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.

 

[ROUSTABOUT]

Also another trailer problem. My dad bought one with a tractor decades ago. Do not like it. I bought it from him in 99. It was built in a shop, built well, all steel, 16' bumper pull, 7'2" between wheels, or inside side rails. That thing was a swervy monster sometimes. Ended up being the cross braces under bed did not reach to the outside and were not welded to uprights for the side rails. I could push down on one corner and it would flex a foot. Whether sitting on the jack or on a hitch ball. That was a problem. So, check for flex on your trailers. Axle placement, I would always want that a little behind center. Just so I had enough weight on tongue so when it was on the jack it won't roll away. I've had them pop up and hit me in the face, only took once, I'm a good learner. I've had a few pop up, but my noggin was not in the way. I haul a lot of vehicles, I don't want the axles too far back. I'm debating making my trailer longer or building another one. I have all the ingredients, it's just labor bound at the moment.

 

[JWR]

One more (barely related) memorable incident: The first time I tried to load a 10K lb tractor on my new trailer I had not lowered the rear jack stands & really did not know why they were there. I found out. When the weight of the tractor got partially onto the trailer the leverage was such that the rear tip of the trailer sunk to the ground while the rear end of the pickup truck was lifted off the ground into the air...until I quickly backed off. These lessons you never forget.

 

[ROUSTABOUT]

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.

I saw something last week, and since you have done identified yourself as having knowledge in this area, here goes... I saw a trailer, helped them with a flat. Trailer had three axles, 8 lug, with three individual sets of slipper springs, no equalizers. Is there any problem with that? I guess it is a pro and con kind of question. Will that be fine for tandem axles? I'm fixing to change my situation up. I have drop axles. Every single living flipping time I have a flat, the bottom of spring u bolts hit pavement before the rim does. Grinds all that off. I mean spring pack comes apart, lost pieces, fixing it on the highway. It has 8 lug axles, but springs with shackles, and I always carry extra those because they stretch and bolt tears out. Never heavy enough for the job. Ive put all new nylon bushings in springs and equalizer many times. I need slipper springs and straight axles. But I'd like your opinion because I have no problem extending the trailer and putting three axles if there is no problem with three individual pairs of slipper springs I already have straight axles laying here, welding machine, crane to flip trailer over. I'm cooking with grease other than the spring question. If it's better with an equalizer, I'll go that way too. I'll even be happy with your answer either way.

 

[K5lwq]

I saw something last week, and since you have done identified yourself as having knowledge in this area, here goes... I saw a trailer, helped them with a flat. Trailer had three axles, 8 lug, with three individual sets of slipper springs, no equalizers. Is there any problem with that? I guess it is a pro and con kind of question. Will that be fine for tandem axles? I'm fixing to change my situation up. I have drop axles. Every single living flipping time I have a flat, the bottom of spring u bolts hit pavement before the rim does. Grinds all that off. I mean spring pack comes apart, lost pieces, fixing it on the highway. It has 8 lug axles, but springs with shackles, and I always carry extra those because they stretch and bolt tears out. Never heavy enough for the job. Ive put all new nylon bushings in springs and equalizer many times. I need slipper springs and straight axles. But I'd like your opinion because I have no problem extending the trailer and putting three axles if there is no problem with three individual pairs of slipper springs I already have straight axles laying here, welding machine, crane to flip trailer over. I'm cooking with grease other than the spring question. If it's better with an equalizer, I'll go that way too. I'll even be happy with your answer either way.

No real reason that would not work. I have built several trailers with drop axles and never had the issue you are describing. The key in doing separate springs will be alignment. If not correct, it will eat tires and bearings like crazy.

 

[ROUSTABOUT]

No real reason that would not work. I have built several trailers with drop axles and never had the issue you are describing. The key in doing separate springs will be alignment. If not correct, it will eat tires and bearings like crazy.

Thank you for your reply. Another thing to watch is the location of the tie bolt in a replacement spring. I saw some fellows not check that. They figured it out, but it was after the truck and trailer was upside down at the bottom of a high levy. I was a lead fitter building drilling rigs. I can keep it square.

 

[ROUSTABOUT]

No real reason that would not work. I have built several trailers with drop axles and never had the issue you are describing. The key in doing separate springs will be alignment. If not correct, it will eat tires and bearings like crazy.

I also add, I think my springs have seven leaves. With axles above springs. So the flat plate and u bolt nuts are lower than rim edge. Grinds them u bolts every time. I carry extra u bolts, spring, shackles, all for just in case. High lift jack. I jacked that trailer up once with a one ton 4x4 wrecker on the trailer, I was impressed with my scrap yard high lift, I bought Three one day at the scrap yard. Minimal problems to get them jacking. One had a piece of 1/2" plate welded to bottom as a base plate. I cut the back out in a semi circle and beveled back, son that has been a tire bead breaking fool around here. Three spares because one day I needed two. Had to leave my baby and come back, hoping it was there. I don't like that. Winch on front, steel ramps, screaming at them crack heads to hook up and haul off. But, she was still there untouched.

 

[Rockbadchild]

I am assuming/wondering if the height of the trailer has a influence on the location of the axle... a lower trailer would need to have the axels further back then a high trailer to accomplish the same hitch weight ... lower a trailer is the more likely it will be aiming upward once hook up as a result it will have less weight on the hitch, compare to a high trailer it will be more likely to be pointing downward or easier once loaded to make the trailer to be pointing downward. yes there is adjustable hitch but with some trailer they are so low they need to be aiming upward to have enough ground clearing...

 

[K5lwq]

I also add, I think my springs have seven leaves. With axles above springs. So the flat plate and u bolt nuts are lower than rim edge. Grinds them u bolts every time. I carry extra u bolts, spring, shackles, all for just in case. High lift jack. I jacked that trailer up once with a one ton 4x4 wrecker on the trailer, I was impressed with my scrap yard high lift, I bought Three one day at the scrap yard. Minimal problems to get them jacking. One had a piece of 1/2" plate welded to bottom as a base plate. I cut the back out in a semi circle and beveled back, son that has been a tire bead breaking fool around here. Three spares because one day I needed two. Had to leave my baby and come back, hoping it was there. I don't like that. Winch on front, steel ramps, screaming at them crack heads to hook up and haul off. But, she was still there untouched.

That explains the problem. I built a trailer for my dad one time to haul lawn mowers and after a few years he wanted me to mount the axle over the springs to lower the trailer some. I told him why he did not tell me he wanted a lower trailer to begin with?

I built some new drop axles for it and cut the fenders off and put new ones on for him. He was mad at me but it was a much better solution and he was glad I did it after a while. He did not want me wasting money but it was the right thing to do.

 

[K5lwq]

I am assuming (and it make sense) that the height of the trailer has a influence on the location of the axle... a lower trailer need to have the axels further back then a high trailer ... lower a trailer is the more likely it will be aiming upward once hook up as a result it will have less weight on the hitch, compare to a high trailer it will be more likely to be pointing downward or easier once loaded to make the trailer to be pointing downward.

I always designed the tongue for the trailer to be level when attached to the vehicle. Who wants to tow a trailer up hill all the time?

 

[Rockbadchild]

I always designed the tongue for the trailer to be level when attached to the vehicle. Who wants to tow a trailer up hill all the time?

lol clever ... but you get what I am saying ... generally if you take a utility trailer place the tongue level measure the distance to the ground and do the same with a car hauler, the car hauler would be lower ? .... I am wondering if what I am saying as merits ?