Can someone explain what max towing weight (braked) means and (unbreaked)? Is that when you slip the breaking cable over the towbar before you hitch the van to the car, the coupling that pulls the breaks on in the case of a van detachment while driving? :S
towing weights
- Thread starter Lonesome-Whizkid
- Start date
Braked and unbraked refers to the trailer - does it have brakes or not.
If the trailer doesn't have brakes then the gross weight of the trailer and contents can only be max of 750 kg by law, or less if manufacturer of towing vehicle says so. This is because all braking forces are supplied by the towing vehicle.
If it does have brakes (normally of the over-run design) then, as the towing vehicle slows down, the trailer brakes are also applied automatically by the fact that the trailer is trying to over-run the towing vehicle.
Articulated vehicles have a different design involving air brakes.
The break-away cable (only used with braked trailers) is there to operate the trailer brakes in the event that the trailer parts company from the towing vehicle, thus ensuring the trailer comes to a stop immediately by itself.
An un-braked trailer generally has a chain between trailer and towing vehicle in order to control the trailer in event of it uncoupling.
If the trailer doesn't have brakes then the gross weight of the trailer and contents can only be max of 750 kg by law, or less if manufacturer of towing vehicle says so. This is because all braking forces are supplied by the towing vehicle.
If it does have brakes (normally of the over-run design) then, as the towing vehicle slows down, the trailer brakes are also applied automatically by the fact that the trailer is trying to over-run the towing vehicle.
Articulated vehicles have a different design involving air brakes.
The break-away cable (only used with braked trailers) is there to operate the trailer brakes in the event that the trailer parts company from the towing vehicle, thus ensuring the trailer comes to a stop immediately by itself.
An un-braked trailer generally has a chain between trailer and towing vehicle in order to control the trailer in event of it uncoupling.
Lonesome-Whizkid said:
Most definitely it will have brakes - because its MTPLM (Maximum technically permissible laden mass) will be far greater than 750 kg, somewhere in the region of 1650 kg. If towing at 85% for a novice then the tow car needs to be at least 1941 kg and the driver needs to hold a B+E licence as the train weight will be over 3500 kg.
Suggest you buy a copy of Practical Caravan magazine which will give you weights and rules, etc for towing.
I don't know if im reading a misprint or not but is it true that the kia sorento 2.5 litre 4x4 diesel can tow a max weight of 3500kg? sounds kinda high especially when the 2.2 litre is only max towing weight of 2500kg. :huh:
It wasn't on PCv forum I read it, It was on the vehicle specifications page on autotrader.co.uk, I just don't understand how the same car with 0.3 litres of a difference in engine size can alter the towing limit of the towing vehicle by up to 1000kg, I thought it was all based on weight? and not torque, power, speed or engine size???? 
- Mar 14, 2005
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Ok,
First point, ALL magazines from time to time make quote specifications of some sort, but they may get them wrong, it just human error and they generally cover themselves with a statement somewhere on the publication to the effect of " Errors and Omissions Excepted"
A quick heads up on vehicle towing specifications.
All new cars produced for sale in the EU have to be type approved, and that process includes a set of tests that establishes each models towing capability. Even the change to type of body shell can affect the results of the tests so you have to check the specification of the exact model you are considering.
The towing ability of what on the face of it appear to be similar vehicles, (such as same car but different engine) is not as simple as saying a bigger engine must be able to tow more.
A classic example of where the towing specification apparently didn't make sense, was the MK1 Vauxhall/Opel Zaffira. What would have been the normally preferred choice for a family tow car was the diesel option, but in fact it was rated much lower than other even smaller engined variants. The reason it seems was that whilst the 2.0L engine had the power, Apparently it was the way it was fitted into the body, and that restricted the cooling arrangements for the engine.
There is also the difference between petrol and diesel engines. In general Diesel engines of the same cc produce more torque and power at low RPM which makes them better pullers, but petrols often have higher powers at higher RPM which makes them more sporting.
Also the gear box ratios may be specifically designed for different working criteria, for example, a high speed cruiser may have high ratios which keep the engine revs lower for any given speed. but having high ratio gearing is counter to pulling ability. So working vehicles tend to have lower gear ratios, gives good pulling but it sacrifices high speed.
Many motor car manufactures also produce a range small and middle sized vans. In many cases the same engines are used both cars and vans, but depending on how they are tuned, and the choices of gear box ratios, you might find the same engine fitted to a 'Transit' sized van and to one of their more sporting saloon cars.
In a further twist, Saab used GM derived 2.2 diesel engine in some of their cars. But in later models they opted for 1.9L diesel (I think it was Fiat derived) which produced more power and torque.
So you cannot make assumptions about towing ability based simply based on engine capacities. You have to dig into the detail a bit more.
First point, ALL magazines from time to time make quote specifications of some sort, but they may get them wrong, it just human error and they generally cover themselves with a statement somewhere on the publication to the effect of " Errors and Omissions Excepted"
A quick heads up on vehicle towing specifications.
All new cars produced for sale in the EU have to be type approved, and that process includes a set of tests that establishes each models towing capability. Even the change to type of body shell can affect the results of the tests so you have to check the specification of the exact model you are considering.
The towing ability of what on the face of it appear to be similar vehicles, (such as same car but different engine) is not as simple as saying a bigger engine must be able to tow more.
A classic example of where the towing specification apparently didn't make sense, was the MK1 Vauxhall/Opel Zaffira. What would have been the normally preferred choice for a family tow car was the diesel option, but in fact it was rated much lower than other even smaller engined variants. The reason it seems was that whilst the 2.0L engine had the power, Apparently it was the way it was fitted into the body, and that restricted the cooling arrangements for the engine.
There is also the difference between petrol and diesel engines. In general Diesel engines of the same cc produce more torque and power at low RPM which makes them better pullers, but petrols often have higher powers at higher RPM which makes them more sporting.
Also the gear box ratios may be specifically designed for different working criteria, for example, a high speed cruiser may have high ratios which keep the engine revs lower for any given speed. but having high ratio gearing is counter to pulling ability. So working vehicles tend to have lower gear ratios, gives good pulling but it sacrifices high speed.
Many motor car manufactures also produce a range small and middle sized vans. In many cases the same engines are used both cars and vans, but depending on how they are tuned, and the choices of gear box ratios, you might find the same engine fitted to a 'Transit' sized van and to one of their more sporting saloon cars.
In a further twist, Saab used GM derived 2.2 diesel engine in some of their cars. But in later models they opted for 1.9L diesel (I think it was Fiat derived) which produced more power and torque.
So you cannot make assumptions about towing ability based simply based on engine capacities. You have to dig into the detail a bit more.
Ok, Very well explained, thanks So what your saying is don't believe anything till you've had a look at the vehicle's user manual? and seen what the manufacturers are putting in black and white? Which should also be on the VIN plate? Or is that just the max train weight on the VIN plate?
So what your saying is don't believe anything till you've had a look at the vehicle's user manual? and seen what the manufacturers are putting in black and white? Which should also be on the VIN plate? Or is that just the max train weight on the VIN plate?
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Lonesome-Whizkid said:Ok, Very well explained, thanks
Sad to say your just about right. Just like chinese whispers, information can be inadvertently changed the further it gets away from the source. Its only fair to say that most data will be right, but the difficulty is you as the reader you don't know which is right or wrong, so its back to the source to minimise the possibility of errors. iIt is important to get it right, as if you get it wrong you could be prosecuted and end up with points on your licence.
Its no defence to claim you based your loading on information on anything other than the official figures for the vehicle.
http://europa.eu/ said:
Most weights plates will contain 4 fields of weight information
1st field is the Gross Vehicle Weight (MAM)
2nd field is the Gross Train Weight
3rd field is the front axle maximum load
4th field is rear axle maximum load.
lol, Who would have thought caravanning would be this complicated complex and detailed. But rules are rules and they must be followed.
if you remember that point was spelled out after your first post yes caravaning is complex and keeping within the law as changes occur frequently makes it very complicated especialy for a newbie, your in for a treat though as we have not even scratched the surface of the technical side never mind started on the practical side of the hobby yet,Lonesome-Whizkid said:lol, Who would have thought caravanning would be this complicated complex and detailed. But rules are rules and they must be followed.
Just adding a quick question to this thread.
Do you go by the minimum kerb weight of the towing vehicle or the maximum kerb weight when working out the 85% match?
Do you go by the minimum kerb weight of the towing vehicle or the maximum kerb weight when working out the 85% match?
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Lonesome-Whizkid said:Just adding a quick question to this thread.
Do you go by the minimum kerb weight of the towing vehicle or the maximum kerb weight when working out the 85% match?
Hello again,
Your re-discovering anomalies that make caravanning more complicated than it should be. What you have now found is, car manufactures are not required to publish the exact kerbweight of a vehicle, there is no legal requirement for them to do so. So to save printing many different user manuals, they often combine several models into one handbook. They then fudge some issues such as kerb weight by offering a range of weights, but not identifying where each model sit within the range.
That leaves caravanner's with a problem because they have no exact baseline for working out match ratio's. As for which figure to use is difficult to be precise, but if you are determined to go for 85%, then to achieve the outfit with best chance of being a good match, you must use the smallest kerbweight figure.
Now you may recall I have pointed out that 85% has no legal relevance, and it its not as if towing is going to dramatically change if you exceed 85%, So even if you were to use the largest kerbweight figure you'll probably not notice the difference when driving.
Alternatively you could split the difference between the upper and lower figures, or more accurately look at the V5c for the Mass in service or Mass in Running Order or the Unladen Weight and use one of those figures.
85% is only a very coarse guidance and the differences between the results obtained using any of the above base lines should not be a problem. But you may remember I have previously told you the 85% is not an exact figure its just guidance and a few percent either way is not going to make a big difference.
When you think about it, the way the ratio is calculated (MTPLM/Kerbweight) bears no relation to the way we actually caravan. No car is ever at its lowest weight when towing a caravan, so the real ratio will always be lower than the calculated figure.
You may have gathered I am not enamoured with the way recommendation is calculated or used. From an engineering perspective its far from consistent, and it has been misused by being colloquially called a "Rule" which has led it to become a caravanning dogma. In some peoples perception matching at 85% equates to "safe" but in fact it offers no guarantees of safety what so ever. safety is more down to the drives skills than the weight ratio.
It does however support the notion that smaller is more likely to be safer, so these days I don't rock the boat too much on this subject.
Parksy
Moderator
- Nov 12, 2009
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I've no wish to complicate the issue further or get into yet another protracted debate regarding the 85% towing weight ratio recommendation, but in the interests of balance I'd add that the 85% figure is recommended by most authoritative sources as being a safe towing ratio for beginners.ProfJohnL said:
As John mentioned however, correct loading, regular tyre maintenance and good driving skills are of paramount importance.
Caravan tyres, no matter how much tread they have on them, should be replaced after 5 years and not used after 7 years.
This means that if you buy a used caravan you need to check how old the tyres are or if they have been replaced to avoid risking a blowout.
hi all,
I have no wish to complicate the issues either, as they are complicated enough as it is!,
however while I understand, the principal and thinking behind the recommendations, ie, the newbie is most vunerable simply because they probably dont understand the importance of correct loading balance maintenance driving techniques ect.
the way in which the organisations Parksy spoke of use to calculate this mysterious magical figure is different and therefore in it's self complicates the issue.
one will say use 85% of the unladen weight of the tow car to the MTPLM of the trailer,
another will say use the kerbweight of the tow car to the MTPLM of the trailer.
and another will quote the actual weight of the tow car to the tow load of the trailer.
the difference between 2 and 3 could be as much as 15%, while most would agree 1. is the most sensible this is not a universal calculation,
the very fact that most newbies using any of the calculations, change their vans after a year or so for a bigger van whlie using the same tow car speaks volumes.
but of course by then they are no longer newbies and have learn the importance of other aspects of towing.
both the Prof and myself have been long standing critics of the term "rule" and while any sensible recommendation is worthwhile, it is far better just to keep the max towed weight of a trailer as low as possible in relation to the tow cars recommended tow weight.
I have no wish to complicate the issues either, as they are complicated enough as it is!,
however while I understand, the principal and thinking behind the recommendations, ie, the newbie is most vunerable simply because they probably dont understand the importance of correct loading balance maintenance driving techniques ect.
the way in which the organisations Parksy spoke of use to calculate this mysterious magical figure is different and therefore in it's self complicates the issue.
one will say use 85% of the unladen weight of the tow car to the MTPLM of the trailer,
another will say use the kerbweight of the tow car to the MTPLM of the trailer.
and another will quote the actual weight of the tow car to the tow load of the trailer.
the difference between 2 and 3 could be as much as 15%, while most would agree 1. is the most sensible this is not a universal calculation,
the very fact that most newbies using any of the calculations, change their vans after a year or so for a bigger van whlie using the same tow car speaks volumes.
but of course by then they are no longer newbies and have learn the importance of other aspects of towing.
both the Prof and myself have been long standing critics of the term "rule" and while any sensible recommendation is worthwhile, it is far better just to keep the max towed weight of a trailer as low as possible in relation to the tow cars recommended tow weight.
- Jun 20, 2005
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Just to further complicate matters for a newbie it is worth mentioning the misleading information given by vehicle manufacturers . Many will say their vehicle can tow a braked trailer of 3500kgs whilst the vehicle is only say 2500kgs. The LR Discovery boasts this very statement yet we all know in practice not a good idea.
- May 7, 2012
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The cars weight is what you use not the towing limit if this is heavier. The towing limit is simply the cars ability to perform a hill start without damage to the clutch. What you have is a car that can say tow a broken down vehicle heavier than itself at a moderate speed, but this does not mean that 60 on a motorway with a caravan is safe, although it can manage it without wrecking the transmission.
I now have a good understanding of external caravan and tow car safety and i would like to thank all who have helped me and given their time and wisdom with this detailed subject, I can now make a better than average decision on the purchase of my first van which i wont be rushing into, Going to make sure i get a good one and hopefully a bargain at that. It's like sitting a driving test all over again lol, there's just so much to take in.
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