A caravan’s tyre placard, which is usually incorporated within the van’s compliance plate, is an important part of a caravan or camper trailer.
The intent is to provide an assurance from the manufacturer to a potential buyer that the selected tyre size and load rating, along with the recommended tyre inflation pressures, have been professionally determined, so as to provide the optimum caravan handling and stability performance, at both the empty and the fully-loaded conditions.
UNDERSTANDING THE PLACARD
The tyre placard must show at least the following information:
- Caravan manufacturer’s recommended tyre size;
- Tyre load rating
- Tyre speed rating; and
- Cold inflation pressures
The tyre placard must also contain the following statement:
“The tyres fitted to this vehicle shall have a speed category not less than ‘L’ (120km/h).”
If the recommended maximum vehicle operating speed is less than 120km/h, it should say, “The tyres fitted to this vehicle shall have a speed category at least equal to the recommended maximum vehicle operating speed, ‘…’km/h.”
In this case, ‘…’ is the vehicle manufacturer’s recommended maximum vehicle operating speed. It is not permitted to state any specific tyre manufacturer’s name or brand.
The tyre load rating must be stated in kilograms and the tyre inflation pressures must be stated in kPa (not psi).
It is essential that caravan buyers fully understand all of the information that is provided by the manufacturer on the tyre placard, before they accept the caravan, in order to avoid possible problems in the future.
All relevant tyre and permitted wheel specifications are listed in the Tyre and Rim Association of Australia’s Standards Manual – visit www.tyreandrim.org.au
TYRE LOADS
For load-sharing suspension systems, the maximum legal individual tyre load equals the GTM rating divided by the number of tyres fitted to the van.
The individual tyre load, when the van is empty, equals the Tare mass minus the empty ball loading divided by the number of tyres fitted to the van.
For non-load-sharing suspension systems (on tandem-axle vans), the front and rear tyres will have different loadings, if the van is not level (in a side view).
For maximum traction and tread life, the loading needs to be spread evenly across the full width of the tread.
This can only be achieved if the correct inflation pressure is used, so that the tread is at the same temperature across its full width. The use of a tyre pyrometer is really the only efficient way of checking this.
UNDER-INFLATION
If a tyre is not inflated to the pressure that is required to match the actual tyre loading, the tyre tread will not have full contact with the road surface, causing the outer portions of the tread to be subjected to increased loading, with subsequent increased temperatures and increased wear.
The traction between the tyre and the road surface will be decreased, and the sidewalls of the tyre will significantly flex, causing the van to wallow and sway.
OVER-INFLATION
If a tyre is inflated above the pressure that is required to match the actual tyre loading, again the tyre tread will not have full contact with the road surface, this time causing the centre portion of the tread to be subjected to increased loading, with subsequent increased temperatures and increased wear.
Again, the traction between the tyre and the road surface will be decreased, causing the tyre to bulge, and the van to bounce and skip.
In both cases, the handling and stability of the van will be impaired, and the tyre life appreciably reduced.
While most of the tread will have plenty of kilometres of travel remaining, the outer peripheries of an under-inflated tyre will be worn down to the tread wear indicators, thus rendering the tyre un-roadworthy, while for an over-inflated tyre, the inner periphery will be worn down to a dangerous and illegal level.
MEET THE AUTHOR
Max Taylor
Max Taylor has been caravanning since he was a kid and was the editor of some of Australia’s most well-known RV publications for almost 10 years.
