Tongue Weights weighed

[ajriding]

I finally weighed.
Someone said something about having no WD hitch and the rear axle as a fulcrum unweighting the front axle, so I did math. I weighed my small trailer only so far.

I weighed about 350 lbs tongue weight. Not a lot.
the distance from rear axle to ball.
the distance from front axle to rear axle.

I divided the wheel base by the distance from rear axle to ball and got about 2.8 then divided that into the 350 lbs to get a number that I think represents the upward lift on the front axle.

So, 350 lbs pushing down on the ball will push up the front axle about 125 lbs (unweight the front end by 125 lbs).
This does not seem like much.
If you made a teeter-totter with similar distances and put 350 on the short end and 125 on the other then it would balance equally.

Add that I will have a small genny hanging from the front receiver hitch (50 lbs) cantilevered out which will multiply its weight slightly too, but I do not always have it.

So, with no WDH I am unloading the front end by 125 lbs at worst. Hit some bumps and I still do not think it will matter much.

Figure the motor and trans are at the front, so Im wondering how much weight will it take to create a situation where steering and unweighted front axle makes a safety concern.

I added airbags so that I can ditch the WDH as tired of removing WD bars for the last few miles of a trip up messy dirt roads, so I ran the numbers...
Im late for work now, so sorry if I explained it not-the-best...

Anyone else run similar numbers?

[BenK]

Basic laws of physics that any farm kid learned from a very young age...

Just go out and weigh the dang thing...fully loaded, ready to go RV'ing and do so to each axle with and without the WD Hitch system tensioned...


Click For Full-Size Image.

[blt2ski]

My example of one truck, a 96 K3500 SW crew can with stock 6500 lb tear springs, put my equipment trailer with 1500-1600 lbs of hitch wt loses 300-400 lbs off the FA. I changed out to 8500 lb springs. I then only list 200&300 lbs off the fa. The heavier springs kept the truck more level. Dispite having the same HW, wheel base, rear over hang to ball, I lost less wieght.
Reality, rear overhang, divided by wheelbase equal percentage wieght you will lose off the front axle compared to hitch wieght is not a good formula.
As my figures above show, lighter spring pack loses upwards of 25%, stronger only 20%. I suppose I could throw in my Navistar with a 16500 rear spring pack, I lose 60-100 lbs off the fa. Your formula says I should lose 400+ lbs.
Reality, stronger spring pack, does what air bags can do too. Level the rear instead of being tail down, asy 6400 lb springs were, 8500, I was level.
If you lose an inch of tail high per 100lbs of HW, first inch you lose maybe 10lb from FA. 2nd inch is an addition 20lbs for 30 total. 3rd inch lose 40lbs for 70 of 300lbs. The % lost goes up as you add hitch wt. If you have stiffer springs, airbags, you can make the first inch 200lbs of HW. 2nd inch 400lbs. Losing the same wight off the fa ad the lighter springs.
Spring capacity, spring drop needs to get factored into the rear overhang divided by wheel base. If you don't, you will not know how much you need to correct the loss to fa. Via bags, more spring, wdh etc.
As Grit points out too, your formula does not include the dynamic part of the rear end of the truck going down. Only assumes you are level, vs initially tail high, to tail low depending upon howuch hitch wieght you have added.

Marty

[Grit_dog]

To put it more simply (maybe?). We generally view the scenario as a statics calculation, simple moment diagram.
At some point, one would think the ratings were derived from taking dynamic loading scenarios into consideration, and they have been. To what extent? Who knows.
But the angle of the vehicle does come into play. Not hugely, as a couple degree difference in angle, still has only slightly less vertical components and a very small horizontal component.

Now add in dynamic loading, hitting bumps and dips at speed, how much does the suspension absorb and what are those stresses on the suspension vs how much load is momentarily added or taken away...
None of us know that, but the fact of the matter remains, there is a practical limit and dissecting that seems to be a popular past time here. Which is contrary to the entire rest of my almost 49 years on this planet, 33 of which have been driving and alot of towing.

[JRscooby]

ajriding wrote:


Sorry, Biscu2ski, I dont follow, info missing. You keep mentioning sag like it is magic and going to throw weight all over and make it go away. I dont know how this is relevant, do you?
The point of bags is to keep vehicle level, so talking about how sag will minutely alter weights slightly is not relevant. Bagged trucks ride level! WDH trucks generally ride level, so we are talking about level.
Put in your formula a 900 lbs motor way at the front of a long truck and see how much hitch weight it takes to lift that motor alone, not to mention other components. I think you will see quick we are talking NOT about front end weight, but, rather, hitch weight and weight limits of the components of the tow vehicle, which is usually wheels/tires.
The only number that seems to matter is what the truck can carry (payload) at the rear.

WDH, and air bags might level the TV, but I don't think they act the same. Tongue on ball, force rear down, the front comes up. A WDH will level the TV by forcing the front back down.
OTOH, air bags will level by lifting the rear.
With no other changes, lower ride height will handle better.

[ajriding]

blt2ski wrote:
Yes the pivot point is rear axle.
As I noted, if you can keep the rear end high vs level vs tail down, the amount of weight removed from the fa will be less vs more as a percentage of hitch weight added....
Marty

Sorry, Biscu2ski, I dont follow, info missing. You keep mentioning sag like it is magic and going to throw weight all over and make it go away. I dont know how this is relevant, do you?
The point of bags is to keep vehicle level, so talking about how sag will minutely alter weights slightly is not relevant. Bagged trucks ride level! WDH trucks generally ride level, so we are talking about level.
Put in your formula a 900 lbs motor way at the front of a long truck and see how much hitch weight it takes to lift that motor alone, not to mention other components. I think you will see quick we are talking NOT about front end weight, but, rather, hitch weight and weight limits of the components of the tow vehicle, which is usually wheels/tires.
The only number that seems to matter is what the truck can carry (payload) at the rear.

[blt2ski]

Yes the pivot point is rear axle.
As I noted, if you can keep the rear end high vs level vs tail down, the amount of weight removed from the fa will be less vs more as a percentage of hitch weight added.
It's why I only list 200-300 lbs off the fa with 8500 lb springs vs 300-400 with the same truck with 1500 lbs of hitch weight. Same truck with 600-700 lbs of he, only list 60-100 lbs. Using your formula, I should have lost way more off the fa than I have with the 600-700 lbs of hw.
The amount lost is not the same percentage for every lb added. It's 1-5 % for the first 100 lbs depending upon rear springs, wb, rear over hang etc. 900-1000 lbs will be a higher %.possibly more taken off the front and added to the rear than HW added. Make it 1500-2000 lbs of HW added, you had better have a large capacity rear spring rating, or you could be adding 2 lbs of fa wt per lb of HW added! It's not a single 1 lb of fa for 3 lbs of HW as you and others say it is.
This is my experience from 40 years of towing multiples of trailers, with different trucks.

Marty

[ajriding]

umm, no. Weight on the ball does unweight the front no matter what. That you can mitigate sag does not erase physics.
You might can nudge the numbers a few pounds one way or the other depending on slight changes to the angle (amount of sag) but nothing except a WDH will change that the RA is the fulcrum.
The 3 lb ball is unweighting the front by a pound!
or so
Everything affects everything. This is not the point.

[blt2ski]

Air bags, add-a-leafs, new stronger stiffer spring pack. ALL do the same thing. Keep the added hitch weight on the RA UNTIL the RA goes rear low. Then you start losing more wt off the front vs when tail high to level.

Marty

[Grit_dog]

^Bingo!
You just de-bunked a good portion of the RV crowd “gotta have a wdh no matter what” myth!!
Now slap them airbags on and sell your wdh to some other sucker. (I mean someone who actually “needs” it...)

[ajriding]

No, driving the truck, no matter how much weight is or is not back there, feels the same. I imagine it would take an extreme situation for the front end to unweight due to a heavy tongue that would have to be bouncing a lot somehow, and cause steering issues. The steering will only feel different if geometries change.
I did ride in a one-ton tow truck towing my class-c (460 motor) and that front end did come off the ground a few times, it felt odd, but that was a 13,000lb vehicle being towed with almost all the vehicle weight in front of the rear axle....

The point is that in my head I am always disagreeing with the people that poopo air bags who say you cannot increase the towing tongue capacity. Well, no, of course not, the tires, wheels, leaf springs and frame always have the same limits, but the weak link has always been the springs. You can increase the spring capacity easily with bags and at the same time stay within the limits of the other components.
Air bags do increase tongue weight (*edit*, tongue weight capacity*) to a limit, of course, bc it removes the sag that is created within the weight limits of the vehicle.

I can drop more weight on my ball safely and drive level safely with bags, where without bags the rear would be sagging so much or riding on the bump-stops that it would be undriveable.
I can stay within the weight limits on all other components safely doing this.

A WDH only helps so much and all the force is transferred to/through the trailer tongue. I think my little rig is light enough that the springs could support having the rear truck axle off the ground, but on a bigger truck with bigger trailer weight something would bend or break if one accidentally drove through a deep dip in the road, and those are out there.

WDH's are springs, smoother springs than leaf springs, and do not have shock absorbers so they do provide a smoother ride for the small bumps, and even big bumps. They do make the rig ride smoother no matter trailer or tongue weight and reduce porpoising by a lot.
The downside is they are not meant for extreme angles where the truck points up and the trailer points down.

So, if you stay within the weight limit of the truck's carrying ability, and do not have so much weight that the front end is unweighted beyond a safe measure then bags are fine. I will poopo anyone who continues to post that bags are a bad band-ade, sorry. I have driven 10's of thousands of miles with bags and also WDHs.

Girtdog, no, I think you are only half way there. Lots still to learn it seems as reality demostrates.

[Devo_the_dog]

ajriding wrote:
I finally weighed.
Someone said something about having no WD hitch and the rear axle as a fulcrum unweighting the front axle, so I did math. I weighed my small trailer only so far.

I weighed about 350 lbs tongue weight. Not a lot.

Anyone else run similar numbers?

The tongue weight on my trailer, when loaded, is always about 1350 lbs. I have a scale and that's what I want it to be when towing.

So, it's similar.

Except for the 1.

[Grit_dog]

350lb tongue weight as you pointed out may need some help with a compact truck.
350lb will not make the truck unsafe to drive though with respect to weight off the front axle although it may be noticeable.
These are the questions you can answer by yourself much better though. Have you not driven it to see how it feels?

[Grit_dog]

So maybe I confused what truck you have.
Yes, there is an unnecessary and weird stigma around wdhs / sway control and RVers.
Yes it’s necessary in some scenarios but use your noggin and look At ALL the other trucks and trailers you see out there.
Then you’ll understand there is a weird brain washing about wdhs in the RV community.

[ajriding]

I am really wondering more for the sake that I hear on here so often people demand we run a WDH. One big reason for their demand is the "unweighting of the front axle". I ran quick numbers and do not see it for a small or medium trailer, even for 600 lbs, which might only translate to 200-250 lbs unweighted off the front.
The bigger the truck the bigger and heavier the motor and trans too.

My current truck is a Frontier with 4WD, not to be confused with WD.
So the number are small compared to my 3/4 ton truck, but this "small" amt of weight does sag the rear quite a bit. I was surprised that the tongue was only 350lbs given the sag. Conclusion, I do need either WDH or bags. Sag cannot be. Running the WDH makes the truck drive and ride a lot better for sure.

I might weigh again just to double check everything but dont expect numbers to be much different if at all. I was surprised at the low weight bc everything is in front of the axle - AC, batteries, electrical, solar, water tanks, sink, kitchen, fridge, propane... The couch and cabinet do straddle the axle and I keep the spare at the back, but thats about it.

So, there ya go. If you ever thought 350 did not warrant a WDH now you know it does on some trucks at least. I even used it on the big 3/4 ton long bed with same trailer loaded more evenly. It just rode better with WDH. Makes me think I gotta have the weight wrong.....

Also, affect and effect is worth researching.