Sandbags in the bed of a pickup truck (2023 Update)

Think about decellerations. Decellerating from 15m/s (30mph) to 0 in 50cm is a decelleration of

22G. This sand will exert a force on the body of the truck as you stop of 22*300 pounds = 6600 pounds.

If the attatchment/chassis cannot cope with this force, then it's on its way to you.

Crashes at higher speeds are of course much worse.

I've long wondered why people do this. While it's true that extra weight will increase your traction, it also increases your inertia, by exactly the same proportion. Thus, while you get extra braking power (from the increased traction) you also require increased breaking power (owing to you rgreater weight). Likewise on acceleration. And, of course, you take the risk of having the extra weight break free of its restraints, and impart abrupt forces to your truck when accelerating, slowing, cornering or going up or down hills. All in all, a bad idea as far as I can see. Of course, I routinely drive a motorcycle, not a truck, so maybe I'm missing something, but I'm pretty sure that traction management isn't it...

Al Moore

Anything of any weight given enough speed is dangerous if not tied down. Your boss is ignorant of the laws of physics. Lane

The extra weight is a give and take like you say. I drive a 4x4 now so don't do this like I used to with my old PU. One thing that isn't mentioned is that the sand can be used for traction if you or anyone else is stuck and can't get moving. I've done this for others a few times. Lane

It isn't so much a matter of getting stopped as it is getting started in the first place.

This probably makes more sense to those of us who own rear wheel drive vehicles with open differentials, and live in areas where it snows.

I got stuck once on a flat road, which was freshly plowed after a snowy afternoon. The snow under my car was packed down and like ice. There I sat, with one tire spinning slowly. I could have gotten out and easily pushed my car, but the road was too slippery, and the ass end of my car was too light to grab.

On my way home from work, I have to go up a rather steep hill from a stop. Many times, over many winters, I have passed cars which couldn't make it up the hill because they had no traction. A hundred pounds of weight in the bed of my truck wasn't enough. Nor was 200 pounds. 300 pounds is just enough. But a little more would be better. Considering 500 pounds is about the weight of my mother-in-law, I don't really consider it to be an outlandish payload.

Dave

I guess I'll start with an example.

I went to college with a guy who's best friend lived in the college town.... and he was off to jail.

The story I heard was that he was found guilty of reckless homicide, because he had a couple of engine blocks in the back of his truck. He was screwing while driving, and hit a telephone pole in town.

The engine blocks slid forward, one penetrated the cab, and killed his passenger.

I don't know if any of the facts were true about anyone getting killed or going to jail, but I did see the truck. It looked like that was what had happened.

Dave

Not to tangle with the now-notorious David A. Webb, but I suspect that story was an urban legend.

I used to own a flatbed and move things for people. They often didn't understand that it isn't normal loads you're talking about, it is "what happens when you are driving down a street at 45 mph and someone blows a stop sign at 30 and hits you front corner - your load is then very dangerous indeed and if it lets go YOU are at fault NOT the driver who ran the stop sign".

I agree with you, David, it makes sense to me to secure your sand. I hate to give someone as um argumentative as you more ammo to use on some innocent boss, though. :-)

On a related note, I never understood why dragsters have wide tires. I always thought that the force generated by friction is pounds per square inch times square inches times some coefficient. If you make the tires wider, you increase square inches but exactly as much as you decrease pounds per square inch. So it isn't clear why those huge slicks which cost so much do ANYTHING to help those guys .. oh, well, I only learned physics up to freshman level.

Grant Erw> >

My reckoning on this is that there is an optimum, too wide not good. But then I've been wrong before. Maybe someone can elaborate on this.

In aviation, this is known as a "Ground Loop"..ass wants to go first. I'd keep the sand belted firmly just behind the cab, and low. That may not help handling, but it will be a good thing to have if you, or others have to negotiate ice. A shovel of sorts would help, too.

~D

David A. Webb wrote: (clip) Considering 500 pounds is about the weight of my mother-in-law, I don't really consider it to be an outlandish payload. ^^^^^^^^^^^^ Yeah, but how are you going to get her to sit back there when the weather is cold?

Roy J wrote: (clip) The one problem that I have run into is that it dramatically increses the 'polar moment of inertia' which means that once it starts spinning it just goes and goes. ^^^^^^^^^^^^ Polar moment of inertia also makes it harder to start turning. In addition, the weight near the back of the truck lightens the front wheel traction, adding to the problem. It is called "plowing," when you try to turn, and the truck says, "When I get around to it."

So the shaft-drive pickup truck can countersteer! I'm amazed that you missed such a trivial issue, Al. :)

How are your eyes doing?

Jim

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Due to weight transfer during acceleration (note that the front wheels are often in the air) there is no shortage of pounds force on the friction surface, therefore the reason for adding more surface area, as in wider tires. The centrifugal force tends to make them narrower anyway.

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Grant Erwin wrote: (clip) If you make the tires wider, you increase square inches but exactly as much as you decrease pounds per square inch. ^^^^^^^^^^^^ It's a very good question, and it has a very good answer. The physics you are quoting applies to a linear system, in which the coefficient of friction is constant. Tires are non-linear--the coefficient of friction generally goes down as the pressure to the road goes up.

Another example where this happens has to do with cornering. If the rear of the vehicle is made stiff with respect to the front, the load transfer to the outside rear wheel results in a loss of grip, and the car oversteers (the rear end wants to slide out.) If the coefficient of friction were constant, the load transfer would produce an increase in traction on the outside wheel, exacly offset by a a decrease on the inside wheel, and there would be no effect on cornering. David A. Webb wrote: (clip) screwing while driving, (clip) The engine blocks slid forward, one penetrated the cab, and killed his passenger ^^^^^^^^^^^ It's called "coitus interruptus."

In the case of tires, friction is not the main component. Rubber in contact with the rough surface of the road is more like a gear. This has been proven over and over in the case of racing cars and dragsters, which can easily exceed 1 g acceleration, something they just could not do if only friction were involved.

Also, if you watch a dragster's tires carefully, you will see they do more than just apply the horsepower to the road. They have a stretchable tread and soft sidewalls. As speed increases their diamater increases, and not just a little bit either. As a result they are actually part of the dragster's gearing.

Hi, I know a guy who use to run a garage/ towing service. One winter's night he got a call from the local cops to come to an accident. As he pulled up to the scene, he recognized his son's best friend's pickup truck. The kid had hit a pole and one of the loose cement block in the bed for traction had taken the off the top of the kid's head. First thing this guy did when he got home even though it was 3 or 4 in the motning was take all of the blocks out of the back of all 3 of his trucks. (A week later he was able to start eating again.)

I would vote to secure the whatever weight you have in the back. For one thing, the back of the truck often comes up when they hit something so it is glass, not steel that is stopping the sand bags. The added weight does help because pickups have a front heavy weight distribution. Adding weights in the bed ( over the rear axle) increases the overall vehicle wight by a small percentage but increase the weight on the rear by a much larger percentage.

Thanks Roger Haar

*************************************************8888 "David A. Webb" wrote:

I've got my monitor screen up on the floor so I can look straight down at it+. Other than that, my condition seems to be improving. Thanks for asking...

BTW if it happens to you, don't waste any time telling yourself "I'll phone in if it isn't gone in the morning." or suchlike nonsense. Keep phoning doctors until you find one that can see you right away. In my case, the doctor who'd been monitoring the situation phoned around to specialists until he could tell me "Head right over, they're expecting you." The corrective work was done before 1:00 PM. The prognosis is good at this point -- as long as I keep looking at the space between my feet for a few days.

Al Moore

Wow, I didn't know I had gained such a reputation so quickly. Thanks!

That story may have been completely false. I seem to remember hearing about it in the news, but people tend to remember things that never happened, if they believe it to be true long enough.

One story that I know to be true, however, is this.

My grandfather was headed home from the farm one evening about 7 years ago. He was on a gravel road, and saw a combine pulling out onto the road in front of him. He slowed down to give the driver plenty of room.

A 16 year old kid was coming up from behind, and didn't see the combine. All he saw was my grandfather going very slow. So he proceeded to pass my grandfather, on the gravel road, at roughly

60mph. And slammed into the big front wheel of the combine.

A toolbox in the trunk of the car tore through the rear seat, and hit the kid in the front passenger seat in the back of his head. Major bodily damage to everyone, but the passenger has permanent brain damage. And not enough insurance to cover all of the bills.

The reason I know all of this is true is because they tried to sue my grandfather. You know how insurance companies get. Sue EVERYONE, and ask questions later. The case against my grandfather was dismissed, but not after worrying him to death for a very long time. Essentially, they were trying to say that my grandfather contributed to a hazard in the road.

Dave