Quick question from someone who has never driven a semi

Yes I believe I have done that before. But I may have been near 60k gross light load.

 

Why would you want to know that?

 

Yes they can that's why the truck AND trailers have abs

 

Best answer!!!

 

You don’t want to lock your brakes if you don’t want to buy 18 new tires often.

 

Sure you can.
Sometimes I wake up in the middle of the night. I may need to use the rest room, be in pain or just cannot sleep. Recently I woke up and wondered if I was dreaming. I was lying in bed and nothing hurt. The room was totally dark and silent. Wondered if maybe I had died but it was just a good day. Sometimes I talk to God just being curious for knowledge before daylight.
Never thought about brakes on semi trucks in those special times of rest or overlooking natures awe.
What is your profession?

Slippery roads

 

Pre- ABS, if you took a tractor trailer loaded by the book to the floor, more than likely she will lock at the trailer first. The weight shifts forward in stopping just like a car noses down and so the trailer wheels get lighter as it piles against the 5th wheel.

I don't recall locking the tractor drives in those situations with max application of service to the floor, that is something due to the immediate life and death issuse in front of me where Im about to hit and kill people. I aint ever looking at my tractor drives.

What she will MOST certainly TRY to do if there is ANY angle whatsoever between cab and trailer is load up too much on the drives for side to side traction, break loose and you have a tractor jackknife. She will very instantly and violently fold. And then the whole thing continues to be pushed by the loaded trailer out of control while your body is gathering in pain over in the passenger seat.

If the tractor is dominant and the trailer has too much pressure against traction side to side, she is going to lose that trailer and that thing will come around. You have at this point a seriously BIG problem. You have about 10 degrees to get it back right way, once beyond 10 degrees angle at your 5th wheel, there is no getting it back.

Traction is a sort of like a bank account. For going forward, for stopping and for holding against a curve force that goes to the outside. There is a big word called centrifugal force. Throw in the center of gravity and you have now a three dimensional problem.

Post ABS trucks may not activate. Maybe. USUALLY. But it depends on the situation. The braking situation is different with those. You put your foot on the floor and ride that steering wheel for better or worse. The computer will take over the ABS side to keep your wheels moving. As long they are moving you can steer out of trouble.

Which is why we have a form of braking called stab. There is a thread talking about that in mountain work as a form of education versus some who apparently are not using the term properly. Humans can stab a certain amount in a few seconds. But it's really inadequate when a computer can buzz a wheel and tire at 60 times a second.

Anything is possible including over steer, understeer and front axle lockup. That is where you the professional is supposed to earn your pay and be safe.

Which is why the American Trucker is lampooned everytime a idiot fails to drive properly and becomes a laughing stock of some city's morning news because he or she has screwed up royally and now either hurt people, killed people or broke stuff or simply snarled a highway.

Essentially physics. 40 tons to keep under control. Cars are pitiful at 2 ton, if that. You can put one of those onto one pallet and toss it into the trailer and that's no weight at all.

That is another dimension. braking is different when empty than loaded. I actually prefer to be loaded with the center of gravity below 14 inches above the trailer deck.

 

About Pre 1994 at full weights the brakes were not strong enough to lock up. Since then with Q-Plus brake pads and the like, plus disc brakes, they are Much stronger now.
Back then when I took the air brake course I was told that the brakes only design requirement was to hold a fully loaded semi stopped on a 20 percent grade.