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Old 10-12-2019, 06:46 PM   #1
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2004 30' Classic
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Fun At The CAT Scales...Kinda Surprised with Result

Hi Team,

Went to the CAT scales today. Here is my setup:
Crew Cab, 6.5 Foot Bed (so a pretty long truck)
HA hitch
6 inch drop Stinger
2004 Arstream 30

Went to the scales with the truck and trailer all ready to travel. All the numbers were fine. Within all the truck specs. As the CAT Scale app allows you to reweigh for $2, I decided to fool around with adjustments.

Made a bunch of runs, with different jack settings. Interesting thing was I could move 220 pounds to the front axle and it only increased the Trailer Axles weight by 40 pounds. Verified this ratio with lesser amounts (moving 100 pounds increased Trailer Axle Weight by 20 pounds). Looking at the geometry (and doing some vector diagrams) I would expect more like 100ish pounds transferred to the Trailer axle for 220 being moved to the trucks steer axle.

Not that it is a problem. All within specs and combo drives great. Just surprised.

Thoughts?
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Old 10-12-2019, 08:59 PM   #2
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Could you post the tickets here? Also, did you do the 3 pass method - truck solo, truck with trailer attached no WD applied, truck and trailer with WD applied...

Thanks!
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Old 10-12-2019, 09:00 PM   #3
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If you do the measurements and the math, your scale findings will be verified by physics. What you found is completely normal based upon wheelbase, "ball" to axle and "ball" to center of trailer axle(s).
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Old 10-13-2019, 04:49 PM   #4
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Hi Rich,

Yeap have done the measurements and run the vector analysis. However,I must be missing something. here are the numbers:

Distance from hitch ball to center of front wheel: 18 Feet
Distance from Hitch ball to between the two trailer wheels 18.5 feet

With No Weight Distribution applied:
Steer Axle: 3300
Trailer Axle Load: 7200

With first increment of Weight Distribution applied:
Steer Axle: 3400 (+100 Pounds)
Trailer Axle: 2220 (+ 20 Pounds)

with second increment of Weight distribution applied:
Steer Axle: 3520 (+220 Pounds)
Trailer Axle: 7240 (+40 pounds)

So considering these two data points.

Of the load removed from the Drive Axle:
17% is going to the Trailer Axle
83% to the Steer Axle.

Given my math, and the relative symmetry of my setup, I would have expected a higher percentage transferred to the Trailer Axles.

I have a few other passes (with different settings) that support about 17% transfer to trailer axles. Keep in mind, this is not 17% of TW, It is 17% of what is transferred off the Drive axles.

As I said, all is good with the trucks specs. Just curious what I am missing.

Thoughts?
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Old 10-13-2019, 05:02 PM   #5
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Is this a function of using a Pivot Point Projection hitch and I am missing an interaction in my analysis?

Anyone else have any data for a PP or HA?

Also, there is a typo in my previous email. For the first increment of WD, the Trailer Axles weight is: 7220
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Old 10-13-2019, 06:52 PM   #6
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I see the 18 foot or so lever arm from the hitch to the trailer axles. But on the truck side you are rearranging weight on the spring system rather than just carrying it on the front axle like the springs and rear axle are not there. I do not know or see how to calculate that re arrangement. I think that is why we use the scales.
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Old 10-13-2019, 08:12 PM   #7
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What bill said, sorta, I think. For you to expect a near 50/50 redistribution, the rear tv axle would have to be at the ball, not some 5 feet forward of the ball. VPP hitch makes no difference. If the forward ends of the spring bars are aft or forward of the ball, it can make a bit of difference. It's really not the ball to * distance that matters, but the bar lever point where it attaches to the head.
The old 1/3, 1/3, 1/3 weight distribution myth is bunk on any realistic tow rig combination.
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Old 10-13-2019, 08:23 PM   #8
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Quote:
Originally Posted by Bill M. View Post
I see the 18 foot or so lever arm from the hitch to the trailer axles. But on the truck side you are rearranging weight on the spring system rather than just carrying it on the front axle like the springs and rear axle are not there. I do not know or see how to calculate that re arrangement. I think that is why we use the scales.
Bill, it can be done. Scales are still needed for a baseline weight data set. I have a very elaborate spreadsheet which calculates all weight distribution changes for adding any item anywhere in my tv, or trailer.
It has been validated by scale tickets a couple times.
Before anyone asks, no I am not really willing to distribute it. It would take hours to try and explain it. Plus it is set up for my specific equipment. It is 3 separate sheets with reference formulas between sheets. I probably have at least 100 hours in it.
It is remarkably accurate.
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Old 10-13-2019, 09:36 PM   #9
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Cru-in, I need to correct my self a bit. The distance between "ball" and rear axle varies a bit between most or all drawbar manufacturers, as the length from pin hole to center of ball varies. Since the pin to ball on a Hensley is about 11" (iirc) longer than the average drawbar, it does make a distribution difference.
I recalled that I do have 2 input sheets for my outcome sheet. One for my Hensley and one for my back-up reese dual cam.
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