Tri Axle Trailer Suspensions

[sae8425]

radman1,

The reason that I'm down on dually trailer axles is the same reason I won't have a dually vehicle when off-road (not on a boat ramp, but rather down some badly rutted farm/forest track), which is where my tow vehicle spends about 50% of its life, having the rear wheels that follow exactly in the front wheels track is virtually an essential requirement for traction and progress (forwards or backwards).

And since this trailer has to be able to go wherever its tow vehicle goes, the trailer wheels must follow (or very closely follow) in the tracks created by the tow vehicle wheels.

Now, I could always just increase the trailer wheel size to 20 inches which would enable me to carry the weight with only 4 tires (20 inch tires with 7,000 lbs capacity each would have plenty of safety margin).

This would negate the need for the tri-axle setup which is necessary using 16 inch tires (ie. the tires are the limiting factor in carrying the load in question).

However, my gut tells me that a tri-axle trailer (where the axle cl spread would be at least 9 feet) would offer a higher level of pitching stability than a dual axle trailer (with only 6 feet of axle cl spread) would.


crazyal,

While I'm certainly no proponent of leaf springs for vehicular use, I certainly recognize that a great many people either feel differently, or at least tolerate these (IMO) abominations.

However, if the bracketry and walking-beam designs that I've seen on numerous trailers from name brand manufactures is indicative of the bulk of the trailer industries take on appropriate leaf spring locating design, I for one do not get a warm and fuzzy feeling when I think about these trailers ability to withstand sideways forces (or any other forces for that matter). I'd never sign off on any of the engineering approaches I've seen so far!

Any manufacturer who touts the fact that they are using 25 lb per foot (or heavier) I beams in their trailers, and then uses 1/4 inch thick steel to fabricate the suspension bracketry from should be hounded out of existence!

 

[CCOUGHRAN1]

I used to know a fella that dealt in military surplus equipment. He had an International 4700 (i think) crew cab 4x4 with a 10' flatbed on it. He then modified a 40' gooseneck flatbed. He pulled the axles and replaced them with a set of tandem axles with what I think were 20" wheels, on an airbag suspension. In addition to the air bags, he had some of the longest hydraulic cylinders that I have seen. I bet they had 10' of stroke. The hydraulics allowed him to move his axle centers along a 10' slide for load distribution.

I'll see if I can dig up any of his old pics, or contact info, as he might be someone that you could talk to about your trailer project. He certainly didn't let the common mfg practices influence how he setup his equipment.

His handle was "Woody" and he used to frequent Ford-Diesel.com, before it became known as TheDieselStop.com. Might be able to utilize google to locate him too.

 

[aczlan]

What if you were to put torsion axles with air ride? It appears that Kelderman makes something to do that: Torsion Axle - Racing / Misc - Trailer - Air Ride Suspension Systems - Kelderman Manufacturing

Then you could drop your trailer 3" for loading by dumping the airbags and if you had enough space, you might even be able to add a "arm" with a 2nd set of airbags to lift 1 or 2 of the axles when not needed to save on tire wear and make moving the trailer easier.

With the unimog you shouldn't have any problems getting enough air to run them.

Aaron Z

 

[davo727]

How about making one of the 3 axles a steering axle???

It can have a tierod connecting the spindles and have a bracket coming out from the center of the axle tube that locates a spring on either side of the tierod that keeps the tierod centered until a certain side load is reached and it then allows the axle to steer. A steering stabilizer shock absorber could also be added.

Some special big rig multi axle heavy load trailers have this setup.

Im thinking of fabbing one up to add another 7K axle to my 20 foot bumperpull.

 

[slowzuki]

Tri-axle torsions eat tires in city use, torsion units off-highway, and are semi-hard on bearings. Friends have them and hate them.

Air-bags, even commercial bags, don't like off-road conditions. Rough dirt roads lead to holes in bags unless you have very good shielding.

In agricultural applications, I have seen triaxle setups so the side loads steer the leading and trailing axles opposite to reducing the turning forces on the tongue. Because they steer opposite, no induced sway. Look a large manure tankers, Nuhn maybe?

 

[slowzuki]

Towing with a unimog? Go to proper sized tires like the military trailers used behind unimogs are. The taller wider tires offer lower inflation pressures and much much lower rolling resistance than little 16" tires for a similar load. Common here are Michellin XML's in 20" rims, cheap via mil surplus.

When you say pitching stability, do you mean roll stability? If pitching stability is important, is your tongue suspended? If roll stability, going with the widest spring spacing helps, as does fitting shock absorbers.

 

[Case485Guy]

Have you considered going with 2 Dexter 15k axles and going with "super single" tire, instead of a dual tire.
I know Dexter makes a torsion axle, they are used on alot of the cattle trailer in the tri axle setup.
I have pulled the tri axles in a commercial operation and loaded upto 18k, in tight turns, the side forces will peel off tires and wreak havoc on the suspension compared to a 2 axle/ tandem setup.
Another thing to consider for the suspension, leaf spring replacement components are readily available at nearly any trailer shop. Torsion axles are not, or atleast not in my area.

Good luck and would like to see pics of the final decision.

 

[Renze]

Have you considered going with 2 Dexter 15k axles and going with "super single" tire, instead of a dual tire.

My idea as well.
My 2$cts on trailers (as a former trailer designer)
-triple axles work on smooth paved highways. they eat tires when used for urban traffic.
-torsion axle triples will bend a swing arm as soon as you hit a kerbstone while cornering
-torsion axles are generally light duty axles which cannot take offroad abuse

At my previous employment we only sold torsion axles as tandem 5th wheels, and discouraged customers to buy triples, but go light commercial instead, with 235/65R17.5 tires and 5.5 ton tandem axles.

Advice: take commecial grade 8 ton axles on leaf or air springs, and take a commercial grade tire (19.5" medium truck tires) instead of 16" pickup truck tires.
The Unimog has air brakes, so electric brakes not being available on HD axles is not a drawback.

 

[Duffster]

radman1,

The reason that I'm down on dually trailer axles is the same reason I won't have a dually vehicle when off-road (not on a boat ramp, but rather down some badly rutted farm/forest track), which is where my tow vehicle spends about 50% of its life, having the rear wheels that follow exactly in the front wheels track is virtually an essential requirement for traction and progress (forwards or backwards).

And since this trailer has to be able to go wherever its tow vehicle goes, the trailer wheels must follow (or very closely follow) in the tracks created by the tow vehicle wheels.

Now, I could always just increase the trailer wheel size to 20 inches which would enable me to carry the weight with only 4 tires (20 inch tires with 7,000 lbs capacity each would have plenty of safety margin).

This would negate the need for the tri-axle setup which is necessary using 16 inch tires (ie. the tires are the limiting factor in carrying the load in question).

However, my gut tells me that a tri-axle trailer (where the axle cl spread would be at least 9 feet) would offer a higher level of pitching stability than a dual axle trailer (with only 6 feet of axle cl spread) would.


crazyal,

While I'm certainly no proponent of leaf springs for vehicular use, I certainly recognize that a great many people either feel differently, or at least tolerate these (IMO) abominations.

However, if the bracketry and walking-beam designs that I've seen on numerous trailers from name brand manufactures is indicative of the bulk of the trailer industries take on appropriate leaf spring locating design, I for one do not get a warm and fuzzy feeling when I think about these trailers ability to withstand sideways forces (or any other forces for that matter). I'd never sign off on any of the engineering approaches I've seen so far!

Any manufacturer who touts the fact that they are using 25 lb per foot (or heavier) I beams in their trailers, and then uses 1/4 inch thick steel to fabricate the suspension bracketry from should be hounded out of existence!

Sounds like you need tandem 10k+ axles with super singles on them.

 

[trailerman]

i sell these tri-axles all the time wholesale...a 24000 gvwr...8 k axles..torsion..stainless hardware...cypress bunks-forward split bunks...led lights.....kodiak disc brakes on 3 axles..pennle hook with electric over hydraulic....19000.00..wholesale...you can see my trailers on kjenterprisesllc.com....i never reccommend leaf suspension.....they cause hair cracks in hulls where torsion absorbs the blunt on the pot hole road conditions...i have been selling boat trailers and working with them for 20 plus years.