Diamond Dave

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Every motorcaravanner must know the weight of their 'van and its limits – read more with advice from Practical Motorhome's technical expert Diamond Dave

Do you know what the legal maximum weight of your motorhome is? Come to think of it, do you know how heavy your motorhome actually is?

All road vehicles in this country have specific limits on their weight, the details of which will be stamped on the VIN plate. Exceeding any (or all) of these weight limits can put you firmly on the wrong side of the law, and might lead to heavy fines; what’s more, if they are broken by too large an amount you might not be allowed to continue your journey.

The issue of motorhome weights can be confusing – so let's clarify matters.

Check your plate for mass information

First things first: look out for the VIN plate, which will be located somewhere on the motorhome. It’s usually a metal plate that’s attached under the bonnet, but it might otherwise be a label stuck in a cab doorway.

On the plate will be the motorhome’s VIN (Vehicle Identity Number), along with details of its Maximum Allowed Mass (MAM), Maximum Train Weight (MTW), maximum front-axle weight and maximum rear-axle weight. The latter will often be listed as ‘axle 1’, ‘axle 2’ and – in the case of tandem rear-axles – ‘axle 3’.

The MAM is simply the maximum weight that the vehicle is legally allowed to weigh: this includes everything carried in the vehicle. MTW is the legal maximum that the vehicle (and any trailer it pulls) may weigh, while the individual axle weights are the legal maximum for each axle. Exceeding any of these limits can result in a big fine, so be careful.

Overload can be avoided

It’s very often the case with motorhomes that, even though the MAM is not exceeded, an individual axle limit can be. It’s usually the rear axle, but sometimes it’s the front. The overload of one axle can usually be rectified by simply moving items to a different location within the motorhome.

A few A-class ’vans built on lighter chassis will struggle to remain legal on the front axle, though: this is because the body adds a significant load at the front, and there’s a large drop-down bed located over the cab. You may well have noticed that the MAM of your vehicle is lower than the total of the axle limits: this is done deliberately to allow for variations of loading.

However, many vehicles can have their MAM uprated: the first step is a relatively simple paper exercise, whereby the MAM is raised to the total of the axle weights. This usually upgrades a 3500kg motorhome to around 3850kg MAM. It doesn’t alter individual axle limits, though, so may not have much real benefit.

Axle limits can often be uprated, but will usually involve upgrading the suspension and tyres. Air-assist rear suspension can be used to increase a rear-axle limit, and therefore also the MAM. Even front-axle limits can be raised; but this will normally involve fitting heavier-duty springs. Tyres will almost certainly need to be upgraded to allow for an axle uprate, so the cost of a new set must be considered.

Increase a MAM with caution

Raising a vehicle’s MAM to more than 3500kg does have other consequences: your driving licence might also require an upgrade. Most people who passed their test before 1 January 1997 will have a C1+E licence: this entitles them to drive a vehicle up to 7500kg, and tow a trailer up to a total outfit weight of 8250kg. Anyone who passed after that date will have a B1 licence (unless a further test has been taken): this only allows them to drive a vehicle of up to 3500kg. In addition, speed limits might be lower for a vehicle exceeding 3500kg MAM on the Continent; in the UK, the speed limit is based on unladen mass.

One benefit of having your motorhome uprated to more than 3500kg is lower road tax: Private Light Goods (PLG) is the category covering motorhomes lighter than 3500kg, and it carries a higher road tax figure than that for the Private Heavy Goods Vehicle (PHGV) category. Strange, but true!

A keen motorcaravanner, Practical Motorhome's technical expert Diamond Dave runs his own leisure vehicle workshop. Find out more at Dave Newell Leisure Vehicle Services.
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