Weights & Measures

[Lane_5126079]

It was suggested by the editorial staff at Practical Caravan that I post the following query on the forum site:-

I thought that at long last I was getting to gripes with how to calculate the 85%, maximum tows etc. However I'm now hopelessly confused. Perhaps I have missed something vital. Can you please let me have an explanation/clarification?

As recently retired, exploring moving into caravanning and want to make the right informed choices. Been buying the Practical Caravan for the last few months and must say I find it an interesting magazine.

Please see the August issue of the magazine and refer to pages 110 and 178.

At the top of page 178 under 'Check max tow' the following is stated:- "Some cars have a maximum towing limit that is LESS than their kerbweight. So when you see the Check max tow symbol, its up to you to ensure that the car you are buying has a towing limit AT LEAST the same as your MTPLM, or risk invalidating your car's warranty."

On page110 within the outfit specifications for your representative Adele Donaghie, the kerbweight of the vehicle is given as 1631kg, the maximum towing limit of 1500kg although the caravan MTPLM is given as 1550kg. Have I missed something or misunderstood the position as these figures appear to contradict the advice given on pages 178.

Perhaps you could clarify?

Many thanks.

Bernard Lane

 

[rob_jax]

Hi Bernard,

Nothing terribly wrong with what you say or have abstracted from the magazine.

If we take the example of our Eriba Triton caravan, that has a "Mass in Running Order" (MRO) of 800 kg and a MTPLM of 1200 kg - giving a payload allowance of 400 kg, of which we probably never use more than 75 kg.

So if you used the MTPLM as a means of calculating what car you can use to tow this caravan, it would remove a whole group of perfectly suitable vehicles.

If the MTPLM is greater than the towing limit of the car, it is important that the owner realises this, and never loads the caravan into an illegal situation.

Robert

 

[Rubix]

I am not new, but a caravan virgin !! , and I too have been looking into this, as my current vehicle is on the low weight side, well for the size of outfit I am lookin at anyway.

So I did sone "surfin" (wot no beach boys) on the internet, and found a very useful site "www.whattowcar.com" BUT I found some major discrepencies with regard to their towing vehicle weights.

I have sent them an email concerning this as there was a difference of 10% on one of the camparisons they did. This therefore put some outfits out of the 85% margin.

there was a difference between using the "compare outfit" and the "compare two cars" sections, and then when you look at the detailed report they generate, this is different too.

On the surface this website seems excellent, but with the errors I found, I find it somewhat unrelieble. I used this site as my car mannual does not have towing info in it, just basic weights.

This problem may only may have been with the two cars I used to compare, but I didn't check other to see.

 

[Damian]

Lane, the question about weights crops up very often,so dont feel bad about raising it again!!

The 85% towing figure is a GUIDE only, it is not a legally enforceable figure, but has been determind to be the best match for "inexperienced" towers, but no information is around to state what an "experinced" tower is!!

The main weights to be concerned about are the car max towing limit, max train weight, and noseweight limit.

As for the van, the MTPLM is the max weight the van can be when fully loaded, with gas bottles, food, clothes, etc etc. Do not exceed this figure as it is illegal, will invalidate your van warranty, invalidate your insurance, and leave youo open to prosecution if stopped and weighed.

 

[ProfJohnL]

Hello Lane,

There is a Chinese proverb which goes something like 'You may be a fool for only 5 minutes if you ask, but you will a fool forever if you don't' So don't feel bad about it.

The towing weights regulations seem mighty complicated, but they are in fact quite logical if you are prepared to sit down and study them.

But to cover your point. I will first assume that you passed your driving test before Jan 1997, when additional restrictions on and driving licenses weight limits were introduced. (for details see your licence documents)

Each new car is specified by the manufacture as having a Maximum allowed towed mass (Weight is a force caused by gravity acting on the mass). This is a legal limit that you must not exceed. It is not a simple fixed proportion of a cars mass, so some cars can tow more than their own kerb weight, and others are less, a few are not type approved towing at all! You must check your cars documentation or ask your supplier to verify the details.

Your caravan will have a Mass In Running Order (MIRO) which is basically the caravan as it is supplied from the manufacture. Provided the MIRO is less than the cars maximum permitted towed mass, then you can tow the caravan. However an empty caravan is no good, so you must be careful when loading the caravan not exceed lower of either the cars Maximum limit or the caravans.

A similar process also exists for the nose weight of the caravan. The car manufacture has one Max limit and the trailer will have another. You must not exceed the lower of the two values. Where possible always arrange the caravan loading to achieve the biggest nose weight within the available limit.

Instability or more accurately the point at which the driver looses control of an outfit, is affected by several significant factors. The one thing that you have the most time to think about, is how the outfit is loaded. It is generally accepted that the lighter a caravan can be compared to tug the better. The caravan egg heads have chosen a figure of 85%. this is only a guideline, it is applied only to caravans and it is not written in any law. I happen to agree with the suggestion as a sensible loading target.

Other significant factors include tyre pressures which should be set for a fully laden vehicle. And nose weight as specified above.

Whilst moving the driver is the most significant factor. Even a lightly loaded caravan is going to make significant difference to the performance of your car. It will react more like a bus, so think of it like a bus, Give it the driving space and time a bus needs. It wont go round corners like a solo car. It will be affected by side winds, and bow waves from lorries.

And like a bus watch your speed, because emergency stops may be good in a straight line but come to curve and you can so easily jacknife.

The above may seem like a lot of negatives, but it is all really just good sense and with proper care and attention caravanning can and should be enjoyable.

Have fun

 

[rob_jax]

Rubix comments on www.whattowcar.com are well founded, but if you bear in mind that it's not a commercial site (with any sort of warranty on the data) but a hobby site set-up by some helpful Dutch caravan owners - then it does what it says - it provides a useful guideline.

Looking at my car, it doesn't have the exact specification of my Mercedes C270 CDI in the database - so I know the car weight, the engine power and torque figures will be out. As in fact is the data in my car log book - it just shows the weight of the basic specification vehicle with that engine and gearbox.

To find the true weight, you either need to visit a weigh-bridge, or in the case of a Mercedes, BMW or Audi (and some others) look on the vehicle data plate for the weight as it left the factory. That includes any extras like electric seats, upgrade 4-zone air conditioning, music system, whatever you were mad enough to tick when ordering.

The MRO for a caravan should be easy to determine - less options - or are there? If your caravan MRO was determined before you added the battery or the electric caravan mover - then you need to include these weights as well.

The Whattowcar web-site can give you representative figures that can be very helpful - but unless you know better expect the weights to vary by +100 kg for a car and maybe +50 kg for the caravan.

Robert

 

[Lutz]

A towing limit of 1500kg does not rule out a caravan with an all-up weight (MTPLM) of 1550kg because the towload specified for the car is not the total weight of the trailer/caravan but only its axle load. Hence, if the MTPLM is 1550kg and the noseweight 75kg, the actual towload will only be 1475kg, which is less than the permissible limit.

 

[JamesFrance]

Hello Lutz,

Can you give us the the source of this information please? That would be most useful if I do what you say and am pulled up by the police.

Thanks,

 

[Lutz]

The defintion of towload (officially called 'towable mass') can be found in EU Directive 92/21/EEC (and various amendments thereof such as 95/48/EC). Annex II item 2.6 covers the subject.

 

[JamesFrance]

The defintion of towload (officially called 'towable mass') can be found in EU Directive 92/21/EEC (and various amendments thereof such as 95/48/EC). Annex II item 2.6 covers the subject.

Lutz thankyou for that. I do wonder how any traffic cop can learn all that lot. No wonder we have to pay so much to be in the EU.

I used to think it would be interesting to be a lawyer but now I think it would drive me mad. Maybe it's just my advanced age.

James

 

[chris_5068897]

One thing that seems to get overlooked in these discussions is the loading of the carboot. Car manufacturers usually specify the maximum load that can be placed in the boot. However, since the caravan applies its noseweight to the cars rear suspension, then the value of the noseweight must be deducted from the allowable boot load.

In other words, if you are trying to avoid excessive caravan loading, you can't necessarily simply stuff it all in the boot! When you check it out, it can be quite a shock to see how little you can carry in the car...

 

[Lutz]

You're right but that limits for the car's GVW and rear axle load of course apply whether you are towing or not. The noseweight issue just makes matters worse because noseweight is treated as part of the payload of the car. And don't forget that the towbar itself can be quite heavy, too, and it is not normally included in the kerbweight that the manufacturers quote. The towbar plus miscellaneous related items like the electrics can easily weight up to about 40kg which further limits what you can put int he back of the car.

Back in the early 90's, Mercedes Benz brought out an S-Class (the W140 series) which had such a high kerbweight ex-factory when fully equipped that the remaining permissible payload was just enough for 3 passengers, leaving nothing for any other luggage in the boot or noseweight.