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Old 09-11-2012, 07:53 PM   #575
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Hi,
Did you do axle weights on your car? Was yours the Honda Pilot?

I'll be working on this later this evening. Probably the one sent to me is the correct one. It does yield a little less than half of mine.

Quote:
Originally Posted by Bruce H. View Post
Yes, the table re the Honda Pilot and the Lance 1575 trailer is mine. Two trips to the CAT scales at the Flying J west of Lodi. Multiple weighs each time--luckily, each reweigh (up to 4) is only $1.

Very much looking forward to learning about your new method. I never had a WDH before this one, so a lot of my emperical research was just an effort to understand weight distribution in general as well as the Andersen hitch.

Bruce
Thanks Bruce. I'm printing out all your information. I am glad you are interested in the calculations. Its fascinating to be able to compute these things and then see how it bears out in your measured weights.

I think it will be fun to know what to expect for any particular TV/TT by just doing some simple math.
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Old 09-11-2012, 08:11 PM   #576
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Quote:
Originally Posted by mstephens View Post
Hi,
Did you do axle weights on your car? Was yours the Honda Pilot?

I'll be working on this later this evening. Probably the one sent to me is the correct one. It does yield a little less than half of mine.

Quote:
Originally Posted by Bruce H. View Post
Yes, the table re the Honda Pilot and the Lance 1575 trailer is mine. Two trips to the CAT scales at the Flying J west of Lodi. Multiple weighs each time--luckily, each reweigh (up to 4) is only $1.

Very much looking forward to learning about your new method. I never had a WDH before this one, so a lot of my emperical research was just an effort to understand weight distribution in general as well as the Andersen hitch.

Bruce
Bruce,

Check your PM
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Old 09-11-2012, 08:47 PM   #577
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I will still caution about using math to calculate how you adjust a hitch on a TV and AS.

It can give you a GENERAL IDEA of where you should be, and maybe for some it's fun to play with the numbers. But only in real life use can it be set right.

There are still lots of variables in real life that a set of calculations won't take into consideration.

Plenty of Engineers over the years have sat in an office and made calculations only to have bridges collapse, rockets fall from the sky, and cars blow up.

Think about the stuff and people in your TV. Stuff on the tongue of the AS (batteries, propane tanks) and all the stuff in your trailer. My water tank is right up front (40 gals) if it is full thats another 332# close to the tongue of the AS. All these things are real world weights and need to be considered when making adjustments.. Adjustments that can only be made when you are hooked up and working with the hitch itself.

The calculations where done at Andersen by Engineers working with the hitch. I trust them, and I trust us to fine tune the thing here and hope they are reading and listening.
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Old 09-11-2012, 10:59 PM   #578
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Quote:
Originally Posted by Bruce H. View Post

The distance from the center of the front wheels to the center of the hitch ball is 155".
Bruce,
What is the distance from TT axle to ball center?
Thanks.
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Old 09-11-2012, 11:39 PM   #579
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I will measure the distance from TT axle to ball center tomorrow morning. The TT is stored at a boat and rv storage facility about 10 miles from home.

Bruce
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Old 09-12-2012, 11:52 AM   #580
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Quote:
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I will measure the distance from TT axle to ball center tomorrow morning. The TT is stored at a boat and rv storage facility about 10 miles from home.

Bruce
It is 164".
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Old 09-12-2012, 12:05 PM   #581
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Improved Calculation

I have attached the improved calculation of chain strain thanks to Ron Gratz, who was kind enough to point out my original error, AND supply the correction. I therefore dubbed this drawing the "Ron Gratz Method."

I think it is fascinating to see exactly how each variable affects the final result. It is easy to see how TV wheelbase and overhang affect the result, and the TT ball to axle dimension. The math only requires some basic arithmetic, so anyone can do it.

No, this is NOT instructions on "how to setup your hitch." You get those instructions from the hitch manufacturer. This is merely an explanation of forces to provide an understanding of how they will change depending on your TV/TT dimensions and how much weight you expect to transfer.

The calculations here take the ball center to chain plate dimension as "6.5" which was reported by Bruce. This is a crucial dimension because of it's effect on leverage. Since I didn't have Bruce's TT wheelbase, I just plugged in a sample of 150".

EXPLANATION
Any downward force on the TV front axle must be countered by an upward force on the TT axle in order to have equilibrium. Using the TV rear axle as a fulcrum (noted in drawing), the ratio of the two distances determines how much upward force is needed at the TT axle to counter the downward force at the TV front axle. In the EXAMPLE a 200# weight shift to the front of the TV requires a 121# upward force at the TT rear axle.

Once the upward force is known - 121# in this case - the remaining calculation computes the amount of torque must be applied to the ball/coupler to equal the 121# upward force. What is crucial here is the ratio of the long lever to the short one. The long one is the ball to TT axle, and the short one is the ball to chain plate. As the ratio increase, the force required to torque the ball gets higher.

By looking at the formulas, you can see that strain on the chains will increase when: The weight to be shifted increases, or the TV wheelbase increases, or when the overhang decreases, or when the TT ball to axle decreases. These are all linear equations, so the effects are proportional on each variable. A 10% increase in TV wheelbase creates a 10% increase in strain. Likewise then, a 20% increase in weight shift will create a 20% increase in strain, and so on.

This is just for information. Some people, like me, enjoy knowing "how things work." This is not an instruction on how to setup your hitch, which should be done by using the manufacturer's instructions.
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Old 09-12-2012, 12:09 PM   #582
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Bruce--
Ok, 164". I'll see if I can correlate to your weight and scale measurements.
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Old 09-12-2012, 01:07 PM   #583
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I sent this to Bruce H yesterday and have revised to it based on his number of 164" on the length of the trailer ball to axle.

This is my take on what is happening. I am an engineer but haven't spent much time on the problem so don't hold it against me. This explaination takes a little time so bear with me.

I think you have to calculate how much moment is applied to the hitch reciever to remove the required weight of on the rear axle then this weight is distributed to the front axle and trailer axle, inverserly proportional to their distance from the rear axle of the tow vehicle (by that I mean the closer to the rear axle the axle under consideration is the more weight it gets in the weight transfer) . Or put another way the WD hitch removes weight from the rear axle based on the moment generated and the weight removed is transferred to the trailer axle(s) and front TV axle due to the effects of weight transfer from raising the back of vehicle. This latter weight transfer is similiar to weight jacking on a race car.

I found this first formula in a book to calculate the weight added to the rear axle of a tow vehicle by a trailer. I went thru it with your numbers to check it.

Rear axle weight added = (dist ball to rear axle/wheel base x TW) + TW

I believe you said the Honda was 155" ball to front axle and Honda says wheel base is 106.3", also a post said TW was 400 lb.

R.A. W. added = (48.7/106.3 x 400) + 400 = 583lb
Your chart says 600 lb so this checks.

Now to calculate the chain forces and axle loads.

Now your chart says you removed 260 lb from rear axle with 3/16 compression of the bushing. The moment at the ball to do this is 260 lb x 48.7 inches = 12,662 in-lb.

This moment is generated by the pull on the chains x the ball to pivot distance which you stated is 6.5 inches.

Force on 2 chains = 12,662 in-lb/6.5 inches = 1948 pounds.

1948 total/2 chains = 974 lb pull per chain

You measured 970 lb on the Sherline if I remember correctly, so that checks.

Now the front axle and trailer axle have to get the 260 lb removed from the rear axle.

I don't have the dimensions of the trailer but your data says there were 180 added to the Honda front and a post said there were 76 added to the trailer. 180 + 76 = 256 or pretty darned close to the 260 removed from the rear.
(Todays addition)
Recently you posted ball to trailer axle distance at 164" so calculate the weight transfer as follows. Remember the transfer is inverse to the distance to the axle when reading these numbers.

Weight added to trailer axle = (W.B of TV/ total distance TV front to trailer axle) x weight tranfered from rear axle = (106.3/106.3+48.7+164) x 260 lbs = 86.7 lb.

I think your post said trailer axle went from 3044 to 3120 = 76 lb

By the same token the weight added to the front axle is (TV Rear axle to trailer axle/total distance front axle to trailer axle) x weight remove from rear axle = ((164+48.7)/106.3+48.7+164) x 260 = 173 lb

Your table shows 180 lbs.

Anyway that is my take.
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Old 09-12-2012, 01:49 PM   #584
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Crisen,

WOW! Like I said in my private response to you last night, I am amazed at the congruence between your predicted weight distribution and the actual weight measurements.

Thank you so much for your research.

Bruce
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Old 09-12-2012, 02:19 PM   #585
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Quote:
Originally Posted by mstephens View Post
Improved Calculation
EXPLANATION
Any downward force on the TV front axle must be countered by an upward force on the TT axle in order to have equilibrium. Using the TV rear axle as a fulcrum (noted in drawing), the ratio of the two distances determines how much upward force is needed at the TT axle to counter the downward force at the TV front axle. In the EXAMPLE a 200# weight shift to the front of the TV requires a 121# upward force at the TT rear axle.
I hope to need a WD Hitch in about 8 months (my new deadline for finishing my trailer). I have appreciated everyone's posts, AND the original "poster", AND want to officially thank everyone for doing so (AND the Mods for keeping it open). Short of some unforeseen event, I will likely purchase this Hitch, seems like it will be a good match for my needs.

Disclaimer: I'm not an engineer, but sometimes pretend to be. Is there a way to manipulate the formula so I can use my "likely" Tongue Weight to find out how much strain will be in the Chain in order to equalize the diagram - seems like it would be possible since I know all the other variables/dimensions/weights . . . just don't know the TV axle weights. And I would be wanting to do this for kicks - to play w/the free body diagram - and nothing else.

Thanks again,
MarkR
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Old 09-12-2012, 02:38 PM   #586
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Quote:
Originally Posted by MarkR View Post
Disclaimer: I'm not an engineer, but sometimes pretend to be. Is there a way to manipulate the formula so I can use my "likely" Tongue Weight to find out how much strain will be in the Chain in order to equalize the diagram - seems like it would be possible since I know all the other variables/dimensions/weights . . . just don't know the TV axle weights. And I would be wanting to do this for kicks - to play w/the free body diagram - and nothing else.

Thanks again,
MarkR
Mark,
You will need to know how much weight you want to transfer to the front wheels, before you can calculate the chain strain. It is the transferring which requires force through the chain and hitch. Just knowing the TW isn't enough.

Looking at Bruce's Figures
I came up with a slightly higher chain strain.

W = 180#
Wheel Base = 106"
Overhang = 49"
Hitch to TT axle = 164"
Ball to chain plate = 6.5"

Then...

F = 180 x 106/213=89
S= 89 x (164/6.5)/2= 1,122 lbs. Clearly higher than the gauge measure.
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Old 09-12-2012, 04:10 PM   #587
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Quote:
Originally Posted by mstephens View Post
Improved Calculation

EXPLANATION
Any downward force on the TV front axle must be countered by an upward force on the TT axle in order to have equilibrium. Using the TV rear axle as a fulcrum (noted in drawing), the ratio of the two distances determines how much upward force is needed at the TT axle to counter the downward force at the TV front axle. In the EXAMPLE a 200# weight shift to the front of the TV requires a 121# upward force at the TT rear axle.
A WD hitch adds weight to the TV front axle and the TT axles so wouldn't it be a downward force on both?
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Old 09-12-2012, 04:27 PM   #588
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Gosh, a bumblebee can fly after all. Big grin.

I believe one other factor may come into the calculations. If you have a drop shank setup, I think the effective distance (I believe the calculations used 6.5 inches) is different depending on the bottom plate to hitch receiver distance, not the ball center. Thus, if you were pulling (twisting) from a longer drop you effectively have more lifting on the TV frame.

But, sitting here on the top of Marias pass, highway 2, just below Glacier National Park, towing with my Andersen, it all seems kinda academic. The hitch does work well. BTW, some white lube or grease on the frame tube ends does seem to help with the chain wear, but time will tell with that. You guys figure out how to solve that issue next please.

I will enjoy towing and camping while it is all worked out.
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