Question How to measure the tongue weight of a trailer when it's attached to a truck while using a weight distribution hitch?

[Boondoggle]

If you've never weighed your setup using a CAT SCALE, it's pretty interesting (and easy). So, I ran my truck through a CAT SCALE twice, once with my trailer attached using its weight distribution hitch, and once with just the truck by itself. Now, if I deduct the weight on the rear axle of the truck by itself from the weight on the truck's rear axle when the trailer was attached, does that give the tongue weight of the trailer or just the difference on the rear axle? If it's just the difference on the rear axle, does anyone know how to determine the tongue weight of a trailer when it's attached to a truck using a weight distribution hitch?

Also, is there a general rule of thumb for what percentage say do weight distribution hitches transfer a trailer's tongue weight to the front axle of a truck (given what tension the weight distribution hitch is set at of course)?

Thanks, Jim

 

[Gizmo]

You have to take the weight of both the front and back axles of the truck and subtract that. Some of the tongue weight is on both axles.

 

[Boondoggle]

Gizmo, subtract the weight of both the front and rear axles of the truck from what? I'm expecting a tongue weight of around 600 lbs, But if I subtract what you say from the combination weight, obviously I get the total weight of the trailer not the tongue weight, so I must be missing something. If you're familiar with Excel, I've attached my worksheet below, maybe you can see what I'm doing wrong from that.

 

[Gizmo]

Add the front and rear axles of the truck add together with the trailer and WD attached.
Minus
Add the truck front and rear axles of the truck added together without the RV attached.
Equals
The Tongue Weight being applied to the truck.

 

[Gizmo]

So if I read you spreadsheet right when you add together the front and rear axles with trailer attached equals 6420. The unload weight of the front and rear axles are 5480 which gives you a 940 tongue weight. You added weight to the rear axle but remove weight from the front axle.


Your profile says you have a Lux 35 GRS which in 5th wheel and not a trailer.

 

[Boondoggle]

Add the front and rear axles of the truck add together with the trailer and WD attached.
Minus
Add the truck front and rear axles of the truck added together without the RV attached.
Equals
The Tongue Weight being applied to the truck.

Well first, thanks for your help and patience and that's what I first thought too.

But I'm still not following you. I think what you're saying is to first add the weight of the truck and trailer together (with the weight distribution bars attached), then subtract out the weight of the truck.
But what we get is the weight of the trailer not the tongue weight.
line 1 12,500 lbs. weight of the truck plus trailer
- line 2 5,540 lbs. weight of the truck without trailer
= line 3 6,080 lbs. which is the weight of the trailer again, not the tongue weight.
What am I missing?

Now, I measured the tongue weight without the truck attached using a scale designed for measuring tongue weight and it came to right around 1,000 lbs. But since the trailer can't be attached to the truck to do that, the weight distribution bars were not attached. And what I'm trying to get at is the tongue weight when the bars are attached. I'm guessing that the tongue weight with the bars attached should be between 600 to 700 lbs. But that weight is critical to know since the truck is only rated for 617 lbs. tongue weight. If it's much higher than that, I may have to sell the truck and get one with more tongue weight capacity, which my manager (wife) tells me is not going to happen. Haha!
Jim

 

[Boondoggle]

So if I read you spreadsheet right when you add together the front and rear axles with trailer attached equals 6420. The unload weight of the front and rear axles are 5480 which gives you a 940 tongue weight. You added weight to the rear axle but remove weight from the front axle.


Your profile says you have a Lux 35 GRS which in 5th wheel and not a trailer.

I currently have a trailer but my wife and I have decided to buy a fifth wheeler. So before I do, I want to do my research. Since it will take almost a year for the truck and trailer to be built (including a month or so before we order it), I'm trying to make sure my current set up is working (which is not). I also want to make sure that my next RV setup is going to work. Oh, and by the way, I will also be buying a GMC one ton dually for the fifth wheeler, which is why I don't want to buy a temporary truck for my trailer. The hard choice will be to sell our current trailer which we've only had for a year.

Yes, you're right, that's what I was looking for. Actually, the unloaded weight of the front and rear axles is 5540, not 5480 which gives me a tongue weight of 880, which is still too high compared to the rated weight of the truck (617 lbs.).

Again, thanks for your help and patience on this, Gizmo, I really appreciate it!