Twin axle Feb06 mag comment

[Steve L]

I got my Feb 06 issue of the mag in the post yesterday and started to read it, but was quite shocked by the top right photo comment on the editors page.

Twin axles pack in lots of kit, but are less manageable to tow.

As a driver with 30 years towing experience spanning from a dinghy trailer to a 60 foot articulated lorry, and towing abnormal loads with cars such as sailing yachts. Also towing caravans from a mere 10 feet long to my current 20 foot twin axle.

I have to say that a twin axle van is far from less manageable. It inherently tows better on the motorway due to it's natural desire to go straight ahead. Due to the load being shared by four tyres, when you corner , it is more sedate and less likely to wallow in corners. Also when you brake, you have four tyres in contact with the road to stop the weight in motion.

The only minor draw back is manual manouvering, but even then I can move our van single handed with the aid of my motor mover.

With the well laid out sites of today if you talk to the receptionist when booking, they will ofte find you a drive on, drive off pitch for your twin axle van. Mind you, that doesn't excuse anyone from learnin how to reverse their out fit.

Finally before anyone rushes out to order a 4x4 to go with the twin axle van they've just bought, you don't need one as a pre-requisit. I quite happily tow our van with a 1998 Laguna estate (2000cc) which is front wheel drive.

I do however agree that storing your van at home is a good point. I store both mine and the father-in-law's van at our house which is very convienientasI look after both vans machanically etc as father-in-law is disabled.

Regards.

Steve.

 

[Lutz]

I get your point and your comments are fair but it is also a matter of one's personal priorities. You say manual manoeuvring is a 'minor drawback'. To me it's a major drawback and one of the main reasons why I wouldn't buy a twin axle unless it were of a size that makes a twin axle unavoidable (i.e. over 1600kg). But then anything over 1600kg will probably not be very easily manoeuverable by hand even as a single axle.

Another disadvantage not mentioned is that the weight of the second axle reduces the available payload if the MTPLM cannot be raised at the same time by the same amount. This may be the case if one is running close to the towload limit of the car. The situation is made even worse if a motor mover is fitted to overcome the 'minor drawback'.

 

[WatsonJohnG]

It just goes to show that what is a little thing for one person is a big thing for another.

A dealer once told me that he could spot a twin axle owner from a distance as they were the ones with a bad back.

I have never felt the need for twin axle -----yet!!

I often wonder how much they are a left over from the days when twin axles were allowed a higher speed limit.

These are just ramblings and not intended to inflame the devotees of twin axles.

 

[RogerL]

In the UK, twin-axle caravans have always had the same speed limit as single axle ones.

There is a category of commercial "close-coupled trailers" but twin axle caravans don't meet the regulations for these, their axles are too close together.

 

[WatsonJohnG]

You do surprise me Roger I was under the impression that it was 60mph for twin axles and 50mph for single axles at one time.

I stand corrected ----another theory bites the dust !!!

 

[sparkes]

In the last 12 months we have changed from a single axle to a twin. The Twin is defiantly easier to tow and a lot more stable.

As for maneuvering, well at 1770kg a mover was the only option with bad legs. Works very well. Also, reversing the twin is a lot easier than a single due to the extra length making it act slower.

In the end of the day, if you have a car that will make YOUR van easy to tow then you should be happy. Our choice for the twin was the size, Two growing kids use a lot of room on a caravan holiday.

 

[Lutz]

I've just gone through all the models available on the market and found some single axle ones rated at 1800kg so a twin isn't an absolute necessity even for such large caravans. I still think it's better to carry less deadweight with you by dispensing with a second axle, if possible, and benefit from better manual manoeuverability and easier levelling of a single axle.

 

[MONKEY1]

What a strange comment for PC to make, for the word manageable should it be "pitch". For years the consensus has been that TA are more stable on the road and harder to reverse, although I think over the years that gap has probably closed significantly to the point where how you load the thing and it's layout are far bigger factors in handling than two extra wheels.

Monkeys Husband

 

[WatsonJohnG]

Just a couple more ramblings.

Lunar made a twin axle with hydraulically liftable wheels for easier manoevering --has that been discontinued now ?

With the fixed towbar height on most cars it must be more difficult to get the two axles level when the hitch is at the towbar height

I saw an outfit where a drop plate was needed to raise the ball to achieve such levelling.In these days of type approval of towbars that would be illegal and so that outfit would have to run very nose down as we see so often these days with single axles

I wonder how that would affect the twin axle stability/trim etc.

 

[metz]

Just a couple more ramblings.

Lunar made a twin axle with hydraulically liftable wheels for easier manoevering --has that been discontinued now ?

With the fixed towbar height on most cars it must be more difficult to get the two axles level when the hitch is at the towbar height

I saw an outfit where a drop plate was needed to raise the ball to achieve such levelling.In these days of type approval of towbars that would be illegal and so that outfit would have to run very nose down as we see so often these days with single axles

I wonder how that would affect the twin axle stability/trim etc.

Hi John, Re Lunar hydrulics, not many of those about now,most of them broke their backs, the hydrulics used to leak all in all not a very good idea in my opinion.

 

[Lutz]

The caravan manufacturers are fully aware that the coupling head should be between 395 and 465mm above the ground when the caravan is horizontal and fully laden and this applies to all caravans, regardless of whether single or twin axle, so unequal load distribution between the axles should not be an problem.

 

[emmerson2]

Rogerl, I believe that many years ago,(early 70s perhaps) there was a short-lived regulation that allowed drawbar trailers with twin axles more than 4ft apart to travel at 70mph.Also, can anyone remember the Sprite experiment with an axle at each end? Around the same time I think. I saw it at high speed on the M4.

 

[Geordie]

T/A vans are supposed to be more stable, but recently I have come across a couple of them where that couldnt be said of the drivers towing them. The first one was so nose heavy, the rear axle wheels had no contact with the road and was being towed by a big Jag,and the second was on a stretch of the A1 north bound and I was not keen to overtake it because it was all over the place, and it was towed by a 4x4. No wonder other motorists have negative thoughts about us vanners.

 

[WatsonJohnG]

Thanks for that geordie.

Lutz and I have debated this before.

What the caravan manufacturere know and what can be seen on any UK motorway in the summer do not tally.

Its very common to see very nose down single axle vans and as you say this can also be seen with twin axles.'If the car is at one extreme of the standard and the caravan at the other then the outfit will ride nose down or nose up (although nose down seems to be the norm)

Its time that more thought was given to two sets of holes on all towbars rather than a few so that better trim can be achieved in reality rather than in theory.

Happy New Year Lutz and best regards

 

[Geordie]

Watson (John G ), I know what you mean about the two sets of holes because I have recently accuired my second shogun and the towbar now fitted has only one setting. I told them I wanted the same towbar that was fitted to my previous vehicle ( two sets of holes ) and was told that was no problem, but when I got the car it was fitted with another type and after telling them to exchange the bar they inform me that is the new model so Im stuck with it, but lucky for me the van sits ok .

 

[Lutz]

The two sets of holes alternative of course only works with a bolt-on type towball, not for the swan neck variety and most factory-fitted towbars are swan neck.

Having said that, I would suggest that if the caravan was sitting abnormally nose down, then either the back end of the car was seriously overloaded or the caravan was empty and consequently its suspension hardly compressed (or both).

 

[mcghee]

as lutz has already said,all caravans have a ground to hitch measurement roughly the same.in my experience about 410-450mm.since any car or towbar manufacturer can easily obtain this measurement there can be no excuse for having a caravan towing at more than a few degrees off the level.i have towed with both single and twin axle and find twin axles to be much better at speed,and much more composed on b-roads,due to the fact that the 4 wheels "track".but if you have a van which is rather heavy for your car this phenomenon will mean the caravan will try to dictate your direction of travel.also the twin axle reverses easier as it tries to straighten up as soon as stop forcing the turn.and really,the fact that a caravan is nose down shouldnt really make any difference to the axle loads.

 

[Steve L]

Here's a note for Lutz. Like Steve sparkes, I too have a bad leg (knee replacement) but also suffer with frozen shoulders which restrict both movement and strength.

I am quite capable of manovering my twin axle van which has a linked axle setup which means that even with the jockey wheel wound right down the wheels still remain in full contact with the road. The benifit is that you don't get excessive weight transfer when going over bumps.

I'm sure a lifting axle such as on some early Lunar Delta's would be a great help, but I must say the benefits of stability on the road and the extra room afforded a twin axle, far out weigh the draw backs.

Steve.

 

[WatsonJohnG]

Hi Geordie I have had two Nissan X Trails and the first with a Witter towbar was a good level ,slightly nose down,match.

The second with a Brink was very nose down and neither vehicle was overloaded.

The Brink bolt on was a factory option as are many UK ones.

Its not rocket science to offer different length towballs/2 sets of holes or swan necks .The Brink for example uses the same bracket but the fittings are for bolt on or swan neck bolt in.

Type approval may be working against more flexibility as it would involve testing with different lengths etc and this is not cost effective if manufacturers can get away without offering a choice.

No towbar manufacturer seems to list the actual(rather than max/min) height of the ball.

One bar may be offered for a range of a model irrespective of tyres fitted(low profile etc)and its really hit and miss as things are at the moment.

I have met this problem with several tow cars and I'm sure I'm not the only one.I have fitted suspension aids in the past when a higher ball would have been quite sufficient.

We get the new Bailey in a few weeks and I am interested to see how much difference there will be in the trim of the outfit.

A while ago I measured towball height at a dealers and there was about 2in difference between makes on new caravans.

The difference between theory and practice can be seen on the motorway every day.

 

[Lutz]

2 inches difference in height between 2 caravans is not going to make a difference in towing and it's well within the tolerance of

 

[RogerL]

Rogerl, I believe that many years ago,(early 70s perhaps) there was a short-lived regulation that allowed drawbar trailers with twin axles more than 4ft apart to travel at 70mph.Also, can anyone remember the Sprite experiment with an axle at each end? Around the same time I think. I saw it at high speed on the M4.

You're referring to "close-coupled" trailers which have had different speed limits. Excluding prototypes, no UK production caravans have been built in this category.

 

[WatsonJohnG]

2 inches difference in height between 2 caravans is not going to make a difference in towing and it's well within the tolerance of

 

[Lutz]

Getting back to Steve's original post where he says that he tows a 20 foot twin axle behind a Renault Laguna estate. I'd advise him to check his weights because I have a strong suspicion that he may be exceeding the maximum permissible gross train weight.

I don't know what the figure is for a 1998 Laguna but for the current one the max gross train weight is 2900kg. If the car is fully laden to its GVW of 1940kg (again, current model), that leaves a puny 960kg to tow with and I don't know of any 20 foot twin axle that's that light. Even disregarding the gross train weight limit, the maximum towload is possibly already lower than the MTPLM of his caravan.

 

[RogerL]

The range of hitch heights is necessary because caravan manufacturers can't be bothered to use different suspension settings for different models of caravan or even different wheel sizes.

Al-Ko produce the Euro-axle chassis in three main load variants so caravan manufacturers simply choose the appropriate one. This means that a 1100kg MTPLM caravan will use the same axle as a 1300kg one but obviously the 1300 unit will sit lower as the ride height isn't altered to suit.

When caravan manufacturers changed from 13" to 14" wheels, with an increased rolling radius, they didn't adjust the ride height so later vans sit higher than earlier ones.

Contrast this with car manufacturers who will often fit different springs to differently trimmed models to bring the ride height to a consistent level. Tow-ball heights have to meet the required standard regardless of equipment or wheels/tyres. That's why some cars with lowered suspension are simply not homologated for towing.

There is, however, a problem with the standard height range for tow-balls. The standards apply to cars but NOT off-roaders which is where mis-matches often occur. In these cases tow-bar manufacturers can put the tow-ball at whatever height they choose.

 

[Lutz]

One cannot compare ride height criteria for cars with those for caravans because the driving conditions are so different. Nobody will expect the same high standard of road holding and handling from caravans simply because these aren't driven like sports cars.

The ride height (and coupling height) tolerances for caravans can therefore be larger than for cars without adverse effects. One must also bear in mind that car manufacturers have much greater development resources at their disposal than caravan builders and can afford to put more effort into getting the setup just right. The production volumes of caravans are so much lower compared to the average car that the cost per unit of differentiating more between models would be prohibitive.

Even car manufacturers do not approve some of their low volume models for towing simply because of the cost of the development tests which would be necessary.