help choosing trailer for diy camper

Submitted: Sunday, Apr 03, 2016 at 19:57
ThreadID: 132014 Views:2784 Replies:3 FollowUps:8
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Hi all,
I need to buy a trailer to cart firewood around, but figured might as well go a bit bigger than the original 6x4 to make it a dual purpose trailer.
What I want to do is get an 8x5, weld some steel posts to fit 2 rooftop tents (that will sit 1 meter above the trailer floor) so I can use the trailer floor as the kitchen/living room and gear storage. Put in a bench, a tv, etc so when the wife and kids are bored, or raining, we can sit in there (or do a folding bed setup and only do 1 roof top tent).
Then after a trip I can drop the tents, fold up the bench and put the cage back on to go collect fire wood.
Does this sound like a viable idea?
My main question though is around suspension. I dont forsee this setup going "out back" mainly dirt, gravel and sand at most while avoiding corrugations as much as possible.
Do I go tandem with standard 6 leaf suspension? Or do I get some customization and tell trailer people to put in independent suspension with coils or airbags to "future proof" it? Any idea of the cost difference in leaf vs IFS (a tandem 8x5 with 6 leaf is around $2000).
Oh and is it worth the extra cost to get it with 17" wheels to match tow vehicle (120 Prado) or not a big deal.
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Reply By: 671 - Monday, Apr 04, 2016 at 00:03

Monday, Apr 04, 2016 at 00:03
There is nothing wrong with your idea. I have built a few multi purpose trailers over the years and one was for camping. It was not like the one you have described though.

Leaf and independent suspensions can both work well but very few of either one that you see under caravans or trailers have been designed properly. It has been well known for about 100 years that vans and trailers have many problems with axle ends shearing off, broken wheel studs, failed wheel bearings and wheels falling off but the cars towing them don’t. It all comes down to design.

You can get some idea of one of the problems in the two posts by Robi on this page. spring rates Hard trailer springs can be fine on good roads because the trailer can pivot freely on its single coupling as wheels move up and down over minor undulations in the road. If you tow them over rough roads though, they can shake the trailer and its contents to pieces. There are plenty of reports on the net of caravans being shaken around with a lot of damage inside.

Trailing arm suspensions in trailers are not designed like cars. They all look like backyard jobs to me but they do look impressive and no doubt appeal to many buyers. This brief description at the top of this page looks at the trailing arm and the semi trailing arm design.trailing arm design I have never seen a car with the trailing arm type but trailers and vans use it. Cars are all semi trailing but that type goes back a few years now and may not be in use any more.

This link explains how the semi trailing design should work.roll steer The centre drawing is how it should be but every trailing arm suspension that I have seen under trailers has been pivoting off a flat chassis and hanging down like the third drawing.

I currently have an 8 x 6 single axle trailer with the rear springs and shocks from a 2004 Hilux 4x4 single cab under it. They are extremely soft making the shocks essential. It tows beautifully and I doubt if it could possibly shake anything to pieces.

This bloke heretrailer plans has a similar set up but he is using Jeep rear springs. Note how the front mounting point is down low and the rear up much higher. My springs are also set up like that. All cars are designed like that to induce a degree of rear wheel steering under load in corners. These two posts, also from Robi, explains it briefly.leaf springs

In your case I would be using a good quality beam axle with ute springs and shocks. If you can find a good hollow axle then so much the better. That will remove a lot of unsprung weight. All of those beam axles under the front of American cars like Ford, Chev etc in the 1930s weighed around 10 to 12 kilos. Unfortunately solid trailer axles are over triple that. All of the big trailing arms under trailers are not much better.

Unless you are going to put a staggering amount of weight into it, you should not need two axles. I have never towed a short dual axle trailer but I have read a few reports that say they are not very nice to tow.

Try and mount the shocks as vertical as possible like cars. The way that Jeep sprung trailer is set up is wrong which is why he had to use four of them to successfully dampen the spring oscillations.

Do not be fooled into thinking those rebound springs are as good as shocks. Trying to create a bit of friction on rebound by clamping the leaves together is no substitute for a good hydraulic shock. Car manufacturers gave up on friction shocks in the 1920s.

You should not need a huge ball weight for something that short. Nothing in it is all that far in front of or behind the axle so it should not swing around of pitch up and down. Keep as much of the heavy items as close to the axle as possible.

The old 10% of total weight on the tow ball rule has been proven to be inaccurate many times. I had my trailer loaded to just over 1000 kg recently on a trip from Sydney to Tumut and it had 48 kg on the ball. It has 38 empty and does not bounce around.

This link goes into the dynamics of caravans but it could be applied to trailers as well.dynamics Note what it says about car rear suspensions and tyre slip angles. Don't start altering factory designs unless you know exactly what you are doing.
AnswerID: 598163

Follow Up By: pop2jocem - Monday, Apr 04, 2016 at 09:57

Monday, Apr 04, 2016 at 09:57
A well thought out and written reply from 671. Agree completely with his idea to use a single axle with heavy duty wheels tyres and bearings, especially if you are going to do much off road work. Shockies are a bit of a pain to accomodate as far as mounting on a conventional trailer design but well worth it in the end. Much less drag turning if you are in soft conditions with a single axle. IMHO it's much better to have the wheels and tyres compatable with the tow car.
The only item he listed that I would be a bit wary of is using a hollow axle. In WA at least it is illegal, or was the last time I looked. From a practical point of view I can't see a problem as long as you used a nice heavy gauge wall thickness, but it might be a bit of a drama if you presented it for licencing and some smarter than average inspector picked it. Probably an idea to check with your local licencing authority before starting your bulid.
Actually Mick O, a prolific contributor to this forum (hi Mick) had a little drama with a hollow axle once.
I had a camper trailer many years ago that I fitted a solid axle to with hubs, wheel bearings, wheels and tyres off a Landcruiser to be compatable with the vehicle I owned back then. Still got it as a trailer, but all it does now is the odd rubbish run, firewood collection etc and still got the original setup under it.
If I was to build another it would still have the above designed wheels and axle.

FollowupID: 867287

Follow Up By: 671 - Monday, Apr 04, 2016 at 11:50

Monday, Apr 04, 2016 at 11:50
The only item he listed that I would be a bit wary of is using a hollow axle


I noticed AL-KO have a 60 mm tube axle listed with a 1450 kg weight axle

I don't know how heavy they are but if they are lighter than a solid bar of similar carrying capacity then they would be the way to go.

Anything that improves the design is worth trying and reducing unsprung weight is definitely one do it. There is no comparison between car suspensions of the 1920s and '30s and what we have today but far too many trailer and van suspensions look like they are still back in that era.

Another one that I forgot last night is the MC2 design as seen in the photo near the bottom of this page MC 2 They were designed to carry electrical equipment for the military. They seem to be a very rare sight on civilian trailers. Maybe trying to get all the geometry sorted out is in the too hard basket for many builders.
FollowupID: 867298

Follow Up By: pop2jocem - Monday, Apr 04, 2016 at 12:15

Monday, Apr 04, 2016 at 12:15

As I said I don't have a problem with using a hollow as opposed to a solid axle per se, as long as the wall thickness is substantial enough to cary the required loading.
This from a practical point of view. I only know that in the past in WA it was illegal. A soild axle was required.
Having said that, as I pointed out this may not apply in other states and may no longer apply even in WA. It's been a long time since I got involved in building or modifying trailers.
Having re-read the OP's post It looks like he might be buying rather than building the trailer anyway.

FollowupID: 867301

Follow Up By: Peter_n_Margaret - Monday, Apr 04, 2016 at 12:38

Monday, Apr 04, 2016 at 12:38
"Having re-read the OP's post It looks like he might be buying rather than building the trailer anyway."

Building a trailer is no biggy and there are certainly advantages compared with the commercial offerings.
If the OP can DIY the camper bit, he can probably DIY the rest too, get a better result and save a few bucks in the process.

Mine serves many purposes.
I modified it to extend the drawbar, added water tanks and jerry holders and made it a tilt which is great for launching the tinny and dumping the load of fire wood and lots of other small mods too.

OKA196 Motorhome
FollowupID: 867303

Follow Up By: Malcom M - Monday, Apr 04, 2016 at 14:24

Monday, Apr 04, 2016 at 14:24
Anyone have a link showing that hollow axles are illegal anywhere in Oz?

Hollow axles are fine provided they are correctly sized. Couple of benefits
1/ the obvious weight saving
2/ Way less unsprung weight which helps the suspension enourmously.
FollowupID: 867310

Follow Up By: shmick - Tuesday, Apr 05, 2016 at 23:30

Tuesday, Apr 05, 2016 at 23:30
Thanks for all that.
671, wow, quite a post.
FYI - I plan to buy one, but they do some customisation, so maybe if I can get the suspension good, without going overboard as it will mainly be in the not so rough stuff.
I will be DIYing the rest of it, just dont want to take chances with chassis/suspension as my welding skills, well, lets say i dont trust them.
The trailer will be 8x5 just so i can get your standard 2400-1200 sheets of whatever for building stuff, and tent up top.
Regards to tent, I really like the 4 person RTT, but at 95kg, will centre of balance be issue on trailer? I want the tent about 1.2m off the floor of the trailer.
FollowupID: 867413

Reply By: Peter_n_Margaret - Monday, Apr 04, 2016 at 12:09

Monday, Apr 04, 2016 at 12:09
Independent suspension on a trailer is a waste of money.

Single axle with 'ample capacity'.
Decent size and quality bearings and especially seals on high quality surfaces.
Wheels and tyres identical to the tug.
Identical wheel track to the tug.
Leaf springs of good length and travel.
Decent hangers and pins that are properly located (not splined) and lubricated.
Quality shock absorbers.
Mechanical override disc brakes.
An off road articulating hitch.
An extended draw bar to allow maximum jack knife ability.
GTM 1999kg.

OKA196 Motorhome
AnswerID: 598179

Follow Up By: shmick - Tuesday, Apr 05, 2016 at 23:39

Tuesday, Apr 05, 2016 at 23:39
Awesome. I'll just send this off to the trailer people :)
FollowupID: 867416

Reply By: swampy - Monday, Apr 04, 2016 at 15:28

Monday, Apr 04, 2016 at 15:28
hi shmick
It is important that the axle assembly is well over rated
Refer to Vehicle Components for your application
To get around trailer short commings
eg 12 inch electric brakes 50 or 60mm axle big bearings etc
The combo allows you to fit any wheel size
The larger brakes will also last a long time

The larger the diameter the wheel the lesser the load carrying on say your typical falcon bearings . [derating occurs ]
235/75/15 are common and not a huge diameter wheel

Rate the springs just above tare weight say eg an additional 400kgs . This allows for luggage food water etc etc and still have supple spring pack
Rating the springs excessively will cause a very rigid ride

AnswerID: 598186

Follow Up By: shmick - Tuesday, Apr 05, 2016 at 23:43

Tuesday, Apr 05, 2016 at 23:43
Yep, I had too stiff springs in the Jeep, great ride with 3 adults in the back, but boy was it a shocker with just me.
FollowupID: 867418

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