Car weight allowances
The Maximum Authorised Mass (MAM) of a car is the heaviest load that the vehicle can safely carry as defined by the manufacturer (this is also known as the Permissible Gross Weight). This includes the carry load, the weight of the car, the weight of any passengers and the weight of the fuel. If the MAM is exceeded it could damage the car’s suspension, reduce the effectiveness of the brakes and further compromise the handling of the vehicle. You can find the MAM for your car in your V5C registration document.
You should also check the listed ‘kerb weight’. This is the total weight of the car with all the standard and necessary equipment included but without any passengers, the load and the fuel. Therefore, to calculate the effective weight load that you can safely put inside and on your car, the kerb weight should be deducted from the MAM. This is very much however, a ‘rule of thumb’ as manufacturers often vary kerb weight definitions so it may not always give you the information you need to calculate a realistic load. It is simply a matter of ensuring you take care and do not overload your vehicle and therefore, put unnecessary strain on it. It is a similar story with your caravan.
The Maximum Technically Permissible Laden Mass (MTPLM) or the Maximum Gross Weight (MGW) is the heaviest weight that a caravan can be loaded to and therefore operated at. It is similar to the MAM for a car. Exceeding a caravan’s MTPLM could damage the tyres, the floor of the caravan or even the axles, making it unsafe to tow.
Another weight definition for caravans is the Mass in Running Order (MIRO). This is the pre-assessed weight of the caravan with standard specification as defined by the manufacturer, the equivalent of a car’s kerb weight. As with the car, the MIRO varies between manufacturers and it has also been known to vary within a model line. Consequently, it should not be used as a definite guide to calculating allowable safe loads, the fluctuations have been known to exceed 100kg!
How do I calculate how much weight my caravan can carry?
One of the best ways to do this is by using public weigh-bridges. These will accurately determine your outfit’s weight both loaded and unloaded. Use of a weigh-bridge can cost between £0-20 and they are available for public use across the UK. Many of our members have found that the following method is one of the most effective and reliable ways to measure the weight of your outfit using a public weigh-bridge.
To begin, ensure your caravan is completely empty except for the equipment that is legally required during transit. All water, waste, gas and luggage, etc., should be removed and only the spare wheel and battery should remain inside. Then, remove all the contents of your car (with the exception of the spare wheel, jack and any vital repair equipment). However, do fill the petrol tank, as the weight of a car with a full tank can be over 50kg heavier than one running with a nearly empty one. This will ensure (car fuel tank excluded) that your car and caravan are at the minimum weight that they are ever going to be when on the move.
Most weigh-bridges allow two measurements to be taken. These are often referred to as the ‘in weight’ and the ‘out weight’. This derives from lorries entering and leaving a depot with a change of goods in between. To get your weight measurements drive onto the weigh-bridge with your outfit and stop with all wheels on the platform and take the first measurement with the driver remaining in the car.
For the second measurement, drive forward so that the wheels of the car clear the platform but the caravan wheels remain on it. Apply the car and caravan handbrakes and lower the jockey wheel to make contact with the platform. Once you have checked that it is secure, uncouple the caravan so that the caravan only is on the weigh-bridge and take the second reading. Then, reconnect the outfit and move off the weigh-bridge. You should then receive a printed certificate from the weigh-bridge office. This will give you the minimum weight of the empty caravan, the combined minimum weight of the two vehicles and (after deducting the caravan weight from the outfit weight) the minimum, or kerb weight of your car. Then, deduct your weigh-bridge car weight from the MAM and the caravan’s weigh-bridge weight from the MTPLM and this will give you the weights up to which you can load your car and caravan. The overall aim here is of course, to not exceed the maximum weight figures and, if you are unsure of the combined weight of the objects you are loading, it is always best to err on the side of caution.