How to Calculate the Combined MAM of a Car and Caravan

Difference between tare weight, MAM, and payload

Before adding weights, it is fundamental to understand what the terms in the technical sheet mean. Tare weight (or empty weight) is the weight of the vehicle without load, without a driver, and with full tanks. The Maximum Authorized Mass (MAM) is the maximum weight certified by the manufacturer for the vehicle, including its own tare, passengers, luggage, and any additional load.

Payload is the difference between the MAM and the tare weight. It is the actual number of kilograms available for people, luggage, and accessories. A common mistake is confusing the empty weight with the available load; the payload is always less than the MAM and is the key figure for knowing how much luggage you can carry without overloading the axle.

Section references: Certifix - Pesos y masas en la ficha técnica de los vehículos ↗

• Tare weight: Weight of the empty vehicle.
• MAM: Maximum total certified weight.
• Payload: MAM - Tare. It is the weight available for load and passengers.

How to calculate the combined MAM and legal limits

To determine if your car can legally tow a caravan, you must calculate the combined MAM. This is obtained by adding the MAM of the tow vehicle and the MAM of the caravan. In Spain, regulations establish clear limits based on the driving license.

If the combined MAM does not exceed 3,500 kg, you can drive it with a standard B license. If the combination exceeds 3,500 kg but not 4,250 kg, you need the 96 code on your license. Exceeding 4,250 kg requires a C1 license. It is crucial to verify these limits before purchase, as the caravan's MAM includes its maximum weight with all tanks full and passengers on board, not just its empty weight.

Section references: DGT - Con caravana, remolque o autocaravana ↗ · Fixlab - Bajar la MMA: cuándo se puede y cómo se tramita ↗

• Combined MAM = Car MAM + Caravan MAM.
• B License: Combination up to 3,500 kg.
• 96 Code: Combination between 3,500 kg and 4,250 kg.
• C1 License: Combination over 4,250 kg.

Calculating the actual available payload

Once you have verified that the combined MAM is legal, you must calculate the actual payload of the caravan to know how much luggage, water, and passengers you can carry. The formula is: Payload = Caravan MAM - Caravan Tare.

It is important not to confuse the caravan's payload with the car's towing capacity. The car's towing capacity is calculated by subtracting the car's Mass in Running Order (MRO) from its MAM. However, to know how much you can load inside the caravan, only the caravan's payload matters. If the sum of passengers, luggage, and water exceeds the caravan's payload, you will be overloading the trailer, which is dangerous and illegal, regardless of the car's towing capacity.

Section references: Certifix - Pesos y masas en la ficha técnica de los vehículos ↗ · Mundovan - ¿Cómo calcular si mi coche puede remolcar una caravana? ↗

• Caravan Payload = Caravan MAM - Caravan Tare.
• Car Towing Capacity = Car MAM - Car MRO.
• The load inside the caravan must not exceed its payload.

Common errors when estimating luggage and water weight

Water is the element that surprises caravaners the most due to its weight: 1 liter of water weighs 1 kg. A caravan with 100-liter fresh water and 50-liter grey water tanks adds 150 kg to its weight. If this is not taken into account, it is easy to exceed the payload without realizing it.

Another common error is underestimating the weight of luggage. A large full suitcase can weigh between 15 and 25 kg. With four passengers and their luggage, you can easily add 100 kg or more. It is recommended to weigh the luggage on a scale before loading the caravan and add the weight of the water according to the tank levels. Overloading affects stability, braking, and suspension, and can invalidate the manufacturer's warranty.

• 1 liter of water = 1 kg.
• Weigh luggage before loading.
• Consider the weight of passengers (approx. 75-80 kg per adult).
• Overloading compromises safety and legality.

Verifying the vehicle's towing capacity

In addition to the combined MAM, you must verify that the caravan's MAM does not exceed the maximum towing capacity indicated in your car's technical sheet. This capacity is usually expressed in kg and is the maximum weight certified by the manufacturer for the tow hitch.

If the caravan's MAM is greater than your car's towing capacity, you cannot legally tow it, even if the combined MAM is below 3,500 kg. For example, if your car has a towing capacity of 1,500 kg and the caravan has an MAM of 1,800 kg, it is not compatible. Always consult the technical sheets of both the car and the caravan to confirm this compatibility before purchase.

Section references: Mundovan - ¿Cómo calcular si mi coche puede remolcar una caravana? ↗

• Caravan MAM <= Car Towing Capacity.
• Verify the technical sheets of both vehicles.
• Towing capacity is a limit independent of the combined MAM.

Documentation required for MOT and circulation

To legally drive with the caravan, both vehicles must be up to date with the MOT (Vehicle Technical Inspection). The caravan must have its own registration certificate and be registered. Additionally, the tow hitch must be in good condition and compatible with both vehicles.

It is recommended to keep the technical sheets of both vehicles handy to verify weights in case of a police check. Overloading can be detected during the MOT or road checks, and can result in fines and vehicle immobilization. Ensure that the load is well distributed and secured to avoid stability issues.

Section references: DGT - Con caravana, remolque o autocaravana ↗

• MOT up to date for car and caravan.
• Caravan registration certificate.
• Tow hitch in good condition and compatible.
• Technical sheets available to verify weights.