Increasing axle load limits

[Acoals]

What I don't understand is the ground pressure is the same loaded, unloaded, or overloaded

I don't follow this ground pressure logic. I don't know what the contact area is for an 18 wheeler, but let me just guess so we have a number; 8x8 contact patch per tire: 64 sq in. Multiply that by 18: 1152 sq in. So we have an empty rig that weighs 35,000lb, that is about 30lb per sq in. Load this truck to 80,000lb, now we are at 69lbs per sq in. I suppose the contact patch may increase some when you load the tires, but it isn't going to increase by 60%.

When the dump truck sinks into the mud, you dump the load and drive out. The ruts going out are way shallower than the ones going in.

 

[Truck Shop]

When the highways were built those were designed with lighter trucks at that time. This state
like many others kept increasing GVW's by adding extra axles-The problem is the higher
concentrated weight in roughly same length. In this state when GVW increased the wear and tear
climbed right with it---quoting a retired wa st dot road forman of 35 years. But since then the
total of truck traffic has more than tripled in some areas.

You can discuss all the psi on deflection, fact is it's more legalized weight in roughly the same
area, just more tires beating the hell out of it X amount more truck traffic than it was designed
for at that time. For every action there is a direct and opposite reaction.

As far as the E Truck---need to figure out a lighter battery system. Rebuilding a highway grid
to accommodate a E Truck is nut's.

 

[Tones]

They actually increased the steer limits to 6500kg-14330lb back a couple years ago. Apparently to allow for the extra weight of the emissions equipment on the engine.
The roads are all falling apart over here now, let alone giving them more of a belting by putting more weight on them.

Rebuilding a highway grid to accommodate a E Truck is nut's.

Economic stupidity over a environmental falsely, kinda like flattening a 1000 acres of trees to build a solar farm.

 

[DMiller]

Entire idea of Interstate system was built around the basics of the WWII Era Autobahn, HOWEVER, the need to STRETCH the Concrete and expenses instead of a FULL 12" equivalent of Concrete with Two layers of reinforcing RODS, the option of 9 to 10" on one layer rerod or Screen Mesh and connector bars at expansion joints was consider More COST Effective. Then Asphaltic Concrete used as a Top Layer as the original Concrete eroded or cracked.

Concrete was ALSO re-enganeared, where a CLAY additive for Plasticity and adhesive value was used instead of Lime, that is in essence adding DIRT which if watch a hand mixed concrete by a old fella, he will pitch a fit if ANY dirt gets in the Concrete. Batch plant operators take Sample of Stone and Sand to MAKE CERTAIN No dirt is shipped in.

Back in the Day as TS Noted, started out 66,000 bumped to 70,000, Can still remember myself, 73,280 and eventually the 80,000 lb loads today, on roads INTENTIONALLY Designed for 60,000.

 

[CM1995]

A tri-axle dump can legally gross 85K (don't remember exact legal gross) and change here in AL on state, county and other secondary roads. We regularly get 25 ton loads of stone delivered.

 

[cfherrman]

I don't follow this ground pressure logic. I don't know what the contact area is for an 18 wheeler, but let me just guess so we have a number; 8x8 contact patch per tire: 64 sq in. Multiply that by 18: 1152 sq in. So we have an empty rig that weighs 35,000lb, that is about 30lb per sq in. Load this truck to 80,000lb, now we are at 69lbs per sq in. I suppose the contact patch may increase some when you load the tires, but it isn't going to increase by 60%.

When the dump truck sinks into the mud, you dump the load and drive out. The ruts going out are way shallower than the ones going in.

Your math is way off, if the tire pressure is 100 psi, then regardless of weight of the truck it stays at 100 psi, even if your just rolling a mounted tire on the ground or the truck is loaded to 200k, it's still 100 psi.

A truck with tires at 100 psi that weighs 35k will have a contact patch of 350 sq inches, a truck of 80k will be 800 sq inches. More tires on the ground means each tire will be touching the ground less.

The ground pressure stays the same with different loads, but the ground contact changes.

I don't have a full understanding.

 

[Shimmy1]

Your math is way off, if the tire pressure is 100 psi, then regardless of weight of the truck it stays at 100 psi, even if your just rolling a mounted tire on the ground or the truck is loaded to 200k, it's still 100 psi.

A truck with tires at 100 psi that weighs 35k will have a contact patch of 350 sq inches, a truck of 80k will be 800 sq inches. More tires on the ground means each tire will be touching the ground less.

The ground pressure stays the same with different loads, but the ground contact changes.

I don't have a full understanding.

 

[.RC.]

They actually increased the steer limits to 6500kg-14330lb back a couple years ago. Apparently to allow for the extra weight of the emissions equipment on the engine.
The roads are all falling apart over here now, let alone giving them more of a belting by putting more weight on them.

Stop complaining about the **** roads. You voted for her and we have to pay for the olympics somehow.
LOL

 

[Tones]

No I bloody didn't

 

[Pony]

I wonder if we talk about Australian politics, they'll hear about it all the over in the US?

---

 

[Acoals]

Your math is way off, if the tire pressure is 100 psi, then regardless of weight of the truck it stays at 100 psi, even if your just rolling a mounted tire on the ground or the truck is loaded to 200k, it's still 100 psi.

A truck with tires at 100 psi that weighs 35k will have a contact patch of 350 sq inches, a truck of 80k will be 800 sq inches. More tires on the ground means each tire will be touching the ground less.

The ground pressure stays the same with different loads, but the ground contact changes.

I don't have a full understanding.

This still isn't making sense, but maybe it is just above my pay grade . . .

Static pressure inside the tires doesn't change, I follow that. This idea of the contact patch doubling with a load not so much, but I guess I have never read any science on it or actually gotten out with a ruler to measure stuff.

I do know as a matter of lot of seat o' the pants science that a loaded truck sinks a lot deeper than an empty one on a muddy job . . .

 

[crane operator]

Your math is way off, if the tire pressure is 100 psi, then regardless of weight of the truck it stays at 100 psi, even if your just rolling a mounted tire on the ground or the truck is loaded to 200k, it's still 100 psi.

I don't have a full understanding.

Tire pressure may stay the same, but the Psi put on the ground increases with weight. The air in the tires is not helium and holding the truck up.

Imagine instead of tires, that the whole truck was supported on 4x4 square tubing. As you add weight , that tubing is pushing harder and harder on the ground. tires are no different than if it was a steel tube. The air in the tire just makes it a "semi rigid" square tube.

The 100 psi in the tire is just whats required to hold it in its "square" form, not what its putting for pressure on the ground.

 

[cfherrman]

The tire squats as you load it more increasing it's footprint, and I can prove it to you.

Take a couple pieces of poster board and slide then under the tire to measure the contact patch, find the square in of the contact patch, then check your tire pressure as it will be the same. Let half the air out and do it again.

You can also do this to see how much weight is on a tire without a scale.

 

[cfherrman]

This still isn't making sense, but maybe it is just above my pay grade . . .

Static pressure inside the tires doesn't change, I follow that. This idea of the contact patch doubling with a load not so much, but I guess I have never read any science on it or actually gotten out with a ruler to measure stuff.

I do know as a matter of lot of seat o' the pants science that a loaded truck sinks a lot deeper than an empty one on a muddy job . . .

It sinks more because of soft ground, in hard ground the tire squats more. Also if you look at slightly sunk ruts from unloaded then drive back loaded the ruts are wider when you sink more.

 

[DMiller]

The average Semi on 18 tires per square inch of tread surface in contact, presents less psi that a common loaded one ton truck on 6 tires, HOWEVER, that 80,000 lbs of continuous weight as opposed to a truck weighing 18-20,000 lbs has significant pressure loading across a larger surface area and creates a pressure wave within that pavement. Where takes at minimum 4 of those one tons to make a equivalent pressure wave they cannot be as compact an area while driving normally at speed yet they imprint heavier footprint in application of PSI. Change that to autos with ever smaller footprint to distributed PSI. The major issue of all the PSI per machine is how much weight these present to a defect area of pavement, a depression, a soft spot, a frost or expansion heave, all have effects. One of those defects hit by 9 tires each carrying 12k payload will self destruct faster than a three tires load at 3k each. Change that up by advancing Max GVW and number of tires, weight per tire does not change but impacts duration and repeated presentation do. Same difference beating a pavement with a 20# hammer, or coming in with a pavement breaker on a mini ex, both can accomplish same thing, just one is faster.

 

[crane operator]

Ground pressure and tire air pressure are two different things.

And I'm quite aware that a tire spreads a little with weight.

The idea that there is only 100 psi of pressure on the ground regardless of weight is the preposterous idea here,

 

[DMiller]

Especially when Air Pressure is NOT weight, but distinguished as a Pressure applied to the containing vessel per square inch.
Woman Plant Helper at the Nuke REFUSED to move O2 and Acetylene Cylinders as had 2000lbs inside them, "Needed special Lifting equipment for the weight of 2000lbs" equates to the above statement.

And YES she was an idiot, and YES she kept her job as well got promoted.

 

[cfherrman]

A tank with psi and a tire with psi are not even apples to oranges. With a tank you are measuring the force expanding outward on the tank so it does not blowout, with a tire you are measuring your ground pressure and also pressure to keep the tire integrity intact

I took this today as a rough practical demonstration after unloading. This truck doubles in weight when loaded, 30k to 60k. Look at the tread blocks moving inwards and the 1x2 was at my finger loaded and it's moved 1" inward unloaded.

If you don't believe me, do it yourself. Check the psi, load the truck, check the psi. Use card to figure up the ground contact area and load the truck and remeasure. No matter of fancy words changes this and if you are not considering the fact that ground pressure doesn't change when the subject is weight tearing up roads I doubt you will ever grasp the answers.

Psi stand for pounds per a square inch by the way, care to explain how the ground contact patch goes up with the psi staying the same?

 

[Acoals]

I didn't think the pressure inside the tire has much to do with this conversation. I thought we were talking about the pressure the truck exerts downward on the road, not the pressure the compressed air inside the tire exerts in all directions within the tire. Unless you are driving a military or sport vehicle tire pressure doesn't change.

Unless you drive over the corner of a portable chain link fence. Then the pressure inside the tire can change rapidly. Fact.

 

[DMiller]

A tank with psi and a tire with psi are not even apples to oranges. With a tank you are measuring the force expanding outward on the tank so it does not blowout, with a tire you are measuring your ground pressure and also pressure to keep the tire integrity intact

I took this today as a rough practical demonstration after unloading. This truck doubles in weight when loaded, 30k to 60k. Look at the tread blocks moving inwards and the 1x2 was at my finger loaded and it's moved 1" inward unloaded.

If you don't believe me, do it yourself. Check the psi, load the truck, check the psi. Use card to figure up the ground contact area and load the truck and remeasure. No matter of fancy words changes this and if you are not considering the fact that ground pressure doesn't change when the subject is weight tearing up roads I doubt you will ever grasp the answers.

Psi stand for pounds per a square inch by the way, care to explain how the ground contact patch goes up with the psi staying the same?

A Tire is nothing more than a donut shaped tank. Think on that.

BTW, next set of portables get to cross, explain that to the DOT Man.