2air' - Thanks for your input (always appreciated)!
I'd like to elevate user info by doing that test...
But I'll have a bit more on my mind when picking up my first Airstream...
Inspection, Walk-through, Orientation, paper work, and the drive home.
So I'd like the dealer to correctly install the right Equal-i-zer the first time around!
All other Equal-i-zer users: Let's elevate our knowledge base:
If you have been reading this thread and have an Equal-i-zer WD Hitch…
Please take a moment and go to "Community Polls" here: http://www.airforums.com/forums/f232/what-size-equal-i-zer-hitch-do-you-use-28204.html
And add to our knowledge base under thread, "What size Equal-i-zer Hitch Do You Use?"
The size of your Equal-i-zer Hitch (600# or 1000#)
Your tow vehicle model and size
Your trailer size… and why you like your hitch.
Well, I went with the 1000 lb. bars and don’t regret it.
Equal-I-zer weight distribution hitch has worked fine for me.
But I do want to acknowledge Nick for starting this fine thread. Thanks Nick – You have elevated our knowledge and understanding of load distribution hitches.
Reads like a college professor’s discourse and likewise should be required reading for newbies!
Thank you for elevating the quality of the forums here by this and your other 1000+ posts!
Yes, that post is amazing (thanks!!!!), and the thread is the kind of quality one hopes to find in an Internet search where the details of safety are being examined.
I've been asking myself a few more questions about load distribution. I regularly read that the ideal distribution of "tongue weight" is an equal one third to each of the TV (tow vehicle) axles and to the trailer axle system. I have never seen any justification for this, either by practical experiment or by engineering calculation. Why should it be ideal to increase the "weight" of my trailer by the same amount as each axle of the TV? Why should I attempt to load the front axle of my truck by the same amount as the rear axle, when the truck is designed to take heavy and varying loads on the rear axle, and a moderate but fairly constant load on the front axle? If I go to a quarry for a load of stone, I center the weight over the rear axle, and just ensure that the front axle is not lifted. I decided to examine this issue with the aid of the equations listed at post #1 of this thread.
From equation 1, C, the corrective force required to load down the front axle of the TV is given by C= (T*H)/W , where T is the tongue weight, H is the rear overhang of the TV, and W is the wheelbase of the TV. From equation 10, E, the final extra load on the TV rear axle, with chains tightened, is given by E=(T*L)/(H+L) , where L is the distance from the hitch to the center of the trailer axle system.
For these two loads to be equal, C = E, hence:
(T*H)/W = (T*L)/(H+L) , and this equation transforms to the quadratic:
(H^2) + (H*L) - (L*W) = 0 Equation 11, the condition for equal loading of the TV axles.
Given that W , the truck wheelbase, and L, the axle distance of the trailer, are fixed, what rear overhang will produce the desired equal loading? Putting my values of L = 170, and W = 160 into equation 11 and solving for H indicates that a rear overhang of 100 inches would be required, rather than the current 60. This huge overhang would be ridiculous and would dangerously increase trailer sway. I therefore conclude that, for my truck and trailer, equal TV axle loading is neither feasible nor desireable.
Those interested in playing with numbers may like to discover what TV wheelbase would be required for equal loading with my present rear overhang and current trailer. The answer is a wheelbase of 81 inches, instead of the current 160. Again, quite absurd. For more amusement, what length of trailer could I tow which would give equal loading, given my current truck? The answer is 36 inches from hitch to axle. Even more absurd.
To calculate the load on the trailer axle when the overhang is increased to 100 inches to equalize the TV axle loadings:
A= (T*H)/(H+L) , equation 4, giving the load transferred to the trailer axles
For my theoretical truck with the huge rear overhang of 100 inches, the TV axles are loaded with 500 pounds each, and the trailer axles by 300 pounds.
I conclude from all this that equal loading of the axles is neither possible nor desireable with my truck, and this is confirmed in practice. Others may wish to try out the numbers for their own rigs.
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
Last edited by CanoeStream; 11-06-2007 at 12:39 PM..
Reason: Add redirect to Nick's Excel spreadsheet
I've been asking myself a few more questions about load distribution. I regularly read that the ideal distribution of "tongue weight" is an equal one third to each of the TV (tow vehicle) axles and to the trailer axle system. I have never seen any justification for this, either by practical experiment or by engineering calculation...
hi nick i agree.
no doubt this is another dictum without complete proof...
perhaps it comes from the days of towing with an impala or country squire...
but most of the towing guides provided by the auto companies and hitch makers STILL include this info...
my goal was to get the tv axles close to 50/50 when hitched and distributed,
and restore steer axle mass to at LEAST the original unhitched number.
with the diesel up front, the super duty was nose heavy un hitched.
so for me load redistribution isn't the same as simply transferring equal amounts to the 3 axle regions...
i've since tried allowing the drive axle to carry a greater load than the steer axle (44f/56r) while towing.
the ONE negative with this arrangement was 4/32nds GREATER tire wear on the drive axle between tire rotations (5kmiles)
cheers
2air'
__________________ all of the true things that i am about to tell you are shameless lies. l.b.johnson
we are here on earth to fart around. don't let anybody tell you any different. k.v.
Impressive analysis folks.
My father was a truck driver. I spent a lot of time loading and unloading trucks. The way a person can load a trailer is amazing, distributing weight front to back and side to side. Just shifting weight can change everything to do with handling.
Also, when you consider what tire pressure can do to handling it is almost beyond words.
I like to look at a tow vehicle/trailer loaded for travel on a level surface. Level is best. Keep it simple.
R
__________________
Robert
"Talk is cheap, Airstreams are expensive," Wally Byam.
Buy in haste, repent at leisure; been there, done that.
"You cannot rush quality," fastRob.
A good FF/RR weight bias would seem to be ideal for the TV.
Solo, mine is at 58%FF, not good. Bringing that down to 52-53% would seem to be acceptable no matter the actual rear weight (respectful of GAWR). Bringing it past 50% starts to raise questions in my mind.
Let's remember that the old cars were also nose heavy with a medium or big block engine. My recently departed 4,780# 1971 Chrysler was 56%/44% FF/RR after pains to get the suspension to stock or better on a mildly used family car; a number that was typical. I've seen this approximate bias also on a 5,650# 130" wheelbase Imperial.
In sense, why bother with W/D if the rear "can handle that and more"?
...most of these tow vehicles understeer in normal driving...
2air'
Whoo hoo! the thought of oversteer while towing gives me the willies
and I'm the guy that made it hard to pass on the race track by spending more time sideways, thus using more track width
I use WD when-
1) the back squats
2) the f/r exceeds 50% rear
or 3) the rear approaches GVWR
Things have changed since the Estate Wagon TV
Top 10 thread Nick!
__________________ Hi Ho Silver RV!
Vernon, Sarah, Mac the Border Collie and- 'Epiphany' the 29' Airstream
Good discussion - but Nick has forced unpleasant memories of all-night sessions doing my Statics and Strength of Materials homework at the Univ. of Florida. In my own case I use 1,000 lb bars - no sway control - with 900 lbs on the hitch - measured with a Sherline scale. Unloaded my truck's front axle weighs 4,400 lbs and the rear axle weighs 3,960 lbs (---notwithstanding a fixed load in the bed.) Loaded, the front axle unloads 200 lbs to a net 4,200 lbs, the rear axle goes to 4,900 lbs, and the trailer axle reads 7,400 lbs. See the rig configuration below. I'm real happy with this setup but recently I was made aware of a factor that I had previously overlooked on my OEM GM hitch. i.e. - the hitch rating is reduced to 7,500 lbs capacity in a dead-load configuration, vs 12,000 lbs with equalizers. You have to look at the placard on the hitch to find this figure since the GM manual only addresses sway control with reference to the 7,500 lb figure. My primary use of the equalizers is to provide a cushion between the TV and the trailer - which they do very nicely. The 900 lb hitch load is within the dead load capacity of the hitch (---which, of course, goes to 1,500 lbs with an equalizer hitch - a change that would appear to be reasonable ---) and well within the rear axle capacity of the truck. What bothers me is that, by the simple incorporation of the very lightly loaded equalizer bars, the hitch towing capacity goes from 7,500 lbs to 12,000 lbs! With full understanding of the basic moment and torsion factors involved, what gives lightly loaded equalizer bars the ability to increase my towing capacity by 4,500 lbs??? I know that others have experienced failures with the OEM GM hitch and now, I'm personally beginning to question its design! My thinking is that the hitch should be capable of handling 12,000 lbs - with or without load equalization - subject only to the dead load restrictions.
What bothers me is that, by the simple incorporation of the very lightly loaded equalizer bars, the hitch towing capacity goes from 7,500 lbs to 12,000 lbs! With full understanding of the basic moment and torsion factors involved, what gives lightly loaded equalizer bars the ability to increase my towing capacity by 4,500 lbs???
Cracker, I agree that this seems strange, so I examined this point at post #29 on page 3 of this thread. I investigated the issue with the equations, and proved to myself that the capacity of the hitch can indeed double when WD bars are used.
Nick.
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
The forum administrator has kindly enabled .xls files, so the calculator should now be freely available to all who wish to download it. Just change the input values in the top cells to your own, and the outputs will be re-calculated. Have fun!
Nick.
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
I've used the Crowhurst calculator for a couple of years and find it very useful. I'll add a little enhancement you might enjoy, which lets you calculate the vehicle balance front and rear, both with and without the spring bars hooked up.
If you are willing to spend some time and take a few measurements, it will even estimate the change in loads for driver and passenger, cargo, and fuel.
The first page is the Crowhurst calculations (in rough formatting), and the second page is the axle load calculator. . . .
. . . . sorry, I am over my download limit. If you want to see it, send me an PM with your email address and I will send it to you.
__________________
Non-contributing deadbeat.
Last edited by CanoeStream; 11-06-2007 at 09:16 PM..
Reason: markdoane's spreadsheet is attached to Post #72.
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