31/03/2020
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Tech advice: Why the weight of your motorhome matters

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Words by Peter Rosenthal

According to the Society of Motor Manufacturers and Traders (SMMT), 10,800 LCVs – including motorhomes – are stopped each year. Of these 88.5% are overloaded. It’s an increasingly common problem that is becoming worse with newer vehicles.

The latest motorhomes have an increasing amount of equipment being added but the demand is for these vehicles to weigh 3,500kg, because motorhomes weighing 3,500kg and under can be driven on a normal car licence (licence code B).

So, we have a situation where more weighty equipment is being added but there is a limit on the maximum overall weight available. This often means payload is compromised.

Most brochures will quote weights for a motorhome in three ways – the MAM (maximum authorised mass), the payload and the MRO (mass in running order).

The MRO is the number we are most interested in here and it includes a set list of criteria. It’s designed to give a representative weight of the vehicle, and is typically quoted with partially filled fuel and water tanks, a gas cylinder and an average-weight driver. However, different manufacturers use different criteria so check what is included.

As the payload is calculated by subtracting the MAM from the MRO, this means that you can’t easily compare payloads between brands.

For example, Swift’s MRO calculations include 75kg for the driver (about 11st 11lb in old money), a 90% full fuel tank and a 6kg Calor Lite gas bottle. It’s calculated with the fresh water tank empty.

Hymer’s MRO figures allow 75kg for the driver, but includes a full tank of fuel, 20 litres of fresh water, gas in an aluminium bottle and an electric hook-up cable.

Auto-Trail’s MRO figures allow 75kg for the driver, a full tank of fuel, a full LPG tank (or one full 13kg gas cylinder) and an empty fresh water tank.

Motorhome accessory weights

Extras such as generators and LPG tanks must be allowed for in your motorhome's payload

Few motorhomes leave a dealership without at least one optional extra added and some buyers tick lots of option boxes and thus have a significant reduction in payload. To give you an idea, here are some popular options and their weights.

Motorhome base vehicle options

Fiat Ducato 160bhp/180bhp engine (in lieu of 140bhp engine) – 15kg

Fiat Ducato nine-speed automatic gearbox – 18kg

Ford Transit six-speed automatic gearbox – 35kg

Motorhome accessories

Towbar – 60 to 80kg (depending on base vehicle)

Fiamma F45S 4.5m awning – 30kg

Fiamma Carry-Bike L80 bike rack – 7.9kg (plus a load of up to 60kg)

Rear corner steadies – 18kg

Wraparound cab blinds – 6kg

Reversing camera and wiring – 2kg

This motorbike garage will add considerably to the weight on the rear axle

Motorhome touring kit weights

While it’s easy to find the weight of big-ticket accessories – cassette awnings and towbars – it’s all too easy to overlook the weight of more basic items that all motorhomers carry.

Most foodstuffs are helpfully labelled (such as a 1kg bag of sugar), but it’s the items that you don’t pay that much attention to that can nibble away at your motorhome's payload.

To give you an idea, here are some common items and their approximate weights:

  • Waterproof coat – 1.3kg
  • Thick fleece jumper – 0.6kg
  • Man’s shirt – 0.3kg
  • Walking boots – 1.5kg
  • Large bath towel – 0.85kg
  • Can of shaving foam 200ml – 0.28kg
  • Shower gel 500ml – 0.58kg
  • Bottle of wine – 1.2kg
  • 4 x 440ml beer – 1.85kg
  • Milk 2-litre – 2.1kg
  • Loaf of bread – 0.8kg
  • Tin of baked beans – 0.46kg

The effect on motorhome rear axles

Adding weight to the rear of a motorhome, such as on a towbar or with a bike rack, can exaggerate the weight on the rear axle due to the cantilever effect. The longer the rear overhang of your vehicle, the more likely this is to be an issue.

You can measure the overhang and work out the extra weight pressing down on the rear axle by the addition of an extra load by using an online calculator. The maths is as follows:

Rear axle loading = axle load (kg) + weight of new item (kg) + [weight of new item (kg) x (overhang / wheelbase)].

Calculated figures are only as accurate as the figure you input and, if you forget to include an item, which is inevitably the case, they can be quite far off, especially if they’re based on brochure weights.

Use a weighbridge to check your motorhome's weight

There is only one way to determine an accurate weight of your motorhome – by weighing it with the driver on board and all your touring kit loaded.

Find your local weighbridge and then visit it, pay a modest fee and weigh the front axle, followed by the whole vehicle.

This will give you three figures: the front axle weight, the total weight and the rear axle weight (total minus front axle weight). Compare these numbers with the maximum chassis weights stamped on your chassis plate (or detailed on the door jamb).

If they’re over the maximum weights, you need to take action.

You can also get a rough idea of what your vehicle weighs on an online calculator – such as that found on SvTech’s website – and these can be a useful way of working out the weight of any planned extras before you get them fitted.

Why motorhome weight matters

Driving a vehicle that’s heavily overladen is dangerous and illegal. It will also invalidate your insurance and you risk exceeding the tyre load ratings, increasing wear on suspension components and increasing your stopping distance.

Where the excess weight is stored can also have a dramatic effect on the handling. Weight mounted high up can increase the vehicle’s centre of gravity and make it far more unstable in crosswinds and when changing direction.

It is the driver’s responsibility to know the weight of the vehicle. The DVSA (which has replaced VOSA) is responsible for ensuring that vehicles are safe to drive on the roads. While the bulk of its attention concerns the haulage industry, it is also increasingly focusing on motorhomes.

With technology including weight-in-motion sensors hidden in road surfaces, it’s not a case of if you get stopped but when. If your vehicle is slightly overladen you risk getting a fixed penalty of £100 if you’re up to 10% overladen and up to £300 if it’s over 15% overladen.

If it’s overloaded by more than 30%, things get far more serious and you will get a court summons.

“You may also be prosecuted for a tyre offence,” adds Richard Drinkwater of SvTech, “If you’ve also gone over the tyres’ load rating.” Tyre offences can carry up to three penalty points and the fine can be up to a maximum of £2,500. As this is per tyre, it could amount to up to £15,000 in the case of a heavily overloaded tag-axle.

In addition, your insurance may be invalid as well as your vehicle warranty. If your overladen motorhome weighs over 3,500kg and you do not have the C1 code on your driving licence things can get very serious.

Richard explains: “If you don’t have the C1 licence category then you’re also driving a vehicle you’re not licensed to drive and committing a licence offence, which can have far more serious consequences.” Licence offences can result in upwards of three penalty points being added to your licence.

The solutions to motorhome weight issues

If you’re only slightly over the MAM, then go through your touring kit and take out any items you can live without. If you haven't used it for a season, get rid of it.

If you travel with a full fresh water tank, then empty it. Emptying a 100-litre tank can reduce weight by around 100kg. The same goes for your waste water tank.

Richard adds: “It might be worth having a towbar fitted so that you can move some stuff into a small trailer. Obviously, check you have sufficient payload for the weight of the towbar and the mounting frame (pictured below).

A towbar also requires a mounting frame, which all eats into your payload

It’s also worth looking at those bike racks that have dolly wheels attached to them as anything you carry on them is classed as part of the overall train weight, rather than eating into the motorhome’s weight.”

If no amount of redistributing or omitting kit helps bring your motorhome down to its MAM and you have the C1 category on your driving licence, then consider replating the motorhome to a higher limit.

Richard explains: “Typically, the issue is with the rear axle of the motorhome and the usual upgrade is to add an air-assistance kit as well as tyres with a higher load rating.

These modifications can add around 750kg of extra capacity. The air suspension upgrade can be relatively inexpensive for vehicles using the original base vehicle chassis, such as the Fiat Ducato, but it can be more expensive if you have an Al-Ko chassis.”

As a general rule of thumb, if your vehicle is around 200kg overweight, upgrading will usually be a paperwork exercise, but if it’s over 500kg overweight you’ll need to look at air suspension kits and uprated tyres.

Replating with no physical modifications costs £312 from SvTech and includes a new chassis plate with the revised axle limits on it.

Payloads and weights with new motorhomes

If you’re buying a new motorhome that quotes a marginal payload – for example, under 300kg, then you can ask your dealer to weigh it prior to you taking delivery and get the paperwork to show the actual MRO of your new purchase before you take delivery of it.

Case study - Renault Trafic LL29 campervan

In the case of my Renault Trafic campervan, the MAM detailed on both the chassis plate and the V5C was 3,100kg. The chassis plate revealed that the front axle weight limit was 1,585kg and the rear’s maximum 1,650kg. I visited a local weighbridge with all my regular touring kit on board and a full tank of diesel. These were the results:
 

                                                                  Front axle      Rear axle        Total

Maximum Authorised Mass                       1,585kg           1,650kg          3,010kg
           

Mass in Running Order (driver 80kg)        1,345kg           1,335kg           2,680kg
 

Payload (to include passengers)               330kg

While 330kg sounds reasonable, with six travel seats on board it would be easy to exceed it – five 80kg mates on board would put the vehicle 70kg over its weight limit. So I’ll be looking to add air suspension to the rear and upgrade the weight limit to gain a couple of hundred kilos of extra payload.

Useful links relating to motorhome weight:


How to find a weighbridge - gov.uk/find-weighbridge
All driving licence/tax/payload information - gov.uk
Replaying/upgrading - svtech.co.uk 01772 621800
Online weight calculator - lda2.svtech.co.uk/vehicleselect

Glossary relating to motorhome weights

DVSA - Driver and Vehicle Standards Agency (government department responsible for overseeing all aspects of vehicle safety, including weight)
GVW - Gross Vehicle Weight (same as MAM)
GTW - Gross Train Weight (MAM plus the weight of any load being towed)
MAM - Maximum Authorised Mass (maximum weight that the vehicle can be when fully laden)
MAW - Maximum Axle Weight
MRO - Mass in Running Order (the calculated brochure weight for a vehicle in running order. It will always differ from the actual weight)
MTPLM - Maximum Technically Permissable Laden Mass (same as MAM and GVW)
Payload - MAM minus the actual weight of vehicle and occupants

 

 

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