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Old 10-01-2014, 06:05 PM   #31
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I believe that Hugh has his calculations done correctly.

Quote:
Originally Posted by DonF View Post
1 - Calculate the difference from the unhitched rear axle weight and the hitched rear axle weight without the WDH engaged.
In this case, subtracting the unhitched rear axle weight of 2,450 pounds from the hitched rear axle weight (no WDH) of 3,000 pounds yields a tongue weight of 550 pounds, not 350 pounds.
Don, you're missing that some of the load which was carried on the tug's front axle get transferred to the tug's rear axle. The trailer tongue weight is a force pushing down on the tug structure like it is a see-saw (teeter-totter, whatever you called it as a child) and partially lifting the person sitting on the other end with his feet on the ground; the load on the pivot in the middle increases by the sum of how hard you push down plus how much the other guy gets lifted.

In this case, 200 pounds of the 550 pounds came from the front axle; you can't determine tongue weight from axle weights without considering both tug axles.

Quote:
Originally Posted by DonF View Post
2 - Calculate the difference from the unhitched rear axle weight and the hitched rear axle weight with the WDH engaged.
With the WDH engaged, calculations show 250 pounds was transferred from the tongue to the front axle and 50 pounds was transferred back to the trailer axle for an effective tongue weight of 250 pounds.
The 250 pound and 50 pound numbers are correct (for those scale readings), but the numbers to compare are between without-WD and with-WD (both with the trailer hitched), not unhitched and with-WD.

Quote:
Originally Posted by DonF View Post
Combining the tongue weight of 550 pounds and 3,250 pounds on the trailer axles in the 1st set of weights yields a trailer weight of 3,800 pounds.
Since the 550 pound value is incorrect, the total is incorrect. With the correct tongue weight of 350 pounds, the 3,600 pound total trailer weight value results.
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Old 10-01-2014, 07:36 PM   #32
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If a trailer weighs 3600 lbs and the tongue weight is 300 lbs with WDH, how is that sufficient.

We always try to have a tongue weight of at least 400 lbs. with similar weight.
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Old 10-01-2014, 08:54 PM   #33
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Quote:
Originally Posted by Floating Cloud View Post
If a trailer weighs 3600 lbs and the tongue weight is 300 lbs with WDH, how is that sufficient.
If this is referring to Hugh's trailer, it weighs 3600 pounds and has about 350 pounds of tongue weight (regardless of whether or not WD is used), so it has roughly 10% tongue weight. That's a perfectly good number, especially if the trailer is loaded for good stability (for instance, no massive lump of stuff hanging off the back).

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Originally Posted by Floating Cloud View Post
We always try to have a tongue weight of at least 400 lbs. with similar weight.
That's a good number, too, but that little bit higher tongue weight is not necessary for all trailers. My current single-axle trailer is very well behaved with 10% tongue weight.
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Old 10-01-2014, 10:35 PM   #34
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Again, his tongue weight on his own numbers is 300 with a WDH which he uses. That is not 10-15% of 3600 lbs.
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Old 10-01-2014, 11:44 PM   #35
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Originally Posted by currinh View Post
XTerra Alone
Front 2550 lb
Rear 2450 lb

XTerra with 19' (no WDH)
Front 2350 lb
Rear 3000 lb
Trailer 3250 lb
for a tongue weight of 350 lb

XTerra with 19' (using WDH)
Front 2600 lb
Rear 2700 lb
Trailer 3300 lb
for a tongue weight of 300 lb
torque from WDH of 625 ft-lb
Sorry, I missed this earlier - I simply didn't notice that a second tongue weight was listed in the post. I hope that didn't cause too much confusion.

The tongue weight is 350 pounds, as calculated from the first two sets of scale readings. The tongue weight is the portion of the trailer's weight supported by the tongue, and use of a WD doesn't move the mass of the trailer, so it doesn't change the tongue weight.

I assume the 300 pound value (shown in bold) was calculated as the difference between the Xterra without the trailer (5000 lb) and the total of axle loads with the trailer and WD in use (2600+2700). Since the WD can push as much load as you want onto the trailer axle this isn't useful to learn anything about the trailer; this isn't the tongue weight.
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Old 10-02-2014, 02:35 AM   #36
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The tongue weight range is 360 to 540 lbs. I would want to make sure that I am definitely within that. Even 400 is just making it to me. Drink all of that beer up front or something gets moved and you are out of the range. We have enough trouble keeping just above 10%.

Use up the propane and there goes the tongue weight. A definite balancing act. Maybe we need sand bags up there.
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Old 10-02-2014, 08:32 AM   #37
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Brian,
Thanks for making this clear for me.
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Old 10-02-2014, 10:56 AM   #38
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I should add - my initial calculations were based on information I found on the source of all information these days - an internet site!
Here's what they said:
How to determine weights in 3 trips across CAT scale
1 - Typical load in vehicle. Front axle on one platform, rear axles on 2nd platform.
2- Same load in vehicle, trailer hitched w/o WDH engaged, front axle on one platform, rear axle on 2nd platform, trailer axle on 3rd platform. DIFFERENCE in rear axle weight equals tongue weight (s/b 10% -15% of trailer weight)
3 - Same as 2 with WDH engaged. Ideally front axle weight should be close to original front weight.

Another reminder to me to look for more than one source when gathering information!
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Old 10-02-2014, 04:23 PM   #39
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Quote:
Originally Posted by DonF View Post
Here's what they said:
How to determine weights in 3 trips across CAT scale
1 - Typical load in vehicle. Front axle on one platform, rear axles on 2nd platform.
2- Same load in vehicle, trailer hitched w/o WDH engaged, front axle on one platform, rear axle on 2nd platform, trailer axle on 3rd platform. DIFFERENCE in rear axle weight equals tongue weight (s/b 10% -15% of trailer weight)
3 - Same as 2 with WDH engaged. Ideally front axle weight should be close to original front weight.
That's not so bad by the (very low) standards of general web sites. The whole thing makes perfect sense for someone adjusting a WDH to restore the front axle to the same load as the unhitched condition (which is one reasonable approach); the only error is in the tongue weight.

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Originally Posted by DonF View Post
Another reminder to me to look for more than one source when gathering information!
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Old 10-02-2014, 10:53 PM   #40
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Brian:

First I agree that the 17B is lighter than our 19, so my numbers won't apply to Al's situation. We did find that adding the WDH increased the stability of our rig, I believe at least partially due to the friction in the hitch. For this reason I think a WDH might help his situation. Certainly can't hurt, but I don't know.

I found GAWR for the 2014 XTerra (ours is a 2013) to be 2676 lb front and 2962 lb rear. I hadn't looked at this before and it means we should be using a WDH. The towing weight and hitch weight are within the 5000 lb and 500 lb specifications. Pretty sure those are correct.

I couldn't think though the weights so resorted to "math". I don't know if this is decipherable but several have asked "how'd you get those". So, my chicken scratchings are attached. I think they are correct but if anyone sees a problem let me know. If they make no sense at all, just ignore them.

To use these one needs the wheel base of the TV, distance from rear wheel to hitch ball, and distance from hitch ball to trailer wheel(s). For our XTerra and 19' I measured:

t = 150.5"
h = 54"
b = 107"

I hope this helps. Thanks.

Quote:
Originally Posted by Brian B-P View Post
So the XTerra starts only slightly front-heavy (with whatever passengers and cargo were consistently used throughout this weighing).

Combining four values each of which have +/-10 lbs precision and potentially greater inaccuracy results in only an approximate tongue weight, but the method is sound, so we can work with the 350 lb value.

Adding 350 lb to the hitch lifted 200 lb off the front axle - seems about right for the proportions of the Xterra (rear axle to hitch ball almost half of the wheelbase, so load shift is almost half of the hitch load; these numbers suggest about 4/7 or 57% of the 110 inch wheelbase, which would be 63").

The result is substantially rear-heavy, so I can understand wanting a WD hitch. The rear axle load increase (including load transfer from the front) is 550 pounds. Hugh, how close is 3000 lb to the rear GAWR (which is not given in the owner's manual)? Reaching or exceeding GAWR would be another reason for wanting WD. I suspect from a post in RV.Net that GAWR-rear may be only 2850 lb so WD would be required.

The Gross Vehicle Weight (GVW) of 5350 is very close to what I think from the manual is the Gross Vehicle Weight Rating (GVWR): 5400 lb.

It doesn't have anything to do with the use of WD, but these numbers provide a Gross Combined Weight (GCW) of 8600 lb, which is well within the Xterra's Gross Combined Weight Rating (GCWR) of 9658 lb.

This says that the WD is forcing 250 lb back onto the front axle, and only 50 lb onto the trailer's axles, for a total of 300 lb off of the rear axle. The total is fine, but the proportion is impossible, since the distance from rear axle to trailer axles is nowhere near five times the wheelbase. This is where the accumulation of scale reading errors can be a problem, or perhaps the scale is slightly sloped up compared to surrounding areas so the WD action is too high when the front axle is on the scale and too low when the trailer is on it, or perhaps slight unlevel conditions around the scale are messing with the ball height and thus the tongue weight.

A reasonable guess might be that the front axle reading should have been 2550 lb and the trailer axle should have been 3350 lb, for the same total load transfer distributed 200 lb to the front axle and 100 lb to the trailer axle... that would be in about the right proportions for the dimensions of the Xterra and Escape 19'.

The WD system only takes about 100 pounds off of the Xterra, so the tug appears to be still very close to its Gross Vehicle Weight Rating (GVWR); WD is not a good fix for GVW problems. On the other hand, taking 300 lb off the rear axle is good for staying within GAWR (that is fundamentally what WD is for).

All of this is about Hugh's Xterra plus Escape 19', not Al's Tacoma plus Escape 17B. The point is that with these scale readings, one can see what the WD is doing, whether is it needed, and if it is doing what you want. The 17B is lighter than a 19', the Tacoma has longer wheelbase than an Xterra (so it will experience less load transfer off the front axle for a given hitch weight), and the Tacoma probably has less load on the rear axle to start with and higher rear axle capacity; for all of these reasons, Al should need WD much less than Hugh; I doubt he needs it at all.
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