Leaf Springs: How Do I Determine a Proper Set?

[charliehm]

I’m starting my build from a HF trailer, Model 90153, which has three-leaf springs. The operating instructions say that the maximum weight capacity of the trailer is 1,350 pounds, but my intended, all-up load will be less than half of that (i.e., under 600 pounds). When I put a spring assembly on the floor upside down so that it makes an arch and I then stand on it, the spring barely deflects and barely slides horizontally.

This was my test setup: I butted the eye-end of the spring against one of the 4”x4” legs of my 500# plus pounds of workbench, so I knew that end of the spring wouldn’t move. Then I stood on the spring and measured the deflection of the arch and the movement of the slipper end with a 1” travel, dial indicator. I repeated the tests and averaged the results.

Admittedly, at 135 pounds (fully dressed), I’m a bit light. But 135 pounds is about 25% of the trailer’s intended working load, and I couldn’t flex the OEM spring assembly except negligibly, suggesting a very rough-riding trailer.

So, I pulled one leaf and ran the same test, and I got the following results:

Vertical Deflection: 0.085”
Horizontal movement: 0.070”

That’s a bit of movement, but still not a lot. Not even 3/32”.

Then I ran the same test with a set of leaf springs that were a part of a VATCO trailer kit I bought 25 years ago (and never assembled) whose weight capacity (according to the instructions which I still did have) is 1,000 pounds. I got these results:

Vertical deflection: 0.265”
Horizontal Movement: 0.335”

(Round those numbers to 1/4” and 3/8” for you tape-measure types). By either method of reporting, that’s a lot of movement. In fact, I’m wondering if it’s too much movement.

Both springs have a single eye and a slipper end. But the HF springs are 20.5” long as measured from the center of the eye to the center of the slipper foot. The VATCO are longer, measuring 30” center to center, which would account for some differences in behavior. I.e., the longer the spring, the easier it should be for me to deflect a spring having the same thickness as a shorter spring. (Both have leaves that are 5/16th thick.) But besides length, there is also another difference. The HF springs are 2” wide. The VATCO springs are 1 ¾” wide.

My question is this: Am I looking at a Goldilocks situation in which the HF springs (even with one leaf removed) are too stiff, and the VATCO springs are too flexible? Do I need to buy another set of springs?

I see that Eastern Marine sells single-eye, 20” spring sets rated for 650 pounds. The expense would be reasonable: $19.10 per spring. Or, should I build my frame in such a way that I could install either of the spring sets I already have and choose whichever seems to work best? And if both prove unsatisfactory, then buy the Eastern Marine springs?

Frankly, that’s the solution I’m favoring. The spring hangers that HF provides are flimsy junk that need beefing up anyway. (Each hanger is no more than a short section of 2-3/8”x2-3/8”x3/16” channel that is bolted to the trailer frame independently of the other one.) My thought is to fabricate a single-piece spring hanger out of channel that would span the overall distance of any spring I own or might buy. (As for being able to accommodate both 1 ¾” wide and 2” wide springs, that could be handled with shims, which the OEM HF spring hangers already need anyway, due to the sloppiness of the fit between the springs and the hanger, which is more than 1/8”.)

I’ve never owned a trailer, never done any towing. So, I’m appealing to your experience for guidance. How much flex should I be seeing in my springs when I stand on them, when my weight is 25% of the intended working-load of the total trailer?

Thanks in advance, Charlie

[doug hodder]

Charlie...if you do indeed build a trailer that falls into those weights, you will be OK....I had 1500 # springs under a tear that when finished weighed in at 1200....I hauled it 1300 miles at high speed and flattened them both....After I got home, I replaced the springs so that my weight is 50% of what the ratings for the springs are...no problems....It's tough to know exactly what the final weight will be once you get going...plans change...just my experience.....Doug

[asianflava]

It's tough to know exactly what the final weight will be once you get going...plans change...

Is that the understatement of the year, or what?

[Gerdo]

Mine is a 3500# axle. When I took it out on my shakedown run around town I noticed a fair amount of bouncing. I talked to a local spring shop and decided to take out only one leaf (the smallest leaf in the 4 pack). They also said that if it was still too rough that they could recut the other leafs to lessen the capacity. They also said that they would not recomend removing 2 leafs (leaving 2). This can cause the sprinfs to crack at the U-Bolts.

I also replaced my trailer type tire ST205/75D15 50 psi, with a passenger tire 205/70R15 32 psi (running about 30 psi). This realy smoothed out the ride. I was cruising at 70-75 mph and it tracked great.

After about 750 miles I think that I'm there. There is still more than 2000lbs to 2500 lbs of springs under mine. I haven't weighed it yet but I'm guessing it weighs around 1200 lbs. I'm staying with my heaver springs, more safety factor.

[charliehm]

Doug,

Yes, plans do change, and final weights can only be a guess, which is why I was doing my informal testing, so I culd get a feel for what the parameters of the problem might be. If I build in the possibility of changing from 2" wide and 20" long springs to those that are 1 3/4" wide and 30" long before I build the chassis, then a swap-out at a later date is no biggie.

It would be easy to set up a formal test stand using a fixed frame and a hydraulic jack with a pressure gage, depress the springs to their maximum rated capacity, and take measurements. But I still wouldn't know by eye what "normal" movement should look like vs. something that will cause me grief down the road. (Pun intended.) I was hoping someone could suggest a shade-tree-mechanic, rule-of-thumb to go by for what is too flexible and what is too stiff.

Charlie

[madjack]

...first off, spring capacity should be around 50% higher than your loaded weight...that is trailer weight plus what ever you load in your trailer, wheels and axle do not count in that weight because they are unprung weight. Rebuilding the mount in the manner you suggest would give you the most options for differing springs. I know of no rule of thumb for measuring spring deflection
Remember that in your test that mass and momentum are not taken into consideration...they will add to the apparent mass of your load while travelling...I think I would stay with your original springs and take one leaf out later if it proved necessary
madjack

[charliehm]

Gerdo,

I knew about the possiblity of using passenger tires for a softer ride, but for the same safety-factor reasons you chose to keep your heavier springs, I'd stay with tires manufactured to be used with trailers. (And since I've always driven little foreign cars with 13" wheels, HF's 12 inchers are fine with me.)

Also, those same safety factor reasons --as Doug's experience of spring failure when they were used at 80% of rated load-- suggests that I shouldn't try to use my 1,000 pound springs or pull a leaf out of the HF set. I should do my build and then do actual road tests, instead of just in-the-shop "dock trials".


Charlie

PS I didn't think about cutting the leaves shorter. That's a drastic, irreversible step, but certainly deserves consideration as Plan "J" or "K", or something to look at if all other possibilities have failed.

[doug hodder]

Charlie....I think if you want to swap out the springs at a later date you'll find that you can get them in the same eye size and length and just swap them right into the hangers...no changing the length....if you want to change from 20-30' in length you are going to have to put new hanger brackets on the frame...both front and rear so that the axle placement doesn't change...for me I just placed the axle where I wanted it. and welded up the front bracket...the spring slips to the rear, I just set the rear hanger so that the springs would slip to the rear on the shackles and not allow it to go over center...there are lots of spring options available in the same width and length ....and after all at 600# it isn't going to be that big of a deal..build it with what you have...and swap them out later if you want....with the same size, just heavier....50$....just my thoughts on it...anyone else have an idea? doug

[charliehm]

Madjack,

Thanks. Your advice is exactly the kind of overview I was looking for. I'll build the spring hanger the way I think it needs to be done and put the third leaf back into the assembly.

Could I impose upon you for a follow-up question?

I want to drop the floor as low as possible. Obviously, space has to be provided for the axle to move upward. I'd never drive faster than 55 with a trailer, but that doesn't mean I won't hit a pothole or rock that would load the springs pretty heavily and, therefore, momentarily move the axle upward by an inch or two or three.

Is there a rule of thumb as to how far down a floor can be dropped before proper axle clearance is lost? (I was going to cue off the the distance the manufacturer provided between the top of tire and the fender, because if tires are rubbing, axles are banging, and vice versa.

Charlie

[madjack]

....sorry charlie(no tuna involved) I don't have an answer for ya on that one...I looked on the dexter axle site and they said to call the engineer/sales person for that info...maybe someone else...
madjack

[charliehm]

Doug,

Thanks for your follow-up thoughts. A huge variety of springs doesn't seem to be available at the lower end of load-ratings. For the heavier trailers, yes, but not the light-weights.

As for having to attach new spring hangers if I change spring lengths, that is what can be avoided by installing what amounts to a one-piece, universal spring hanger to begin with (that mounts both ends of the spring). At worst, should I change lengths, I would have to drill a new holes for the bolt for the eye or slipper foot. Also, should I want to change the axle position, I could do so by moving the springs forward or backwards, which is a flexiblity I might want.

As the 40"x48" HF trailer has been manufactured --which I'm modifying by extending another 24-32"-- changing spring length or axle position requires drilling new holes in the frame, which already looks like swiss cheese for all the holes it comes with. What I want to do is leave the frame as intact as possible and do my swiss cheesing in a separable part that would be built much stronger than what the manufacturer provides.

What really got me going on this train of thought was waking up this morning and saying, "For my next trailer, I'm going to ...." which I immediately realized was crazy.

"Why not do it right the first time?"

And since I don't know what "right" is, I have to build-in from the beginning a lot of design flexiblity. HF's wheels are good-enough, as are their axles and hubs. It's everything else about the way they put the trailer together that I'm questioning. Obviously, I should have welded my own frame, but until I could see an actual example of a frame, I didn't know what I wanted. So I had to buy a frame, so I could see what a frame looked like. Then I assembled it and disasembled it several times so I could get a feel for its logic. And I've read hundreds --if not thousands-- of the very helpful posts to be found on this forum, doing topic searches, looking for answers to my questions.

For the tow vehicle I intend to use, a 40" axle is perfect, as is a chassis length not much more than 8' and an all-up weight no more than 2/3 of my vehicle's 1,000 tow capacity. So, that's where I'm starting my build, from the ground up, not the chassis down, one piece at a time, all the while building in the possibility of accomodating later changes that are deemed necessary or desirable. The "costs" for that sort of flexibilty are a bit more weight and a lot of thinking, but as one poster wrote: "I'm now on teardrop time, where the process is as important as the product."

Charlie

[charliehm]

Madjack,

Thanks for trying to answer my axle clearance. And, actually, your answer was helpful: "Ask the manufacturers of axles."

Obviously, I can't call HF.

"Uhh, I'm doing some serious mods on one of your trailers, and I was wondering what you thought about..." LOL.

But I can call people who deal with building one-off trailers, like the guys who sell trailer parts.


Charlie
--------------

"Charlie the Tuna"? I've haven't heard that one in a while. Are they still using that commercial? (I don't have a TV.) Or do you know the commercial because you have about as much gray hair and years as me?

[madjack]

"Charlie the Tuna"? I've haven't heard that one in a while. Are they still using that commercial? (I don't have a TV.) Or do you know the commercial because you have about as much gray hair and years as me?

yeah, they still trot out ol' charlie every now and again but my grey hair and years do put me back to my families first TV back in "58
madjack

[charliehm]

Powderburn,

Staying with the OEM springs --rated for 1,350 punds-- would give me the 2x dynamic loading factor that everyone has suggested -- in one way or another-- is both prudent and necessary.

But HF's spring hangers are trash, and I'm going to replace them. The slop between the walls of the hanger and the sides of the spring is excessive. The little, add-in wear plate is going to deform, and it is going to wear quickly. I need to mitigate those problems, as well as fab the inevitable replacements before I actually need them. Obviously, I want the wear plate (that the slipper foot slides against) to wear out, not the spring. But as Haul-Master has designed that sub-assembly, everything is going to get gnarly: the spring, the wear plate, the bolts tucked away under the wear plate, and the hanger itself. Their design is clever, for its use of bolts holes common to other parts and fasters common to the rest of the trailer, but I can tell by eye that assembly won't stand up to ordinary use, much less true punishment. Fixing the problem is both easy and necessary. So I'll do it.

Charlie

PS Yes, I need to start submitting pictures of what I'm talking about, as so many posters do so helpfully. But learning how to use a digital camera and then uploading the photos is going to be harder for me than building the trailer. I already own one, still sitting in its box for 2 years now, unopened. But documenting my build is something I owe myself and the forum members, who are so generous with sharing their own experiences. A picture really is worth a thousand words.