He further states that "It's only true because trucks are designed without adequate braking systems and computer-controlled jackknife preventers, solely for economic reasons. There's no engineering reason why a big truck could not stop as quickly as a car."
He wraps up his arguments with:
quote
A final issue is that trucks often have higher tire loading than cars do — their tires must bear more weight than in the above example, and most people assume this affects braking efficiency. But as it happens, when you increase the loading on a tire, it presses down on the pavement with more force, and this should make the braking action more effective. So this should not prevent the truck from stopping efficiently, as long as it has an adequate braking system.
The above explains why there only needs to be one braking-distance chart for all cars, regardless of their size and weight (and assuming dry, level pavement) — the difference between car weights, tire surface areas and other factors all cancel out in the physics. The only reason this explanation doesn't apply to large trucks is because large trucks are not designed safely.
What do you think of this argument?
[This message has been edited by spark1 (edited 04-26-2015).]
Does he know how big the brakes would have to be? I drove truck for 10yrs and even with bigger brakes you won't change the weight of the load. I've had plenty of times I've had to lock up the brakes and skid all 18 wheels. More mass will always equal more stopping distance no matter how big the brakes are.
Mass times acceleration. There is only so much that can be done. Sure you can put bigger brakes on them and use engine brakes but there is only so much you can do. A large truck hauling a trailer will never stop as fast as my cars.
Theoretically, a large vehicle could be made to stop as well as a small one. But here in the real world, they aren't built that way. There are some very good reasons for that. So the argument is pretty pointless.
[This message has been edited by Blacktree (edited 04-26-2015).]
I cant take the author of this article seriously when he doesn't take numbers very seriously. He makes a statement that a 4 ton car has 4 wheels and a 20 ton truck has 20 (except for the fact that most cars are closer to the 2 ton mark and a loaded semi is closer to the 40 ton mark, and has 18 wheels not 20) Its hard to make a convincing physics argument when you play that loosely with numbers.
I certainly leave room for advancements in braking systems and technologies to produce better results.
I will agree that there is no reason a large truck could not stop with in the same distance as a car only if we are comparing the distance per ton of weight from the same speed down to fully stopped.
Added : however he does not mention the fact that the weight of the cargo and trailer is are pushing the truck when braking. The problem has little to do with the downward force of the weight but much to do with the inertia throwing weight forward.
[This message has been edited by jmclemore (edited 04-26-2015).]
That guy needs to take a ride in a truck with 40 tons of liquid loaded on it.
It's not the truck that's the problem, it's the load that doesn't want to stop.
Trucks are designed to stop better when loaded, but inertia has its limitations.
Brad
He should be given a ride with one of those Old tanker trailers, you know Brad the ones that after you stop the liquid pushes you another 10 or so feet after you come to a stop.
I cant take the author of this article seriously when he doesn't take numbers very seriously. He makes a statement that a 4 ton car has 4 wheels and a 20 ton truck has 20 (except for the fact that most cars are closer to the 2 ton mark and a loaded semi is closer to the 40 ton mark, and has 18 wheels not 20) Its hard to make a convincing physics argument when you play that loosely with numbers.
Pretty much.
"Do trucks require more stopping distance?" That's a good question, but this guy doesn't understand the physics enough to reach a conclusion. His srgument reads like a middle-school kid who watched a single episode of Bill Nye and now thinks he understands physics.
Then there's his understanding of trucking. In the US, 80-100,000 lb GVW isn't uncommon. That would be 40-50 tons. So even if you give him 2 Mulligans for the "20 wheeler" truck, it's still not uncommon for them to weigh two to three times what he's estimating. He needs to not only learn what physics is, but he needs to learn what a "truck" is.
His "knowledge" makes me think this was written for him:
[This message has been edited by Formula88 (edited 04-27-2015).]
He further states that "It's only true because trucks are designed without adequate braking systems and computer-controlled jackknife preventers, solely for economic reasons. There's no engineering reason why a big truck could not stop as quickly as a car."
He wraps up his arguments with: What do you think of this argument?
I think he's an idiot. The author makes the same "Physics Professor" assumptions that friction is independent of surface area. In the laboratory, this can be proven true. In reality, tires have a grip on the road that interacts with the surface irregularities, and does not follow textbook physics.
quote
The above explains why there only needs to be one braking-distance chart for all cars, regardless of their size and weight (and assuming dry, level pavement) — the difference between car weights, tire surface areas and other factors all cancel out in the physics.
Here is where he loses all credibility. Simplistic physics equations will tell you a Corolla will stop as fast as a Porsche. We all know that's just not true. This guy doesn't. He knows a little physics and thinks he knows everything.
Now, the question "Can a truck stop as fast as a car?" could be answered Yes. But only if a truck was constructed with a massive brake system, AND equipped with very special (currently non-existant) tires. Only then could it come close to matching the stopping distance of Aunt Matilda's Corolla.
I would think a physics professor might know something about physics. Its not practical in any way to stop 40 tons moving 60mph as fast as 2 tons. Sure its theoretically possible I guess but it would take refrigerator size calipers on 60" rotors on all 5/6 axles to do it. Thats asking a loaded semi going on the freeway to stop in twice its length... since average car stopping distance is like 115 feet or so. That just aint gonna happen. They cant stop in that distance even if they hit a concrete bridge abutment...which they usually go right on thru.
Its scarey driving my motorhome. People will cut in front of you by a few feet and stop at a red light. Ive had to drive into the median or berm to keep from running completely over them. They have no comprehension of trucks stopping power. Train is a good comparison...takes a train miles to stop after running over a car or truck.
[This message has been edited by rogergarrison (edited 04-27-2015).]
I see a few things that are off in what is said there.
Cars do not weigh four tons. Most passenger vehicles weigh between 3000-5000 pounds. That is 1.5-2.5 tons. We will just say 2 tons for the sake of argument. He is off by a factor of two on that assumption.
The next thing that stood out is he is using tire count. In order to have the same braking power by his tire count math, there would have to be the same number of brakes per tire. Brakes are not mounted per tire but per axle.
I'm no engineer, but those items stood out to me as I read over that posting.
Drove truck for 7 years. Even if you could get a big truck to stop that fast, stopping that much weight, that quickly, would be violent. Imagine a freight train stopping as fast as a car, or a ship. Both would be extremely violent events. Kinda like running into a concrete wall and stopping instantly.
[This message has been edited by dennis_6 (edited 04-28-2015).]
After re-reading the original article and the posted comment. "There's no engineering reason why a big truck could not stop as quickly as a car."
He's technically correct.
If you think about it as a design/engineering problem, most of us could come up with a design that may just work.. You could go the caterpillar route and slap 20 more tires on it to increase road and brake surface area. Or the monster tire route and just have 40" brake surfaces. Maybe throw in some magnetic braking while were at it.
So in theory yes, and like he stated, not economically viable. The ROI just isn't there.
After re-reading the original article and the posted comment. "There's no engineering reason why a big truck could not stop as quickly as a car."
He's technically correct.
If you think about it as a design/engineering problem, most of us could come up with a design that may just work.. You could go the caterpillar route and slap 20 more tires on it to increase road and brake surface area. Or the monster tire route and just have 40" brake surfaces. Maybe throw in some magnetic braking while were at it.
So in theory yes, and like he stated, not economically viable. The ROI just isn't there.
Tha statement may be technically correct, but he draws faulty conclusions from his "logic."
quote
The only reason this explanation doesn't apply to large trucks is because large trucks are not designed safely.
For someone who is supposedly discussing physics, that's a surprisingly subjective conclusion. Everything is designed to a certain level of safety. The only question is how much safety is necessary and for how much cost? (going back to your ROI point)
IMO, it's not inadequate brakes but inadequate tires. Most brakes on any vehicle will lock up but the tires can't grip the road and you slide. ABS actually releases the brakes to avoid lock up. I figure there is a compromise between dry and wet surface contact.
But in the end, it's what the tires can do. If you can lock the brakes and the tires will grab 100%, you will stop on a dime. Unfortunately anything not tied down won't.
truck tyres are the weak link they are made for long life=mileage not grip= braking distance if they made softer sticky tyres they would ware-out quickly
------------------ Question wonder and be wierd are you kind?
truck tyres are the weak link they are made for long life=mileage not grip= braking distance if they made softer sticky tyres they would ware-out quickly
There is a lot of the answer, right there. Tires are the third biggest expense for a trucking company, right behind fuel (driver's wages being #1). So, important design considerations are high tread life and low rolling resistance. Hard compounds facilitate both.
[This message has been edited by williegoat (edited 04-28-2015).]
The Volvo truck sort of looks impressive at first glance. Some things we dont know is if the trailer is loaded to gross weight. Its also only a flatbed with vinyl sides and top, so knock 35,000 pnds off. Second is the truck is only going 20-30 mph (speedo appears to be kms showing a max of 60kmph. Now show the trailer is loaded to an average load and drive it 70 mph and repeat it. Ill guess the Volvo wagon will be 6' shorter.
The Volvo truck sort of looks impressive at first glance. Some things we dont know is if the trailer is loaded to gross weight. Its also only a flatbed with vinyl sides and top, so knock 35,000 pnds off. Second is the truck is only going 20-30 mph (speedo appears to be kms showing a max of 60kmph. Now show the trailer is loaded to an average load and drive it 70 mph and repeat it. Ill guess the Volvo wagon will be 6' shorter.
I'll partially agree with you on the speed bit. If the speedo is in kms that would put the truck at just under 40. Still an impressive stopping distance in the wet. As for the load, it was clearly stated in the description of the video.
What's even scarier is all it takes is some yahoo on a cell phone, touch screen, making out, or whatever to send one of these Beasts right into you path. Far more accidents are caused by dumb people driving Cars, SUV's, and Trucks. It's too damn easy to get a license.
Just be thankful you don't drive in Russia, it's really bad over there, check out YouTube.
[This message has been edited by California Kid (edited 04-28-2015).]
Do the volvo test with a standard load in a van trailer, it will come through the front wall, and through the truck cab, and through the truck driver. Now the truck is out of control, and the driver is dead. The load has to be secured in a way that is not economically feasible to do, and shippers certainly can't be bothered.
Do the volvo test with a standard load in a van trailer, it will come through the front wall, and through the truck cab, and through the truck driver. Now the truck is out of control, and the driver is dead. The load has to be secured in a way that is not economically feasible to do, and shippers certainly can't be bothered.
There are specific performance requirements for load securement systems, including the front end structure (trailer bulkhead or headboard), designed to prevent such an occurrence. If brakes were significantly improved, these criteria might have to be reconsidered.
(a) Performance criteria —(1) Breaking strength. Tiedown assemblies (including chains, wire rope, steel strapping, synthetic webbing, and cordage) and other attachment or fastening devices used to secure articles of cargo to, or in, commercial motor vehicles must be designed, installed, and maintained to ensure that the maximum forces acting on the devices or systems do not exceed the manufacturer's breaking strength rating under the following conditions, applied separately:
(d) Penetration resistance. The front end structure must be designed, constructed, and maintained so that it is capable of resisting penetration by any article of cargo that contacts it when the vehicle decelerates at a rate of 20 feet per second, per second. The front end structure must have no aperture large enough to permit any article of cargo in contact with the structure to pass through it.
[This message has been edited by williegoat (edited 04-28-2015).]
I'll partially agree with you on the speed bit. If the speedo is in kms that would put the truck at just under 40. Still an impressive stopping distance in the wet. As for the load, it was clearly stated in the description of the video.
The stopping distance of a semi is shorter when loaded.
The major stopping problems come from either the load shifting. The trailer being light, or empty, or not having a trailer at all.
There are specific performance requirements for load securement systems, including the front end structure (trailer bulkhead or headboard), designed to prevent such an occurrence. If brakes were significantly improved, these criteria might have to be reconsidered.
(a) Performance criteria —(1) Breaking strength. Tiedown assemblies (including chains, wire rope, steel strapping, synthetic webbing, and cordage) and other attachment or fastening devices used to secure articles of cargo to, or in, commercial motor vehicles must be designed, installed, and maintained to ensure that the maximum forces acting on the devices or systems do not exceed the manufacturer's breaking strength rating under the following conditions, applied separately:
(d) Penetration resistance. The front end structure must be designed, constructed, and maintained so that it is capable of resisting penetration by any article of cargo that contacts it when the vehicle decelerates at a rate of 20 feet per second, per second. The front end structure must have no aperture large enough to permit any article of cargo in contact with the structure to pass through it.
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.
[This message has been edited by dennis_6 (edited 04-29-2015).]
The stopping distance of a semi is shorter when loaded.
Brad
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.
