Dual versus single axle vans

Phlipper · Senior Member

Dual versus single axle vans

Peter_n_Margaret · Guru

I have an unsubstantiated view that is different from most.
I agree that a tandem axled caravan will track straighter than a single axle caravan, while going in a straight line, but that is not necessarily always a good thing.
If a van get the wobbles, a single axle van will be easier to correct. Once a tandem gets "off track" it will want to stay "off track", despite a tug wanting it to go in another direction.

From all respects, a single axle van is easier to manouver both on the driveway when un-hitched and in difficult off road conditions.
Even a supposed load sharing tandem axle has limits which are easily exceeded and will transfer huge loads on and off the hitch when crossing severe dips and mounds. That can have the effect of bogging the tug or overloading the tow bar.
If you really want to go "bush", stay with a single axle.
Cheers,
Peter

PeterInSa · Guru

Had a Blow-out with a single axle pop top... scary. ( near new tyre 2500Kms)

Had similar on a Tandem with TPMS, no real issues.

Radar · Guru

Phlipper wrote:
Curious, I have a dual axle 18ft caravan, and must say it's a pain to try and move it around the driveway, duals just dont like to pivot. Starting to wish I'd bought a single axle. What, if any are the major advantages of dual axle, do they tow mores table, or are single axles just fine ?

We have owned both a single axle caravan weighing around 2000kgs and a dual axle caravan weighing around 2700kgs and total preference is the 6 metre dual axle caravan.

450 longer with a ensuite. Top bonus

Bigger refrigerator which is good.

Weight limit allowing us to carry enough water for a week.

Costing less then 2 litres per hundred to tow compared to the single axle.

I really do not find it difficult to screw around into places to park, if anything in our narrow suburban street the dual axle goes into it parking spot easier.

We are really enjoying our larger caravan.

erad · Guru

PeterinSA wrote
"Had a Blow-out with a single axle pop top... scary. ( near new tyre 2500Kms)
Had similar on a Tandem with TPMS, no real issues."

We have a single axle 16.5 ft Jayco poptop for 22 years, and it has done at last check around 143000 km. In that time, I have had 3 tyres blow out on it, and physically worn out 3 sets of tyres due to misalignment. On each occasion, the only way I knew I had trouble when the tyre blew was noise coming from behind the car. One of these actually I thought I was losing power - I was on a winding road, double lines for about 6 km and doing about 60 km/h. I heard rumbling, but had nowhere to stop, so kept going slowly. There was nothing left of the tyre, and the rim beads were well and truly damaged, but no pulling or sway. I now have a TPMS. Another blowout was on the Bruce Hwy at 110 km/h, 2 full lanes of traffic. Noise was the only indication of trouble, but golly, changing the tyre (R side) was fun...If you have a blowout whilst cornering savagely, yes you could get some sway, but how often does that happen?

The main advantage of a dual axle setup is reduced loading on the wheels, tyres and wheel bearings. Yes, when turning the rig, there is high lateral loading, but this doesn't occur very often and it is done slowly. Modern single axle caravans are rather heavy and I suspect that the wheel bearings are getting near their limits with the hubs provided these days. Regular checking and repacking of the bearings will help minimise the risk of failure, but even that has limits. I put new bearings in my caravan and after about 500 km, one of the bearings failed. I carry a spare bearing already packed with grease should replacement be required on the road.

I think that the ultimate choice swings on the overall weight of the caravan. My preference is definitely for single axle, unless the weight of the rig is too much for a single axle.

-- Edited by erad on Monday 29th of November 2021 09:07:07 PM

Phlipper · Senior Member

Thanks, pros and cons, as I guess I should of expected, just really frustrating trying to maneuver the dual in the driveway,

Peter_n_Margaret · Guru

Adding a second axle with everything that goes with that adds a LOT of extra weight.
There are wheels and bearings to take any weight you want, so weight is no reason to add another axle.
I have a spare rear axle for our OKA which I will build into a trailer. It could be rated to 3.5T ATM and be fitted with 16" wheels if I wished. It will also have disc brakes. All with a single axle.
Cheers,
Peter

Warren-Pat_01 · Guru

G'day Phlipper,
Our van is a single axle (17') & I back erad's comments whole heartedly! At times it would be nice to be able to carry another 50kg but that's life! We have a combination ensuite - it's adequate, especially the toilet.

I blew a tyre just east of Hughenden a couple of years ago (before I fitted a TPMS). All I heard was the "BANG!" There was no sway & I never thought we were in danger except being on the edge of the Flinders Highway on a very hot day with little room to get off the road.

PeterInSa · Guru

re (Had a Blow-out with a single axle pop top... scary.)

This happened while a B Double was passing us and we would have be going at around 95Km/hr.

Possum3 · Guru

Phlipper wrote:
Thanks, pros and cons, as I guess I should of expected, just really frustrating trying to maneuver the dual in the driveway,

Phlipper, Always reverse and park dual axles after engaging low range 4WD - Also hosing down driveway may assist water is a lubricant for rubber,

Aus-Kiwi · Guru

Have to consider a single axle with have extra strength around chassis to support weight in area. this is a little offset with duel axle .

darjak · Senior Member

Sorry but, having both Id rather have dual over single any day.
Id never have a van with axles, only independent load share suspension.
Have had van 3200kg in places where single axle vans hadnt a hope in hell of getting.

Erad my previous set of bearings were changed out at just over 200,000ks were repacked
every 2yrs nothing wrong with them but was just as a precaution as was going remote.
Bearings gone in 500ks sounds like someone did something wrong.

Im pretty much like P&M would rather be off than on the bitumen more peaceful.

Radar · Guru

Aus-Kiwi wrote:
Have to consider a single axle with have extra strength around chassis to support weight in area. this is a little offset with duel axle .

Aus-Kiwi.

come to think about your point, and a very good point, yes our single axle would jam the door shut or be hard to shut because of flex, the caravan had very little use when the first time it happen. I would need to adjust the drop down legs to straight the show out.

KJB · Guru

Radar wrote:
Aus-Kiwi wrote:
Have to consider a single axle with have extra strength around chassis to support weight in area. this is a little offset with duel axle .
Aus-Kiwi.
come to think about your point, and a very good point, yes our single axle would jam the door shut or be hard to shut because of flex, the caravan had very little use when the first time it happen. I would need to adjust the drop down legs to straight the show out.

Flexing has more to do with short comings in "chassis/body rigidity". Build it rigid and let the axles/suspension carry it and absorb any road impacts (bumps, corrugations etc..) . KB

Phlipper · Senior Member

hmmm...wetting the drive may be a good idea, I'll try that next time

PeterD · Guru

KJB wrote:
Radar wrote:
Aus-Kiwi wrote:
Have to consider a single axle with have extra strength around chassis to support weight in area. this is a little offset with duel axle .
Aus-Kiwi.
come to think about your point, and a very good point, yes our single axle would jam the door shut or be hard to shut because of flex, the caravan had very little use when the first time it happen. I would need to adjust the drop down legs to straight the show out.
Flexing has more to do with short comings in "chassis/body rigidity". Build it rigid and let the axles/suspension carry it and absorb any road impacts (bumps, corrugations etc..) . KB

I have become very aware of body flex in vans since having to adjust the door lock on our 15' regent van. The open side of the door moved around 2.5 mm between the time you put it on site and after you had wound the steadies down and stabilised the van. I had to adjust the door lock so that the door did not jamb either when onsite of on the road.

My subsequent two vans are both around 19' long. The tare weights are both 1500 kg. The second of the two is a little shorter as it has a tunnel boot. the layouts differ in that one has an L-shape and the current one has a café dinette. They are both pop-tops from the same manufacturer and both on a Preston chassis. The flex with the door is the same in both vans. Radar, you can not attribute the difference in flex in your two vans to the number of axles. KJB is correct with his assertions, it is to do with the build differences in the two chassis and not the change of axle style. Your assertions are a bit like comparing apples with pears, their taste is completely different.

In saying that, yes I have had door jamming problems with my current single axle van. That only presented itself after the door was removed and replaced when some repair work was carried out on the van. The jamming was caused by the door frame being replaced out of square. Until that was fixed I had to watch out how much pressure the rear steadies were wound up to.

Peter_n_Margaret · Guru

It is not just the chassis that makes a very big difference, it is also the body construction.
A fibreglass sandwich body will be 10 times as rigid as a "stick and tin" body.
Just like modern (well, decades now) car construction. No chassis at all, yet quite stable.
Cheers,
Peter

Hylife · Guru

1./ The vast majority of sway induced rollovers are tandems.
2./ Singles do see-saw more than tandems.
3./ Ignore the old myths about weight or size limits on singles. A bit like the old rated shackles myth. So long as its axels and tyres are engineered to carry the weight and the rear overhang limits are not exceeded your single can be long and heavy. Mine is 20' and 3 ton.
4./ Modern vans use independent suspension so aren't really a single "Axel", more a single pair of wheels.
5./ Ignore the old blowout myths, that's just in the movies. Cars with flat tyres don't flip and explode in real life either. Modern vans have Electronic sway controllers (ESC) that will apply braking to the wheel/s on the side the van is violently swaying towards, and this straightens it out.
6/. Tandems with a flat tyre often go unnoticed unit the tyre is shredded. Singles with a very fast decompression flat such as a sidewall blowout will tilt a bit very quickly and the ESC will lock that flat tyre up to prevent sway. Worst case resulting in a shredded tyre that was already unrepairable. Had "two such instances this last season on cheap sh!t Chinese tyres that blew their sidewalls on the Stuart Hwy just north of Daly waters. One going north and one on the return trip a month later. The ESC smoked those tyres instantly but the van was stable and remained in a straight line.