How to calculate tongue weight with a distribution hitch

[JayArr]

Hi All

Since I'm adding a generator to my tongue I've been thinking of how to measure or calculate the tongue weight. My first instinct was to either buy a tongue scale or do the 2x4-bathroom scale rig and measure the weight in the driveway. Then I thought about the Curt distribution hitch which pushes some of the weight of the tongue onto the front axle and now I have to wonder about adjusting for that.

The trailer is 4800 pounds, let's say tongue weight should be 10% of the trailer weight, 480lbs. Where is that measured? Do I measure the tongue without the vehicle and then let the hitch move some of that 480lbs of weight forward or do I increase the tongue weight so there is 480 pounds on the ball and let the hitch move some amount over that forward?

I'm concerned that if make the tongue 480lbs on a scale and the hitch moves, lets say 1/2 of it 240lbs, forward I'll then be light and unstable because the ball has only 240lbs.

Any engineers know how this works?

 

[Bugford]

I have a tongue scale, but have also weighed mine on CAT scales. Interesting point about some of that weight being distributed. I've wondered about that myself. But I would not try to calculate it off the whole trailer weight, because the tongue weight is what it is, regardless of whole trailer weight. You then can adjust the load so that it becomes 10-15 percent of whole trailer weight.

 

[Gary RV_Wizard]

You are overthinking this. You can get deep into the physics and engineering, but it makes more sense to stick with the simple and just measure the tongue weight with the trailer unhitched, e.g. the scale & 2x4 method. It doesn't make any real difference how much of the weight gets redistributed to the tow vehicle front axle vs the rear - the weight is still being carried and still applied through the hitch. And the trailer still "sees" that as tongue weight, i.e. weight that is NOT on the trailer axles. In other words, tongue weight is whatever is applied to the tow vehicle rather than the trailer axles/suspension.

 

[JayArr]

Thanks Gary/Bugford, sometimes I do overthink stuff.

tongue weight is whatever is applied to the tow vehicle rather than the trailer axles/suspension.

That's what I'll base my thinking on.

 

[Kirk]

Weight distribution works to distribute the tongue weight of a trailer up to the front axle of the tow vehicle so that it will sit more level and handle/brake better. That being said the systems do not "reduce" tongue weight or allow you to tow beyond the capacities of the vehicle.

How Towing Weight Distribution Systems Work

Most people who've driven a trailer have experienced at least a few heart-pounding moments when the trailer started to sway and they worried they might lose control of the vehicles. A weight distribution system can help.

auto.howstuffworks.com

 

[MoInEd]

You are overthinking this. You can get deep into the physics and engineering, but it makes more sense to stick with the simple and just measure the tongue weight with the trailer unhitched, e.g. the scale & 2x4 method. It doesn't make any real difference how much of the weight gets redistributed to the tow vehicle front axle vs the rear - the weight is still being carried and still applied through the hitch. And the trailer still "sees" that as tongue weight, i.e. weight that is NOT on the trailer axles. In other words, tongue weight is whatever is applied to the tow vehicle rather than the trailer axles/suspension.

A WDH acts to put upward force at the tongue and moves the weight toward front axle of the tow vehicle AND the axle of the trailer.
You can check this by scaling the weight at the axles of the tow vehiyas well as the trailer with and without WDH.

 

[Sooeycute]

Like the post above I use a tounge weight scale and weigh my loaded truck and trailer at a truck stop scale. I also redistribute weight in the trailer to balance the load. You certainly don't want to be light in the front end.

Sherline LM Trailer Tongue Weight Scale

 

[Rob&Deryl]

I take my rig to cat scale and position it so the the ball is over the gap between scales (cat scales are actually 4 scales end to end).

I then ask for a weight (about $12) then put down the jack and lift off of the ball and get another weight (sometimes they only charge $4 for the 2nd). You can now easily calculate tongue weight.

 

[BillB3857]

I have always used the measure method. I measure all 4 corners of the tow vehicle without the trailer. After hooking up, I adjust the chains on the hitch so that all four corners of the tow vehicle drop the same amount.

 

[steveblonde]

That genny is going to add 100% of its weight to your hitch, so if it weights 100lbs on your bathroom scale it will add 100 lbs to your cargo weight if your trailer has a GVWR of 4800lbs your pin weight will be closer to 570lbs (12%not 10% - 10% is not really realistic in most cases ) plus that 100lb? Genny 670lbs hitch weight

 

[grashley]

I believe BillB is referring to measuring HEIGHT, not weight.

Here is a great link on a few methods to measure tongue wt.
https://www.etrailer.com/faq-how-to-determine-trailer-tongue-weight.aspx

 

[Enyain]

I've been using the CAT scales my entire life, and it's the best choice. These scales are the most reliable and accurate ones. But, I have to agree with Gary RV_Wizard here. You are overthinking as this is a way easier task to do. Actually, I have heard someone saying there are some digital scales for weighing the RV tongues. Honestly, it seems to be like something fantastic. However, a couple of years ago, I thought that a smart bathroom scale was unreliable and unrealistic, so I might assume that scale wasn't that bad.

 

[JayArr]

I have since bought a tongue scale and weighed the weight (with the new genny) at 659 lbs which works out to 13.22% of total weight. Pretty much in the sweet spot.

 

[CharlesinGA]

I saw the above post, thought I'd add if anyone is interested.

Take the truck and trailer to the CAT scales, fully loaded, full tank, ready to go on a trip.

1)Weigh the rig with the weight bars disconnected, just unhook them before you pull on the scale.
2)Get the three weights (or four on the ticket) steer axle, drive axle, trailer axle, combined weight.
3)Pull off the scale and drop the trailer, then back on the scale and get the truck weight, steer and drive axles.
4)subtract the weight of the unhitched truck from the combined weight of the rig. This gives you the trailer weight.
5)subtract the trailer axle weight from the total trailer weight you just figured.
6)what remains is the tongue weight.

Charles

 

[steveblonde]

I have since bought a tongue scale and weighed the weight (with the new genny) at 659 lbs which works out to 13.22% of total weight. Pretty much in the sweet spot.

how much does the genny weight full of fuel?

 

[JayArr]

I don't think I weighed it by itself. There is no fuel anymore, it's been converted to propane so I removed the gas tank. My guess would be about 100lbs, the frame and box may be another 25?