Trailer Suspension Design

[me3@neuralfibre.com]

I'm looking at options for Camper Trailer Suspension Design.

Basically the toss-up is the usual - solid axle vs independent. Whilst the play part of me says independent, I'm having some trouble justifying the solution.

Now the 2 key design thoughts are
a) Articulation doesn't matter with a trailer. All that matters is the amount of impact adsorbtion. So the "up" travel should match the car, but the droop and total travel could be significantly less.

b) Weight does matter, especially unsprung weight.

c) Wheel Alignment - Track Trailer (TVAN) has the best travelling suspension I have ever seen on a trailer, and are well known for it. It's a combination of soft springs, good shocks, long travel, long arms for even geometry, and they claim, suspension that self steers the trailer to reduce the effects of impacts. It's the last bit I really think hard about.

Live Axle (leaf sprung)

• Leaf spings distribute load along frame further (lighter frame)
  Less wheel alignment issues
  Parts are everywhere
  Simple, cheap, few welds etc to fail
  Weight is average
  Shock mounts and angles are often less than ideal
  Travel should equal
  Can travel till spring is "flat" and axle nearly touches chassis. Spring needs no room in body.
  No idea on self steering
  Springs - Parabolic vs normal
  Springs - Short trailer vs long car
  Springs - Gal vs lubricated slippers
  Axle - could the centre be hollow pipe?
  It uses minimal space under the trailer compared to many independent setups, leaving space for water tanks front and rear between the springs.
  Impact on one wheel affect camber - dynamic stability?

Independent

• Independent movement
  More weight or less weight? Less is the theory, but most I see I think are more.
  Coils seem to be "softer" than leaves.
  Coils may need "room" in body to avoid coil binding
  bumpstops can go inside coils
  It's "cooler"
  More wheel alignment options
  More complex
  Most stuff custom
  Issues with brakes (may affect geometry)
  Perhaps torsion bars w/ trailing arms?
  Weight is to one point - above the spring - chassis needs to spread loads further - larger chassis.
  Trailing arm mounts need to be strong, but that's not where the spring is -means more stress in more areas.
  Trailing arms vs Longitudional and Lateral arms (TVAN)
  Coils vs torsion bars
  Reuse some car suspension parts? Hilux front etc?

Anyone got any thoughts on this stuff?

Catchya
Paul

[GRIMACE]

b) Weight does matter, especially unsprung weight.
Paul

I hope your gonna use rivets to hold it all together

[locktup4x4]

What about torsion suspension??

http://www.dexteraxle.com/torflex_axles

Jason

[HSV Rangie]

either the above or alko

http://www.alko.com.au/vehicle/axles/irs.html

regards
Michael.

[Slunnie]

Dude, its a trailer, not a comp rig.

Leafs..... strong, reliable, cheap and compact. Shocks if need be. It also distributes the load into the chassis a lot better to reduce stresses. If you're worried about the travel arc, the bolt is at the front of the leaf so it will work like a reverse shackle setup anyway.

[tweak'e]

depends entirly on what use have for it, how much weight its going to carry over what types of terrain.
eg if you need dual axles or not.

[sierrajim]

Dude, its a trailer, not a comp rig.

Leafs..... strong, reliable, cheap and compact. Shocks if need be. It also distributes the load into the chassis a lot better to reduce stresses. If you're worried about the travel arc, the bolt is at the front of the leaf so it will work like a reverse shackle setup anyway.

You ever towed something with leaf springs at speed on a corrugated road?

[me3@neuralfibre.com]

depends entirly on what use have for it, how much weight its going to carry over what types of terrain.
eg if you need dual axles or not.

Sorry - my bad

Camper trailer (large and light) - say 600 lightest to 1100kg heaviest.

[tweak'e]

depends entirly on what use have for it, how much weight its going to carry over what types of terrain.
eg if you need dual axles or not.

Sorry - my bad

Camper trailer (large)

large, i assume to big for any serious off road. so i would simply go tandem axles, leaf springs with shocks. big thing is to match the springs for the weight. if the springs are to stiff it will bounce around.
also look at the braking system you will have. if it brakes to quick it will jar the hell out of the trailer and the tow vechile.

[KiwiBacon]

Tandem live axles, coil springs with shocks.

The tandem axles will stop it getting stuck in holes, coils ride far better than leaves.
Live axle means zero wheel alignment issues (until you bend something) and you'll still have enough ground clearance.

[tweak'e]

coil springs means more suspension arms. also not to sure how a rocking suspension would work with coils. however i have seen one that had the coil spring (free floating) mounted above the tire guards with pivoting arms down to each axle.

[fester2au]

On a camper trailer which are generally light comapred to vans and tend to be packed tighter it;s maybe not that big a deal. Maybe best to have a look around at some of the better handling vans for ideas.

We had a Golf offroader at one stage, single axle, about 1700kg. It had independant coils with A arms pivoting from front to back. I liked this idea as the wheel only moved upewards in an arc so wheel well coul dbe quite narrow. It also handled significantly better than a mates similar sized and weighted Windsor which had independant as well but pivoting side to side. We could travel into Landcruiser Park at about 40+k's and have nothing in the van move much at all. Their van would have everything loose insid ethe cupboards etc totally tossed about.

Big question is if you are thinking independant are to talking making it yourself or buying a weld/bolt in kit etc. If you make it from scratch would it need to be engineered in any way.

How about a bit of both. A mate had a camper a couple of years ago that had leaf springs that were attached through pivoting shackles but also had long a frames that the actual axle was attached to. These a frames pivoted from the centre of the trailer out to the leaves and were fairly light given they did not carry the bulk of the load. Handled both weight and bumps very well.

[-Scott-]

1100kg (worst case) doesn't need tandem axles - unless you mean one per side.

Whichever way you go, I'd say soft springs for long travel, with well matched dampers. How to "match" properly I have NFI.

I would lean towards independent, as this improves the potential for ground clearance - although you could possibly design a "portal" style hub arrangement to lift the "crossbar" (for want of a better term) above the axle line.

If you must go leaf, what happens if the shackle's at the front? Under compression, the axle will move forward slightly; is this beneficial for "self steering" - thinking about "sway" at highway speeds.

[jet-6]

I run "outback" springs on my box trailer, greasable shackle type with over riders on the tops of the leafs, you can get heaps of weight sizes and there not that expensive, but are very well built

You could add a shock to a lighter set and they would be good, mine a very heavy so i can carry 1500kg of wood in it, they handle it very well

It used to have slipper springs, dont even think about using them, there just a waste of money and will fall apart(or come apart if you flex the trailer to hard)

[Slunnie]

Dude, its a trailer, not a comp rig.

Leafs..... strong, reliable, cheap and compact. Shocks if need be. It also distributes the load into the chassis a lot better to reduce stresses. If you're worried about the travel arc, the bolt is at the front of the leaf so it will work like a reverse shackle setup anyway.

You ever towed something with leaf springs at speed on a corrugated road?

I'll just think about that statement.

[KiwiBacon]

coil springs means more suspension arms. also not to sure how a rocking suspension would work with coils. however i have seen one that had the coil spring (free floating) mounted above the tire guards with pivoting arms down to each axle.

It can be done as simply as an A frame underneath with panhard. This setup has been called a "one link", it's basically two radius arms triangulated to meet at the front mount.

1100kg (worst case) doesn't need tandem axles - unless you mean one per side. Very Happy

Whichever way you go, I'd say soft springs for long travel, with well matched dampers. How to "match" properly I have NFI.

I would lean towards independent, as this improves the potential for ground clearance - although you could possibly design a "portal" style hub arrangement to lift the "crossbar" (for want of a better term) above the axle line.

If you must go leaf, what happens if the shackle's at the front? Under compression, the axle will move forward slightly; is this beneficial for "self steering" - thinking about "sway" at highway speeds.

No you don't need tandem axles for carrying capacity, but more axles is an advantage on uneven ground. Tandem axles also stop sway at speed.

If you go independent, you don't have a crossbar.

[sierrajim]

I wonder wheather there is any advantage in independant coil sprung suspension as opposed to a rigid axle single triangulated 4 link coil spring suspension system on a traier.

[KiwiBacon]

I wonder wheather there is any advantage in independant coil sprung suspension as opposed to a rigid axle single triangulated 4 link coil spring suspension system on a traier.

Depends on how much ground clearance you do or don't want. You can get the trailer body lower with independent.

There's not much point in a 4 link suspension on an unbraked trailer as there are no acceleration or braking reactions to jack or squat the suspension. So a swingarm/radius arm setup can cut the complexity.

[ISUZUROVER]

On a slightly related note, I am interested if anyone has any suspension design suggestions for an "offroad" boat trailer.

[Dirty]

Camper I just built was essentially done the same as on the front of the cruiser/patrol. Even used Cruser/Patrol bushes to ensure spares where easy to get. Then it is held up with a pair of air springs that I dump the air out of when setup for camp.

The anti-roll in this design was needed to carry my boat on top of it all.

Works a treat.

- David.

[sierrajim]

So you've run radius arms and a panhard?

[-Scott-]

I would lean towards independent, as this improves the potential for ground clearance - although you could possibly design a "portal" style hub arrangement to lift the "crossbar" (for want of a better term) above the axle line.

If you go independent, you don't have a crossbar.

Sorry - didn't express myself too well.

I was thinking independent could offer better clearance over non-independent, unless "drop hubs" were used on the non-independent design.

[me3@neuralfibre.com]

I would lean towards independent, as this improves the potential for ground clearance - although you could possibly design a "portal" style hub arrangement to lift the "crossbar" (for want of a better term) above the axle line.

If you go independent, you don't have a crossbar.

Sorry - didn't express myself too well.

I was thinking independent could offer better clearance over non-independent, unless "drop hubs" were used on the non-independent design.

With the diff's in the middle, I reckon if my cruiser gets through, a solid axle on a trailer would have to clear it.

I worry more about hanging up springs etc when sliding rocks past tyres.

Paul

[me3@neuralfibre.com]

On a slightly related note, I am interested if anyone has any suspension design suggestions for an "offroad" boat trailer.

If it's big enough to go dual axle you can do some cool stuff.

a) Normal rocking leaf springs with dual axle have suprising travel, and this could be increased. The rocker allows a lot of movement. I would consider a modifed version of this.

b) There is a design kicking round that uses 2 L shaped arms, one for each wheel, with a horizontally mounted coil spring between them. Basically instead f springing off the chassis, you spring between the suspension members. This means they can rock, but still have impact adsorbtion.

Paul

[MARKx4]

Does anyone sell the inderpendent A-arm coil set up that you can weld in?

[berad]

My old mans mate built an independant offroad camper trailer, articulates well, set up as wide as a 80series that it tows behind, ill see if i can get some pics of the setup over the weekend for ya.

[Sixty's Guy]

I used 60 series front springs, shackles, bushes and mounts on my Jayco, along with Ironman 40 series Cruiser shocks. It's amazing how much softer 2" 60 springs are than the standard slipper springs were. I like how mine rides now.

[Bush65]

On a slightly related note, I am interested if anyone has any suspension design suggestions for an "offroad" boat trailer.

Moving up my list is the project to convert my boat trailer for off road (I want to do long trips across the top end).

My plan is to use radius arms (reversed from normal front end duty so they trail), panhard rod, and air springs - to adjust suspension height so I can have high ground clearance off road, and lower the trailer for launching/retrieving the boat (and long telescopic drawbar for launching off beaches).

[ajsr]

on a semi related note
is or has anyone used the independant rubber torsion axle systems in the above posts???
Im looking to remodel my tandum car/machiney carrier trailer and was thinking these may be the go.it hauls near 3 tonnes and the trailer is around 1 tonne.
it runs a rocker tandum setup at the moment on 50mm axles but wears bushes regularly and the U bolts keep comming lose every few tousand kms (I think they stretch) and it does a heap of dirt roads.
any help would be tops
cheers andrew

[KiwiBacon]

on a semi related note
is or has anyone used the independant rubber torsion axle systems in the above posts???
Im looking to remodel my tandum car/machiney carrier trailer and was thinking these may be the go.it hauls near 3 tonnes and the trailer is around 1 tonne.
it runs a rocker tandum setup at the moment on 50mm axles but wears bushes regularly and the U bolts keep comming lose every few tousand kms (I think they stretch) and it does a heap of dirt roads.
any help would be tops
cheers andrew

I know of a couple of four wheel trailers which use duratorq and are approaching 30 years old each. No problems with either, but these are dolly trailers, not tandem axle rigid trailers.