Tongue Weight Calculation

[dlakeman]

I want to ask Forum members if they believe I calculated my tongue weight correctly.

I weighed my F-150 loaded as I would tow with it, and with my 2020 21C attached, loaded as I would tow it. Propane tanks full. Water tanks empty. F-150, 36 gallons of gas, wife and I in truck.
The weights were:
F-150 Front axle - 3220 lbs
F-150 Rear axle - 2900 lbs
Trailer axle - 4100 lbs (Note: Per my final Build Sheet, shipping weight was 3956 lbs.)
Combined Gross Weight - 10,220 lbs

I then disconnected my 21C and weighed the F-150 only, wife and I in truck. I left the E2 hitch on the truck and put the weight distribution bars in the truck bed.
The weights were:
F-150 Front axle - 3220 lbs
F-150 Rear axle - 2660 lbs
Gross Weight - 5880 lbs

Subtracting the F-150 rear axle weights 2900-2660 = 240 lbs. I believe that is my tongue weight.

Weighing was done at a Certified Automated Truck Scale so the weights are accurate.

240 lbs seems a little light to me based upon what other Forum members have calculated. I'm thinking the E2 WDH did it's job when the trailer was attached to the truck and balanced the load.

Thoughts?

[Bobbie54]

If front axle stayed the same, I don't think the equalizer hitch was doing anything.

[TTMartin]

Originally Posted by dlakeman

I want to ask Forum members if they believe I calculated my tongue weight correctly.

I weighed my F-150 loaded as I would tow with it, and with my 2020 21C attached, loaded as I would tow it. Propane tanks full. Water tanks empty. F-150, 36 gallons of gas, wife and I in truck.
The weights were:
F-150 Front axle - 3220 lbs
F-150 Rear axle - 2900 lbs
Trailer axle - 4100 lbs (Note: Per my final Build Sheet, shipping weight was 3956 lbs.)
Combined Gross Weight - 10,220 lbs

I then disconnected my 21C and weighed the F-150 only, wife and I in truck. I left the E2 hitch on the truck and put the weight distribution bars in the truck bed.
The weights were:
F-150 Front axle - 3220 lbs
F-150 Rear axle - 2660 lbs
Gross Weight - 5880 lbs

Subtracting the F-150 rear axle weights 2900-2660 = 240 lbs. I believe that is my tongue weight.

Weighing was done at a Certified Automated Truck Scale so the weights are accurate.

240 lbs seems a little light to me based upon what other Forum members have calculated. I'm thinking the E2 WDH did it's job when the trailer was attached to the truck and balanced the load.

Thoughts?

Your 240 lb tongue weight checks also by CGW minus Truck GVW = 4340, 4340 minus your trailer axle weight 4100 = 240. So both the change in the rear axle loading and the changes in GVWs equal 240 lbs.

Tongue weight is not static. It is impacted by how you load the trailer. Everything loaded rear of the rear axle reduces the tongue weight, every thing loaded in front of the front axle increases the tongue weight.

If you have a handling problem, you should probably reload your trailer to increase your tongue weight to 10% of your trailers weight. Approximately 435 lbs.

[Vermilye]

Your math is correct although I'd use combined weight minus truck weight minus trailer axle weight, however I find it hard to believe the tongue weight could be that low. I'd recheck the actual weights, particularly the rear axle weight with the trailer attached - much lower than mine...

[TTMartin]

Originally Posted by Bobbie54

If front axle stayed the same, I don't think the equalizer hitch was doing anything.

Probably, not needed on an F150 anyway.

[sherminator]

Weight distribution goes two ways. My guess is that there is +100lbs transferred to your trailer axles. You really should weigh the tongue separately to get an accurate picture. My 21NE tongue averages around 550lbs.

[Rossue]

Same here(550); 240 sounds off- that is lower than a 17B.

[Brian B-P]

Originally Posted by Bobbie54

If front axle stayed the same, I don't think the equalizer hitch was doing anything.

No, if the front axle weight was the same without the trailer and with the trailer & WDH, the weight distribution system was perfectly adjusted.

Without a weight distributing hitch, the front axle load will be lower with the trailer than without the trailer.

[Brian B-P]

The subtraction is correct, but that's not the trailer's tongue weight. To get the actual tongue weight by weighing the truck with and without the trailer, you would need to use the weights without the WD system engaged. With the WD system, the tongue weight of the trailer adds to both the truck axles (the rear only in this case) and the trailer axles.

The actual trailer tongue weight is likely at least 100 pounds more than the difference observed in these scale readings.

How readings change...
Without trailer:

• F-150 Front axl: 3220 lbs
• F-150 Rear axle - 2660 lbs
• Gross Weight: 5880 lbs

With trailer and no WD:

• F-150 Front axle: 3220 lbs - load shifted from front axle
• F-150 Rear axle: 2660 lbs + actual tongue weight + load shifted from front axle
• Trailer axle: actual axle weight
• Gross Weight: 5880 lbs + total trailer weight = 10,220 lbs

With trailer and no WD:

• F-150 Front axle: 3220 lbs - load shifted from front axle by trailer + load shifted to front axle by WD
• F-150 Rear axle: 2660 lbs + actual tongue weight + load shifted from front axle - load shifted to front axle and trailer axle by WD
• Trailer axle: actual axle weight + load shifted to trailer axle by WD = 4,100 lbs
• Gross Weight: still 5,880 lbs + total trailer weight = 10,220 lbs

So you know that the total trailer weight is 10,220 - 5,880 lbs = 4,340 lbs. We just don't know how it is distributed between the trailer axles and the tongue... only that 4,100 pounds ends op on the trailer axle when the WD is engaged.

[Gasguy]

Next time you weigh your combo remove your WDH bars from the L brackets to get your pre WD axle loading. Front & rear axle without distribution & hitched will give you more info.

[gbaglo]

Or, just get a Sherline tongue scale. You can weigh it each time you load it until you've got loading down and get the same result every time. The 1,000 lb. gauge will be easier to read and more accurate for the weight involved.
https://www.sherline.com/product/she...-weight-scale/

[JeffreyG]

Originally Posted by gbaglo

Or, just get a Sherline tongue scale. You can weigh it each time you load it until you've got loading down and get the same result every time. The 1,000 lb. gauge will be easier to read and more accurate for the weight involved.
https://www.sherline.com/product/she...-weight-scale/

Or get a 550 lb capacity bathroom scale designed for the morbidly obese. More accurate than the Sherline and available from Amazon for around $60.

[Brian B-P]

The suggestions for additional scale reading without WD engaged, and for direct tongue weight measurement, are all good. Just ensure that the tongue is at normal towing height for those measurements to get the correct value.

An example of possible readings is the tongue weight is (for example) 500 pounds...

Without trailer:
F-150 Front axle: 3220 lbs
F-150 Rear axle: 2660 lbs
Gross Weight: 5880 lbs

With trailer and no WD:
F-150 Front axle: 3220 lbs - load shifted from front axle (200 lbs) = 3020 lbs
F-150 Rear axle: 2660 lbs + actual tongue weight (500 lb) + load shifted from front axle (200 lb) = 3360 lb
Trailer axle: actual axle weight: total trailer weight (4340 lb) - tongue weight (500 lb) = 3840 lb
Gross Weight: 5880 lbs + total trailer weight (4340 lb) = 10,220 lbs

With trailer and WD:
F-150 Front axle: 3220 lbs - load shifted from front axle by trailer (200 lb) + load shifted to front axle by WD (200 lb) = 3220 lbs
F-150 Rear axle: 2660 lbs + actual tongue weight (500 lb) + load shifted from front axle (200 lb) - load shifted to front axle and trailer axle by WD (200+270 lb) = 2890 lbs
Trailer axle: actual axle weight (3840 lb) + load shifted to trailer axle by WD (270 lb) = 4,100 lbs
Gross Weight: still 5,880 lbs + total trailer weight = 10,220 lbs
- the rear axle load doesn't come out quite right, but this shows generally how the load shifts work

The actual tongue weight is likely something close to 500 pounds.

Actual axle loads will depend on the actual tongue weight, the relative distances between axles, and the adjustment of WD system. Fortunately, to determine tongue weight from the scale readings all you need to do is exactly what was described in the first post, but without the WD engaged.

[Brian B-P]

In post #9, I had "With trailer and no WD" twice... obviously the last set of numbers is for "With trailer and with WD".

[thunderworks]

Neophyte followup question . . . isn't it most important to know the tongue weight WITH the WDH installed . . ., as you actually tow the trailer? If a WDH redistributes the weight both to the trailer axle, as well as the truck, that relationship seems to be the critical one for how it effects handling, sway, etc.

Do I understand all of this correctly?

[dlakeman]

This morning before I read you folks' responses, I thought about not having the WDH bars installed therefore there wouldn't be any weight transfer. So I weighed the truck and trailer combination again.
Here's the weights.
Front axle - 2980 lbs (was 3220 lbs)
Rear axle - 3300 lbs (was 2900 lbs)
Trailer axle - 3980 lbs (was 4100 lbs)
Gross weight - 10260 (was 10220)
I had a man with me that weighs more than my wife so that explains the 40 lb Gross Weight difference.
The rear axle difference is 400 lbs, which is more in line with what the tongue weight ought to be.
I like the idea about buying the scale. I'll do it. Thanks to everyone who responded.

[Brian B-P]

Originally Posted by thunderworks

Neophyte followup question . . . isn't it most important to know the tongue weight WITH the WDH installed . . ., as you actually tow the trailer?

Fair question... but no. The actual tongue weight (not how much weight is carried by the hitch) indicates the weight distribution of the trailer, which is the important thing. If a trailer weighing 4340 pounds actually had only 240 pounds of tongue weight (tongue weight 5.5% of total), the centre of mass of the trailer would be very close to the axle, and the trailer would probably not be very stable. The real tongue weight in this case is probably about twice that, and suitable.

Most people seem to think that a WDH reduces the weight on the hitch, but it does not. Compared to towing without the WDH, a conventional WDH actually increases the downward force on the ball, and applies torque to the hitch head as if a big prybar where stuck in it from the back and pulled up.

Originally Posted by thunderworks

If a WDH redistributes the weight both to the trailer axle, as well as the truck, that relationship seems to be the critical one for how it effects handling, sway, etc.

It's necessary to keep all of the axle loads (both tow vehicle and trailer) within their rated limits, regardless of the tongue weight, and the scale readings show that. It's helpful if the WD system restores the front axle load with the trailer close to what it is without the trailer, regardless of the tongue weight, and the scale readings show that. For stability it is important to keep the tow vehicle's rear axle load from being too low, regardless of the tongue weight, and the scale readings show that.

[Brian B-P]

Originally Posted by dlakeman

This morning before I read you folks' responses, I thought about not having the WDH bars installed therefore there wouldn't be any weight transfer. So I weighed the truck and trailer combination again.
Here's the weights.
Front axle - 2980 lbs (was 3220 lbs)
Rear axle - 3300 lbs (was 2900 lbs)
Trailer axle - 3980 lbs (was 4100 lbs)
Gross weight - 10260 (was 10220)
I had a man with me that weighs more than my wife so that explains the 40 lb Gross Weight difference.
The rear axle difference is 400 lbs, which is more in line with what the tongue weight ought to be.
I like the idea about buying the scale. I'll do it. Thanks to everyone who responded.

My guesses were within about 100 pounds for each axle, so everything is roughly as expected.

The tongue weight is not simply the difference in rear axle weight. The truck axle weights with trailer and no WD total are 2980 (front) + 3300 (rear) = 6280 lbs, versus the 3220 + 2660 + 40 = 5920 that it would have been without trailer (but with the heavier passenger), so the tongue weight is 6280 - 5920 = 360 pounds. There's no way the tongue weight is that low, so I assume that what is going on is that with the WD not engaged and no change in the hitch, the tongue and hitch are riding significantly lower than normal; with tandem axles, the reduces the weight carried by the tongue. That's why the tongue weight needs to be measured with the tongue at the normal towing height.

[TTMartin]

Originally Posted by dlakeman

This morning before I read you folks' responses, I thought about not having the WDH bars installed therefore there wouldn't be any weight transfer. So I weighed the truck and trailer combination again.
Here's the weights.
Front axle - 2980 lbs (was 3220 lbs)
Rear axle - 3300 lbs (was 2900 lbs)
Trailer axle - 3980 lbs (was 4100 lbs)
Gross weight - 10260 (was 10220)
I had a man with me that weighs more than my wife so that explains the 40 lb Gross Weight difference.
The rear axle difference is 400 lbs, which is more in line with what the tongue weight ought to be.
I like the idea about buying the scale. I'll do it. Thanks to everyone who responded.

Rather than worrying about truck axle loading to determine tongue weight, without a WD hitch the trailer weight is carried by the trailer axles and the tongue.

So from your first weighing you know your trailer weighs 4340 lbs
1st Combined Gross Weight - 10,220 lbs minus 1st Truck Gross Weight - 5880 lbs = Trailer weight of 4340 lbs.

With your second weighing without the WD hitch your trailer axle weight was 3980 lbs. So 3980 lbs of the 4340 lbs of the trailer was carried on the trailer axles. So that means the remaining 360 lbs (4340 - 3980) of the trailer was carried on the tongue.

[TTMartin]

Originally Posted by Brian B-P

The truck axle weights with trailer and no WD total are 2980 (front) + 3300 (rear) = 6280 lbs, versus the 3220 + 2660 + 40 = 5920 that it would have been without trailer (but with the heavier passenger), so the tongue weight is 6280 - 5920 = 360 pounds. There's no way the tongue weight is that low.

While I don't disagree that there is some lever created by more weight being carried on the front axle if the trailer is nose low.

Tongue weight is dynamic based on trailer loading, so without knowing where everything is loaded in the trailer, there is no way to know for sure what a a possible tongue weight might be.