How to weigh axles on a scale that only gives you gross weight?

When I was a student ten years ago, my trainer told me how to get the weight of the drive axles on a scale that only gave the gross weight, but I was very tired at the time and just let what he said go in one ear and out the other. I didn't pay close attention. I thought about this when I was more refreshed, and I believe I have deduced how to get the weight of the drive axles on a scale that will only give the gross weight and does not break down axle weights. Here's my theory on how to get the weight of the drive axles:

Drive the tractor-trailer so that both the steers and the drive axles are on the scale without the trailer tandems being on the scale. Write down the weight of both the steer axle and the drive axles combined. Then back the truck up so that only the steer axles are on the scale, but the trailer tandems and drive axles are not on the scale. Write down the weight of just the steer axle. Then do the following arithmetic:

Weight of drive axles and steer axle combined
- weight of steer axle
___________________________________________________
Weight of just the drive axles

In other words, weight of drive axles and steer axle combined minus weight of the steer axle equals the weight of the drive axle.

Then to get the weight of the trailer tandems, just position the tractor-trailer so that only the trailer tandems are on the scale, and the drive axles and the steer axle are not on the scale. The weight is the weight of just the trailer tandems.

Is my understanding correct?

Let me give a backstory on why this is important information to know: The other day I had a live load at a paper mill that weighed approximately 41,000 pounds. After 5:00 p.m., this paper mill will not load any more trailers that were not already in line at 5:00 p.m. I got my load at about 4:30 p.m. There is a scale at the paper mill, but the scale won't break down the weights of each individual axle. When the live load was completed at 4:30 p.m., I did not know how to scale each individual axle. So I drove about ten miles to a truckstop with a CAT scale. There was heavy traffic on the way to the truckstop, delaying me at least half an hour more. I slid both the 5th wheel and the trailer tandems all the way forward, and the drive axles still weighed 34,520 pounds. By the time I got back to the paper mill, it was around 06:00 p.m. The paper mill was closed for the day. I had to leave the property and go take a 10 hour break. If not for all this back and forth, I would not have needed to get emergency fuel. Then I had to take the time to drive back to the paper mill in the morning. If I had just scaled each axle at the shipper on the day I picked up, I could have got the load re-worked that same day, making it so I did not have to waste extra time with driving to and from a truckstop to scale the load and making it so I did not have to waste time with having an extra fuel stop to get emergency fuel and making it so that I did not waste about an extra hour driving to and from the location where I took my ten hour break. So if I had been able to get the weight of the drive axles separately, I would have delivered at the receiver about five hours earlier.

 

Steer only, write down.Pull up.
Then tractor only on scale, subtract steer weight for drive weight.
Whole unit on scale, that's your gross,
subtract total tractor weight for tandems.

 

Or, to get trailer tandems weight, a trucker could just pull all the way forward so that only the tandems are on the scale; correct?

 

1) Weigh Steer Axle
2.) Weigh Steer Axle & Drive Axles together
3.) Weigh Trailer Tandems
4.) Subtract Steer Axle Weight from #2

1 + 2 + 3 = Gross Weight
1+2 + 3(2 - 1) = Axle Weights

 

Your understanding is correct and it’s the same way weight station’s with small scales do it.

You could have probably shed the 500lbs by moving your 5th wheel all the way back.

Also if you have an apu you wouldn’t be bothered at the weight station.

 

What are you talking about? The drive axles were overweight.

If the 5th wheel is all the way to the rear, it would put more weight on the drive axles.

 

Only issue with this method is if the ground in front of and behind the scale holding the rest if the truck isn't level with the scale it will throw off the weights.

If there's an incline, especially a steap one, when doing the steers only they will read heavier than they really are due to being lifted higher than the rest of the truck. Same will happen when pulling the drives onto the scale and having the trailer down the incline, the steers will now be lighter and the drives will have more weight than they would normally have.

 

Steer = A
Steer + Drive = B (Drive = B - A)
Gross = C (Tandems = C - B)

So pull up to A, get 12k
Pull up to B, get 46k
Pull up to C, get 80k.

A = 12
B - A = 46 - 12 = 34
C - B = 80 - 46 = 34

 

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