Double Trailers; Heavier Trailer before Lighter Trailer 23 CFR

Bison · Mar 20, 2017

moloko said: ↑

I know, I have felt the difference, and watching that back trailer sway around in the mirror really scares the doo doo out of me. Not gonna be me.

BUT can we get some actual facts to back all this up?? Of course we all know, this is the stupidest idea ever. We know this from experience. It's about as stupid as showing up to a job interview stoned on PCP. It's about as stupid as robbing a bank with a note, and on that note, you're asking for a cashier's check made out to your own personal name. It's about as stupid as reaching into your pockets while a cop is telling you to walk towards him slowly with his gun drawn. You just don't do this.

But where are the facts and examples. I just need to know that.

I'm already finding an overwhelming amount of evidence in my favor, in reading the STAA of 1982 and reading the cited CFR section. But, we could simplify this. I need an example of how this went wrong in real life--the more tragic, the better. I need our assertions that the rear trailer will continue pushing the power unit, to be backed up by calculus (this is pretty common if you read the text of the STAA or CFR actually, when they spell out weight limits etc).. Anything you guys can give me. Pages from a company handbook stating this is prohibited. Anything at all, will help.
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The net force on an object is equal to the mass of the object multiplied by the acceleration of the object. F=ma

moloko · Mar 20, 2017

daf105paccar said: ↑

@moloko can you explain how you end up with that 1 compartement loaded on the trailer?

Second,you ask about doubles when you drive a truck trailer.
Completely different.

Do you have liftaxles on your truck?
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I wouldn't think it's completely different. In all of my training, it has been prohibited to drive with weight in the trailer with the truck empty. The rear trailer being heavier, pushes the power unit all over the place.

In response to how I was left with that one compartment loaded, I have an idiot for a dispatcher who can't schedule loads properly.

moloko · Mar 20, 2017

CasanovaCruiser said: ↑

My mother actually has her doctorate in physics so let me send this through to her and get some "official" mathematical reasoning for ya lol
Her & her friends will probably love this ####
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I'm going to need a proof as well.

moloko · Mar 20, 2017

daf105paccar said: ↑

@moloko

Second,you ask about doubles when you drive a truck trailer.
Completely different.
Click to expand...

Okay, so this is taken directly from the CALIFORNIA CMV DMV handbook. I'm guessing the rearward amplification is more dangerous even in a tanker vehicle, because it has a higher center of gravity. In the specific circumstances of the rear trailer, front compartment only, being loaded 2000 gallons or about 12300 pounds... I'm guessing, the rearward amplification is even worse. You think about the whip cracking effect, transmitting down the line, growing exponentially...and then BAM, it hits that loaded compartment full-force. One of two things are going to happen, and I suspect it is the latter; either the weight in that compartment, is going to STIFLE the whip-cracking effect, or the weight is going to INTENSIFY the whip-cracking effect.

I'm going to partially agree with your assertion that they are different than a true set of doubles--but here is an illustration of the various types of doubles. Which one of these more closely resembles a truck-trailer? I think it is the one with the rearward amplification of between 1.5 and 2; but I'm not sure. In any case, what makes it dangerous isn't the presence or absence of the initial 5th wheel directly behind the tractor. What makes it more dangerous, is the converter dolly, which really allows for that "whip cracking" to transmit down the line in the form of rearward amplification.

Bison · Mar 20, 2017

moloko said: ↑

Okay, so this is taken directly from the CALIFORNIA CMV DMV handbook. I'm guessing the rearward amplification is more dangerous even in a tanker vehicle, because it has a higher center of gravity. In the specific circumstances of the rear trailer, front compartment only, being loaded 2000 gallons or about 12300 pounds... I'm guessing, the rearward amplification is even worse. You think about the whip cracking effect, transmitting down the line, growing exponentially...and then BAM, it hits that loaded compartment full-force. One of two things are going to happen, and I suspect it is the latter; either the weight in that compartment, is going to STIFLE the whip-cracking effect, or the weight is going to INTENSIFY the whip-cracking effect.

I'm going to partially agree with your assertion that they are different than a true set of doubles--but here is an illustration of the various types of doubles. Which one of these more closely resembles a truck-trailer? I think it is the one with the rearward amplification of between 1.5 and 2; but I'm not sure. In any case, what makes it dangerous isn't the presence or absence of the initial 5th wheel directly behind the tractor. What makes it more dangerous, is the converter dolly, which really allows for that "whip cracking" to transmit down the line in the form of rearward amplification.

View attachment 174178
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So more pivot points=greater "crack the whip effect"?

daf105paccar · Mar 20, 2017

moloko said: ↑

I wouldn't think it's completely different. In all of my training, it has been prohibited to drive with weight in the trailer with the truck empty. The rear trailer being heavier, pushes the power unit all over the place.

In response to how I was left with that one compartment loaded, I have an idiot for a dispatcher who can't schedule loads properly.
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Doubles have 3 pivot points whereas you have only 2.

Your trailer,is it with a turntable/ballrace or a 5wheel coupling?

What stopped you from pumping the load from the trailer onto the truck?

daf105paccar · Mar 20, 2017

Truck trailer combo's are rare beasts.
If it works good it is very good but if it has faults then it can be the worst.

With a good truck trailer i would not have a problem driving with the load as you described it.
Disclaimer i am not telling it is legal or illegal.

upnorthwpg · Mar 20, 2017

moloko said: ↑

It is written in 23 Code of Federal Regulations, regarding double trailers;

"In the event that the gross weight of the trailers vary by more than 20 percent, they shall be coupled according to their gross weights with the heavier trailer forward."

This is a policy in several states, such as Alaska, Ohio, Oklahoma. It is a question of great debate lately. My common sense tells me this is because of the 'crack of the whip' effect, or Rearward Amplification.

I just wanted to get some experienced drivers advice on pulling double trailers with the first trailer closest to the power unit being lighter than the rearmost trailer. Don't ask me why I'm asking--that is too complicated. Just tell me, why you think this is a bad idea.

Show me some examples of horrific accidents that have happened because of this, while you're at it.
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I've been pulling double and triple combos for 17 years. Ltl pups. With doubles, I will pull a lighter trlr in the front, only on dry roads. My state allows 2000 difference. With triples I will not do it. Nothing worse than the pushing effect you get. Also greatly decreases your braking efficiency. Can you explain what situation your in, or is it a hypothetical discussion?

Cat sdp · Mar 20, 2017

moloko said: ↑

I wouldn't think it's completely different. In all of my training, it has been prohibited to drive with weight in the trailer with the truck empty. The rear trailer being heavier, pushes the power unit all over the place.

In response to how I was left with that one compartment loaded, I have an idiot for a dispatcher who can't schedule loads properly.
Click to expand...

If it's that big a deal....
Couldn't you pump the left over product out of the trailer into the truck....?

miss elvee · Mar 20, 2017

I haven't driven a truck/trl combo like this. I can tell you dry van wise, when the rear trailer is heavier you have tons of issues. Braking, turning, heck even just staying in your lane on a rough road.

This is complicated by the tanker aspect and carrying hazmat fumes on top of it.

Unfortunately, I don't have the statute. It will vary state to state, how far you travel and even by what you haul. (Outfielders come to mind).

If it was me, I'd contact OOIDA. They have folks that look this stuff up. Or you can call the state DOT with your question. They can cite chapter and verse for you.

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