The right pressure for truck and bus tyres
Choosing and maintaining the correct inflation pressure is key for optimum performance.
Tyres are the only point of contact between your vehicle and the ground
Tyres are fundamental to the safety of users and the freight you carry. For a given load and application, in clearly defined conditions, there is only one appropriate inflation pressure for each tyre.
So it is important to find the correct tyre pressure. The air pressure in a tyre is crucial for tyre performance: it is what will carry and move a load or people:
However, Michelin's surveys reveal that pressure is one aspect of maintenance that is often not monitored as well as it should be.
Pressure and safety
The wrong pressure has a negative impact on some fundamental aspects of safety performance, such as:
- Casing strength
- Vehicle stability and handling
- Sensitivity to kerbing
Variation in inflation pressure
While in use, a tyre can lose pressure for various reasons:
- Airtightness of the rim (e.g. cracks or welds)
- A hole that goes through the structure
- Natural infiltration through component parts
Apart from on-board monitoring systems, a regular, visual pressure check using a pressure gauge is the most common way of detecting problems with air leaks.
the right pressure
REASONS FOR INFLATION PRESSURE CHECK
■ Pressure checks should be made on all the tyres on the vehicle:
- If the inflation pressure is too low, the result is an abnormal rise in running temperature which may lead to damage to the internal components. This damage is irreversible and may cause the destruction of the tyre and rapid deflation.
- The consequences of running with insufficient pressure in the tyres are not necessarily immediate and may even become apparent after the pressure has been corrected.
- The spare tyre should also be checked.
- Tyre pressures must be checked on cold tyres regularly or when the vehicle is serviced, using a calibrated pressure gauge.
- Insufficient inflation pressure also greatly increases the risk of aquaplaning.
- Over-inflation can cause rapid and irregular wear and increased sensitivity to impact (tread damage, casing failure).
- Even if tyres are inflated with nitrogen, the pressure still needs to be checked regularly.
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- Check the pressure of tyres when they are cold.
- Pressure increases while driving; you must never reduce the pressure of a tyre when hot.
- Never reinflate a tyre that has been driven on while under-inflated without a careful interior and exterior examination of the tyre.
- Cold inflation pressures of over 10 bar (145 psi) are formally discouraged.
- Cold inflation pressures that are over 0.6 bar (8.7 psi) higher than the recommended pressure should be corrected immediately.
- In all cases, adhere to current regulations in the country of use.
- Use an accurate, calibrated pressure gauge and handle it with care.
- If a tyre when checked hot has an inflation pressure lower than the recommended level, the tyre should be removed and checked in accordance with safety instructions.
- If one tyre seems markedly hotter than the others, it should also be removed safely.
- The inflation pressures of tyres on a single axle should usually be approximately the same.
- Tyre pressure should be checked 24 hours after fitting and must not be more than 5% lower than the original pressure.
- Adhere to the inflation pressures recommended by the vehicle or tyre manufacturer.
The influence of tyre pressure on mileage performance
Under-inflation by 1.5 bar (21.7 psi) = 10% performance loss
The influence of tyre pressure on fuel consumption
Inflation pressure has a proven influence on fuel consumption. An unsuitable inflation pressure increases the rolling resistance of tyres and therefore the vehicle's fuel consumption.
Under-inflation by 1.5 bar (21.7 psi) = 1% excess consumption
Excess consumption when tyres inflated to 7.5 bar (109 psi) not the recommended 9 bar (130.5 psi), i.e. 17% over-inflation
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