Suspension Geometry.

[charlesshoults]

I got back from Oklahoma today. On the way there, I saw two teardrops on the road. One was all white with aluminum bands and the other had a white curved surface with yellow sides. In Ponca City, I saw a third under a car cover. Additionally, I saw a Tesla, of all things. Interesting.

My parents recently bought a couple old trailers at an auction. They were both built the same way, but seem pretty much a hack job. The ends of the axle are quite unusual. The ends are cast, with the center section welded and with studs for shocks.

I don't know what the small bar under the tongue beam is for at all. It goes about half way down the trailer bed, angles up and ends.


The trailers are pretty rickety and don't really serve my purposes any, but still interesting.


I found stub spindles and hubs at Atwoods in Stillwater. The spindles were about $22 each and the hubs $40 each and will get me started on my 3500# trailer. The spindles have a zerk fitting allowing the bearings to be greased. For axle assemblies, leaf springs are fairly straight forward and I've seen designs using trailing arm suspension. Has anyone ever tried something like a triangulated 4-link? I know it's overkill for a trailer, but has anyone done it?

[del]

I don't know what the small bar under the tongue beam is for at all. It goes about half way down the trailer bed, angles up and ends.

It gives the tongue more weight carrying ability. As weight is added it tries to stretch the bar.


del

[tonyj]

I found stub spindles and hubs at Atwoods in Stillwater. The spindles were about $22 each and the hubs $40 each and will get me started on my 3500# trailer.

3500#? Building a big trailer?

[charlesshoults]

Well, while the trailer won't be monstrous in size, I want to ensure that I will never overload it. When a camper shell isn't on it, the flatbed needs to stout enough to handle anything I'm likely to throw at it, like supporting the weight of a Mini Cooper.

[bobhenry]

There is really nothing rickity about that little trailer. You have a triangulated tongue with a tension rod truss reinforcement under the tongue there is no way you will overload that little guy.
That "little rod" does a great deal to stiffen that tongue. As the load increases it try to stretch the rod and actually distributes the load by placing the main tongue member in compression. Think of it as an archery bow as you pull back the cord there is more and more power transfered to the arrow. The little stub is the arrow an as the load increases it tries to lift the front edge of the trailer. I had to use this trick on "the barn" tongue was flexing vertically all most 2 "



It is hard to see in the shadows underneath but trust me it is there. You can see the crushed area above the tongue that occured before the truss was installed.

[Wild Bill]

I will agree with a heavier axle, nothing more unsafe than an over loaded trailer, Not trying to offend the many out there jerking a HF trailer but I suspect the axles are rated at 1000-1500 lbs at most. Those Harbor Freight trailers are made for hauling a 500 pound lawn mower. I am building on a 1988 boat trailer with a 3500 lb axle under it with 14" 5 lug rims and tires with a #1750 load rating each. I know that what ever I decide to hang on it, bikes, dutch ovens, coolers, food, beer, grills, charcoal, beer, etc, etc, etc, it all adds up to pounds, and with the food, pounds on me. My trailer is going to have a 13'-6" long by 6'-3" wide body. Tongue has a battery box, place for 2 propane tanks, a 20 and 10 pounder, then a large diamond plate pickup truck tool box, then the body. I want to be able to keep all of my gear stored in the trailer and always ready to move out. This will free up some space in my garage so that I can go to more estate sales and buy more junque. I cannot resist buying the old green coleman white gas stoves and bringing them home. I will not be able to tow this with a 4 cylinder car, but that is a personal choice, I still hope to be lighter than a popup camper and under 2000lbs. and have the option of using my Chrysler T&C with a 3.8 to tow with. Bill

[charlesshoults]

For anyone who finds this, how big are your axle spindles? Not that I don't trust weight ratings, but I don't trust weight ratings. I'm comparing three spindle designs and will use the image below to talk about them. The weight rating I'm talking about is for the pair, not individuals.

The first spindle has the zerk fitting in the end and the brake flange welded on. It states that it's rated for 3500# but dimension G is 1.44", which to me, doesn't seem like much. Dimension F is 1.88", which also seems short. These sell for $24.95 each. Overall length is 7.625".
The second spindle I'm looking at does not have a brake flange and does not have the grease fitting, which just means teardown to pack. The spindle has the same 3500# rating but dimension G is 1.75" while F is unspecified. This one definitely seems more substantial. Overall length is 8" and they sell for $11.95.
The third spindle is a big one. G is a full 2" while F is a mighty 8" long. It is a straight shaft spindle, not the taper like the other two. It's rated at 4000#, has an overall length of 13" and sells for $32.95.

I tend to over-engineer everything I touch.
So, the question is, what diameter stock are your spindles made from and what size beam do you use for the axle tube? If I go with the middle size, I'm looking at using 2.25" DOM with a .25" wall. My reasoning is influenced by the Bantam T3-C trailer down the street that was overloaded and has a nice bow to the axle tube. It only has a 500# capacity afterall. Whether I go with the middle one or the big one, 6' of DOM tubing will weigh about 36# and cost me about $120. Eek.

[teardrop_focus]

I'd think that one would have to work pretty hard to get a teardrop trailer to weigh 3500 lbs... that is, if you want to build a teardrop. You don't exactly say so.

Overkill in axle and chassis strength is an understandable goal, but springing that axle for 3500 lbs then tugging a 1200 to 1500 lb teardrop around on top of it would have the trailer bouncing into the air over any major pavement imperfection and trashing the contents of the trailer while doing so.

Talk to a reputable trailer axle engineer, say, at Dexter Axle; they do both leaf-sprung solid axles and they do rubber torsion axles.

There are folks here on the forum, experienced teardroppers, that used to use leaf-sprung solid axles, and when they changed to a rubber torsion axle, as they say, they "never looked back".

Either one appropriately-rated will do the job, but, again, first talk to an expert on the matter to put your mind at ease about spindle, axle and trailer chassis durability.




Here's the number of a man who knows his stuff:

Duane Belisle @ Dexter Axle

(574) 296-7334