Towing up to 100% of your Kerb weight

[Andrewbutcher]

Hi all, we are looking around for a new van, i have always stuck to the 85% rule and have towed for more years than i care to remember.

However, most of the caravans we are looking at are heavier than 85% of our 4x4's kerb weight, we are possibly going for a twin axle for better towing stability!

Any views and opinions greatly appreciated.

regards Andrew.

 

[Steve L]

First of all Andrew, as you have stated you have tow'd for a number of years and as you don't mention any accidents, I would suggest you have gained experience by carefull loading and driving.
As you have a 4x4, you can go over the kerbside weight quite safely as most 4x4's are geared with heavy towing in mind.
Having towed well over the kerbside weight with a Diahatsu F70 4x4 I can tell you that you still do have to pay attention to braking. I regularly towed a 3500 Kg fully loaded Ifor Williams trailer, taking my Diahatsu to the full gross train of 5500 Kgs, which meant that the Diahatsu was only 2000Kgs fully loaded. I did have one scary moment when I had to jump on the brakes while fully loaded and cornering at about 20 Mph. The trailer being nearly twice the weight of the car took over and tugged me into a tree stump buried in the hedge of the country lane. So would urge you to brake in a straight line and approach corners at a low speed for the road. Had the tree stump not of been hit by the trailer headboard, I probably would of been dragged in a backwards jack knife through the hedge, causing a lot of damage to the car. I was fortunate enough to get away with a football sized dent which I pulled out with a suction handle.
I've also towed both single and twin axle caravans. The twin axle is better for stability but a well loaded single can tow just as well. The main problem with a twin axle van is that you do need to be able to reverse it with the car as the tyre scrub is too much to do manual handling.
I think most caravans stop at about 1900Kgs fully loaded so you will be around equal weight for car and caravan, which shouldn't present the jack knife I had unless your doing a serious speed.

Driving steady, patiently and thinking & observing much further ahead of your self will pay dividends and provide a trouble free journey.

But then I might be teaching you to suck eggs.

Good luck.

 

[ProfJohnL]

Hello Andrew,

First and fore most 85% is not a rule and never has been, it has no legal significance it is only guidance, Whilst i disagree with the naming of an exact figure like 85% because it implies keeping to the ratio will gurantee a safe and legal outfit - when infact it may not be safe or legal for some combinations, I do support the principal that you should always keep the trailer as light as possible, regardless of how much experience you have.

Having said that, providing you have Cat BE or B+E on your licence then you can legally tow any trailer up to the maximum towed weight advised by your tow vehicels manufacture. If you only Have cat B (i.e basic driving test passed after jan 1997), then you are legally restricted to a trailer whoes MTPLM is no greater than the ULW of the tow vehielce and theri combined MAM's are no greater than 3500Kg unless you have taken the +E extention to cat B

Regardless of the size or weights, good safe towing is not just about weight ratios, it is a combination of factors that need to managed. Probaly the greatest impact on safety is the driver - who is also legally responsible for ensureing the outfit is safe and legal to take on the public highways.

I largely suppot Steves answer above but beware, jackknifes can occur with almost any outfit and it is not solely the realm of high or over 100% ratio outfits that suffer them. Carefull driving and particularly anticipating and modifing your speed and approach to conditions ahead is the best protection you van have.

I hope you find a great caravan and continue to have great holidays.

 

[RogerL]

Exceeding to 100% kerbweight with a caravan is not recommended in any circumstances - where a towing limit exceeds the kerbweight, that's for other types of trailers. Many 4x4s have a 3,500kg towing limit but that's intended to cover agricultural trailers which are limited to 20mph.
Having a big 4x4 should make it easier to find a caravan well under the 100%.

 

[John_374564913]

Andrew

I tow at nearly 100% and have towed all over England and Europe as far a field as Croatia

My unit is a twin axle and I had fitted the ATC system and I have trailer control fitted to my car.
I see know problem with towing at 100% but I would say if you are going to do this then the key is AWARNESS.
Always look for what other raod users are doing, going to do or might do Let the trailer do the baraking rather than the tow vehicle.
You can have accidents at 85% also so remeber the key word AWARNESS

I hope this helps you in making your decision

John

 

[ProfJohnL]

Hello Roger,

I have previously stated and maintain that I believe it is wise to keep trailers as light as possible which is why I abhor the use of specific percentage figures such as 85 and 100%.

These figures are based on theoretical rather than real values and consequently even though a ratio may calculate out 85 or 100% the real outfit, if measured, for any outfit will be significantly different, so the figures are not a sound basis on which to base a mechanical limit.

Empirically nothing magically happens at 100% to make any outfit significantly different to one at 99 or 101%.

A caravans large size and low density makes them a particularly difficult towing proposition, but towing characteristics are affected more by external factors such as road conditions weather, and of course the drivers skill or bad habits rather than just the towing ratio.

But legally a car could tow a caravan weighing up to the towing limit of the car - providing it is a safe outfit. The question of what is safe or not, that is open to personal opinion, but perhaps high ratio outfits may be unsafe at normal road speeds, but safe at reduced speeds as per the agricultural equipment.

 

[RogerL]

John,
There's simply no need for owners of heavy towcars to exceed their kerbweight, end of.
It doesn't need a long-winded debate about the effect of different towing ratios - instability increases as the towing ratio increases, fact.

 

[Lutz]

While there is no denying that the risk increases as the weight ratio increases it still has to be left to the owner to decide what is a reasonable or sensible limit. On the one hand a low weight ratio of, say, under 85% is no guarantee that an outfit will reamin stable under all conditions, and on the other hand, with due care and attention, a 100% weight ratio is quite manageable, and safely, too. There simply isn't a magical weight ratio ratio limit over which disaster is a foregone conclusion.

 

[ProfJohnL]

Hello again Roger,

There is nothing wrong with maing a personal decision on a maximum ratio that you are prepared to tow at, but the point is the figures you use do not represnt the real life ratio, and if your desicion is based on precept that if the car is lighter than the trailer, the trailer will 'wag or drive' the car, then the fundamntal criteria you are using are not real values, and there is a lot more to stability than just the towing ratio.

There is a very strong probability that where instability is cited as a factor in an RTI, there will be a significant proportion of incidets where the trailer will be less than the weight of the tow vehicle, and in other instances even less than 85% which means that even in these circumstances a lighter trailer will have 'wagged' the car. That rather puts paid to the concept that 85 and 100% being universal critical stability thresholds.

I agree with you that low ratios are preferable, which conversly means you are generally better with a heavier car to pull a larger caravan, but that in its self does not guarantee stability or ease of towing.

 

[Surfer]

What type of 4 x 4 are you driving at the moment as most 4 x 4s should be able to handle most caravans on the market unless you have one of those toy 4 x 4's i.e. Suzuki Jimny

 

[Steve L]

Two points here.
Firstly 4X4's are not restricted to agricultural towing at all. Most agricultural implements don't have brakes and are only legally towable by tractors. The tow capacity of any vehicle is derived by the manufacturer to take into account performance and safety factors.
Secondly. So long as you load your trailer correctly towing at or above kerb weight is not a problem. The only figures you need to abide by are those on the vin plate of the tow car & caravan and the nose weight for car & caravan. By virtue of the much heavier weight of the trailer, your vehicle will be going slower, thus giving you more time to plan your drive.

 

[xtrailman]

Hi all, we are looking around for a new van, i have always stuck to the 85% rule and have towed for more years than i care to remember.

However, most of the caravans we are looking at are heavier than 85% of our 4x4's kerb weight, we are possibly going for a twin axle for better towing stability!

Any views and opinions greatly appreciated.

regards Andrew.

I'm presently towing at 92%, i certainly wouldn't consider towing near 100%, or over, i'm not suicidal.
I have yet to tow with my present setup in strong winds, i'm expecting the tow to be interesting.
I have towed in blustery conditions, and found a speed reduction helped.
The most noticeable thing is the increase in fuel consumption, was 28/29 mpg towing 1333kg
Now only 24/26 mpg towing 1565kg.

 

[xtrailman]

Having recently taken my caravan in for repair work, i took out the contents, including carpets and upholstery.
The car was empty with half a tank of fuel. Just me and a passenger.
I was amazed at how well the outfit towed, still with a NW of 90kg, the outfit was completely stable and a pleasure to tow.
I haven't bothered to calculate the ratio, but it must be well below 85%.
Why anyone trys to justify towing at a high ratio beggars believe.

 

[Lutz]

What makes you so sure that the only reason for the caravan towing so well was because of the low weight ratio? Seems a very hasty conclusion to me.

 

[xtrailman]

What makes you so sure that the only reason for the caravan towing so well was because of the low weight ratio? Seems a very hasty conclusion to me.

What makes you think it isn't?

 

[Lutz]

For a start, the caravan magazine that I subscribe to regularly test towcars at the manufacturer's towing limit, even if this allows a 100% weight ratio and they have often come up with positive results. Personally, I towed for many years at around 100% and never felt uneasy with the outfit. Also, German regulations allow towing at 100km/h so long as, among other conditions that must be fulfilled, the ratio doesn't exceed 100%, so it would be logical to assume that they must have carried out some investigations to make sure that such a rule makes sense before putting it to paper.
As John has pointed out, the weight ratio doesn't reflect the actual state of the majority of outfits on the roads, but a worst case scenario, anyway. It is therefore more of use as a guide for comparison purposes than of practical relevance.
There are just too many factors which determine the stability of an outfit that it would be incorrect to point to the weight ratio as the one and only reason.

 

[xtrailman]

For a start, the caravan magazine that I subscribe to regularly test towcars at the manufacturer's towing limit, even if this allows a 100% weight ratio and they have often come up with positive results. Personally, I towed for many years at around 100% and never felt uneasy with the outfit. Also, German regulations allow towing at 100km/h so long as, among other conditions that must be fulfilled, the ratio doesn't exceed 100%, so it would be logical to assume that they must have carried out some investigations to make sure that such a rule makes sense before putting it to paper.
As John has pointed out, the weight ratio doesn't reflect the actual state of the majority of outfits on the roads, but a worst case scenario, anyway. It is therefore more of use as a guide for comparison purposes than of practical relevance.
There are just too many factors which determine the stability of an outfit that it would be incorrect to point to the weight ratio as the one and only reason.

Yes but is that for a trailer, or a caravan?
I agree many factors determine stability, we both know what they are with out listing them.
But from my personal experience towing, not theory, but real life, the lowest ratio i have towed with well below 85%, was my first caravan. This was my best tow.
Progressively as my caravans have got heavier, and the towing ratio higher, the towing experience has become less enjoyable.
Mainly due to the apparent increase in instability, as the ratio has climbed.
Theres no doubt in my mind that towing near 100% with a high sided, long caravan is a mugs game.

 

[Lutz]

Yes but is that for a trailer, or a caravan?

In all cases for a caravan. The tests that I referred to were all conducted with caravans and the 100% legal maximum in Germany also applies to caravans only. It is 120% for other types of trailers.

 

[Gafferbill]

Theres no doubt in my mind that towing near 100% with a high sided, long caravan is a mugs game.

.......... there is no doubt in my mind either.

I always consider axle weights .........and I want the rear axle of my tow vehicle to be as high as possible relative to the axle weight of the caravan.
For axle weight of the caravan even if it is a twin axle, read weight of caravan less noseweight.

The best way to achieve this is to tow with as low a towing ratio as possible

Some people argue that it is OK to tow at 100% pointing out that there are many factors relating to outfit instability.
Yes there are many factors but they are all tamed and kept under control by the stability of the tow vehicles rear axle.
If the instability of the caravan becomes too great causing the rear axle tyres to loose grip and break away, a snake will then develop. The tyres will eventually regain grip due to their increased slip angle, the rear ot the tow vehicle and the caravan will then snatch back in the other direction. Inertia kicks in to promote the pendulum action of the snake and is relative to the weight of the caravan.

The critical factor is the grip performance of the rear axle of the tow car.

Increase the weight of the tow car relative to the caravan and load the rear of the car in as much as common sense and the law allows, will lead to a more stable tow.
Maintain tyre pressures and tyre condition to ensure best performance.
Reduce the forces likely to cause instability by fitting ATC, correct loading of caravan and reduce speed etc.

Towing a caravan is a leisure activity.
100%…….. Why go there?

 

[Lutz]

Reduce the forces likely to cause instability by fitting ATC, ......

ATC (or any other electronic stabiliser for that matter) will not reduce the forces likely to cause instability, but will only react appropriately if it occurs. It does not prevent instability, but it prevents the instability from getting out of control.

 

[Gafferbill]

Lutz you are of course right……..
I will change the wording by adding the word dangerous as below if it makes you happier.

"Reduce the forces likely to cause dangerous instability by fitting ATC"

ATC works by applying the caravan brakes after instability of the caravan has been sensed by a lateral motion detector.
It replaces the unwanted lateral forces on the coupling that cause instability of the rear axle of the tow vehicle.
This takes place because braking the caravan will result in an overriding rearward force of tension on the coupling.
The unwanted lateral forces decay as a result as they cannot compete except in very extreme cases of caravan instability.