Assessing Nose Load

[ProfJohnL]

There are many questions posted about nose weight, and clearly it is a subject that is not fully understood, and that is partly because it is a quite complex factor to measure accurately.

I believe I can suggest a simplified approach that whilst it will lack the ultimate accuracy, it will always provide a result that is at or just below the real figure.

If a nose load gauge (either a propriety product or a bathroom scale with stick) is set to give a tow-hitch height above the horizontal of 350mm to the centre of the ball, then any measured nose load will be at or just below the real figure for any EU compliant tow car and tow-ball.

Through the regulations, it is essential that a trailer (including caravans) must have vertical nose load that presses down on the tow vehicle, this can only be achieved if the caravan's centre of gravity is forward of the main axle. Given these conditions, and the fact that the C of G will always be higher than the axle, it is an inherent feature that the nose load produced will always become greater as the height of the tow hitch is lowered.

EU regulations set a limits for the height of a tow-ball on a car with a trailer attached of between 350 to 420mm. By selecting the lower limit for the height of the nose load gauge, the nose load will be maximised. The difference between the lower and upper hight limits is relatively small (70mm) and the change in nose load produced between the two height extremes will be quite small but always less than measured figure at the minimum height.

 

[Lutz]

I go along with that, but it is also important to point out that the caravan must be standing on level ground when nose load is measured at a specific coupling height.

 

[ProfJohnL]

I go along with that, but it is also important to point out that the caravan must be standing on level ground when nose load is measured at a specific coupling height.

Third para - "horizontal"

 

[Lutz]

I go along with that, but it is also important to point out that the caravan must be standing on level ground when nose load is measured at a specific coupling height.

The term 'above the horizontal' is perhaps a bit ambiguous as it doesn't say at which height the horizontal line passes through. The intent of your statement is understandable, but I just thought that 'level ground' makes it clearer.

 

[Howard_374311998]

The term 'above the horizontal' is perhaps a bit ambiguous as it doesn't say at which height the horizontal line passes through. The intent of your statement is understandable, but I just thought that 'level ground' makes it clearer.

Hi

I'm almost entirely new to this - just had first tow. I couldn't reduce the noseweight to the prescribed value, but I have a spare wheel and a standard calor bottle in the front locker. I loaded the van sensibly but didn't try to apply a cantilever solution. No water in the hot water tank - battery also front O/S. together these weigh almost 60 kg.

I was interested and encouraged (I think in the current issue) to read Doug King admitting he has a noseweight problem in response to an owner enquiring about putting the spare under the van - I had considered this.

Although I measured on the drive with the stick gauge and tried to achieve the correct tow height the van was on a slight incline. I towed over the noseweight for my car, which I tried to load toward the front.

Howard

 

[ProfJohnL]

Hello Howard,

If you tow over the permitted nose load you are breaking the law. Your outfit is not road legal and that invalidates your insurance.

You must rearrange your loading to achieve a nose load within the prescribed range. Or stop towing.

 

[Lutz]

There is always a way to get the noseweight within the specified limits. If there's nothing in the front of the caravan that you can redistribute, you'd still have the possibility to add ballast behind the axle.

 

[Paul_5099000]

There is always a way to get the noseweight within the specified limits. If there's nothing in the front of the caravan that you can redistribute, you'd still have the possibility to add ballast behind the axle.

I must admit to being totally "ill at ease" with measuring the noseweight of my rallye 640. Its says "must be on level ground" ...finding a level bit of road is ni on impossible, they all slant one way or another even slightly would be enough to give a false reading.

Then brakes on or off...differing opinions,

id like a real idiot prof way of measureing the noseweight, ive got one of the gauges, rather than the bathroom scales approach.

sigh...

Paul.

 

[trucker]

If your on a slope can you not adjust the van to level with a spirit level then check the nose weight??

Kevin

 

[Lutz]

No, the caravan does not have to be level. It just have to stand on level ground. It would be pure coincidence if the height of the towball on the car is such that it results in a level caravan when it's hitched up.

 

[ProfJohnL]

Hello Kevin,

The simple answer is no.

I may have caused some confusion in my headline item, by failing to be more specific about the surface on which this measurement should be done.

It must be level ground, and all my points are based on that assumption and requirement. This does not mean the caravan its self will be level.

The EU regulations for tow balls allows the centre of the tow ball to be between 350 and 420 mm from the ground when the trailer is attached. with this potential variation, it is unlikely that any caravan will be exactly level.

So, as there is a variation, and the imposed nose load does change depending on the height of the hitch, the worst case scenario is the hitch at its lowest height (350mm) which will generate the maximum nose load.

A caravan may not be level under these conditions.

 

[Lutz]

Also, in the case of a twin axle, the weight distribution between the two axles is would be different from normal if the caravan is standing on a slope. This would falsify the noseweight readings.

 

[Howard_374311998]

Hi Guys - thanks to you all, and particularly John L for the sound advice. i have in fact now changed the car, do you guys recommend using the cantilever effect? i didn't think it would be good practise and would encourage pitching on what was already a marginal tow.(?) i hope we like caravaning.

regards to all

Howard

 

[Chrisbee]

Whilst I understand that noseweight will alter depending on hitch height, by just how much? Does a difference of 70mm between max & min height really make a difference? Obviously noseweight is measured stationary but when moving the load imposed on the towball must alter as bumps are hit.

 

[Lutz]

Oh yes, the dynamic variation of noseweight will be quite considerable and, in the worst case, probably up to ten times the static value, but this is taken into account in the design. It is not only the level of the applied load that determines the durability of a component but also the number of times it is applied. The standards require 2 million cycles to be carried on a shaker test under specified conditions.

 

[ProfJohnL]

Hello Howard,

I think I understand you question, but to clarify when you write 'cantilever' I assume you mean adding weight at the back of the caravan to reduce the nose load.

Well the answer to that is a qualified yes.

All trailers use the cantilever principle because they behave like a see saws. The qualification I add is that it is poor practice to add heavy items at either extreme ends of the caravan to address nose load problems.

In general it is better to remove weight from the front rather than add it to the rear. Alternatively some items mav be moved from the front towards the rear to reduce nose loads, typically items like the awning, or spare wheel. Such items may not need to be moved very far to make the necessary difference.

I have never yet found a caravan that cannot be rebalanced to give a 75Kg nose load.

 

[ProfJohnL]

Hi Chrisbee,

Your question has three answers, Lutz has given perspective on the dynamic impact load under towing conditions.

It is unlikely that the actual nose load difference over the 70mm range of hitch height will technically overstress the hitch assembly.

Legally for example, if your outfits nose load limit is 75Kg, and you set your caravan up to give that with a gauge set to a hitch height of 420mm, but when you attach the caravan to your car the hitch drops to 350mm, the effective nose load increases to over 75Kg at this lower height, and thus your outfit is not legal. So yes the height is important.

 

[Chrisbee]

Hi John

I know that the noseweight would increase as you lower the hitch height but was wondering by how much? The reason I ask is that although my van is parked on the level my drive slopes steeply up so the hitch is almost on the ground. If using a standard noseweight gauge the nose would be higher than normal running. At the moment I use the (short) broom handle/bathroom scales method but am increasingly getting grief from Mrs Chrisbee!

 

[Lutz]

The degree by which the noseweight increases as hitch height is reduced depends on the dimension from towball to axle of the caravan and the height of the centre of gravity of the caravan. The shorter the caravan and the higher the centre of gravity, the greater the effect. Therefore, among other things, it also depends on how many heavy articles are stored in the upper lockers. Because of this, it is impossible to put an exact figure on how much 70mm height difference will make to the noseweight, but an educated guess would lead me to assume that, for the average caravan, the difference would be no more than about 5kg.

 

[Howard_374311998]

Hi All and John L

the noseweight measured 70kg with the van empty - only battery o/s front. with the locker loaded it was about 100 kg and with only spare, calor and light items (spare waste pipe etc) 90 kgs. to tow i moved a heavy box of tools / jacks etc to inside door, i was running with Aquaroll and Wastehog in rear bathroom, chocks and shoes and a microwave on the axle. i could of course have put as mush weight as possible in the rear, but thought this would encourage pitching? i would be grateful for views from you experienced guys. as it was it towed very well indeed.

i hope this is interesting

thanks and regards

Howard

 

[Lutz]

The degree of pitching depends as much on the towcar and especially its suspension as it does on the caravan and the way the load inside is distributed, so it's impossible to say whether more load at the ends would necessarily result in more pitching. What is fairly certain, however, is that a heavy load far away from the axle is increases the likelihood of instability.

 

[ProfJohnL]

Hello Howard,

Ditto Lutzs' comment, but it is not usually just the pitching that is the main concern where an outfit is unstable. Pitching is basically the caravan rocking rather like a see saw and is up and down. The more serious motion is I believe called yawing, where the caravan tries to turn left or right, whilst the car is trying to pull it in just one direction.

Yawing is made worse for the reasons you suspect; heavy masses at extremes of the caravan. Each outfit will have a different thershold where the normally controlled motion becoems too energetic and out of control or unstable.

There is no simple calculation that will tell you if an outfit is going to be unstable, and some outfits with quite large masses at the ends may be more stable than much lighter systems in other caravans.

If you are happy with yours, and you are legal then no worries.

 

[Howard_374311998]

Hi Guys

thanks for advice both. as said i think my van is front heavy with the battery front o/s corner, then spare and bottle in locker gives me 60kg at front before i start. i fully intend to concentrate the weight around the axle, and lighter bulkier itmes at back, eg Aquarolls. its good to learn from others. spare - i think i will leave it where it is now i have bigger car.

as a completly new observer - i have noticed some either very down or very up attitudes which dont appear stable.

thanks again

Howard

 

[ProfJohnL]

Hello again Howard,

I am not trying to perpetuate this thread unnecessarily, but I am wondering what you meant by your last comment regarding 'very up and down' attitudes.

Are you saying that they look unstable because they are up or down, was this stationary or moving or have you seen them under way and behaving badly?

 

[Lutz]

Stationary up or down attitudes do not tell one anything about how stable or unstable an outfit is. Stability refers to side to side movement.

If the up and down movement is dynamic, i.e. while towing, then this could be due to very soft suspension of the towcar, defective shock absorbers on the tow car or lack of shock absorbers on the caravan, or a combination of all three.