Independent Trailer Suspension

[section8]

I am building an offroad trailer and looking for alternatives to the standard leaf spring setup. The torsion axles have proved to be ineffective. I am looking into doing a trailing arm setup and looking for some sort of resource to start a design. Everything that I have found, mostly books for designing your own auto suspension, spend a paragraph denouncing the trailiing arm suspension and move on. The most prominat problem being flexing of the arm during lateral acceleration, not an issue on a trailer. Adventure Trailers in the US as well as several Australian manufacturers of offroad trailers build in this arangement and it seems to be universally praised.

If this wasn't going to be pulled down the highway, I would be more inclined to experiment, but is it as easy as it looks? A pin located beam with a spring/damper system locating a wheel hub? I can almost see that problem in an old text...

 

[GregLocock]

The problem is that the trailing arm's lateral compliance is oversteer in nature. Given the number of problems people have with trailers, that sounds like a bad move.

On the other hand, as you say, it makes for a neat package.

How about a leading arm instead? Same package and you should find it tracks better.







Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

Trailing arm handles bumps well as well moves back and up in compression.

I think a semi trailing arm can have toe in on compression and from memory, I think the system used on post swing axle rear engined VWs and Porsches do give some toe in on compression.

I think the amount of negative camber and toe gains is dependant on initial ride height and inclination of the pivot point axis in both for aft and horizontal planes.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Tmoose]

"The torsion axles have proved to be ineffective. "

Please tell me more.

Dan Timberlake

 

[section8]

The arms are to short to provide enough travel for washboarded roads. Or alternatly, the spring rate is to progressive to provide a smooth ride on washboard roads, so the trailer bounces around alot. There is a shock kit available from Monroe that can help with this, but since I am using identical wheels/tires to my tow vehicle for redundancy, the offset is to high to allow for the kit to be mounted. The biggest problem is that the axles are not very capable of varying their load. You buy an axle for a particular trailer weight, but my maximum trailer weight would be different with 400 pounds of water and fuel at the beginning of a trip compared to the end when you have used them, and for the majority of trips, which are for 3 day weekends, the trailer would start out light compounding the bouncing.

 

[CSLufkin]

What if you went with the trailing arm setup, but leave the dampening to an adjustable coil over?

 

[patprimmer]

If I were to build a system, I would use light coil springs and air bags to adjust for load.

Shocks would also help.

If you intend to go without shocks, use leaf springs as they are self damping to a degree.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[section8]

CSLufkin/pat

I had intended on using the adjustable Rancho shocks, and had been thinking about an airbag setup, but might go with coils with an inflateable bladder in them for weight compensation and ease of installation/set up.

THe Adventure Trailers setup uses straight airbags.

 

[GregLocock]

A lot of durable off road trailers use leaf spring suspensions, easy to package, robust, can be configured to give a rising rate, robustly, by varying the shackle configuratiion and with a second stage.If you put the shacle at the front of the trailer then you might even get some compliance understeer.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[mishar]

Weld those arms to the steel L profile and hang it to the frame. Shock/spring units could be horizontal too. Springs highly progressive for that big weight difference. L profile will act as a sway bar so it should not be too stiff. Be sure to have toe in angle for strait following.