What's wrong with this simple method of weighing?

[excelrvguy]

When I was President of an RV manufacturing company, I weighed many trailers. I've always subscribed to a simple method of weighing our 5th wheels. I was often met with resistance and engaged in several debates about my method being wrong, but no one could ever explain why.

I never felt that weighing the truck & trailer, then weighing the truck empty, then weighing the trailer.... blah blah blah was an inefficient way to weigh, not to mention being a real hassle.

When I weigh a 5th wheel, I pull the unit across the scales until the rear truck tires are off the scales, but not the jacks of the 5th wheel. Then I let the jacks down on the unit, just BARELY taking the weight off the hitch. (Not enough to actually lift the hitch.. Like maybe 1/8" to where I could barely see daylight between the hitch plate and the pin box)

Then I get a weight stamp. This would be the total weight of the unit. I would raise the jacks back up and have them stamp the weight with only the axles on the scales (I haven't moved a thing).

Example = Total weight 14,500
weight on axles 11,600
leaves only the pin weight. 2,900

I'm not talking about weighing each axle or each wheel. To me, this method saves time and effort and hassle.

What say you?

[Vanished]

bpounds wrote:

SoCalDesertRider wrote:
...
Now, on the pin weight versus jack weight issue, if you were weighing just the jacks by themselves, no trailer axles on the scale, that would not be the same as the pin, because there is about an 8 foot length difference between the pin to axle measurement, versus the jack to axle measurement. The jack weight will be significantly higher than the pin weight.

Interesting thing about this statement (which is true), is that it means the weight on your tires is less when your trailer is sitting at camp, than when you are hitched up. The weight forward of the landing gear is lifting weight off of the tires.

Just thought I would add that in to further confuse some.

I'll bite - again (and hopefully I read it correct this time..)

The trailer has a center of gravity.. the distance to the rear wheels from the center of gravity hasn't changed any - I don't think the weight on the rear wheels changes any if it's supported by a tripod or the jacks..

[azrving]

bpounds wrote:

SoCalDesertRider wrote:
...
Now, on the pin weight versus jack weight issue, if you were weighing just the jacks by themselves, no trailer axles on the scale, that would not be the same as the pin, because there is about an 8 foot length difference between the pin to axle measurement, versus the jack to axle measurement. The jack weight will be significantly higher than the pin weight.

Interesting thing about this statement (which is true), is that it means the weight on your tires is less when your trailer is sitting at camp, than when you are hitched up. The weight forward of the landing gear is lifting weight off of the tires.

Just thought I would add that in to further confuse some.

Interesting and I can see how that is true. So, when we get in bed there is a reduction in axle weight. If we start jumping around up in bed I hope we dont lift the wheels off the ground. We are wild 60 year olds. 😉

[bpounds]

SoCalDesertRider wrote:
...
Now, on the pin weight versus jack weight issue, if you were weighing just the jacks by themselves, no trailer axles on the scale, that would not be the same as the pin, because there is about an 8 foot length difference between the pin to axle measurement, versus the jack to axle measurement. The jack weight will be significantly higher than the pin weight.

Interesting thing about this statement (which is true), is that it means the weight on your tires is less when your trailer is sitting at camp, than when you are hitched up. The weight forward of the landing gear is lifting weight off of the tires.

Just thought I would add that in to further confuse some.

[Vanished]

bpounds wrote:

Vanished wrote:
I'm not sure why everyone still states it's the same and it works for getting pin weight - the OP method does NOT give pin weight.. Period..

Because you are wrong. Period...

When the trailer is supported entirely by the scale, you get a total weight. When only the wheels are supported by the scale, you get axle weight. A little quick math, and waaala.

The only argument against this would be that the scale is not accurate unless the load is centered on the platform. But that isn't true either.

There are no levers involved in any of this.

After rereading the OP I realize the 2900 lbs in the example is from the math, not the front scale reading on the jacks.. In his example he only gives theoretical values for overall weight and subtracts the axle weight AFTER he puts weight back in the truck bed..

My point was pin weight and jack weight would differ - I misread the OP..

[nickthehunter]

I get a laugh from the people that have a great understanding of the intricacies of physics, but a total lack common sense.

[bpounds]

I think what is confusing people, is the pin weight versus jack weight. Hence all the mentions of leverage. But this method does not give you jack weight.

Yes, jack weight is not the same as pin weight, but I don't think anyone cares about jack weight.

It really is a simple as:
TW - AW = PW

Where
TW = Total Weight
AW = Axles Weight
PW = Pin Weight

[Mandalay_Parr]

excelrvguy wrote:

Mandalay Parr wrote:
It's not the pin weight but rather the Jack weight.
Pin weight would be less.

That's the debate that always comes up... Jack weight would be different than pin weight because of the lever effect. My point is that with the jacks down, I'm weighing the TOTAL weight of the trailer. Then the weight on axles. doing the math tells me that what's not on the axles, has to be on the pin.

The trailer doesn't weigh more because it's sitting on it's jacks vs if you had a tripod under the pin. Total weight would be total weight... correct?

I stand corrected. You are correct.
Jerry Parr

[azrving]

This should be good for at least 15 pages as long as the ones who want to make rude remarks can control themselves. Good post op. We need to keep our old brains working 🙂

[bpounds]

Vanished wrote:
I'm not sure why everyone still states it's the same and it works for getting pin weight - the OP method does NOT give pin weight.. Period..

Because you are wrong. Period...

When the trailer is supported entirely by the scale, you get a total weight. When only the wheels are supported by the scale, you get axle weight. A little quick math, and waaala.

The only argument against this would be that the scale is not accurate unless the load is centered on the platform. But that isn't true either.

There are no levers involved in any of this.

[bpounds]

Lantley wrote:

RustyJC wrote:
In theory, nothing's wrong with your method. In case 1, you have the total weight of the trailer on the platform - it doesn't matter what it's resting on; jacks, wheels or anything else. In case 2, you have the axle weight of the trailer on the platform - the difference is pin weight.

In practice, for this to be absolutely accurate, in case 1 you must have no pin weight whatsoever left on the truck, but you must also not lift too high such that the pin is pulling upward on the jaws of the hitch and transferring some of the weight of the hitch/truck to the front jacks of the trailer.

Rusty

I agree the OP's method is relatively accurate but itallows for too much subjectivity. When are the front jacks raised high enough to support full weight of truck? When are they too high?
What is the difference between pin weight and jack weight?
If you have taken the time to go to the CAT scale why not just spend the extra time to complete task accurately as possible vs. winging it.

If in doubt, just pull the truck forward a foot. You wouldn't even have to disconnect the cable, and it will be quick to hitch back up too. This would not be an issue with the typical 16k hitch, that usually have thinner jaws. More likely to be an issue with heavier hitches, which have thick jaws and little pin clearance vertically.

[Vanished]

I'm not sure why everyone still states it's the same and it works for getting pin weight - the OP method does NOT give pin weight.. Period..

[bpounds]

excelrvguy wrote:
...I pull the unit across the scales until the rear truck tires are off the scales, but not the jacks of the 5th wheel. Then I let the jacks down on the unit, just BARELY taking the weight off the hitch. (Not enough to actually lift the hitch.. Like maybe 1/8" to where I could barely see daylight between the hitch plate and the pin box)

Then I get a weight stamp. This would be the total weight of the unit. I would raise the jacks back up and have them stamp the weight with only the axles on the scales (I haven't moved a thing)...

It's exactly what I do. Works perfectly for getting a total weight and a pin weight of a trailer.

Doesn't get a weight on the truck though. So I got that weight on a separate trip when I wasn't towing. But you could do the same thing by having the truck on the scale, the trailer jacks barely off the scale, and lifting the pin off the hitch. But it is more fooling around and the scale is usually a busy place.

[SoCalDesertRid1]

The method you're using is accurate.

You can also do it another way, just as easily-

If you use that method of raising the trailer just off the hitch, but do it with just the truck on the scale, instead of with just the trailer on the scale, then you will be weighing just the truck, and then the truck with the trailer's hitch weight on it. Subtract those 2 numbers and there you have the pin weight.

So either way will work.

Now, on the pin weight versus jack weight issue, if you were weighing just the jacks by themselves, no trailer axles on the scale, that would not be the same as the pin, because there is about an 8 foot length difference between the pin to axle measurement, versus the jack to axle measurement. The jack weight will be significantly higher than the pin weight.

[Lantley]

RustyJC wrote:
In theory, nothing's wrong with your method. In case 1, you have the total weight of the trailer on the platform - it doesn't matter what it's resting on; jacks, wheels or anything else. In case 2, you have the axle weight of the trailer on the platform - the difference is pin weight.

In practice, for this to be absolutely accurate, in case 1 you must have no pin weight whatsoever left on the truck, but you must also not lift too high such that the pin is pulling upward on the jaws of the hitch and transferring some of the weight of the hitch/truck to the front jacks of the trailer.

Rusty

I agree the OP's method is relatively accurate but itallows for too much subjectivity. When are the front jacks raised high enough to support full weight of truck? When are they too high?
What is the difference between pin weight and jack weight?
If you have taken the time to go to the CAT scale why not just spend the extra time to complete task accurately as possible vs. winging it.

[azrving]

Class 2 lever. So the weight has to be less if lifting out at the handle ends vs closer to the load. I never move my hands closer toward the tub of the wheel barrow when moving a load.