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...

 

[tommu56]

When I was building my trailer I measured quite a few I came across
To the center of the axel on single axel or center of the equilizer on tandems was from 53% to 58% of the trailer length not including tung for bumper pull's.

Do like I did drive up to a lot on sunday and break out the tape I measured 3 or 4 different makes at different places and the all came in around that number.

Note the Landsacper and dovetails trailers don't follow that rule bevause of the gate weight throws them off.

tom

 

[RWolf]

When considering GN style tongue weight will increase to about 25% of total weight. That's why when you see a GN you'll see the wheels a bit farther back. I think it was something like 75/25 on my horse trailer.

 

[J_J]

I found this site that might be of interest.

What makes a good trailer design?

 

[powerstroke444e]

If you don't have enough tough weight the average joe homeowner overloads the trailer and the truck jackknifes when he hits the brakes hard because the truck don't have enough weight on the rear tires. When the trailer is 60/40 old Joe homeowner stops loading the trailer when the bumper hits the ground on his not so heavy duty SUV that don't have trailer brakes. Thus if you know what you are doing order what you need.

This is one of the trailers we have & yes behind a 1/2 ton its easy to overload but behind a 3/4 or 1 ton we put 6 ton plus on this and it handles great.

 

[Reg]

I remember a fairly extensive article from someone who had converted a single axle trailer to a tandem.
Two things have really stuck in my mind about it.
1) The axles should be spaced evenly forward/backward of where the original single axle was (this was a surprise to me, but he had a LOT of arithmetic to support it).
2) The center of gravity of a tandem axle trailer is actually AHEAD of the front axle's center line.
I doubted this too, but took a tape measure to one of my own tandem axle trailers and verified that with 11 or more percent tongue weight this is true.

All that aside; on gooseneck or 5th wheel trailers it doesn't matter that much, put them wherever you want to to suit the load.
On a LONG trailer you risk bellying out if they are too far back, tail dragging if they are too far forward.
Wherever you put them distribute your load to get the right % load on the coupler.

 

[Egon]

What type of Boat is that on the trailer Diamondpilot?

 

[Diamondpilot]

2003 32' Wellcraft. It is powered by 2 5.0L Volvo engines, 270Hp each. Weighs 15,600# on the trailer full of fuel.

Chris

 

[Slippy]

You also have to remember in the deck over trailers with the dove tail, and large wedge loading ramps like shown on the PJ trailer, you have some weight back their to balance against the front.

Some of the manufactures now have trailers designe to haul almost as much weight, but come in on the lighter side. 8" I beams instead of 10". Mortiz has 2 series of deck over trailers. Check out their UD series trailer. Moritz International Inc. - Quality Trailers
It comes in about 1000lbs lighter than the F-series but can haul a pretty good weight. Also, there usually is not much difference in price or weight between a 12gvw and 14gvw trailer.

 

[Diamondpilot]

One other thing I was thinking of is if you have a trailer with the axles in the middle or there abouts and the load is even on the trailer within reason the tail will wag the dog. What I mean by this is a trailer loaded this way will wag the truck very easily. You have a lot of weigh back there and its a simple leverage thing. With that type of arm you dont need much push to make things rock.

Chris

 

[J_J]

How many of you think that a balanced load is when the load is centered over the axles. Raise your hands. Now , put them down. Sometimes it is very hard to know when the load is situated right to give the proper towing response, and that is a smooth pull, with no fishtailing, etc. No matter what kind of load you have, you have to consider the load on the tongue, and it should not be above the rated load or above what the hitch is designed for. I believe you can cheat a little if you use the equalizing hitch to get the right load on the front tires, which is where you lose proper steering. The sway bar is another accessory that is useful . Too much weight on the tongue will push the rear end down thereby raising the front wheels, causing steering problems. It does take some effort to get the trailer set up right, be it trial and error, or whatever. I have pulled different kinds of trailers, with different vehicles, and that does not make me an expert, but it is just my opinion on things. Don't forget correct air pressure. But also consider an unloaded trailer being pull a long distance will give a better pull if you let out some air to keep the wheels from hopping and bouncing.