Tandem Trailer Geometry

[yooperdave]

I was wondering why it appears that often the dual axles are located at or near the back of the trailer? Specifically, whith a ball hitch hookup.

It seems to me that the load on top of the trailer should be near centered over the axles. This would mean that the axles should be moved forward somewhat. Otherwise, the truck hitch is going to be realizing a whole-lot-o-load in addition to towing the load.

Any thoughts are appreciated.

Yooper Dave

 

[Diamondpilot]

They are not that way in from what I have seen. Now boat trailers are that way because most of the weight is in that position. Here is a pic of my trailer. The idea of a bumper pull trailer is to have 10% of the weight on the tongue of the trailer.

Most trailers are about 60/40. That is 60% of the deck before the axles and 40% aft of the axles.

Chris

 

[radioman]

it's a 60/40 weight ratio for better trailering. You dont want all the weight on your pin, overloading your tow vehicle. you dont want too much weight in back and have excessive sway. just a thought.

 

[Runner]

Dave,

I wonder about that too. Most of the lowboys I've looked at seem to have the axles located about right, but the deckovers seem to have them too far back.

I was looking at this trailer, but the more I looked at it, the more I realized that it's made for something like a dump truck, where the tongue weight doesn't matter.

I was afraid just the tongue weight, even without a load, would be too much for my pickup.

 

[kthompson]

I have noticed it with 5th wheel and goose necks and thought it was due to that. Not sure had noticed it with bumper pulls. But lots of local or regional trailer builders.

 

[Diamondpilot]

What you guys need to remember is the trailer like the one pictured above is meant to haul large equipment, not a car or CUT. For that purpose a utility trailer or car hauler is much better suited unless you have a 1 ton Diesel truck.

Put a Case Backhoe on that trailer like the one pictured above and the load would be right, 60/40. Most of the reason these trailers are setup like this is the bucket of the FEL takes up 4' of the deck space and is relatively light, then you have the engine and tranny to finish off that first 60%. In that last 40% you have the cab, large rear wheels and diff, and then the weight of the BH itself hanging off the back.

Chris

 

[Runner]

"Put a Case Backhoe on that trailer like the one pictured above and the load would be right, 60/40."

Like I said, meant to be hauled behind a dump truck...Still some mfgrs., like Anderson, seem to place the wheels a little farther forward. This looks like what I need, but, unfortunately, there aren't any Anderson dealers around here that I know of...

 

[yooperdave]

I always felt that the beaver tail style trailer had the dual axles in the right spot - well suited for hauling equipment around.

However, this style of trailer is not well suited for moving long flat objects like lumber.

I also thought the dual axles were moved further ahead on aluminum trailers than steel trailers - maybe due to the decreased weight of the trailer?

Yooper Dave

 

[Diamondpilot]

Being a trailer dealer I can tell you I have had a trailer for a 7,000# boat that pulled great with noting in the boat. We brought the boat home from Chicago to the Cincinnati area like this. The next day we loaded it full of fuel (80 gallons), and put all the customers gear in it and took it to the lake and it pulled like crap. The fix was to move the boat 4" further forward on the trailer to shift more of the weight to the truck. This was all done after weigh the rig and consulting the trailer manufacturer. Mind you we were pulling this boat with a Diesel F-350 and like I said a 7,000# trailer loaded improperly took over control of the truck.

I am not sure how much weight was transferred by moving the boat 4" forward but that was the figure given to me by the trailers manufacture once given all the data and weights. I can tell you it fixed the problems. The customer tows the boat with a F-150 and says it does great. My guess is with the boat loaded there was only 1-2% of the total weight on the tongue. I am sure when I brought it down from Chicago it was at around 10% with no load in the boat and only 5 gallons in the fuel tank. Its probably now on the heavy side of 12-15% with the boat loaded.

Anyway, the manufactures put the axles in that position for a reason for the trailer type. Even moving things a few inches will greatly vary how it pulls.



Chris

 

[Runner]

One neat thing about a lot of boat trailers (both of mine are this way) is that they have moveable bogies. I had to adjust the wheel position on both of mine to get the tongue weight right. Easy to move, just by loosening the U-bolts. Can't move them very far, but like Chris says, you don't need much...