Axle Placement along Length of Trailers

[JWR]

This is a learning/education thing, NOT trying to solve some specific current problem. Over the last decade or two I have seen several TBN threads that talked only slightly or indirectly about axle placement along the length of trailers. I have never seen a good discussion much less tutorial (as opposed to speculation and guessing) about why axles are located as they are along the trailer bed. The closest I have seen was in 2006 when a guy stated a "60/40 rule of thumb" advocating or suggesting that axles be placed 60% of the bed length from the front of the bed. No rationale. No reasoning. Just a statement. So what I would like to hear is a reasoning/rationale for location.

I know there are all sorts of complexities involving dual axles versus single, gooseneck vs bumper pull, etc. but I am hoping to learn the mechanical engineering kind of reasoning as to Why rather than tangents.
Anyone really knowledgeable please speak up. [I'm thinking that trailer manufacturers, metal fabricators, trailer experts ... would be the best to speak on this.]

I think most routine users who are not experts on trailer design already know that factors include

• the type of load (evenly distributed, heavy on one end, typical farm tractor distribution, etc.)
• achieving best tongue weight
• maneuverability, fish-tail avoidance, etc.

Are there technical articles or handbooks or tutorials out there that provide a good education on the topic?

Note: One thing I've seen that makes this puzzling is the fairly wide and dissimilar examples on the market. I will post a few examples...(can't seem to find good pictures of the extremes)

First a Pequea dual axle with roughly a 50/50 placement.

Custom yellow trailer also seeming to be mid-placement but actually forward of center of bed. This trailer was made to tilt too.

Small utility with very oddly almost exactly middle location

Pequea deck-over again but loaded

CO Brand in VA with two trailers , both with axles much more aft, esp the dual axle very far to the rear. Wonder why?

Bix Tex utility -- maybe a 70 - 30 placement?

Maybe an 80-20 axle placement? or more like 75-25? Anyway well to the rear.

This car hauler has the axles way to the rear.

 

[K5lwq]

I had a custom trailer business many years ago and built countless trailers. Because they were all custom I spent a good bit of time with the customer going over exactly what the were going to haul on the trailers. I would adjust my designs accordingly. I also paid close attention to the vehicle that was going to be towing the trailer.

60/40 was the rule of thumb but sometimes I would move axels back or forward depending on the use. If the cargo was more fragile I would move the axels back because the ride is much worse behind the axels. But most of the time I would try to have the trailer carry as much of the load as possible and still have good capacity with enough tongue weight to ensure the trailer tracked well. I also would put longer tongues in to ease the backing pains of novice trailer owners. Never had a trailer come back with issues and every customer was happy. My tilt trailers all had 3 pt pivot designs to make sure the trailer always came down square regardless of terrain. I did not see many others do that but they always came back down nice and smooth.

So from my perspective the placement of axles are really dependent on the type of trailer and what is being hauled. The biggest thing is to have enough tongue weight so the trailer tracks nicely. But all of the designing in the world goes out the window if the person loading does not load properly.

 

[bcp]

Because.


It all depends.



This goes into it more than most sites, but not as much as I hoped for.

Trailer Axle Position - Trailer Building: Where Does The Axle Go?

Build with the trailer axle position correct. Where does it go? Here are the calculations and explanations to set axle(s) in proper location.

mechanicalelements.com

Bruce

 

[MTGreen]

I have a book series Trailers : How to Design and Build by M.M. Smith in 2 volumes (out of print but still available) that goes into great detail about axle placement but basically states the same thing as K5lwq in post #2

 

[JWR]

Because.


It all depends.



This goes into it more than most sites, but not as much as I hoped for.

Trailer Axle Position - Trailer Building: Where Does The Axle Go?

Build with the trailer axle position correct. Where does it go? Here are the calculations and explanations to set axle(s) in proper location.

mechanicalelements.com

Bruce

Actually, that is about as good as/better than any I have seen. Pretty much satisfies my curiosity. It also mentions the 60% rule of thumb and does not say where that came from.

 

[JWR]

I had a custom trailer business many years ago and built countless trailers. Because they were all custom I spent a good bit of time with the customer going over exactly what the were going to haul on the trailers. I would adjust my designs accordingly. I also paid close attention to the vehicle that was going to be towing the trailer.

60/40 was the rule of thumb but sometimes I would move axels back or forward depending on the use. If the cargo was more fragile I would move the axels back because the ride is much worse behind the axels. But most of the time I would try to have the trailer carry as much of the load as possible and still have good capacity with enough tongue weight to ensure the trailer tracked well. I also would put longer tongues in to ease the backing pains of novice trailer owners. Never had a trailer come back with issues and every customer was happy. My tilt trailers all had 3 pt pivot designs to make sure the trailer always came down square regardless of terrain. I did not see many others do that but they always came back down nice and smooth.

So from my perspective the placement of axles are really dependent on the type of trailer and what is being hauled. The biggest thing is to have enough tongue weight so the trailer tracks nicely. But all of the designing in the world goes out the window if the person loading does not load properly.

You are exactly the person I was hoping to get to speak to us. Thanks.

 

[Torvy]

Actually, that is about as good as/better than any I have seen. Pretty much satisfies my curiosity. It also mentions the 60% rule of thumb and does not say where that came from.

I'm no expert. Given the long history of the use of wheels, I would guess that rule's origins may be lost to history. Maybe the Mandalorian said it best..."This is the way".

 

[Jstpssng]

I'm no expert. Given the long history of the use of wheels, I would guess that rule's origins may be lost to history. Maybe the Mandalorian said it best..."This is the way".

I believe that it goes back to what I said in another thread… for a generic utility trailer it makes it easier to keep the tongue weight. I once had a homemade tandem axle with the pivot right at dead center of the 16 foot deck. It also was way too heavy (7” channel steel). When empty, it didn’t even need a tongue jack. That thing was a bear to pull, and was all over the road at over 45 mph.

 

[mini14]

i asked about that when my skid steer trailer was being built, it all has to deal with proper tongue weight so you dont get the trailer fish tailing going down the highway. there are many youtube vids of that happening

 

[JWR]

i asked about that when my skid steer trailer was being built, it all has to deal with proper tongue weight so you dont get the trailer fish tailing going down the highway. there are many youtube vids of that happening

Agree. I have had severe fishtailing a very few times and almost lost the whole rig once (going down a mountain) many moons ago. Probably keeping tongue weight within reason to fit the towing vehicle, the load and above all, preventing fish-tailing outweighs everything else. For nearly everyone those bridges are burned at purchase time. You cannot move the axle... normally.