Input on VW IRS for Off-Road Trailer?

[kozaz]

I'm looking for some input on using a VW IRS Torsion Housing for IRS on a off-road trailer. I keep thinking if the trailer was under 400lbs loaded (this would be a pretty basic trailer) it could handle the washboards better. Tires would be no larger than 31s.

The stock VW trailing arms get about 4-6 inches of stock travel, but can get 12 plus if lengthen, and/or converted from torsion bar to hiem joints. Extra shocks could be added to increase weight carrying capacity.

Any input on the downfalls or upgrades would be appreciated.

Pics:
http://www.blindchickenracing.com/Projects/MarksCars/bc1/page1/bc1travel9.jpg
http://lapeersandrail.com/gallery/albums/userpics/build_12~0.JPG

Thanks,
Ryan

 

[TheGillz]

Was 400#'s a typo? I submit if you don't have 400 lbs of gear, you don't need a trailer. Let alone having a loaded trailer only weigh that much. Get a hitch rack.

 

[kozaz]

No, 400lbs was not a typo. Again, this is for a basic trailer, just enough to carry a cooler, fuel, water, and basic camping gear for weekends.

The tow vehicle is small (Tracker) and has under 100 hp. Hitch rack is not an option, due to departure angle, and lack of lift on the Tracker. I would like the option of leaving a lockable trailer at the camp site, so the the vehicle can go explore without the additional weight.

Not looking for anything heavy and fancy, just a little more cargo room.

 

[TheGillz]

Colman stainless cooler filled: approx. 75lbs
10 gallons of water: 83lbs
10 gallons fuel: 61lbs
tent (mine): 40lbs
coleman stove: 8lbs
5 1# propane tanks:5lbs
Kitchen supplies: 15lbs

Also this is not close to a comprehensive list and what we have here is 287 lbs. That leaves you 113 lbs for your trailer.

Just trying to help adjust your expectations.

 

[Photog]

The VW IRS suspension could easily handle the weight. A beetle weighs about 1900 lbs, and more than 50% on the rear axle. You might need to get the lightest spring rate available.

Are you planning to use an actual VW housing, or are you going to buy an aftermarket housing (lighter weight)?

 

[kozaz]

The VW IRS suspension could easily handle the weight. A beatle weighs about 2000 lbs, and more than 50% on the rear axle. You might need to get the lightest spring rate available.

Are you planning to use an actual VW housing, or are you going to buy an aftermarket housing (lighter weight)?

I did not realize there were lighter aftermarket housings? The ones I've seen on sandrails and VWs are all stock and the chassis is welded to them. However, the guys do look for the VW bus torsion housing since they are stronger.

The only way I know of making it lighter, is to ditch the torsion bars, and convert to a hiem joint. But even that, may only drop 15-25lbs.

As for spring rate, the torsion bars come in a variety of springs rates which is one of the reasons why I would like to do this. After it's built, I can load it, weight it, and order specific torsion bars that are dialed in for the weight.

I also imagine that I would see lots of forest roads with washboards. I would think this setup would be an excellent alternative IRS that would absorb the vibration.

I rode in a sandrail on desert roads and could not believe the difference in the ride quality compared to my yota.

 

[kozaz]

Colman stainless cooler filled: approx. 75lbs
10 gallons of water: 83lbs
10 gallons fuel: 61lbs
tent (mine): 40lbs
coleman stove: 8lbs
5 1# propane tanks:5lbs
Kitchen supplies: 15lbs

Also this is not close to a comprehensive list and what we have here is 287 lbs. That leaves you 113 lbs for your trailer.

Just trying to help adjust your expectations.

Thanks for the info, that gives me get a better idea on how heavy the camping gear could be.

 

[ntsqd]

An off the shelf complete solution is found in the Type III's (Fastbacks, Squarebacks, and Notchbacks). Their whole rear suspension assembly unbolts from the car. They're surprisingly heavy considering. I'll guess above 100 lbs. for the subframe, t-bars, and trailing arms.

Most of the ACVW vendors can supply a new fabricated torsion housing and the trailing arm brackets to go with them. Moore Parts and McKenzies are my two favorites to deal with. Search "Tweed" for some lower cost trailing arm options. At all costs avoid anything branded "Latest Rage". They are the clone/rip-off company in that arena.
The Samba.com is the ACVW forum to check out.

Torsion bars are a mixed blessing. They are nice and compact, but their spring rate rise in bump is very large. Makes getting the damping worked out difficult if a lot of travel is part of the picture. It will need damping.

The SRE conversion ("Hiem Joint") removes the torsion bar, so some other springing & damping method would need to be designed and built. In off road buggies this is usually in the form of a coil-over. Street Rod co-axial air spring/damper assemblies would also likely work.

The VW IRS trailing arm pivot axis is canted relative to the chassis centerline. This means that Camber and Toe settings change throughout the range of motion.

Wheel bolt pattern on the IRS cars is 4 on 100mm (AIR) though there are various wheel adapters made. The popular 5 lug conversion parts get you a 5 on 205mm bolt pattern. To my knowledge only VW's and SAAB 96's use this pattern.

Personally I think if you're going to go this far that you'd be better off starting from scratch as too many compromises have already been made by VW.

 

[Photog]

Those are good points; but I think the VW parts will work fine for the purpose of a trailer. He is probably not looking for 18" of travel; so the camber shouldn't be an issue. The canted travel motion does require attention to the upper and lower shock mounting positions.

Use the aftermarket torsion housing (maybe even the adjustable version).
Use lightest rate torsion bars.
Use an adjustable shock.
Chevy bolt pattern wheel adapters

This makes for the least amount of design and fabrication issues.

There is another thread, where a fellow is designing and independant suspension, similar to the AT trailers. I'm not sure if it ever got finished.

There is also another one, with a 3-link design.

These two threads might provide all the info you need, to finalize your design thoughts. And "ntsqd" has some very thoughtful input in these threads.

 

[ExpoMike]

I was playing around with this idea a while back. I was going to ditch the torsion bars in favor of an air bag setup. There were a few ways I was looking at, either using an aftermarket housing or build my own. By not using the torsion bars, it's not to build your own housing. Figured I would cut down the diag. arm to remove unneeded weight. Nice thing is you can build the whole unit of the trailer and then build mounts to bolt it in.

Got side tracked on so many other things, it become a low priority for me.

 

[ntsqd]

I don't disagree, they could make a reasonable trailer. I considered exactly that, only the plan was a trailer for my glass buggy. This was many years ago, the idea has been abandoned.

Toe change is enough to notice within the stock travel limits. At least it is in an 80" wheelbase. Not spooky or something, but noticeable.

There are 3 different length rear T-bars used on ACVW's. I'd use the longest version if at all possible.

The T3 shock towers are fairly close together. May or may not work depending on how wide they need to be for the use. They certainly aren't wide enough for me to be able to drive the buggy up between them.
Were I to consider it now I'd dump all of the stock shock mounts and move the shocks outboard and up on top of the trailing arms. I'd do this even for a utility trailer, not just my old idea.

FWIW, if this will see off road use with stock trailing arms I'd suggest buying & installing the common trailing arm plating kit. Bent trailing arms are a pita when out on the trail.

Were I going to go sans t-bars I think I'd still use the stock spring plates, rubber bushings, and retainers. I'm not fond of how those "T-bar eliminator" kits put the SRE in single shear.

Thanks for the kudos!

 

[Root Moose]

IIRC the tow rating capacity on a SWB Tracker is 1500 lbs. 2500 on the LWB.