nominal rim diameter of the rim, expressed in inches - 16
C: Nominal section width expressed in mm - 205
h/C: Tyre’s technical series. This expresses the ration between the section height (in mm) and the nominal section width (in mm) - 65
Radial construction - R
d: Nominal rim diameter of the rim, expressed in inches - 15
The treads of the various versions of rally tyres are described by one or two letters followed by a number. The letters identify the type of tread.
The number after the letter indicates the type of use, for example: RX 7
Make sure that tyres are fitted by experts, with specialised dedicated machinery and equipment, who follow safety procedures.
Before mounting the tyres clean the surface of the beads and the area of the rim that comes into contact with the tyre.
Use ONLY special tyre lubricants for mounting tyres. Do NOT use silicone or petroleum lubricants.
Check the state of the valves to prevent air loss: Check the seals and the tightness for metal ones and check also for any tears or cracks in rubber seals. If necessary, replace them. When the tyre is being used, always use the valve cover top.
Follow the indications provided on the sidewall of the tyre referring to the rolling direction and the correct positioning of the internal and external sidewalls, if specified.
Use the safety cage when inflating tyres.
Before unseating the tyre from the rim during disassembly, make sure that the tyre has been fully deflated, removing the inner valve mechanism.
Temperatures measured on the tread are an excellent indicator for deciding the best choice of final compound and for optimising corner adjustments of the vehicle, such as camber and toe.
We recommend measuring the temperature at three different points: inner (innermost side of the vehicle), centre, outer tread.
In particular, average temperatures must be the ones shown in the table, the difference between the values measured internally, in the centre and externally must be maximum 20°, while the difference between the front and rear axles must be no more than 25°.
If these values are exceeded, we recommend a different final compound should be used or the vehicle’s geometry should be adjusted.
Working pressure values depend on the size of the tyre in relation to the load that it is subjected to. In other words, it will vary according to the type of car, the weight and conditions of use.
In particular, as the weight of the vehicle, speeds and accelerations that the tyre is subjected to increase, the working pressure must be increased. In any case, tyres should not be used at pressures below 1.6 bar.
Using excessively low pressures would bring about the breaking of the tyre due to excess force on the sidewall or unseating from the rim. “Hot” working pressures are usually in the range of 2.2 – 2.5 bar.
Initial inflation pressures vary in order to obtain these values, depending on whether the tyres are preheated or used “cold”. Indeed, preheated tyres can be inflated to slightly lower values than cold tyres.
The difference will depend on the type of heater, the time it remains and the environmental conditions.
The tread on some types of tyres can be hand cut to increase the size of the existing grooves.
Hand-cutting is useful for improving grip in certain intermediate situations, between dry and thoroughly wet surfaces, or on mixed gravel/rock and sandy surfaces.
The tread efficiency in the conditions for which it was originally designed will no longer be the same.
Hand-cutting must be carried out by experts using specialised equipment, suitable for use while observing safety regulations.
The colours are used to highlight where grooves can be hand-cut.
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