Offroad Chassis

[angib]

make the tongue 1/4 hitch steel so it won't be a weak point.

Or, better still, make it from bigger not thicker tube.

3"x3"x1/8" tube is 50% stronger than 2"x2"x1/4" tube but it weighs 25% less and costs about the same.

Andrew

[deepmud]

You can do that - but keep in mind whatever type of hitch you plan to use, mine fit 2" but I'm sure there are 3" versions. I also have reservations about it being "50% stronger" - clearly that is true in a pure bend-resistance measurement, but the 1/4" wall resists crushing, denting, twisting and Murphy's Law better - in my opinion. I have seen 2" hitch steel fail - but it was a an over-loaded, jack-knifed double-axle flatbed trailer. I believe in a smaller trailer it is sufficiently over-engineered to give complete piece of mind.

[Prem]

Off road trailers should be build extra stout at the stress points. What's the most likely to fail if not built extra stout? Just what we saw: the tongue and the spring hangers.

The tongue doesn't have to be 1/4 inch thick 2x2 tube IF you fish plate/gusset it along just the major stress area. I trussed one that was flexing. I trussed it on the bottom only with 1/2 inch square rod. That killed the flex. It only ran for 5 feet of the 8 foot x 3/16th inch thick square tube. (Didn't quite come up to the coupler. Ran back past the front cross member.)

I welded the spring hangers all the way around on more than one trailer, not just front and rear on the chassis. I put the bolts in the hangers before I welded them on to maintain the hole alignment under the stress of heat warp. I also drilled a 1/2 inch hole in the center of each spring hanger and filled that flush with weld. They never broke off.

Water gets under the welded spring hangers if they are welded just front and rear on the chassis and the water eats away at the welds, especially on a sailboat trailer that goes in and out of salt water. The above method fixes that issue.

I've seen stacks of leaf springs crack also. Weird that it's sometimes the bottom leaf (overloaded light duty boat trailers esp.) and sometimes one in the middle of the stack (Toyota Tacomas esp.).

I once put those single, thick leaf springs from mobile home axles on a tandem axle sailboat trailer I built. Those didn't break. Heck, they barely flexed. (Too overbuilt.)

I like torsion axles best now. My trailer has a 3,500 pound torsion axle with a 1,250 pound total load on it. Doing 45 miles of rough dirt road in it early this summer, I just let some air out of the tires for a smoother ride.

For what it's worth,

Prem

[ntsqd]

The term is "Section Modulus" and it relates to the strength and stiffness of a component. In the case of steel tube the height and width are far more important to strength than is wall thickness. Even in torsion with a square tube! As angib was pointing out, you can gain strength with dimension without gaining weight. This is a well documented engineering fact, not "net theory". I don't know that the 50% stronger number is perfectly correct but, A) it would not surprise me in the least if it is and B) it is easily calculated. Search "Section Modulus formulas" if you want to look into this for yourself.

I'm sensitive to the easily dentable concern, so obviously wall thickness needs to be chosen to be appropriate for the location that the tube will occupy in the frame. The 2" tube for a coupler to fit restriction is a PITA, but there are ways around it if need be.

Where you need wall thickness to avoid the stressed parts from acting like a can opener lamination is the preferred method over thicker walled tube. That way you only carry the extra wall thickness where it is useful and not over the whole length of that tube. Quite common to see this sort of approach used in everything from Indy cars to highway bridges.

Martyn @ AT pointed out a while back that the failure mode for rubber torsion axles is grit ingress into the rubber zone. If I understood him correctly the way that rubber torsions fail is that very flex cycle works to loosen the vulcanizing once the grit is in there. Once the vulcanizing fails there is nothing to laterally locate the swing-arm + wheel/tire assembly.
I prefer them too, but this is their ultimate short coming. Torsion bars, as would likely be in the Subaru rear suspension and is used in VW Bug rear suspensions (real bug, not the late models), won't have this problem.

[angib]

FiberglassRV is interesting on the subject of rubber torsion axles. They have plenty of members with 20-30 year-old fiberglass trailers such as Scamps, Bolers, Casitas and U-Hauls. Nearly all have torsion axles (and nearly all of them were overloaded on their axle rating from day one).

Axle failure always seems to be gradual settling of the axle combined with lack of travel - or stiffening spring rate, whichever way you want to look at it. Age always seems to be the main culprit, usually more than 25 years, and mileage doesn't seem to be a factor. I've never seen any other type of failure reported and certainly not a catastrophic failure or breakage.

Of course, with this sort of trailer, off-road means logging trails, not canyon exploring. But it makes me wonder where all these torsion axles breakages are, that the leaf-spring guys are avoiding?

[ntsqd]

That is a good question, where are they? Adventure Trailers has influenced the "Overland" crowd away from them. Presumably this is based on their own testing and one known to me failure of theirs. I know that early versions of their trailers used rubber torsions, but I've only ever seen one failure reported.

I now own a rubber torsion equipped VentureCraft TrailBlazer that had several (not slow) trips to Baja as well as a Copper Canyon trip under it's belt before I got it. I've towed it to the Oregon Coast and out through the CA deserts without trouble.

My theory about the possible first failure mode was heat induced de-lamination resulting from rapid cycling of the suspension due to high speeds over washboard roads. I publicly wondered if the Rancho shocks added to my trailer's suspension didn't provide an alternate thermal dissipation path that allowed the axle to stay cool enough. It took a while, but eventually Martyn said that the problem was grit and not heat. The more that I examine that, the less that I'm inclined to accept it unchallenged.

I may eventually replace the rubber torsion, but that is more for the project of building an ITS than any need for replacement. As such, it is far down the projects list.

[deepmud]

The term is "Section Modulus" and it relates to the strength and stiffness of a component. In the case of steel tube the height and width are far more important to strength than is wall thickness. Even in torsion with a square tube! As angib was pointing out, you can gain strength with dimension without gaining weight. This is a well documented engineering fact, not "net theory". I don't know that the 50% stronger number is perfectly correct but, A) it would not surprise me in the least if it is and B) it is easily calculated. Search "Section Modulus formulas" if you want to look into this for yourself.

I'm sensitive to the easily dentable concern, so obviously wall thickness needs to be chosen to be appropriate for the location that the tube will occupy in the frame. The 2" tube for a coupler to fit restriction is a PITA, but there are ways around it if need be.

Where you need wall thickness to avoid the stressed parts from acting like a can opener lamination is the preferred method over thicker walled tube. That way you only carry the extra wall thickness where it is useful and not over the whole length of that tube. Quite common to see this sort of approach used in everything from Indy cars to highway bridges.
.

I've started to reply a couple times, but want to be careful I don't sound like I'm starting an "internet pissing match"

I did not intend to indicate that a larger diameter tube being stronger was "net theory" - but I do think that on a tongue where 2" 1/8 tube MIGHT be adequate, that going to 2" 1/4 WILL be MORE than adequate - not that 3" in not stronger (MUCH stronger at resisting flex - maybe even close to 50%), but that it's advantage will not justify it's complication or weight - one might as well advocate 4x4 tube as "better" - it's only better if it WORKS better.

No question that on a very long, heavily loaded trailer tongue that 2" may not suffice regardless of wall thickness - but to someone considering 2" 1/8 I wanted to be sure to recommend upping to 1/4 wall hitch tube - it has been shown to "WORK better" in terms of durability over 2"x1/8 - while in my opinion it wins on cost, weight and ease of installation over larger 3"/3.5"/4" etc x 1/8 wall in those cases where their advantages of overall load capacity may not be required.

I also think 2" hitch tube may be a stronger alloy - but I don't have anything but anecdotal evidence (really, it's just a feeling I get from having worked with it - cutting/welding etc - so that's not real evidence) - perhaps the next time I get supplies at the welding supply shop I can ask about that. It might explain why it gets used so much to make hitches, hitch extenders for campers, etc.

[ntsqd]

No pizzing match here. I just see it stated so often that, effectively, adding mass makes things stronger when adding geometry with the same mass makes things much stronger and it seems that the poster doesn't understand the difference. So you got lumped in with "them." Sorry, No offense intended.

I agree, going to a larger tube does complicate the design and fabrication. Whether it is worth it or not depends on the project's goals. I just don't want to see such a decision made on poor or lacking info.

In round DOM tubing there are usually two alloys available, 1018, and 1020 or 1026. Both the 1020 and the 1026 are noticeably harder to cut and to bend than the 1018 is. That these stronger alloys might be used in socket receiver tube would come as no surprise to me. I was not aware of a tube made specifically for receiver sliders. Does such a thing exist?

[deepmud]

When I recently got 2"x1/8 it wouldn't fit a 2" receiver without a LOT of grind/fitting ( it was a license plate frame for a front hitch - strength not an issue) - it's much "squarer" - the 2" hitch-tube I have purchased has a much more rounded corner to snug-fit the receiver - and given that it is specially sized, I'd buy it being special alloy.

YES! - thicker isn't always better. I advocate the bigger/thinner tube in the rest of the trailer for certain - I am amazed at the unladen weight of some of the small trailers used for off-road. Weight adds up really - a pound here, a pound there, next thing you know your little box-trailer weighs 6 or 8 hundred pounds before you get any supplies in it.

[boxcar]

Here's one.... And if you look there are Manny more. I am not a "leaf spring guy" ether . More of a trailing arm air bag guy. In my experience ,
Nothing is sailor proof. Maintanance and frequent inspections can and will prevent most failier issues with all suspension designs. Boxcar...