I cant believe that at all. That would defy the law of inertia. Your really trying to convince me a semi with 40,000 pnds of rolled steel can stop faster than a semi with an empty one ???? My motorhome (albeit different from a semi) takes a lot farther to stop with full gas, holding and water tanks, with other people and supplies than it does pretty much empty with just me in it. Towing my van on its trailer makes it even worse.
It's because you have more weight to keep the wheels from sliding in a loaded truck. Trucks are designed to stop with a load.
Every trailer in the USA would have to be replaced, New ways to secure loads would have to be developed. Freight would be damaged in such a stop even still. Imagine a box containing 4 bottles of bleach, in such a stop they will burst with the pressure of each other, and the pressure of other freight pressing on them. This happens today with current brakes. I have also seen where freight come through the front and/or sides of a trailer with current brakes. Not to mention, that the trucks already stop well enough, that things in your cab go flying in a panic stop. Ask me how I know, lol. The more mass, the more violent the reaction is, for a given braking distance.
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I'm going to call that improperly secured/faulty securing equipment. I've seen flatbeds in 10-15' ditches with steel rolls still chained down and upright. By far a much more violent stop than braking.
I'm going to call that improperly secured/faulty securing equipment. I've seen flatbeds in 10-15' ditches with steel rolls still chained down and upright. By far a much more violent stop than braking.
I will agree. I would guess that coil to be at least 40,000 lbs and it looks like he has 3/8" chains hanging from his headboard. A 3/8" grade 70 chain should have a WWL of 7,100 lbs, so it would be good for 14,200 lbs of cargo. It also looks like he was using coil racks. Three of those chains should be good for 42,600 lbs of cargo, but since it is not blocked from forward motion by a front end structure of other cargo, it requires one additional chain, so four 3/8" G70 chains are required at a minimum.
It could have been a failure of the attachment points, damaged or insufficient tiedowns or that the coil was not suspended off the deck, allowing it to rock within the bunks. Whatever happened, the headboard probably saved his life.
edit: I found the article from which that picture was taken: http://www.thenewsherald.co...8b0e76d719736844.txt The news source claims that the coil weighed 10,000 lbs. If that is what the driver believed, there is the problem right there. That coil is a LOT more than 10,000 lbs!
I once had a driver come in the yard with a track from a very large crane on his trailer. That track weighed 65,000 lbs and he had it tied down with two 5/16" chains. If he had had to stop in a hurry, that track would have run right over his tractor.
[This message has been edited by williegoat (edited 04-29-2015).]
I will agree. I would guess that coil to be at least 40,000 lbs and it looks like he has 3/8" chains hanging from his headboard. A 3/8" grade 70 chain should have a WWL of 7,100 lbs, so it would be good for 14,200 lbs of cargo. It also looks like he was using coil racks. Three of those chains should be good for 42,600 lbs of cargo, but since it is not blocked from forward motion by a front end structure of other cargo, it requires one additional chain, so four 3/8" G70 chains are required at a minimum.
It could have been a failure of the attachment points, damaged or insufficient tiedowns or that the coil was not suspended off the deck, allowing it to rock within the bunks. Whatever happened, the headboard probably saved his life.
edit: I found the article from which that picture was taken: http://www.thenewsherald.co...8b0e76d719736844.txt The news source claims that the coil weighed 10,000 lbs. If that is what the driver believed, there is the problem right there. That coil is a LOT more than 10,000 lbs!
I once had a driver come in the yard with a track from a very large crane on his trailer. That track weighed 65,000 lbs and he had it tied down with two 5/16" chains. If he had had to stop in a hurry, that track would have run right over his tractor.
I even run into this running dry van. The loader will put 4 straps on the back, but nothing on the front. Trucks rarely have an issue with things sliding back, it's that forward motion that gets you in trouble.
For instance. I unloaded 42,000lbs the other day, double stacked from the back forward to three rows from the front. Nothing along the front rows of double stacks to stop them from falling forward if I stopped suddenly.
I'm going to call that improperly secured/faulty securing equipment. I've seen flatbeds in 10-15' ditches with steel rolls still chained down and upright. By far a much more violent stop than braking.
The picture was just to show what happens when freight comes forward. It most likely wasn't secured properly. That said, van loads are really never secured properly, and they do come through the front of trailer time to time. Forklifts put their forks through the front accidentally all the time, it doesn't take much,
Truck brake systems are about as good as they are going to get... An air brake system is not like a hydraulic system.. there is a delay from when you see the brake lights, to when your foot hits the valve to when the air finally locks up the brakes. Trucks use all drums. Some companys have been experimenting with disk brakes which do stop it faster but they wear way to fast. The only way a truck is going to stop in a safe amount of time is keeping a good distance from the vehicle in front of you, that's it.. Take it from someone who pulls double trailers every night.
It's because you have more weight to keep the wheels from sliding in a loaded truck. Trucks are designed to stop with a load.
Brad
I can see the basis of that idea...but dont that great anti lock brake design eliminate that problem completely ? (for the guys who like anti lock systems) the wheels are NEVER supposed to slide under any condition. My motohome is on a GM P-30 truck chassis with disc brakes, and that same theory dont hold up in my reality at all...heavier I load it, harder it is to stop...it also has anti lock but I cant eliminate that because of the way the brakes run off the power steering pump instead of a vacumm booster.
[This message has been edited by rogergarrison (edited 04-30-2015).]
Even if you could shorten the stopping distance of a big rig that doesn't solve the major problem, IDIOT DRIVERS!!! I drove for over 10yrs and all the close calls I've had was because some idiot though that I could slam on the brakes to let him cut in so he wouldn't have to follow me. Or the ones that would pull out in front of me on a major highway and then sit there when I'm coming up on them at 55. Or trying to pass in a no passing zone. I could go on but you get the idea. The study they did here cited 90% of the big rig accidents were caused by an idiot in a car. After my years on the road that's a stat I fully believe.
I can see the basis of that idea...but dont that great anti lock brake design eliminate that problem completely ? (for the guys who like anti lock systems) the wheels are NEVER supposed to slide under any condition. My motohome is on a GM P-30 truck chassis with disc brakes, and that same theory dont hold up in my reality at all...heavier I load it, harder it is to stop...it also has anti lock but I cant eliminate that because of the way the brakes run off the power steering pump instead of a vacumm booster.
Semi's have anti lock brakes. It has to do with pressure on the tires, they can design it to work best unloaded or loaded, and a truck needs it brakes most loaded. Not to mention they use air brakes, which are a completely different ball game.
[This message has been edited by dennis_6 (edited 04-30-2015).]
So, as I understand it then, with air brakes as opposed to hydraulic brakes, the physics are opposite, meaning with air brakes the heavier you are the faster you stop ? I thought science was a solid thing that didnt vary in its basics. Now add this observation. A 747 jumbo jet (all are mostly the same but picked this for a best comparison) has 18 wheels/tires each with its own disc brake (hydraulic). It takes off with full load and fuel and shortly thereafter has to make an emergency landing. It has to dump or burn off thousands of pounds of fuel in order to make the landing because its too heavy to stop on the runway length fully loaded...even with added braking of thrust reversers. It also has the ability after it would slow down to use the controls to add aerodynamics to 'push' it down harder on the runway. Using the theory that heavier can stop faster, wouldnt the jet stop much faster with its full load of fuel and lightening the weight would only take it longer to stop....??? I dont understand how the same science works both ways. If heavier stops faster, shouldnt that work equally in either case ? Im comparing the semi to the aircraft because of the same number of tires and both being fully loaded, with the only differences being air and hydraulic brakes. I realize the jets gross weight is MUCH more than the truck, but it also has more brakes, and the reverse thrust of the engines that the truck does not have. The engines have enough power to push it into the sky, so reversers more than compensate for the weight difference between it and the truck percentage wise.
[This message has been edited by rogergarrison (edited 05-01-2015).]
The reason trucks, and trains use air brakes is for swapping trailers and rail cars. If they used hydraulic brakes every time you hooked to a trailer or rail car you would have to bleed out all the brakes.
So, as I understand it then, with air brakes as opposed to hydraulic brakes, the physics are opposite, meaning with air brakes the heavier you are the faster you stop ? I thought science was a solid thing that didnt vary in its basics. Now add this observation. A 747 jumbo jet (all are mostly the same but picked this for a best comparison) has 18 wheels/tires each with its own disc brake (hydraulic). It takes off with full load and fuel and shortly thereafter has to make an emergency landing. It has to dump or burn off thousands of pounds of fuel in order to make the landing because its too heavy to stop on the runway length fully loaded...even with added braking of thrust reversers. It also has the ability after it would slow down to use the controls to add aerodynamics to 'push' it down harder on the runway. Using the theory that heavier can stop faster, wouldnt the jet stop much faster with its full load of fuel and lightening the weight would only take it longer to stop....??? I dont understand how the same science works both ways. If heavier stops faster, shouldnt that work equally in either case ? Im comparing the semi to the aircraft because of the same number of tires and both being fully loaded, with the only differences being air and hydraulic brakes. I realize the jets gross weight is MUCH more than the truck, but it also has more brakes, and the reverse thrust of the engines that the truck does not have. The engines have enough power to push it into the sky, so reversers more than compensate for the weight difference between it and the truck percentage wise.
It is not a function of Air brakes changing physics, aircraft suspension is not the same as semi suspension. Maybe you will believe this site
quote
Effect of Vehicle Weight on Stopping Distance
The heavier the vehicle, the more work the brakes must do to stop it and the more heat they absorb. But the brakes, tires, springs and shock absorbers on heavy vehicles are designed to work best when the vehicle is fully loaded. Empty trucks require greater stopping distances, because an empty vehicle has less traction. It can bounce and lock up its wheels, giving much poorer braking. (This is not usually the case with buses.)
Truck brake systems are about as good as they are going to get... An air brake system is not like a hydraulic system.. there is a delay from when you see the brake lights, to when your foot hits the valve to when the air finally locks up the brakes. Trucks use all drums. Some companys have been experimenting with disk brakes which do stop it faster but they wear way to fast. The only way a truck is going to stop in a safe amount of time is keeping a good distance from the vehicle in front of you, that's it.. Take it from someone who pulls double trailers every night.
I'm all disk brakes (on my tractor) and love em. I can stop a little better, but it's not a lot different in feel. I'm not noticing a lot more wear.
Many companies have installed tattletails in the truck so they know if the driver does things that they consider dangerous or costly.
Slowing down really fast is one of the things that they monitor, and monitor closely.
For me (for instance) having to stop too fast, while I can do it, would cost me a $400.00 bonus. (Regardless of the reason)
Companies are training (as I've always been taught) to increase distance, and start slowing down miles prior to your stop. (our company wants a 5 mile average)
Doing this saves fuel, brakes, and decreases liability from accidents. BUT, on traditional trucks and trailers the brakes adjust under pressure. Light braking does not adjust them. Hard braking is what you need. >_< It's time for a redesign of the system.
I can see the basis of that idea...but dont that great anti lock brake design eliminate that problem completely ? (for the guys who like anti lock systems) the wheels are NEVER supposed to slide under any condition. My motohome is on a GM P-30 truck chassis with disc brakes, and that same theory dont hold up in my reality at all...heavier I load it, harder it is to stop...it also has anti lock but I cant eliminate that because of the way the brakes run off the power steering pump instead of a vacumm booster.
You would need to change the suspension, tires, and brake system.
All of it effects stopping distance. And currently all of it is pretty much all we have for hauling 40k in stuff across the country.
I can see the basis of that idea...but dont that great anti lock brake design eliminate that problem completely ?
Anti lock brakes don't increase the amount of traction between the tire and the road. They just keep you from applying more brake force than the tire can transmit to the road to prevent lockup. It's why ABS doesn't make you stop on ice as fast as dry pavement, even if it does keep the wheels from locking.
Anti lock brakes don't increase the amount of traction between the tire and the road. They just keep you from applying more brake force than the tire can transmit to the road to prevent lockup. It's why ABS doesn't make you stop on ice as fast as dry pavement, even if it does keep the wheels from locking.
I agree Fats. That's why I disable all of mine if at all possible. I can always stop my own cars faster without them than with them. I conducted some impromptu tests a few years ago to see. The two vehicles ive had with them, that I could not figure out how to, were the only 2 vehicles I ever had in a fender bender. Makes the motorhome WITH them even scarier to drive...like mentioned with idiot drivers all on the same road who think I can stop in 20' like their Kia. To eliminate them would be a major rebuilding job from pedal to wheels.
Little different but what about motorcycles? You'd think they would stop way short, but it doesn't stop that much shorter than an average car. I ride, and tested this haha. Most say the same.
the wheels are NEVER supposed to slide under any condition. My motohome is on a GM P-30 truck chassis with disc brakes, and that same theory dont hold up in my reality at all...heavier I load it, harder it is to stop...it also has anti lock but I cant eliminate that because of the way the brakes run off the power steering pump instead of a vacumm booster.
