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Open Roads Forum  >  Towing

 > Tongue Weights weighed

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Grit dog

Black Diamond, WA

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Posted: 05/16/21 11:25am Link  |  Quote  |  Print  |  Notify Moderator

^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...)


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blt2ski

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Posted: 05/16/21 01:12pm Link  |  Quote  |  Print  |  Notify Moderator

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


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ajriding

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Posted: 05/16/21 05:42pm Link  |  Quote  |  Print  |  Notify Moderator

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

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Posted: 05/17/21 11:48am Link  |  Quote  |  Print  |  Notify Moderator

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

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Posted: 05/18/21 07:38am Link  |  Quote  |  Print  |  Notify Moderator

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.

JRscooby

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Posted: 05/18/21 08:34am Link  |  Quote  |  Print  |  Notify Moderator

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.

Grit dog

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Posted: 05/18/21 09:29am Link  |  Quote  |  Print  |  Notify Moderator

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.

blt2ski

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Posted: 05/18/21 11:27am Link  |  Quote  |  Print  |  Notify Moderator

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

BenK

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Posted: 05/18/21 11:39am Link  |  Quote  |  Print  |  Notify Moderator

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...

[image]
[image]Click For Full-Size Image.


-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...

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