Experiencing weight problems?

Who’s experiencing weight problems?

Your back end sways uncontrollably, your front end is on the heavy side and you have a few extra kilo’s that don’t need to be there.
Yes your caravan is overweight and probably needs to go on a diet.

EXTRA-BITS-RViewAccording to all available information, it is the responsibility of a caravan manufacturer to correctly badge a van’s weight and legally you can’t go over what is on the plate.

If you are purchasing a new van then you can work with the sales team and manufacturer to make sure all of your weight limits and payload requirements are met.
Be sure to take into consideration future additions like the awning, generator, solar panels, extra battery etc.

But, who has bought a second hand van where previous owners have adapted, added or altered a few things or just between us, have you added anything yourself? Ball weight is not right, van’s tare weight is over and no way can you fill both water tanks or even add an extra pair of undies without going over the required ATM. You find out the manufacturer has gone out of business or changed hands and no records are at hand.
I suspect heaps of people are in this situation, either not caring, turning a blind eye or simply not understanding, but what about legal implications, insurance claims and naturally safe driving practices.

Let’s look at some common terms used in caravan weights (in simple terms).

Tare mass is the base weight of the van at manufacture without payload or after-market accessories, without water in the tanks or the gas bottles filled.

ATM (Aggregate Trailer Mass) is the maximum manufacturer specified weight of your loaded caravan or trailer and is measured unhitched and sitting on it’s jockey wheel and axle(s).

GTM (Gross Trailer Mass) is the maximum weight your trailer can be at its axle(s) and is sometimes referred to as the axle capacity. Typically this is measured while the caravan or trailer wheels are sitting on a weighbridge but the hitched tow vehicle isn’t.

TBM (Tow Ball Mass) is the effective mass on the tow ball from the trailer hitch. The maximum TBM is not typically specified by the manufacturer but as a guide should be up to 10% of the ATM.

GCM (Gross Combined Mass) is when you weigh your tow vehicle and your caravan or trailer when they are all loaded up.

Payload is all the bits you add on or load up to take away (usually about 300kg allowance).

Here’s a few graphics that might make it easier.

RView-combined-TARE-ATM-ETC copy

OK let’s go back to the van’s weight problem … what can you do?

Well, it’s probably a good idea to strip back to the basics as best you can, take out all the goodies, cups and saucers, towels and blankets etc, empty water tanks and if you can use empty gas cylinders, it needs to be as basic as possible.

Then take it to a registered weigh-bridge, not just the sand and metal place down the road, you need to get an accurate and recorded measurement. I did this recently and it cost $15, money well spent.

Next, contact the manufacturer and see if they can help or contact your state’s transport department and see if they have a list of registered engineers, because it’s these professionals that can help you.

We contacted Josh Smith from Autest Automotive Transport in South Australia and asked a few questions.
Note: All vans are different and need to be looked at individually, this is just a general guide, plus each state might differ with rules and regulations.

What can be done to get it right?

Refer to the identity tag on your trailer and be clear on what you can legally carry. Also, ensure the total weight of your loaded trailer (the ATM) does not exceed the towing capacity of your car. Check the placard on your tow bar and make sure it is also suitably specified to tow in accordance with the vehicles maximum tow rating.
Confirm you are legal and check weights at a registered weigh station. You want to check at least the following weights with the car and trailer fully loaded (including people, fuel etc.);

  1. Park your entire trailer, removed from the vehicle on the scale (axle and jockey wheel).          It should not exceed the trailer ATM.
  2. Then, with the loaded trailer hitched to the vehicle, park your trailer axle(s) only on the scale. It should not exceed the trailer GTM or the rated axle capacity as specified on the trailer identification tag.
  3. Next, with the loaded trailer still attached, park the loaded vehicle wheels only on the weighbridge. This measurement cannot exceed the GVM of your vehicle.
  4. The sum of 2. and 3. Above should not exceed the GCM rating of the vehicle (note the GCM is typically the GVM plus the tow capacity when not specified otherwise).

In some instances, a poorly loaded trailer with an excessive tow ball mass (TBM) can result in an uneven load distribution on the tow vehicle axles. For tow weights greater than 750kg I suggest using a load distributing hitch. If you suspect you may have an excessive rear axle load, it is recommended to check the mass of the front axle of your vehicle with the loaded trailer attached and deduct it from the measured figure from 3. above. This will provide you with the rear axle weight in the loaded configuration. Manufacturer axle loads should not be exceeded.

I recommend putting weight (payload) over or behind the trailer axles where possible. Avoid heavy items toward the front of the trailer. It can result in unnecessarily excessive loads on your towbar and your rear axle which can diminish steering and braking performance of the vehicle.

What information can we provide to help you (tyre size / rating, axles, type of brakes, safety chain rating, coupling, A frame size), and where do we find this info?

Typically, if I am contacted in relation to the above, providing information such as the tow vehicle type, make and model including manufacturer specifications is useful (GVM, GCM, tow capacity). Information regarding the trailer would include GTM, ATM, number of axles etc. If the owner can provide weighbridge figures as per above, we can quickly assess the vehicle/trailer configuration and advise as to what options might be available. Modern trailers should have an identification tag that is accompanied with relevant information. When purchasing a trailer or caravan check that this tag exists.

Do you normally do an on site inspection?

Yes – In some instances, the owner may not have the relevant trailer information or it may get to a point where inspection and assessment is required. In such cases, we would inspect the trailer on site and may take measurements of axles, drawbar and chassis dimensions if necessary to derive the relevant specifications and advise on options to rectify any possible issue or risk.

What do you provide and what do we do with it?

The most important aspect of our role is to work with the vehicle owner to ensure their specific needs are met as almost every case is slightly different.
Depending on the nature of the assessment, we typically provide a report that details all relevant information and confirms that the trailer can (or cannot) be towed in the preferred configuration.
In some cases, we can increase the towing capacity or the GVM of the vehicle to provide greater towing and carrying capacity. We can also provide advice on upgrading trailers to increase ATM or GTM. Again such assessments are included in a summary report which is submitted to the local transport authorities who then review, acknowledge and approve the upgrade. This documentation should then be provided by the vehicle owner to their insurance company for reference.

If any structural work is needed, can we do it ourselves or who do you recommend?

In some cases, where we advise on trailer upgrades to increase the ATM or GTM for a specific purpose, any structural reinforcement or upgrades should be undertaken by a qualified person and in accordance with our advice. Any welding should be performed by a qualified welder and all workmanship is inspected upon completion. A quality job provides the right outcome and safe motoring.

Anything you want to add?

Be safe!

In all cases when towing, drive to the conditions of the road, weather conditions and traffic. Make sure the tow vehicle is suitably matched to the trailer or caravan and be sure your capabilities are also aligned! If you haven’t towed a specific vehicle/trailer configuration make your first trip a short one to familiarise yourself with the set-up.

If you are not sure, seek assistance or advice from those who know. If you have any uncertainty as to the specific ratings of your vehicle or trailer, contact the manufacturer in the first instance. Secondly, contact an accredited engineer who can guide you systematically through a series of checks to confirm you satisfy legal and manufacturer requirements.

Thanks Josh.

So there you have it, a bit of work but it is worth it … costs will vary to work done.

In some cases, all relevant information is readily available and a job takes an hour or two whereas other projects can take days – particularly if modification to vehicles and/or trailers is required.

Typically a phone call and a conversation can go a long way to establishing options and potential costs. Yes it’s going to cost, but let’s consider the alternative, oh and if you ever want to sell the van, being overweight could also affect the back pocket weight.

I’m afraid the good old Aussie attitude of “she’ll be right” doesn’t cut it when road safety is concerned and like your body, having your van overweight isn’t very healthy, not just you but for everyone on the road.

Safe driving everyone.

Josh Smith is a Chartered Professional Engineer from Autest Automotive Transport in South Australia
T: 0438 827 350     E: josh@autest.com.au     W: www.autest.net.au

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