Specification and inflation pressure - Toyo Tires H08
KEY POINTS
- The rear axles of single-wheel axle motorhomes are vulnerable to over-loading with possible subsequent tyre failure due to the potential for users to inadvertently place excessive load items in the vehicle without realising they have exceeded the stipulated gross vehicle mass
- Rated vehicle Gross Vehicle Mass (GVM) are often not indicative of the actual loaded vehicle weights
- Excessive heat generated by flexing from excessive load and/or incorrect tyre pressure damages the bonding between tyre components and can result in in-service failure
- Due to the nature of how they are used, motorhomes require precise tyre pressures determined by weigh bridge readings. This is critical for single rear-wheel axle motor homes
- Toyo Tires H08 product is the most common product used for fitment to caravans / motorhomes
- Contact Toyo Tires technical manager Steve Burke for assistance on sburke@toyo.com.au, (02) 8796 0271 or 0407 235 150
THE ISSUE
Tyre failures caused by under-inflated / overloaded tyres are known to occur on motorhomes and caravans. Toyo Tires has identified specific incidents where the H08 product has been incorrectly specified and fitted, or incorrectly inflated, on these vehicles.
Any tyre failure has serious consequences – placing vehicle occupants and road users in potential danger.
Over-loaded tyres generate excessive heat due to increased flexing. Over time, excessive heat damages the bonding between the tyre components. This creates the potential for tyre disintegration in service.
When loaded, the actual weight of caravans and motorhomes can exceed the vehicle’s factory rated GVM. On motorhomes with single-wheel rear axles where there is excessive loading, the rear axle load is usually problematic, with some vehicles having rear axle loads greater than the manufacturer’s maximum ratings. For this reason rear tyres are most prone to failure due to over-loading / under-inflation.
THE SOLUTION
To determine suitable tyre inflation pressure, correct loaded axle weights are required. Each axle must be individually weighed on a weigh bridge, when the vehicle is fully loaded.
With this information, accurate cold tyre inflation pressures can be determined. If you are uncertain about inflation pressures please contact Toyo Tires technical manager Steve Burke with an accurate GVM for a technical recommendation.
Recommended cold inflation pressures will provide a safety margin, which is standard engineering practice. Safety margins also take into consideration the fact that when in service tyres will often have loads (dynamic loads) that are much higher than those measured on the weigh-bridge (static-loads), due to factors such as road camber and weight transfer.
WHAT TO DO WITHOUT WEIGH BRIDGE READINGS
Where tyre dealers are fitting tyres to caravans and motorhomes or on loose wheels in the absence of recent weighbridge results or tyre manufacturers recommended inflation pressures, it is recommended that tyres are inflated to the maximum rated inflation pressure.
Tyre dealers have a responsibility to ensure that tyres they supply are inflated to the correct pressure and that the consumer is aware of the correct pressures for their vehicle/application.
For tyre dealers, taking this course of action is the most effective way of preventing tyre fatigue or failure due to under-inflation. It is highly recommended to tyre dealers that caravan and motorhome users weigh-bridge their vehicles when loaded to ensure actual tyre loadings are known, and all steps are taken to prevent tyre over-loading.
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