TOW BALL WEIGHT

[John_374564913]

Mt tow ball is limited to a manufacturers weight of 75KG which seems standard for a lot of manufacturers now a days

However I have the following question do car manufacturers build in a plus or minus of X percent

I was just wondering because most engineers when designing something build in a safety factor

if anybody knows would appreciate there comments

John

 

[Lutz]

75kg is the maximum allowable so there is no plus (+) tolerance. The car manufacturer does not specify a minimum, only the law does that (25kg or 4% of the weight of the caravan, whichever is the greater). However, it is wise to stay close as possible to the maximum without actually exceeding it.

 

[Damian]

It is not the towball itself which is limited to 75kg as towballs on different vehicles may have a higher limit.
However, the 75kg is the limit imposed by your vehicle manufacturer as being the correct max weight allowed to be placed on the towball.
Even if your limit was 120kg, as some are, you would not be able to load to that limit with a caravan as the caravan chassis has a max load limit of 100kg.
You should never exceed either the car limit or the van limit, whichever is lower.

 

[garyc]

ok you load your caravan to specified noseweight limit then when you stop for a brew and you and your partner are sat in the front of van how much are you overloading the hitch/towball by? I ask this because all the vans i see parked up have only rear steadies down. in my case it must be 100kgs or more. Or is this assumption rubbish?

 

[Damian]

Not rubbish at all, you are overloading the hitch.
Simple answer,,,,put the front steadies down as well

 

[ProfJohnL]

Hello Garyc

It is wise to put the steadies down in the car park, but it is unlikely you would do any harm if you didn't. The reason is the manufactures as part of the type approval process have to state the "Static vertical load limit" on the tow ball. This may be only 75Kg, but the important word is 'static'

When actually towing there is a very real dynamic effect due to the inertia of the caravan and the car and the actual maximum load can be several times the 'static' value. So the car manufacturers have to take that into account and ensure the cars structure can handle the dynamic loads safely.

So whilst the outfit is parked up the actual load on the hitch can be allowed to exceed the limit, but under no circumstances should the load limit be exceeded when the out is being moved.

 

[Lutz]

Yes, the maximum permissible noseweight, while being a figure measured in the static condition, actually has more relevance dynamically. Peak dynamic noseweight can easily exceed the static load by a factor of 5 or 6 or even more. Therefore, so long as you do not drive with a higher noseweight, it is perfectly alright to exceed the limit within reason when the outfit is standing still.

 

[NigelHutson]

Lutz,
Just out of interest, where do you get the minimum weight for a noseweight (25kgs)? It may apply in Germany, but doesn't seem to exist in law here. I would be interested to know where the legislation is please as the question has come up before.
Thank,

Nigel.

 

[Lutz]

It is a European Directive (95/48/EC) so it applies just as much in the UK as it does in Germany. Paragraph 3.3.2. of that directive states, quote:
The technically permissible static vertical load on the coupling device is that stated by the manufacturer; this load must be not less than 4% of the maximum permissible towable mass and not less than 25 kg. The manufacturer must specify in the owner’s manual the maximum permissible static vertical load on the coupling device, the mounting points of the coupling device on the motor vehicle and the maximum permissible overhang of the coupling device.

 

[NigelHutson]

Lutz,
Thank you. Not that it would ever be enforced here, and the issue is generally restricting excessive noseweight.
Nigel.

 

[JTQ]

It is wise to put the steadies down in the car park, but it is unlikely you would do any harm if you didn't.

However it is definitely not a good idea if your tow vehicle has active pneumatic rear suspension and probably also not if it has self-levelling.
The poor caravan’s chassis, steadies and hitch, and the cars towball will be holding up a significant part of the cars weight as the vehicle settles, so be way over loaded. Our Disco 3 settles significantly some ten minutes after it has been stopped.

 

[Guest]

That 25kg and the rest of it, it very much seems to me, is part of construction and use regulation, ie to make sure the Vehicle is capable of towing what the manufacturer says it can?
There is an obvious case not to exceed the maximum but for the minimum, there is not,
Simply, as far as caravans are concerned 25kg or anywhere near is exceed by default, but in the case of an empty garden trailer for instance , it would be hard to get up to 25kg!
In the case of my trailer, 25kg is probably about 30% of it's weight or should that be MIRO?!

 

[Lutz]

Simply, as far as caravans are concerned 25kg or anywhere near is exceed by default

Not necessarily. If the load distribution in the caravan is poor, i.e. lots of heavy things at the rear, it is conceivable that the noseweight could fall below 25kg. The 25kg minimum is purely to make sure that the outfit is at least somewhat stable although a higher noseweight will, of course, improve stability further.

 

[trickydicky]

Lutz
You refer to "peak dynamic noseweight" which you say is a factor of 5 to 6 times that of the static noseweight.Are you saying that when the car is parked the static load on the towball is 75kgs,then after setting off going down the road this increases to 450kgs or more on the towball?
Could you please clarify this.
Thanks.

 

[Lutz]

If you go over a bump or a pothole, for example, for a split second the load going through the towball can easily be in the region of 450kg or more even though the noseweight is much less. This wouldn't be a problem if such a short sharp jerk only happens once, but depending on how rough the roads are, it can happen many thousand times during the course of the lifetime of the vehicle and this can substantially affect durability.

 

[Guest]

Lutz, While I totally agree with your last post, infact wrote a post in a similar vein myself, (wherever that got too?), sadly, why then do you introduce silly argument regarding poor loading to produce very low noseweights in reply to my last post?
More to the point, anyone so foolish would hadly be likely to know of such a rule to obey in the first place?!
This then is very much akin to JohnL replying about swinging arms and legs about on a seesaw, that was his reply in the 'other' thread, an irrelevance to the real question, a very poor reply, and why I refrained from further involvement.
(And in point of fact, any trailer of a similar weight to a caravan with a 25kg noseweight, (being way to light), would become un-towable as speed approached 40mph, so it does not help your point of view in any way shape or form).

 

[Lutz]

I didn't suggest that anyone with any sense would intentionally set the noseweight as low as 25kg or less. I only wanted to highlight exactly what you also imply, i.e. that there are people who may not give their load distribution much thought, and then inadvertently tow with a dangerously low noseweight and then wonder why their outfit has become untowable at 40mph. My point is that no caravan will always achieve at least 25kg, no matter how poor the load distribution is. In other words, 25kg or more are not exceeded "by default", as you have stated.

 

[ProfJohnL]

Hello Gary,

I did not introduce the idea of a see saw, but you did on Thu, Sep 2 2010, 10:49PM

As it was an analogy you seemed to be happy with, I merely followed your lead to try and explain the processes involved and to show that contrary to your assertion the caravan and a see saw have a lot in common.

You may have tired of the debate, but there may have been others who wanted to know more, and glean an understanding of how things actually work.
The introduction of the 25Kg minimum into this thread is not irrelevant, it forms part of a legal regulation. And if introducing it prevents one person from making a mistake, then it fully justified.