Understanding proper placement of a trailer axle

[LeRepeteur]

Hello everyone,

General discussion type of question to see what others are thinking, I have noticed that some companies when buying a trailer have multiple axle placements for for the same size trailer, for example a 8.5X26 from one company has a different placement than a 8.5x26 from another. How would you calculate your axle placement in order to have the most optimal placement? With that, I mean do you take into account a max load scenario? Do you consider a buckling scenario and move the wheels as far apart as you can? Do you calculate the placement off of an empty trailer or a full trailer?

I know the equations to find the best placement but I just wanted to see if you take into account a fully loaded trailer or if you do the calculation with how it leaves the facility/empty. Just want to understand this more as we are talking about this in my Machine Design and Statics classes. I know a 60/40 is nominal but I really want to be finer than "recommended" and under stand from a real life scenario of how a trailer leaves the facility.

Please let me know what you think, any insight is helpful!

Cheers,
LR

 

[SwinnyGG]

They're all slightly different because there is no hard and fast rule. The trailer manufacturer has no idea how the trailer will eventually be loaded.

 

[BridgeSmith]

Generally, for stability of a 'bumper-towed' trailer (goosenecks are another matter entirely), it's recommended that the tongue weight be 10% of the total weight of the trailer when towing, so you'd want to place the axle(s) to achieve that in the loaded condition. Axle placement varies because the assumptions of the loading pattern varies based on the use. Utility trailers generally assume a uniform loading pattern, while a car hauler would consider the typical weight distribution and wheel placement of the vehicles it's intended to haul.

That's how it should be done, anyway. It seems most times, builders just build them 'the same as we always have', assuming that the guy who built the first one knew what he was doing.

 

[waross]

Tongue weight is important. For 10% tongue weight (recommended by many experts) axle placement will vary with tongue length.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[LeRepeteur]

BrdigeSmith, that's exactly what I am trying to stop over here. We have some math from a prior employee that used the worst buckling scenario in order to calculate the axle placement. I just don't see why they did it that way as the axle is now placed for when the trailer weighs 6K lb heavier. Since our tandem axle's are always a specific distance apart, wouldn't you test for the spacing we use and not worst buckling scenario? For example, our tandems are 33" apart from bracket to bracket but the equation that they used had 100 some inches for the seperation distance of the reaction forces. I'm just wanting to make sure that when I do this calculation I am doing it correct and accurately to the best of my ability without knowing the information of what and how it will be loaded.

Something to note is this hasn't been built out yet and only created in solidworks, so I am proofing before we make a proto. Confident in my statics and machine design, as well as FMEA, just looking to see everyone's inputs because the old employee's way of doing it just seems not viable for mass production.

Cheers,
LR

 

[BridgeSmith]

I'm not following you on what you're trying to determine. I thought this was about getting the correct percentage of weight on the tongue. That is accomplished by the correct placement of the axle(s), based on the assumed loading pattern. After the axle placemment is determined, then you design the frame to carry the loads.