Where to Mount the Trailer Axle

Lanse · Sep 14, 2013

Goodevening everyone!! I'll just ask you to hold on for a second as I finish... putting on... *zip* this here... flame suit... *click*

Alright, now thats out of the way ...

I've got a trailer building question here... I'm working on installing the axle on the rolling BBQ that I'm building... I got the leaf spring hangers all welded in place and the axle I'm using has a 3" diameter, very heavy duty. I know its overkill, but hey, it was cheap...

And the leaf springs are the smaller 2,000 pound ones if that makes a difference.

Anyway, I got the big axle bolted to the little leaf springs and I thought to myself "wow, thats not a lot of suspension travel" theres only like 3-4 inches which isnt good for rough roads and potholes...

So, I'm thinking of mounting the axle UNDER the springs instead of on top of them. Almost every trailer I've ever seen has the axle "inside" the area between the springs and the frame, why is that? I understand ground clearance might be why... I'd almost like to raise this frame up... I mean, the trailer isnt "too" low to the ground, but I wouldnt want to build it any lower.

Long story short, should I mount this axle UNDER the springs or ON TOP of them? Are there any compelling arguments in favor of one or the other, or is it "six of one and a half dozen of the other?"

Thanks guys...

js305 · Sep 14, 2013

I don't have a preference on the placement, but if you have some travel due to the weight, etc., you might consider putting shocks on the trailer. I have two trailers, one an open utility and the other is a converted service body with a welder and bottles along with a bunch of tools. They kinda bounced a little on a rough road so I fabricated shock mounts and put the cheapest ones I could find. Made a world of difference in the way they pulled.

dpendzic · Sep 14, 2013

Us beach campers typically move the axles to underneath the springs to get the extra height because of the deep ruts in the sand on the beach.
functions pretty well except having the CG of the trailer a little higher makes it rock sideways a little bit more.

Owen Aaland · Sep 14, 2013

I would mount it so you get a good working height for the BBQ.

Anonymous-0 · Sep 14, 2013

I agree with going for proper BBQ height. I've seen things like that where there were no springs but the axle could be flipped up so the BBQ or whatever could sit at the proper height. Just make sure you put the axle back far enough so you have decent tongue weight. If the axle is too far forward it is very dangerous and the trailer wont track straight at speed. Basically it's like the tail wagging the dog. Off the top of my head, I'd say the axle should be about 3/4 of the way back. If you have a wide spacing for the spring hangers and the axle ends up about in the middle, you'll have to change your design. I had a really old Hobart welder, from the 40's, at one time on a home made trailer with the axle in the middle and I couldn't pull it faster than about 30 MPH or it would start whipping all over the place.

Speaking of Hobart, are you finished and what's your plans for the immediate future?

Pops1532 · Sep 14, 2013

I've had car hauling trailers that didn't have 4" of suspension travel. Something as light as what you're building shouldn't need more than 2 or 3" of travel. I agree with those that say to mount the axle in the position that will give you the best working height.

Fore and aft location is critical. You want 10-15% tongue weight to prevent swaying.

willie in mn · Sep 15, 2013

Depends on the axle.
The spring perch on the axle has a hole for the spring center bolt head. Should be a snug fit for the round head of the center bolt. I don't have a chart handy, but different spring ratings have different sized center bolts, to match the hole in perch of same rated axles. This keeps the axle in place, otherwise it can slip in the U bolts & run "dog tracked". Light duty solid square bar axles might just have a shallow hole drilled to accept the spring center bolt head.
Also, believe it or not, there is a "right side up" to the axle. If you look closely, there is a slight curve,bend, or camber to the axle. When installed correctly, the center of the axle will be slightly higher than the ends, & the wheels will tilt just a bit outward at the top. When loaded this affects tire & bearing loading.
A skilled welder can reposition the spring perch, but exact location in relation to the camber is critical. Just a few degrees off in locating the perch will set the wheels toed in or out, making it pull harder & increasing tire wear.
So much for axle position, more thoughts to follow.
Willie

willie in mn · Sep 15, 2013

More design factors.
The 3 in tube axle & its hubs, wheels can get pretty heavy. Auto engineers call it "unsprung weight". Don't have the exact numbers, but to ride decently, it has to be a small percentage of the total weight. Too much "unsprung" weight will make it bounce all over the road.
Spring travel or deflection- even class 8 trucks with air suspension have only 4 or 5 inch deflection. Super off road trucks such as concrete mixers & dumps sometimes advertise 8 inches deflection. Your BBQ rig should be okay with 2 or 3 inch deflection.
How about the grill itself? Is it charcoal fired or propane? If propane the tank must be solidly fastened to the trailer. If no permanent guard around the valve the steel cap must be installed over the valve when in travel. Also the regulator/hose must be disconnected on portable tanks over 40# capacity. It's a safety thing. You don't want a flaming rocket in case of mishap & the valve,regulator gets knocked off. Except for a few applications such as 30# tanks on forklifts, RVs, etc, the tank must be mounted to ride upright.
Ready to be flamed.
Willie

Bus Driver · Sep 15, 2013

With the axle above the springs, the U-bolts carry all the weight. Not necessarily a bad arrangement but the U-bolts must be inspected regularly. I had the U-Bolts fail on one such trailer but the axle was captured within the spring and it's shackles.

jon f mn · Sep 15, 2013

Axle springs are made to have only about 3" of travel and if they go farther than that can get bent. You can put then under, just make sure the crown of the axle is still up, but it won't likely give you more travel anyway. 3" is a lot more that it looks like and as said with 2000 lb. springs on a bbq they won't likely flex much anyway.

Pops1532 · Sep 15, 2013

Don't worry about the u-bolts carrying the weight. That's how most leaf sprung vehicles came from the factory.
If you do put the axle under the spring do as mentioned and carefully relocate the perches...then straighten the axle after you're done welding. I don't mean take the camber out. Welding the perches on will distort the axle and you'll need to align it. Unless it's way off you should be able to do that with a rosebud tip on your torch.

showcrop · Sep 15, 2013

(quoted from post at 19:37:12 09/14/13) Goodevening everyone!! I'll just ask you to hold on for a second as I finish... putting on... *zip* this here... flame suit... *click*

Alright, now thats out of the way ...

I've got a trailer building question here... I'm working on installing the axle on the rolling BBQ that I'm building... I got the leaf spring hangers all welded in place and the axle I'm using has a 3" diameter, very heavy duty. I know its overkill, but hey, it was cheap...

And the leaf springs are the smaller 2,000 pound ones if that makes a difference.

I am no trailer building expert but I would say that your flame suit hasn't taken too much of a licking, LOL.

Anyway, I got the big axle bolted to the little leaf springs and I thought to myself "wow, thats not a lot of suspension travel" theres only like 3-4 inches which isnt good for rough roads and potholes...

So, I'm thinking of mounting the axle UNDER the springs instead of on top of them. Almost every trailer I've ever seen has the axle "inside" the area between the springs and the frame, why is that? I understand ground clearance might be why... I'd almost like to raise this frame up... I mean, the trailer isnt "too" low to the ground, but I wouldnt want to build it any lower.

Long story short, should I mount this axle UNDER the springs or ON TOP of them? Are there any compelling arguments in favor of one or the other, or is it "six of one and a half dozen of the other?"

Thanks guys...

504-1 · Sep 15, 2013

I will let you in on a trailer building secret, on a single axle, mount the axle 1/4 inch crooked(front mounts staggered) That will put a small amount of side pull built in, that eliminates the tendency to wiggle at speed.

Anonymous-0 · Sep 16, 2013

Mounting the axle straight in the right place is a much better idea.

Pops1532 · Sep 16, 2013

(quoted from post at 01:51:45 09/16/13) I will let you in on a trailer building secret, on a single axle, mount the axle 1/4 inch crooked(front mounts staggered) That will put a small amount of side pull built in, that eliminates the tendency to wiggle at speed.

That won't have any affect on swaying. It will just make a trailer track wrong.

showcrop · Sep 16, 2013

Some how my response ended up in the middle of your original post, Lanse, so here it is again "I am no trailer building expert but I would say that your flame suit hasn't taken too much of a licking, LOL".

Brad Buchanan · Sep 16, 2013

Mount 'er right between the wheels.

Brad

Where to Mount the Trailer Axle

Lanse

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js305

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dpendzic

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Owen Aaland

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Anonymous-0

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Pops1532

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willie in mn

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willie in mn

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Bus Driver

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jon f mn

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Pops1532

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showcrop

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504-1

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Anonymous-0

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Pops1532

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showcrop

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Brad Buchanan

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