Kerbweight v 85% ratio

[Raywood]

I am afraid if you want the kerb weight as used in the towing guide the only way to get it is to use a weighbridge.
At the end of the day the figures used for the calculation are a rough and ready guide though and somewhere near for beginners should work and for he rest use a bit more. In practice the makers figure will probably be low, which also helps.

 

[Darren.H]

I've towed at around 95%
Caravan has ATC, car stability stuff and all the other gubbins as do most cars nowadays
But
I did keep the mph down to 52 as experience has taught me the higher the ratio the lower the speed HAS to be.

 

[JTQ]

I did keep the mph down to 52 as experience has taught me the higher the ratio the lower the speed HAS to be.

Though surely if you were encountering issues above 52 mph, and within the speed limit, then the rig in question can't be anything but flawed in basic design or in how it was loaded or used

.

 

[Darren.H]

Though surely if you were encountering issues above 52 mph, and within the speed limit, then the rig in question can't be anything but flawed in basic design or in how it was loaded or used

.

I think its more to do with modern cars are built lighter, 52 mph gave massive fuel savings too.
Above 58mph the car became twitchy, not a comfortable drive tbh.
I always do the nose weight before every tow, I even have weighed the content of the caravan which is why I dont have the underslung spare wheel on and the carpets weren't used from 2016 until now.
The caravan was around its mtplm even with very little in it, and certainly not the awning. Nose weight was always bang on 85kg, I did enjoy that game as its informative how little you have to move from back to front or vise versa to see a change, and why I cant understand Swifts obsession with rear bike racks!

 

[Buckman]

I think its more to do with modern cars are built lighter, 52 mph gave massive fuel savings too.
Above 58mph the car became twitchy, not a comfortable drive tbh.
I always do the nose weight before every tow, I even have weighed the content of the caravan which is why I dont have the underslung spare wheel on and the carpets weren't used from 2016 until now.
The caravan was around its mtplm even with very little in it, and certainly not the awning. Nose weight was always bang on 85kg, I did enjoy that game as its informative how little you have to move from back to front or vise versa to see a change, and why I cant understand Swifts obsession with rear bike racks!

Actually in many cases as long as you do not exceed the limit on the towbar and keep it under 100kg, generally for many drivers the higher the noseweight the bettrer the tow. We always had our Lunar Delta at 100kg.

 

[DaveA1]

I'm a man with very little education and to read some of the theories given, and I'm sure they are relevant, as far as stability is concerned but, I just do not understand some of them.
I have a Vauxhall Insignia Elite with almost all the bells and whistles that can be fitted to a motor, with me sitting behind the wheel, it's close on 2000kg, but, with a towing limit of 1600kg . MTPLM of van is1350kg. I load mostly in the car Awning etc lighter items in van . I have a possible load of 350kg in the car (me and wife are150 between us) and 210kg in the van. There is approx 140kg in the car and 130 kg in van., including motor mover etc. Nose weight as near as 85kg as possible, usually below..


Not a thought of some of the things suggested above, my brain turns to mush if I do

 

[Darren.H]

I'm a man with very little education and to read some of the theories given, and I'm sure they are relevant, as far as stability is concerned but, I just do not understand some of them.
I have a Vauxhall Insignia Elite with almost all the bells and whistles that can be fitted to a motor, with me sitting behind the wheel, it's close on 2000kg, but, with a towing limit of 1600kg . MTPLM of van is1350kg. I load mostly in the car Awning etc lighter items in van . I have a possible load of 350kg in the car (me and wife are150 between us) and 210kg in the van. There is approx 140kg in the car and 130 kg in van., including motor mover etc. Nose weight as near as 85kg as possible, usually below..


Not a thought of some of the things suggested above, my brain turns to mush if I do

Nose weight is important, having it at the permissable maximum is always a good idea.

As we tow the caravan, and do bare in mind speed, the front of the caravan encounters resistance, this then transfers to the front of the caravan wanting to lift which in turn reduces the influence of the tow car hello snaking regardless of what the car weighs hence the importance I put on getting it right on the button.
Millennco do a very nice gauge, the cheaper ones in my experience arnt accurate, digital bathroom scales work a treat too

 

[ProfJohnL]

Nose weight is important, having it at the permissable maximum is always a good idea....

I beg to differ on your reasoning.

There is no point in having a nose load that exceeds what is necessary to maintain a stable outfit.

If you always aim for the maximum allowable there is a very good chance on some occasions you might exceed the limit unless you are scrupulous with your measurements. One of the down sides of operating at a maximum is the possibility you may accelerate unnecessary wear on the hitch, body fixings and suspension.

 

[Hutch]

I beg to differ on your reasoning.

There is no point in having a nose load that exceeds what is necessary to maintain a stable outfit.

If you always aim for the maximum allowable there is a very good chance on some occasions you might exceed the limit unless you are scrupulous with your measurements. One of the down sides of operating at a maximum is the possibility you may accelerate unnecessary wear on the hitch, body fixings and suspension.

I am with the Prof on your statment, going to the Max permissable nose weight is not always the best. Also caravans do not always lift as going along as the airflow overthem, is not a true aerofoil. . But yet again we are getting away from the Original posters Question, about Kerbweight.
And into the " Pandorras Box " of nose weights.

 

[DaveA1]

As I said I'm usually below my max nose weight. I've had the odd wobble, never had a true snake,

"Pandora's box." Feel and ed ach coming on Enough said.

 

[JTQ]

There is no point in having a nose load that exceeds what is necessary to maintain a stable outfit.

Fine, but If you always aim for what is "necessary" there is a very good chance on some occasions you might just be below the limit unless you are scrupulous with your measurements.

That one time error, could have very much more serious implications, than all the odd times the hitch might be statically be marginally overloaded.

I aim for a mean static of 90kgs, which creeps up to nearer 100 kgs with a full Gas bottle.
The maximum the chassis is rated at is 100 kgs, the hitch "S" is 150kgs, and 76 kgs equates to the 4% minimum of the Maximum Authorised Mass, the figure quoted by the van maker.

I have never intentionally or otherwise explored down to the weigh "necessary", nor ever intend to, hopefully the maker has worked that out for me before quoting a value.

Knowing the "S" refers to a static load, and having some insight how dynamic loads can build up, I have zero concerns about the consequences that on an occasion I might leave a gas spanner in the locker and just go over the static loading.

 

[RogerL]

I beg to differ on your reasoning.

There is no point in having a nose load that exceeds what is necessary to maintain a stable outfit.

If you always aim for the maximum allowable there is a very good chance on some occasions you might exceed the limit unless you are scrupulous with your measurements. One of the down sides of operating at a maximum is the possibility you may accelerate unnecessary wear on the hitch, body fixings and suspension.

The limits are there to allow the user to go up to that limit - provided the noseweight is targetted within permissible limits then any potential overload would be handled by the safety margin.

There are good reasons why caravanners in other parts of the world use much higher noseweights than we do, and at higher speeds.

 

[JTQ]

Also caravans do not always lift as going along as the airflow overthem, is not a true aerofoil.

I suspect any aerodynamic lift is very second order to the drag slamming the frontal area into the wind, at 60 mph, with the real wack of an oncoming Luton's bow wave taking it up to 130 mph even assuming that hired van keeps to the speed limit. (In real life it possible is about 110 mph, but remember this is a speed squared related force.)
As all that strikes above the car's air flow, it slams way above the caravan's axle line with a high tipping back force that lifts the hitch with consequent real reduction of noseweight.

IMO, its exceedingly bad advice to run too light a noseweight, unless you are going to drive slowly, in no wind and on roads where nothing will pass you head on.

 

[ProfJohnL]

x

The limits are there to allow the user to go up to that limit - provided the noseweight is targetted within permissible limits then any potential overload would be handled by the safety margin.

There are good reasons why caravanners in other parts of the world use much higher noseweights than we do, and at higher speeds.

I have not excluded going to the limit, only that in most cases its not necessary. But I do agree going higher is better than going for a lower value provided its within the limits.

 

[ProfJohnL]

I suspect any aerodynamic lift is very second order to the drag slamming the frontal area into the wind, at 60 mph, with the real wack of an oncoming Luton's bow wave taking it up to 130 mph even assuming that hired van keeps to the speed limit. (In real life it possible is about 110 mph, but remember this is a speed squared related force.)
As all that strikes above the car's air flow, it slams way above the caravan's axle line with a high tipping back force that lifts the hitch with consequent real reduction of noseweight.

IMO, its exceedingly bad advice to run too light a noseweight, unless you are going to drive slowly, in no wind and on roads where nothing will pass you head on.

It's very difficult to evaluate the effect of frontal wind on the caravan, because the air flow is radically modified by the tow vehicle and it might actually be deflecting much of the air flow upwards towards the roof of the caravan largely avoiding the frontal area. Besides which most modern caravans don't have slab fronted designs most now offer a continually changing rake angle which flattens near the top to an angle of less than 45 degrees. Air flow at this incline will tend to push the nose down, more so than the drag trying to lift the nose.

Who has suggested using a "too light a noseweight" I certainly didn't!

 

[Buckman]

However by the same token when travelling on the road your nose weight could vary between zero and 100 or more kg. a nose weight at maximum pessible may help slow down the pendulum effect.

 

[JTQ]

t's very difficult to evaluate the effect of frontal wind on the caravan, because the air flow is radically modified by the tow vehicle and it might actually be deflecting much of the air flow upwards towards the roof of the caravan largely avoiding the frontal area.

Of course, aerodynamic predictions are difficult, but I would far from minimise the impact of the frontal area drag.
Physically, its effects can so often can be felt as an oncoming vehicle's bow wave slams the unit, a slam noticeably more than when running solo, suggesting the caravan's presence is a major factor. That, even with our near 5.2 tonnes of unit.

That the flow is inevitably in part deflected upwards, increases the drag force's "lever arm" over axle height, compounding the hitch load easing.

 

[ProfJohnL]

I still think you are over estimating the nose lift effect. Yes there will be some, but you must also consider that as the air flow is accelerated over the top of the caravan, like on a wing the accelerated air flow has a low pressure which generates lift and that will apply along the length of the caravan. As caravans are effectively counter balanced around the axle, much of the lift generated ahead of the axle will be countered by the area of roof behind the axle.

It still doesn't change the fact you only need enough noseload to maintain towing stability.

 

[JTQ]

As caravans are effectively counter balanced around the axle, much of the lift generated ahead of the axle will be countered by the area of roof behind the axle.

Or not, as the "lift" component if there, applies its force at about a third of the chord,
So it will add to the reduction of the hitch loading, though with skylights, solar panels, aerial etc clobber on the roof the whole over roof airflow will be so broken, that as I stated earlier to be a very low order effect.

It still doesn't change the fact you only need enough noseload to maintain towing stability.

Agreed, though a reduction on a lower value moves nearer critical earlier than that same reduction does from a higher static point.
That is the inherent danger and why it is unwise to explore using lowish noseweights the more so where the facts are unknown.
Plus, directly following a bow wave front end slam, a sway inducing bow wave transits along the van's offside flank. There is very little danger working towards a high nose weight, but very real working towards a low one.

 

[RogerL]

Or not, as the "lift" component if there, applies its force at about a third of the chord,
So it will add to the reduction of the hitch loading, though with skylights, solar panels, aerial etc clobber on the roof the whole over roof airflow will be so broken, that as I stated earlier to be a very low order effect.



Agreed, though a reduction on a lower value moves nearer critical earlier than that same reduction does from a higher static point.
That is the inherent danger and why it is unwise to explore using lowish noseweights the more so where the facts are unknown.
Plus, directly following a bow wave front end slam, a sway inducing bow wave transits along the van's offside flank. There is very little danger working towards a high nose weight, but very real working towards a low one.

Of course there's also aerodynamic effect from airflow under the caravan - which is greatly affected by the car aerodynamics.

I'm not convinced that the spoiler shape at the top rear of a caravan helps it's aerodynamics - if anything it'll lift the nose.

 

[Raywood]

I do agree with the Prof on nose weight. The nose weight should be sufficient for safe towing, but does not need to be the maximum, but I would advocate something just sort of it.
If the caravan is nose down to any extent you are not going to get nose lift rather the opposite as the air coming under he car should be about the same as under the caravan. To some extent the tow car will force air towards the top of the caravan, although the extent depends a lot on the car. This should deflect air towards the roof and hold the front down. This was basically the advice given out by the Caravan Club that you tow a little nose down or level many moons ago and seems to make sense to me.

 

[JTQ]

This was basically the advice given out by the Caravan Club that you tow a little nose down or level many moons ago and seems to make sense to me.

Also nose down, the van's Cof G is further ahead of the axle than it would be level or nose up, therefore undulations in the road's inclinations a bit better accommodated.

 

[Parksy]

How do any of the recent comments relate to the original question which was:

Hi
Looking at a towcar with 95% towmatch for my caravan. As an experienced driver my question is if I place the awning in the car will that decrease this ratio?

No wonder that people ask one question here and are never seen again.

 

[ProfJohnL]

Also nose down, the van's Cof G is further ahead of the axle than it would be level or nose up, therefore undulations in the road's inclinations a bit better accommodated.

Its the location of the caravan's centre of gravity (or Mass) that determines nose load. So regardless of how the caravan settles on the hitch and its resultant inclination (nose down, level or even up) provided the correct nose load has been created (i.e. force acting downwards) it automatically means the CofG must be horizontally displaced forward of the axle far enough to meet the conditions you have suggested. This basically negates the point you make.

However it does conform the fact that true noseload can only be measured with the trailer hitch at its ride height and no other height.

 

[RogerL]

How do any of the recent comments relate to the original question which was:

No wonder that people ask one question here and are never seen again.

It's been answered directly a couple of times.