MAM stands for Maximum Authorised Mass. This is the most your lorry (chassis, body and contents) is allowed to weigh. It can be changed through VOSA, using minor alterations and/or paperwork (a process called down- or up-plating or rating, depending on the type of work involved. GVW stands for Gross Vehicle Weight. It is an older term, now replaced by MAM in official terms, but meaning the same thing.
Kerb Weight or Unladen Weight is how much your vehicle weighs 'empty'. Sometimes manufacturers will add a driver, oil, water and fuel to the kerb weight, some won't. You can find establish the kerb weight of your lorry or trailer by taking it to a public weigh bridge (see below).
Payload is how much you the stuff you put in your lorry or trailer can weigh.
One tonne = 1000kg
Your driving licence allows you to drive vehicles up to a certain maximum MAM. So if you're lorry has a MAM of more than 3.5t, you need C1 or C entitlement on your licence (pre-97 licences have C1 through grandfather rights). If the MAM is more than 7.5t, you need a C licence.
It's the MAM that counts for your driving licence. So you would not be allowed to drive a 12t lorry (a lorry with a MAM of 12 tonnes) even if physically weighs less than 7.5t on the day.
How much can you carry?
You can't carry more than your payload. The payload is the difference between your MAM and the kerb weight. For example, take a lorry with a MAM of 7.5t. If it has a kerb weight of 6.25t, you can carry a maximum payload of 1.25t.
A horse can weigh anything between 200kg of a 11hh pony, to 700kg for a 17hh warmblood.
You also have to take hay and feed, water (1 litre of water = 1kg), fuel (1 litre is a little less than 1kg), you and your passenger and luggage, tack, and so on.
If you're towing a trailer behind your van or lorry, the trailer's load on the towbar will also add weight to your back axle, this will be exaggerated if your tow bar is far away from your rear axle.
Kerb Weight
It is saddening that when a horsebox is advertised for sale, the vendor (be it private or trade) almost always neglects to inform the reader what the kerb weight of the vehicle is.
It is my opinion that any horsebox vendor ought be legally required to show a weight certificate to definitively state the unladen weight vehicle (produced when taken to a horsebox to a public weigh bridge).
However, I would strongly recommend that as a buyer, one should insist that you see a weight certificate at the very least, if not have the vehicle taken to the nearest public weigh bridge in your presence, before you part with your cash!
Do some makes of lorry weigh more than others?
Firstly, the weight of the horsebox body itself needs to be taken into account. A horsebox body fitted with 50 tack lockers and a hot tub will weigh more than a simple aluminium box with a simple playwood living sectoin.
However, the base chassis do weigh siginifcantly different amounts.
Take the 7.5t segment: German makes (MAN and Mercedes Benz) do tend to be very well engineered, so do only have a body and payload allowance of between 4 and 4.4 tonne (approximately). Iveco and DAF lorries tend to have body and payload allowances of just over 4.5t, making them far more popular as base models for conversions.
In recent years, these traditional main stays of the 7.5t market have faced competition on two fronts.
Firstly, Japanese 7.5t lorries tend to be lighter duty (mainly because the European chassis are also used for 10 or 12 tonne lorries), so can carry more. Isuzu, Mitsubishi and Hino (Toyota) are producing 7.5t lorries with body and payload allowances of up to 5t!
Secondly, Iveco are doing very well selling large 6.5t or 7t 'mini lorries' with payloads that are comparable to the full 7.5t vehicles (4t - 4.6t).
How do I use a public weigh bridge?
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| Reading at a public weight bridge. |
After you find them on search engines or in the Yellow Pages, you can make an appointment and for small fee (usually £5-£20) you can weigh your lorry.
I've taken a loaded 7.5t lorry to a weigh bridge at a ferry port and the process was very simple. They didn't even charge (though if I wanted a weight certificate - an official print off - they would have charged me £5). I would advise taking a high visibility jacket as these are often compulsory to wear in busy haulage yards.
You could take your empty lorry along and see how much the kerb weight is, then work out how much everything you put in weighs. Alternatively, you can load up your lorry with every thing you would want to take and, provided you are travelling to an appointment at a public weigh bridge, you are actually permitted to be overweight. Hopefully, you won't be.
