Truck & Bus Tyres

Aspect Ratio
Section Height
---------------------   x 100 %
Section Width 

Overall Diameter (OD)
The measurement of the distance of an unladen tyre from tread surface to tread surface on opposite sides of the tyre.

Overall Width (OW)
Measurement of the cross section of an unladen tyre, including ribs and protrusions. Usually the same as section width on radial tyres.

Section Width
Measurement of the cross section of an unladen tyre across the casing only – not including ribs or protrusions.

Tread Width
Distance across the tread face of an unladen tyre.

Tread Depth
Distance from tread surface to major groove base at a designated measuring point.

Section Height
Distance from the bead seat to the tread surface of an unladen tyre.

Rim Width (RW)
Distance between the rim flanges.

Nominal Rim Diameter
Diameter of the rim from bead seat to bead seat in inches.

Static Loaded Radius
Distance from the centre of the axle to the ground of a loaded tyre under maximum dual load and inflation pressure.

Loaded Width
The maximum section width of a loaded tyre under maximum dual load and inflation pressure.

Minimum Dual Spacing
The minimum allowable distance between the wheel centre lines in a dual arrangement.

Revolutions Per Kilometre (RPK)
The number of tyre revolutions in one kilometre, measured at: 100km/h, maximum dual load and inflation pressure.

NOTE: All dimensions measured following a 24-hour inflation period.

Dual tyre assemblies are commonly used on drive and trailer axles, however, they do
require attention if tyre life is to be maximised.

Diameter Variations

Dual assemblies with significantly different diameters will return less than optimum wear results because:

• The tyre with the larger diameter will carry more of the load, causing rapid wear.
• The tyre with the smaller diameter will be subjected to very high levels of slip, creating rapid and irregular wear.

Pressure Differentials

When tyres in a dual assembly are inflated to different pressures they will return less than optimum wear results because:

• The tyre with the higher inflation pressure will have a higher contact pressure with the road, carrying more of the load causing rapid wear.
• The tyre with the lower inflation pressure will have a lower contact pressure with the road resulting in rapid and irregular wear.

Recommendations

Bridgestone recommends that the same brand, pattern, size, load index and speed symbol be used when matching duals. The following upper matching limits for dual tyres should also be observed:

A vehicle’s wheel alignment can have a dramatic effect on how evenly and quickly the tyres wear. The following diagrams illustrate the key alignment parameters.

Typical Alignment Settings*

Load and Inflation Pressure
It is the air in the tyre that carries the load. Lowering the inflation pressure is equivalent to increasing the load on the tyre. 

It should be noted that the maximum cold inflation pressure allowed in Australia is 825kPa (120psi), which has been accounted for.

Recommended Pressure
The correct inflation pressure will depend on: tyre size, service description, actual load, actual speed, fitment (tyres in dual configuration are able to carry less load per tyre because of unequal loading conditions) and operating conditions. Incorrect inflation pressure can result in irregular wear, reduced wear life, damage or even tyre failure.

Inflation pressures should be checked on cold tyres at least every month using a reliable pressure gauge. Always use a sealing type valve cap as the valve core seal is only secondary and must not be relied upon.

Why Rotate
Tyre rotation is a practical means of reducing operating costs by helping to overcome irregular wear patterns and minimising the effects of different wear rates. Rotation can ensure that a tyre’s tread is fully utilised—reducing the cost per kilometre.

Avoid Steer Tyre Vibration
In some cases the driver’s side steer tyre on a prime mover can wear one half of the circumference of the tyre more than the other half (mini-max wear). This creates a light point, which unbalances the tyre and causes a vibration. By rotating steer tyres regularly, this effect is minimised and steer tyre vibration is usually prevented.

Method
Tyres should be rotated to the positions shown in the diagrams. Note that dual pairs should be rotated in the same pairing, ie. outside tyre remains on the outside, but in the new position.

Typical Frequency:
Steer Tyres: 25,000km
Drive Tyres: 50,000km

Otherwise, rotate as often as required to minimise irregular wear or vibration.

Single axles with dual tyres should be rotated as shown

If the application allows, steer tyres can be rotated onto the drive and trailer axles and drive tyres can be rotated onto the trailer axle.

Storage
Tyres being stored should be kept away from direct sunlight, heat sources, ozone creating generators, motors and welders, moisture, dirt, oils and chemicals in order to prevent the tyre from degrading.

Mounting The Tyre-Wheel Assembly
Wheel nuts should be done up in the sequence recommended by the vehicle manufacturer. Furthermore, wheel nuts must be checked within 50km of fitment. Torque levels and sequences are recommended by the vehicle manufacturer. Always use a torque bar to tighten wheel nuts.

Damage
Ignoring tyre damage is dangerous. Damaged tyres must be assessed and where possible repaired by a qualified Bridgestone technician as soon as possible in order to avoid further deterioration of the tyre structure.

Warranty
Any new tyre or tube manufactured by Bridgestone is guaranteed to be free of material and manufacturing defects. Should any such tyre or tube develop a material or manufacturing defect within 5 years of manufacture, Bridgestone will make a pro-rata allowance towards the purchase of a new tube or tyre.