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Old 11-03-2011, 07:20 PM
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Building a car trailer questions

Is there a formula or something for figuring axle placement when building trailers?

I got this 16' utility trailer I bought specifically made so it's 84" wide between the fenders. It has twin 3500lb axles and it pulls great hauling many cars behind many different trucks making many 1500 mile round trips. I wanna put a storage box on the front(3x5x84 with integrated tire rack) and a 2' dove on the back end with slide out ramps. I'm also considering taking the side rails off or at least shorting them to less than 6". I'm worried I might have to move the axles back to get the right tongue weight after the changes.

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Old 11-03-2011, 09:24 PM
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build a slider.

A lot of generic boat trailers have the springs, asles, fenders mounted to an angle iron carriage so that the trailer bed nests in the carriage. then the slider can be adjusted to get the propper tongue weight. I have been thinking that I should redo my fenders so they will drop in like the side boards on the truck..Sometimes I need to load farm machinery that is wider than the trailer, Here if you red flag the overhang and drive in daylight it's OK
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Old 11-03-2011, 09:40 PM
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Another option would be to extend the reach so you get a bit more of tongue weight if needed..that may be a lot easier on an existing trailer..

Sam
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Old 11-03-2011, 09:42 PM
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This is what I used to build single axle utility trailers long ago , the formula (of sorts ) was to take the length of the trailer ,not including the tongue and take 10% of that measurement,find the center of the trailer (from front to back)and move the center line to the back of the trailer the amount of the 10% .I would then center the axle on that center line. Now that was on single axle trailers ,i would think that with double axles that center line would be where the "walking beam or center spring knuckle "would be mounted. Just a guess,and on your weight placement both front and back as long as you could make the weights about the same that your weight bias would stay the same. I built many single axle trailers like this and never had a problem with any of them ( and I pulled every one that I built ) of course like I said they were single axles.I am sure there are members on here that can give you a answer on the duel axles.
Good Luck
Kenny
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Old 11-03-2011, 09:43 PM
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Since your adding something on Both ends,, I really think your still going to be OK.... If you was adding on just one end,, I would say different...

When I was building trailers I would go 60-40 And set the axle in between..Worked out great for me..
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Old 11-04-2011, 06:58 PM
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I think I'll be adding about 300lb to the front and 150lb to the back overall. The front being 10' foot in front of the axle and the back is 6' behind the axle. I do have plenty of #25 blocks of lead to bolt to the front if its needed when all said and done. I'm using a 08 F-250 Superduty so tongue weight shouldn't be a problem if it's ends up heavy.
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Old 11-04-2011, 07:18 PM
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Your project is like stacking your kids on a teeter-totter. You are putting more weight on the long side of the lever so your tongue weight will increase over what it is now.. Since you are adding the dove tail, you will be able to place your load further back to lighten the tongue weight if it gets too heavy. I don't like to carry ballast any more than I absolutely have too.

Trees
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Old 11-04-2011, 07:37 PM
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Yea.. Moving the load 1 foot back makes a big difference sometimes..
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Old 11-05-2011, 07:55 AM
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balanced load.

An out of balanced load can make things scarry, We finished up a construction job and the contractor asked my son to drive the Dodge dually back hauling the large bobcat. Someone had backed it on the trailer and chained it down. It had little or no tongue weight, mabe a tongue lift, When he got up to 60 MPH it started to whip back and forth, I thought it was going to tip the truck and trailer over. He eased it down to 25 and it was 5 miles to the next off ramp, A lot of angry drivers on the freeway having to slow down. I have Easy Lift load levers on most of our trailers and the side mount sway control. If I am going to haul something heavy I use them. The trailers track good without hooking them up but when you get in to rough road construction pavement they help. A lot of large trailers have axle off set so the driver can see out the driver side mirrors and see half of the lane back a ways . I always set the trailer axles dead on, squared to the frame. They tow easier and I have extendable mirrors
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Old 12-28-2011, 12:28 PM
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Axle Placement

Your standard tandem axle placement is a 60/40 split. That is the center of the two axles is placed 60% from the front of the frame and 40% from the rear of the frame. If you are adding that big of a race car box on the front you would not want to move the axles back. If anything you would want to move them forward. I would not move them at all until you have the box and all the contents in it on the trailer and test pull it. You will probably find that by moving the car back will shift enough weight back to make it still pull good.
I would even try backing the car on and test pulling it before I went to cutting on the running gear. Keep in mind if you cut the running gear off you will have to put a piece of angle over the area you cut to make sure the frame will hold up.

As for cutting the top rail off DO NOT DO THAT !!!!!!!!!!!!! Most of the trailers built with a top rail do not have a heavy enough frame to have the top rail removed. This includes adding a dovetail to the trailer. If you do not reinforce the cut for the dovetail and reattach the top rail after you drop the frame the 3-4" it will not hold up to the force of the car going up and down on it.

I hope this helps. If you have any other questions let me know always glad to help.

Mike Edwards
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Old 12-28-2011, 09:58 PM
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I haven't even started this project yet for its an outside only project thing for me. I did get the floor off though and I reconsidered the removal of the top rail. The whole trailer is made from 2"x1/4" angle except for the tongue. Even before I add a box I'll beef up a few places and incorporate the box into strength rather than just adding on top of the existing frame pieces. Would adding 2x3" C- channel down both main rails be enough to compensate if I were to remove the upper rail? Or at least know the load bearing specs and Ill do the math on my intended payload.
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Old 12-30-2011, 09:46 PM
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Trailer design

A good rule of thumb is that with ONLY the front axle in place, it should be about balanced, with maybe only a few pounds (up to 50 pounds or so) on the tongue. THEN put the rear axle in place.

If buying a tandem axle trailer and you want to see how it will tow, take the back wheels off and see if you can lift the tongue (or if you have to hold it down!) - then you'll know how it balances. After that its all up to how you load it!

(Used to own a dealership that sold them - there were a few makes I refused to carry because they couldn't pass a balance test, so I knew they wouldn't tow worth a ****)
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Old 12-30-2011, 09:54 PM
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Quote:
Originally Posted by johnsongrass1
The whole trailer is made from 2"x1/4" angle except for the tongue. Even before I add a box I'll beef up a few places and incorporate the box into strength rather than just adding on top of the existing frame pieces. Would adding 2x3" C- channel down both main rails be enough to compensate if I were to remove the upper rail?
I would say, that would be fine
I used to have 16 foot car trailer that was the angle iron only
the tongue helped support the front half
I used to haul a big toyota p-up on it, with no problems at all
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