Single axle vs tandem axle caravan. I need advice

Submitted: Wednesday, May 20, 2020 at 09:55
ThreadID: 140043 Views:4196 Replies:17 FollowUps:14
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Hi all,
I'm looking at buying a new van. I've towed 17'6 tandem for 10 years many years ago and now it's time again.

Two choices, both around 2100 tare, 2500 atm, I will tow with a NT Pajero that has a ball weight restriction of 180 over 2500.

Single axle 18'8 and tandem axle 19'6. So they are close in length and weight (and price). The question is: does a tandem have better road manners? Does it track nicer, easier to reverse, does a single axle tend to hop around?

Would really appreciate a comparison from anyone who has towed both (around the same size and weight) and anyone who can tell me what to expect from a single axle.

Many thanks,
Alister
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Reply By: Glenn C5 - Wednesday, May 20, 2020 at 10:32

Wednesday, May 20, 2020 at 10:32
One Word. TANDEM
AnswerID: 631682

Reply By: Erad - Wednesday, May 20, 2020 at 10:58

Wednesday, May 20, 2020 at 10:58
There is always a lot of discussion about single vs twin axles. I offer the following comments...

1 A twin axle setup weighs a lot more than a single - at least 100 kg, b the time you add the extra axle, springs and wheels.
2 A dual axle setup will have slightly more drag due to friction in flexing the tyres. Yes - the tyres are nominally carrying less load than a single axle but there will still be more drag.
3 A lot of hoo hah has been put up about stability if you get a blowout on a single axle. My caravan is a 16.5 ft Jayco Poptop and I have done over 140000 km with it. In that time, I have had 2 blowouts, and the only way I knew was a rumbling noise which didn't sound right. The first time was on the Bruce Hwy on a Sunday afternoon - 2 solid lanes of traffic travelling at 100 km/h, just over the crest of a hill. Nowhere to pull off. I just kept driving until I could get off the road a bit. Other than noise, no dramas. The second time was on a narrow, winding road, double lines for about 5 km and I thought the car felt a bit sluggish. I heard a noise but then that went away. AA car behind me started flashing it slights and I knew I had trouble, but there was nowhere to pull off, so I kept going for about another 3 km until I came to a driveway and then pulled over. That little trip did wonders to the wheel rim... As for the caravan tipping over - not a chance. Incidentally, I now have a tyre pressure monitoring system which covers the van and the Pajero. Hopefully a worthwhile investment.
4 Reversing the caravan: The most critical part of reversing a van is the distance from the towball to the van axle(s). Obviously, a twin axle setup is going to scrub the van tyres as you reverse, but the amount of reversing yo do is minimal anyway, so there is no difference. For what it is worth, a rear kitchen van typically has the axles set further back (the centre of gravity if well back with a rear kitchen) and thus the length between the towball and the axles is greater. This means that you have to get the car at a wider angle to reverse the van into a spot and therefore it is much easier with the longer distance.
5 Manhandling the Caravan: You can manhandle a single axle caravan (n a level firm site) to position it in a site or a garage, but there is no way you can do this with a dual axle setup.
6 General Towing: A dual axle setup is probably better for towing, but the difference should be minimal if the van is loaded correctly. A dual axle van badly loaded is just as dangerous as a single axle one.
7 Caravan Length: More and more caravan parks are having problems with the size of modern vans. They are getting too large for their sites. A few years ago, we accidentally arrived in Alice Springs the week of the Finke Desert Race. We tried 3 caravan parks to get a site - all booked, but the 4th park asked us how big our van was. I told them and they said it was very tight but we could have the last site. It was tight but we fitted (just) and we had a fantastic week there.


So if you are looking at different vans and all things are equal, I would go for the smaller van - it will most likely be lighter, you will use less fuel and it may make the difference as to where you can get a site if that is your wish.
AnswerID: 631686

Follow Up By: Peter_n_Margaret - Wednesday, May 20, 2020 at 12:35

Wednesday, May 20, 2020 at 12:35
In addition to the above, if you want to traverse anything but "roads" choose a single axle. The harder it gets, the bigger the advantage of a single axle.
A single axle wants to follow the tug. A tandem axle van wants to go in a straight line, even if that is not the direction that the tug is going in.
Cheers,
Peter
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Reply By: PeterInSa - Wednesday, May 20, 2020 at 14:02

Wednesday, May 20, 2020 at 14:02
Had a Blow out on a single axle 16ft Pop top, while a B Double was passing me. Me doing 95 the B Double? The van kept swaying after it passed so pull over and checked the van. Tyre had only done 2500Km. Distributor was reluctant to replace free of charge until I threatened to go to the media. Van normally rock solid behind the Tug.

I like the larger living space so would go with the Tandem. Our Traveller is 21'6"

400Kg payload is not great, from memory ours is 650Kg.

Peter
AnswerID: 631689

Reply By: Gbc.. - Wednesday, May 20, 2020 at 14:10

Wednesday, May 20, 2020 at 14:10
Any big single axle trailer I've towed hasn't been as well behaved as a similar tandem on road. I've towed single and tandem boat trailers up Fraser Island. Both were OK. I like a single axle trailer but at the sizes and weights you are talking I would prefer a tandem.
A load sharing tandem should also have a lower ball weight than an equivalent single axle which will be a consideration with the Pajero.
AnswerID: 631690

Reply By: Notso - Wednesday, May 20, 2020 at 16:02

Wednesday, May 20, 2020 at 16:02
I've owned 3 vans, first one 18 foot single axle independent . Had three blowouts in it, wouldn't have know unless I notice the van had a funny lean on it. Second one Tandem axle, 18 foot 6, towed well no major issues but as said above, dirt tracks could be a pain. Third one Single Axle independent, 18 foot 6, The best of them all, Off Road, owned if for 7 years or so. Did some outback roads and tracks. So my preference up to about 19 foot would be single axle. But of course if you want much larger then dual is the only way to go.

The big issue is to make sure it is fitted with High Load Carrying capacity tyres with plenty of leeway between their max capacity and the GTM. Don't under inflate them!
AnswerID: 631691

Reply By: Rob A2 - Wednesday, May 20, 2020 at 17:12

Wednesday, May 20, 2020 at 17:12
Well our experience with our AOR campers after towing the Q+ for over 40,000km around outback Australia is that it's been utterly reliable in the wide variety of conditions we have been. For example Tanami and GCR as well as sitting at a comfortable, safe and legal speed in the NT that would be illegal in every other place in Oz.

The only advantage, for our use, a twin axle may offer is a lighter down ball weight.

So you need to consider what places you intend to go and what you want form your camper. You have mentioned ball weight as a major consideration so unless you want to do a GVM upgrade on the Pajero I suggest the outcome is inevitable, tandem axle.

But without knowing where you tow a harder question to answer with any more detail

Rob
AnswerID: 631693

Reply By: Nomadic Navara - Wednesday, May 20, 2020 at 17:29

Wednesday, May 20, 2020 at 17:29
I agree with Erad's reply above. Most people who relate their experience and compare the towing of single and twin axle vans have towed vans of difference lengths, They have upgraded from a short single axle van to a long twin axle van. About 14 years ago a mate and I changed vans All four vans were about 19" body length. In both cases, we changed vans to get a more desirable layout. His had a floor to ceiling cupboard modified to get a longer kitchen bench. I changed from an L shape dinette in the rear corner to a cafe style one. In both cases, we went from a twin axle van to a single axle. Neither of us noted any change in the towing characteristics of our vans.

The difference in apparent stability between long and short van is due to the length. A longer van will appear more stable because of the yawing resistance. The longer van resists yawing more than a short van. Just like long arrows fly straighter than short ones. It has nothing to do with twin axles being more stable than single axles. Don't let people feed you with all the BS regarding the superior stability of a twin axle.

I have been involved in shifting vans around caravan sales lots by hand. There is no way I can spin a twin axle van on its axis. However, once we had the vans travelling at a walking pace I could easily steer a van by myself. If a van loses its resistance to turning at walking speed, consider how much more turning resistance is lost ah highway speeds. Again I say, don't fall for all the BS about twin axle stability.



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AnswerID: 631694

Follow Up By: Gbc.. - Thursday, May 21, 2020 at 07:24

Thursday, May 21, 2020 at 07:24
Of course a similar length tandem is more stable than the equivalent sized single. You just need to get into an extreme manoeuvre to find it. It has wheels closer to the extremities so less overhang, and it has 4 sets of tyre sidewalls resolving those yaw forces into the ground.
It isn’t the length of the van, it is the length of the tow to the point where the wheels hit the road, and the rear tandems will always be further back than a single. Any overhang behind that point is a definite double pendulum liability and a single has more.
Again, I like a single, I have one currently and it has been everywhere, but for a smallish trailer (rear fold hard floor) with 32” LT’s it still needs 55 psi per tyre to carry the load and stay stiff enough in an emergency swerve to follow the car. In an emergency swerve the sidewalls on mine are going to let go much sooner than if it was a tandem trailer with 4 tyres carrying the load without any effort at all. I had an 18ft cruisecraft on a big single trailer on 31” tyres for beach work. An emergency swerve on the highway and suddenly having zero control over the trailer as the sidewalls went in a different direction to me was the wake up call I needed with regards big single setups. They are closer to their max stability limits at all times than an equivalent tandem setup. Keep within those limits and you’ll never have to find out the hard way. I like more insurance than that though.
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Follow Up By: Nomadic Navara - Thursday, May 21, 2020 at 13:47

Thursday, May 21, 2020 at 13:47
Gbc, You did not seem to take into account what I said above regarding being able to steer a van by hand. It is all explained by the slip angle of tyres. I have provided you with some links to tell you what that is about. It is the tyre slip angle that allows me to turn a van that is moving whereas I could not turn it when it was at rest. Thyr slip angle increases as speed increases. You see this in a car that has large amounts of understeer, the faster you go the greater the understeer is and the extreme is when you lose all directional stability and exit the road.

Slip angle - -Tyre slip angle - -Tyre slip angle explained

You also talk of overhang. An overhang is measured from the centre of lift of the axle group, not from the rear axle. You must consider the dynamics of the rear axles as a group, not the rear axle. The centre of lift will be in the same place no matter how many axles there are. If the centre of lift changes the ball weight of a pig trailer will change in sympathy.
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Reply By: Member - nickb "boab" - Wednesday, May 20, 2020 at 20:17

Wednesday, May 20, 2020 at 20:17
The big question will be what's your travel plans & how well will the pajero tow a 19.5 tandem ?
Cheers Nick b
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AnswerID: 631697

Follow Up By: Member - Phil 'n Jill (WA) - Sunday, May 24, 2020 at 11:55

Sunday, May 24, 2020 at 11:55
We towed 20'6" vans (two models) for over six years with and NP Pajero then an NW without any issue.

Last year we added a third water tank to the van and it lowed the ball weight below 135kg - - both vans were dual axle.

Not as easy to park in some places but towing is a dream.

Cheers - Phil
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Reply By: braincell - Thursday, May 21, 2020 at 11:41

Thursday, May 21, 2020 at 11:41
Agree with not so , I'm in the same boat .Picking up a 17,10 off road crusader at years end and have a Nw pajero , little light in the ball weight so i'm upgrading to a dmax . Moving from offroad camper to my first Van so I;m no expert , however I tow our 3 .4 tone vessels around at work and they are hard on tyres etc .
I think a lot people go a bit overboard with there van size these days, most are travelling with just two people and spend a lot of time outside when camping etc .
AnswerID: 631701

Reply By: axle - Thursday, May 21, 2020 at 19:04

Thursday, May 21, 2020 at 19:04
G/Day Alister p

I've owned both single and tandem axle vans and have not had many problems with either.

I do think depending on drawbar length the tandem always felt a little bit more stable.

The only thing with tandem axle vans, the axles have to be perfectly inline or they will chew tyres like no tomorrow.

Cheers.
AnswerID: 631707

Reply By: Member - Bigfish - Friday, May 22, 2020 at 08:12

Friday, May 22, 2020 at 08:12
Tare at 2100kg and max weight at 2500 means only 400kg load. Doubt if you will make it . 180kg ballweight on Paj is also a limiting factor. I,m buggered if I know why people want bigger vans. I,d go for a single axle van with a tare of around 1900kg...give you more room to move as your Pajeros tow ball weight limits you. I have a Paj and tow 2100kg. In all honesty thats as much weight as I would like to tow. Why/ Because I can safely sit on 100kph not holding up traffic and I also have power left to overtake if need be. Hell of a lot less stressful pulling that weight as well...both on me and the vehicle. Choose carefully mate as there are many out there who tow overweight illegal rigs . Dont join the club. Good luck with your search...you,ll get a million opinions..lol.
AnswerID: 631716

Follow Up By: braincell - Friday, May 22, 2020 at 16:31

Friday, May 22, 2020 at 16:31
good post Bigfish , agree there . Hence why I am going for a dmax , Think my Van will be about 2.7 t max single axle .I was a bit keen for a hybrid type but the war department shot that one down , true about overweight rigs out there
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Reply By: tim_c - Friday, May 22, 2020 at 13:49

Friday, May 22, 2020 at 13:49
A couple of years ago I upgraded from a 750kg 5m single axle 'van to a 1350kg 5.5m dual axle 'van. The suspension on the dual axle is all fully independent (not load sharing) and it's horrible on concrete freeways because the wheels are independently going over the undulations from when the road surface was poured and it shakes the car around uncomfortably. If I was going dual axle again, I'd be trying to get a load-sharing arrangement which should behave better.

No one seems to have mentioned it yet, but a dual-axle 'van has higher maintenance costs (and time if you're not afraid to get a bit of grease on your hands) - twice as many tyres, twice as many bearings and brakes to service.

Others have also mentioned this, but the biggest difference I notice is when trying to move it on the driveway or site - when backing the car up to the 'van to connect them, near enough is good enough with the single-axle, but with the dual-axle it'll be hard work to push the drawbar sideways if you haven't lined up the towball exactly on centre.

All else being equal, your decision could come down to where you can park your van at home, and whether you need to manually manoeuvre it into that spot.
AnswerID: 631722

Reply By: ALISTER P - Friday, May 22, 2020 at 14:12

Friday, May 22, 2020 at 14:12
A number of years ago I was in then Flinders Ranges, the camp spot they gave us was at the end of a long driveway, the only way was to reverse. A big crowd gathered, fortunately I was quite good at reversing a tandem so there was no entertainment for them.

Backed up nicely straight, but I wonder how it would have been with a single axle. Does a single axle track like a tandem in reverse or can it be a bit sensitive and twitchy?

Thanks for you comments so far everyone, appreciate them a lot.

AnswerID: 631723

Follow Up By: Frank P (NSW) - Friday, May 22, 2020 at 15:15

Friday, May 22, 2020 at 15:15
Your average camper or van has a fairly long drawbar - ie distance from wheels to hitch. They are easy to reverse. Use your side mirrors and keep your hands at 10 to two or nine 15 on the steering wheel.

If you start to see too much of the trailer in a mirror, pull that hand down on the wheel. ie too much trailer in the left mirror, left hand down.

I had to back up about 2km once due to an idiot parked and blocking a turning circle. I was very glad I knew that technique.
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Follow Up By: ALISTER P - Friday, May 22, 2020 at 15:33

Friday, May 22, 2020 at 15:33
Hand on the bottom of the wheel. Turn the wheel (from the bottom) in the direction you want to caravan to go.
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Follow Up By: Frank P (NSW) - Friday, May 22, 2020 at 15:36

Friday, May 22, 2020 at 15:36
Yep, I use that one too.
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Follow Up By: Nomadic Navara - Monday, May 25, 2020 at 22:33

Monday, May 25, 2020 at 22:33
"Backed up nicely straight, but I wonder how it would have been with a single axle. Does a single axle track like a tandem in reverse or can it be a bit sensitive and twitchy?"

The biggest thing that makes things easy for reversing is the distance between the tow ball to the centre of the axle group. The shorter the length the quicker they will go off line if you are not quick enough with your reactions.
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Reply By: Member - David M (SA) - Friday, May 22, 2020 at 16:47

Friday, May 22, 2020 at 16:47
Be interesting to know how often blowouts occur. Towed a single axle for 15 years out in WA and never had one. Mind you I did have Bridgestone Duelers
fitted and not Goodyear.
Dave.
AnswerID: 631725

Reply By: Member - DOZER - Sunday, May 24, 2020 at 19:11

Sunday, May 24, 2020 at 19:11
If you have the option, dual axle, they are not as easy to reverse, but are more stable, less pitchy, better brakes if both axles have them, less towball weight compared to single, and a better ramp angle....now all ive said is dependant on setup, but generally true. Your GVM will be more with a dually aswell. Do your homework, there are lots more police out there checking weights and measures, keep it legal and enjoy.
b4 you bag me out, walk a mile in my shoes, then your a mile away and have my shoes :)

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Follow Up By: Frank P (NSW) - Sunday, May 24, 2020 at 20:54

Sunday, May 24, 2020 at 20:54
"Your GVM will be more with a dually aswell. "

I don't understand that, Dozer. How does a dual axle increase the GVM?
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Reply By: Member - DOZER - Monday, May 25, 2020 at 12:17

Monday, May 25, 2020 at 12:17
Gday, what I meant was the carrying capacity of a dual van is higher than a single, so you can legally carry more stuff in a dual axle than a single. I should not have mentioned GVM, it’s like what tyre is best or model 4wd. This is all subjective, not always the case, so a 4wd single axle may have close to a std dual axle. Then there is load sharing vs independent to consider. The best van I have ever towed was a full shower toilet golf van with dual independent, 4 wheel brakes. Didn’t know it was there.
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Follow Up By: Peter_n_Margaret - Monday, May 25, 2020 at 14:10

Monday, May 25, 2020 at 14:10
"Gday, what I meant was the carrying capacity of a dual van is higher than a single, so you can legally carry more stuff in a dual axle than a single."

I can not imagine how you come to that conclusion.
Load carrying capacity is the difference between tare and GTM, neither of which have any relationship to how many axles there are.
Here is a trailer with a single axle and a GTM of 4.5T.

The trailer I tow behind the OKA has a single 3T axle, 2.5T springs, wheels and tyres rated to 6.1T and a GTM of 750kg because it has no brakes.
Cheers,
Peter
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Reply By: Ron N - Thursday, May 28, 2020 at 10:53

Thursday, May 28, 2020 at 10:53
I've owned a 30 foot single axle 'van, three 27 foot triaxle 'vans, three tandem axle 'vans, two single axle 'vans and two, twin axle, turntable type 'vans.

A tandem axle van copes with rough roads, dips, potholes and sunken culverts better because of its load-sharing suspension.

A tandem axle van is more resistant to sway than a single axle, because the four wheels provide the resistance, and there's less overhang behind the rear axle.
Excessive overhang is a primary cause of sway (as well as poor design and poor 'van loading)

A blowout at speed is easier to control on a tandem axle 'van. You only lose one quarter of your rubber on the road, not half.

I would choose a tandem axle 'van every time, unless it's a only a small 'van.

Cheers, Ron.

AnswerID: 631826

Follow Up By: Peter_n_Margaret - Thursday, May 28, 2020 at 11:39

Thursday, May 28, 2020 at 11:39
I suggest that "overhang" has little or no bearing on "stability".
I towed glider trailers for many years. They were all single axle and they have an exemption to the 3.7M limit put on maximum overhang that applies to other vehicles.
Towing was always totally under control and I never heard of any one else's glider trailer being otherwise. A few were tandem axle.
To add to that, the tow ball weight was quite light. This one was a "tilt" trailer and standing on the back with the door open was sufficient to lower it to the ground for loading and unloading the glider (which weighed up to 750kg on its own).



I suggest that load distribution (particularly load which is at the ends of the trailer) is much more relevant to controllability as this affects the "yaw stability" and that this applies equally to single and tandem axle trailers.
Cheers,
Peter
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Follow Up By: Ron N - Thursday, May 28, 2020 at 13:15

Thursday, May 28, 2020 at 13:15
Ahh, but you're cheating there, Peter! You've got a fin on the tail of your trailer for longitudinal stability! [;-)

Cheers, Ron.
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Follow Up By: Peter_n_Margaret - Thursday, May 28, 2020 at 14:03

Thursday, May 28, 2020 at 14:03
Yep, that would certainly help at speeds over about 150 or 200kph..... :)
Cheers,
Peter
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