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Open Roads Forum  >  Towing

 > Help Deciphering CAT Scale Weights

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MHay

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Posted: 08/25/20 11:52am Link  |  Quote  |  Print  |  Notify Moderator

RobWNY wrote:

RCMAN46 wrote:

RobWNY wrote:

I'm confused how you lost 20 pounds completely using WDH bars (14,140 compared to 14,160 for the other two weight rating passes).


I will assume the OP used a CAT scale.

CAT scale weights are in 20 lb multiples. If you look at the OP's weights they are in 20 lb multiples.

I checked several of my CAT scale receipts and they were all in 20 lb multiples.

I also checked some weights I got at my local garbage transfer station and they were also in 20 lb multiples.

Thus a difference of 20 lbs on separate weights can be expected.

That tells me the scales aren't calibrated. It shouldn't matter. A 20 pound increment transferred from one scale to a different scale because of a weight distribution system doing what they're supposed to do doesn't make the weight just disappear. it should take that 20 pounds from one scale and it should show up on another scale.


Yes, confirming it was a CAT scale.

MHay

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Posted: 08/25/20 12:07pm Link  |  Quote  |  Print  |  Notify Moderator

wing_zealot wrote:

Your WDH is moving 400 lbs of weight out of a total of 940 lbs. That's 42% which is pretty **** good. Your tongue weight is also 12.7% which is good also. The only thing you can do is try to shift 150 lbs of weight inside the trailer so it's off the tongue and onto the trailer axle. If you can't do that, then It's just to much trailer for that vehicle.


Thanks -- that's the confirmation I wanted to get.

I guess I'm still trying to understand how 1,000 lbs. is being added to the axle when the WDH bars are on despite tongue weight being 940 lbs.

JIMNLIN

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Posted: 08/25/20 12:09pm Link  |  Quote  |  Print  |  Notify Moderator

Quote:

I also checked some weights I got at my local garbage transfer station and they were also in 20 lb multiples.

Thus a difference of 20 lbs on separate weights can be expected.

'zactly.
Just 20 lbs loss or gain is excellent scale numbers.
A first weigh may say 3005 lbs but the scale rounds off to the next highest at 3020 lbs.
The second weigh may say a 2996 lb but rounds off to 2980 lbs for a 40 lb difference.
Wind speed....failure to release the service brakes...fuel/water/liquid slosh in containers/how much fuel was used between re weighs.... can all contribute to different scale weights.

OP...maybe I read it wrong about being over a RAWR I would take some weight off the trucks rear axle. A RAWR is the lessor of a wheel/tire/rear spring pack or the axle itself. Most trucks today weak link can be the OEM wheels or rear spring pack.


"good judgment comes from experience, and a lot of that comes from bad judgment" ............ Will Rogers

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Mike134

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Posted: 08/25/20 12:26pm Link  |  Quote  |  Print  |  Notify Moderator

RobWNY wrote:

I'm confused how you lost 20 pounds completely using WDH bars (14,140 compared to 14,160 for the other two weight rating passes).


The scale can be off as much as 20lbs high or low and still be "certified" So it's possible to have a 40lb difference if the scale settles high one pass and low the second pass.


2019 F150 4X4 1903 payload
2018 Adventurer 21RBS 7700 GVWR.

MHay

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Posted: 08/25/20 12:50pm Link  |  Quote  |  Print  |  Notify Moderator

JIMNLIN wrote:

Quote:

I also checked some weights I got at my local garbage transfer station and they were also in 20 lb multiples.

Thus a difference of 20 lbs on separate weights can be expected.

OP...maybe I read it wrong about being over a RAWR I would take some weight off the trucks rear axle. A RAWR is the lessor of a wheel/tire/rear spring pack or the axle itself. Most trucks today weak link can be the OEM wheels or rear spring pack.


No, you read that correctly. I'm over by 180 lbs. which is why I was trying to figure out if I can move more off of the rear axle with the WDH, or just try adjusting the cargo in the trailer. [emoticon]

BarneyS

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Posted: 08/25/20 12:57pm Link  |  Quote  |  Print  |  Notify Moderator

MHay wrote:

As I think about the numbers some more, things don't add up to me. When using the weights in my original post to calculate tongue weight, I get 940 lbs. However, looking at the drive axle weight on Pass 2 (connected to trailer, no WDH bars), the change in axle weight is 1,400 lbs. from the unloaded weight (Pass 3). If tongue weight is 940, how is the axle weight increasing by 1,400 lbs. when hitched to the trailer without WDH bars? I might need a physics refresher to set me straight.

That increase is because the weight is being removed from the front axle when you put the trailer tongue on the ball. You get the weight of the tongue PLUS the weight from the front axle that was teeter-totter removed. Thus the scale shows the tongue weight plus the removed front axle weight. It is the goal of the weight distributing hitch to place all or most of that weight back on the front axle. In other words, your truck front axle should weigh the same AFTER hooking up the WD bars as it did solo BEFORE you hooked up the trailer.

In your particular case, I would try to adjust the hitch or take up some more on the WD spring bars to transfer some more weight forward.
Barney


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valhalla360

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Posted: 08/25/20 01:34pm Link  |  Quote  |  Print  |  Notify Moderator

RobWNY wrote:

I'm confused how you lost 20 pounds completely using WDH bars (14,140 compared to 14,160 for the other two weight rating passes).


The specs for scales provide an error tolerance. 20lb is nothing on a truck (and yes, they typically error on the conservative side as truckers get upset if they get an over weight ticket). So with slightly different placement of the vehicle, a little fuel used or other minor changes, it may come up slightly different but still well within spec for the scale.

In the non-WDH, loading the rear axle picks up more weight because some of the front axle weight is moving back to the rear axle (think of the rear axle as the center of a teeter tautter. That also moves more of the trailer weight to the hitch for similar reasons (harder to explain as force distribution is a little more complicated as the WDH is applying a moment arm in the opposite direction around the hitch). This is perfectly normal. I don't have the stationary scale specs but I just checked and for weigh-in-motion systems I work with, the top spec allows 6%+- for GVW. Stationary has closer tolerances but still you aren't going to get it down to the nearest ounce.

Looks like you are about 180lb over on the rear axle. I don't think you can reasonably just crank down harder on the torsion bars to make that up.

I'm coming up with 840lb hitch weight (7400-6560 = 840) and 11% (840/7400). So I would be hesitant to shift weight to the back of the trailer to reduce hitch weight or you could create a sway issue.

Do you have cargo in the rear of the truck that could be moved to the trailer (without exceeding the trailer GVWR). Cargo in the rear of the truck is almost 100% going on the rear axle.

You can check details on the individual rear suspension parts and see what is creating the limitation on the RAWR. The Expedition is likely different but the F250 and F350 (SRW) were for many years identical except for the spring pack, so if you upgraded the springs, you effectively got a F350 (not in legal terms but in practical terms).

What the GVWR on your truck? I did a quick check online and it looks like 7300lb but you are at 7580lb already but you might have a different model from what I found.


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Mickeyfan0805

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Posted: 08/25/20 02:52pm Link  |  Quote  |  Print  |  Notify Moderator

valhalla360 wrote:


What the GVWR on your truck? I did a quick check online and it looks like 7300lb but you are at 7580lb already but you might have a different model from what I found.


This is the piece of this conversation that I think is getting overlooked in all of this. What is your GVWR, and were you fully loaded, with both people and gear, when you got these numbers? You are not only over RAWR, but likely over your GVWR. If you weren't fully loaded, it means things only get worse from there. If this is a full load, WDH adjustment might help, but that depends on how much you are already dialed in - and you still may be be over weight. If you still have additional passengers or gear to load on top of the weights you are sharing, that just exacerbates the problem.

BenK

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Posted: 08/25/20 03:29pm Link  |  Quote  |  Print  |  Notify Moderator

Some IMHO comments...and CONGRATULATIONS on actually going out and weigh it. Note that every trip has a potential of different loading, so these numbers should be your base line. Another person & their ‘stuff’, find something along the trip and buy it for the trip home...things have a remarkable tendency to add and add...

What are your WD bars rated for ?

Agree with Barney, try to WD some weight off your TV’s rear axle and over to the TV’s front axle. Note that by doing that, you will also WD a bit more weight back onto the trailer tongue...that is how WD systems work. This will get your TV’s rear weight into a better place in regards to the RGAWR. This is why you need to know where you are in reference to the WD Hitch system bars ratings....do you have enough head room or are you already at their max rating?

The finally orientation of the whole setup, after all of the dials/knobs have been adjusted, is to have enough weight is WD’d to the TV’s front axle as per the manual (some require weight returned to some +/- of stock, others +/- height of stock...stock = before hooking up) and the trailer tongue level at it’s highest pointing and prefer pointing slightly down...they follow better that way

Forget the MTW (Max Tow Weight) listed for a TV. More marketing than anything and that they ‘wiggle’ the setup to get the highest trailer weight for their marketing brochures. The GCWR is better and since you have weighed the whole setup, take the sum of the TV’s axle weights and subtract it from the GCWR (note that GCWR is fairly new to the towing world and is subject to much discussion...many say it is only a performance thing...okay, hows about the ability to manhandle the setup during an emergency situation...of which all ratings has been designed for...among many other things)

Bottom line = I’d tow that with some adjustments and know it is at the limits. Therefore drive accordingly and enjoy the ride...


-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
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51 cylinders in household, what's yours?...

MHay

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Posted: 08/27/20 09:20pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks for all the great responses so far!

The GVWR for the Expedition is 7,720 based on the sticker on the door jamb. So based on these weights, I have a little room to spare (pass 1 with the WDH was 7,580 for vehicle weight).

The real issue is the GAWR for the rear axle. The rating is 4,380, but I'm sitting at 4,560. I'm using a Curt TruTrack hitch rated at 15,000 GTW and 1,500 TW. Currently I have the brackets on the trailer as high as they'll go. I have not tried tilting the hitch head yet, which I believe would apply more tension. As it is now, the trunion bars seem to be exerting lots of force on the angle brackets, to the point where they are wearing through the black paint on the front of the brackets and starting to mar them. Should I try tilting the hitch head back in an attempt to get more weight off the rear axle, or does it seem like I'm fairly maxed out already? Here's a link to the instructions: Curt TruTrack Hitch.

We're headed on a trip tomorrow, so I'll try to get a picture of the current setup once I'm hooked up.

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