Tongue Weight Spreadsheet

[Shrug53]

Oh my head! My math skills are 2 1/2 decades behind me now. I will just have to guess and hope for the best. Or maybe I will just post all the weights here, and let all you engineer types go at it!

I have decided to go ahead and weld this up myself though. I have read many books on welding, watched a few videos, and my broter-in-law is going to give me a few lessons when he comes out for Christmas.
If I stick to 2x2x1/8" stock, I should be able to weld it up even using one of those small welders from Harbor Freight.

This way I can do like it was suggested and move the axle around as I build and weld it in to place last.

Though I will probably let you braniacs have a crack at the numbers anyway. Serves me right for going to college and getting a degree in philosophy!

[tdthinker]

I hate math, but I always pass. I am on summer brake right now and I really dont feel like turning the old brain back on yet, bye

[R Keller]

Chip: I always preferred the two girlfriends and one toolbox on the galley method. But maybe that's just me...

Shrug: We can walk you through this no problem. It would probably help if I posted a diagram. I was a political science/philosophy major myself (though I started in physics and have had some structural engineering courses since then), so you can do it too. Just feed your estimated weights and distances to Andrew or me and we'll do the calcs.

1/8" stock might be too thick. Grant Whipp recommended 0.095" wall (#13 gauge) for mine. Of course, my frame is 1.5"x2.5" rectangular steel tube, which gives a lot more stiffness in the vertical plane than equivalent 2x2" tube.

I'd be interested in figuring out why Mike's tongue weight was so large. Mike: can you give us the basic specs for the Baja Benroy?

Rik

[mikeschn]

Basic specs...

It's 10' long, 6' wide and 5' high.

The frame is built out of 2x2x1/8 square tube

And the tongue is built out of 2x3x1/8 tube

The sidewalls are 3/4" ping pong table plywood with waterproof glue

The subfloor is 2x2 studs
The floor is 3/4" plywood

The joists are 2x2 studs
The inner and outer roof skin are 1/8" plywood

The tongue is 4' beyond the body

The CG of the body is probably about 12" behind the center of the body

Here's a picture of the frame...


Oh yes, the axle is about 48.5" from the rear of the trailer.

And the air conditioner is directly above the axle

What more do you need?

Mike...

[tdthinker]

nice frame mike.

[MikeM]

Tony,

I had someone tell me once for placing the axle Use use a simple fomula like this:

34.5" from rear bumper for a 4x8' teardrop; then add 6" for each additional foot of lenght after the 8'.

8' trailer = 34.5"
9' trailer = 40.5"
10' trailer = 46.5"

Simple and seems to come out the same as all these physics whizzes.

I got all A's in math and even took extra math classes to keep my grades up, and I'm having problems grasping some of these figures (sorry guys, I guess the noggin has thickened with age).

On a utility trailer I built I left the spring brackets to weld until the last. Another person mounted the springs on angle iron just larger than the frame so the could slide on the frame until the trailer was done. Then he could set the tongue weight to just the right weight.

My boat trailer has u-bolts that attach the axle frame to the trailer frame. Then depending on what I am towing the boat with I can move the axle forward or back to change the tongue weight. I don't do this very often, maybe three times in 20 years.

Hope this helps,

Mike

[R Keller]

MikeM:

I think that's Bill Adkins' formula? I used that as starting point for mine also. But since I had a non-standard weighting situation (tongue box and footwell), I wanted to do a double check. It's not very hard to do it, but unless you've had a basic structural mechanics course, it all looks very confusing I'm sure.

My spindle center came out at 45" from the rear of the floor, which is about the same as the formula would indicate, as you say. I couldn't go much further foward due to fender/door clearance.

Mike Schneider: still don't know what happened to the Baja Benroy. Perhaps part of it is that you have a torsion axle with, I believe, 6" trailing arms? The "axle" measurement should actually be at the spindle center when the trailer is loaded, since that is the axis around which the body rotates.

Just doing a quick 10-minute exercise on my lunch break here, I estimated a lot of these figures based on what I can recall/guess about your trailer:

Total weight: 1,500 lbs.
Tongue weight (tongue steel, hitch, jack, chains, etc.): 70 lbs.
Remainder of body and chassis weight: 1,430 lbs.
main body length: 10 ft.
distance to hitch from front of body: 4 ft.
spindle center from rear of body: 42.5" (48.5" axle from rear minus 6" for trailing arm)

Making a simplifying assumption that the body and chassis weight is evenly distributed across the 10 foot body and that the tongue weight is centered on the 4' length in front of the body, I calculate a tongue weight of 256 lbs. Is that close to what it is?

Moving the axle 6" forward in this scenario would reduce the tongue weight by about 60 lbs.

Or assuming an additional 200 lbs. in the galley centered 12" from the rear of the body, would reduce the tongue weight by about 50 lbs.

I could be wrong about your spindle center placement. If it is 48.5" from the rear of the trailer, then I am a little more baffled. It looks like you have a lot of steel in your chassis in front of the axle though. That is probably part of the reason too...

Rik

[mikeschn]

Mike Schneider: still don't know what happened to the Baja Benroy. Perhaps part of it is that you have a torsion axle with, I believe, 6" trailing arms? The "axle" measurement should actually be at the spindle center when the trailer is loaded, since that is the axis around which the body rotates.

Total weight: 1,500 lbs.
Tongue weight (tongue steel, hitch, jack, chains, etc.): 70 lbs.
Remainder of body and chassis weight: 1,430 lbs.
main body length: 10 ft.
distance to hitch from front of body: 4 ft.
spindle center from rear of body: 42.5" (48.5" axle from rear minus 6" for trailing arm)

Making a simplifying assumption that the body and chassis weight is evenly distributed across the 10 foot body and that the tongue weight is centered on the 4' length in front of the body, I calculate a tongue weight of 256 lbs. Is that close to what it is?


Rik

You're amazing. You taken some excellent guesses, and got very close to my actual tongue weight.

My axle center is 47 3/4 from the rear from the rear of the frame
my spindle center is 41.75 from the rear of the trailer.

When I level the tongue and put it on an electronic bathroom scale it weighs 275 lbs.

My guesstimate was that moving the axle forward by 12" would shave off 100# of tongue weight. Because my wheels are inside a wheel well, that's not an option.

I had my buddy come over and watch me drive the truck and trailer over some bumps at low speed. It seems the problem is a "too soft" suspension on the truck. The truck is rated for a max tongue weight of 350#, so I am running almost at the limit.

Mike...

P.S. Did you or could you convert your 10 minute exercise into a spreadsheet that I could plug different values into?

[R Keller]

Mike:

For what it's worth, I'll e-mail you the spreadsheet tonight...
With the spindle center at 41.75" from the rear of the trailer, it calculates a 263 lb. tongue weight for you. Now only 12 lbs. off!

One more question: when you use the bathroom scale, are you measuring the weight at the tongue jack or at the hitch?

I've heard some folks say you can get leaf spring (if that's what you have) "helpers" to stiffen the rear of the tow vehicle. Or stiffer coil springs?

Rik

[Shrug53]

Hey I would really like to see that spreadsheet too. My wife says if she can see how you figured things, she can do the same for me.

[R Keller]

Here are the numbers. Copy and paste this into a spreadsheet. The cells that have calculated values show the formula in brackets. You can recreate it easily:

1 total weight = 1,500 lbs.
2 tongue weight = 70 lbs.
3 body weight [=#1-#2] = 1,430 lbs.
4 body length = 120 inches
5 tongue distance from front of body = 48.00 inches
6 spindle center from rear = 41.75 inches
7 spindle center from front [=#4-#6] = 78.25 inches
8 weight per inch of body [=#3/#4] = 11.92 lbs.
9 body weight behind spindle center [=#8*#6] = 498 lbs.
10 body weight in front of spindle center [=#8*(#4-#6)] = 932 lbs.
11 body moment behind spindle center [=#9*(#6/2)] = 10,386 ft.-lbs.
12 body moment in front of spindle center [=#10*(#7/2)] = 36,483 ft.-lbs.
13 tongue moment in front of spindle center [#2*(#7+(#5/2))] = 7,158 ft.-lbs.
14 tongue weight [=#13+#12-#11)/(#7+#5)] = 263 lbs. 17.6%


Rik

[Shrug53]

Ok here is a question. I have been concerned with keeping the tongue weight down. What happens if it gets too light? Will it start lifting up the rear end of the car while driving?

[angib]

To save anyone having to create Rik's spreadsheet, I've stuck an Excel version (credited to Rik) on my web site at:

Tongue Weight Estimate

Andrew

[mikeschn]

Thanks Andrew and thanks Rik,

That's an awsome spreadsheet!!!

Mike...

[Shrug53]

Many thanks. You guys rock!