I was going to post the question in the overload of the day thread, but then figured I'd just start a new one. Having a few beers with some mates and started talking about what we call GVM's (Gross Vehicle Mass) here in Australia and how they relate to the real world capacity of the truck. Now we were talking real trucks, air brakes, 11R 22.5 tyres etc, but the conversation can go to smaller vehicles as well. I'll stick with with the details of my new truck as it's fresh in my mind, but question can apply to any vehicle. Truck is bogie drive, single steer, flat bed, 400hp. Australian?, Queensland for sure, road limit mass for 3 axle truck as above is 22,500kg. GVM for my truck is 24,000kg. Front axle 6,500kg. Rear axle group 21,600kg. Rear suspension group 18,000kg. 295/80 22.5 steers and 11R 22.5 drives. Truck is speed limited as required to 100kph. The argument we were having was around the 'safety factor built into the mass limits. My theory was that speed is a factor in determining these limits. My peanut brain says that a truck weight 22,500kg going 100kph hitting a bump in the road produces 'x' amount of stress on all components. However same truck hitting same bump at 120kph will produce 'x+?' stress. Therefore same/same at 80kph will produce 'x-?'. Therefore if my truck were speed limited to 80kph would the GVM be, say 28,000kg? Following on, speed limited to 40kph would the GVM be 35,000/40,000kg? Again, my mind says speed would increase stress exponentially. Obviously there comes a point where static load is simply to high and permanent deformation of components occurs. Getting back to the Overload thread, my idea is that it mostly reverts back to speed, more specifically the ability to stop the overloaded vehicle safely. So if the speed were taken out of the equation, at what point does it become unsafe? Most of the photos in that thread are of pick ups towing overloaded trailers, steer tyres very light, limited braking, lethal accident waiting to happen at highway speeds. How about on your own property at walking pace, I'm assuming that none of the pictured pick ups/trailers had permanent deformation from the loads, therefore would that be ok? Long rambling post I realise, but just wondering what safety factor is built into components?
First off-22.5 or 24.5 have a speed rating {L} in most cases, 75 mph. It's not really about speed it's the GVW rating on combined suspension components and braking distance at 60 mph. Plus parking brakes have to hold on a 20% incline and can roll back no more that three inches. On class eight trucks there are so many calculations in design such as frame material, axle material, suspension material and designed weight it can safely carry, steering components, wheel weight rating, drive axle diameter and bearing loads. Class eight trucks are designed as trucks not a large pickup that doubles as a car.
I'm not trying to take you out of context but I suppose this was my point, if braking distance is 'x' metres/yards at 60mph then if you're only going 50mph then obviously its going to stop in a shorter distance. Therefore all other things being equal GVM should be higher?
No-for the simple fact no one drives the limit. I don't have the Kenworth calculation on braking anymore. But from memory if you have a 350 hp diesel pulling a 80,000 lb load up a 6% grade for 5 miles in the proper gear, at 20 mph it will take almost 3000 kinetic brake HP to keep it under control at the same speed 20 mph down the other side. The heat created will boil a bath tub full of water in three seconds.
Yeah I suppose when I said real world earlier, that was a bad choice of words. We're talking hypothetically about a real world senario. How about if you were driving my (or any truck), would there be a relationship between speed and what you would consider a "safe" overload. And I'm happy to take it to extremes, eg 40mph limit 10% over and then walking pace 50% over. Again I don't know, I just made those figures up for an example. And for the record, no, I don't support or encourage overloading, as stated was simply a discussion over a few beers.
Realistically on flat ground your theory works what your taking out of account on the simplist part weather suspension tires and other components can handle it is at slower speeds there is less room left between you and the car in front of you so yea it takes less distance but the people on the road will leave you less space Get on any grade witch is all you have running 11 western and without bigger brakes it ain't happening There are milk trucks here grossing 120 on enough axels they do 55 down the freeway creating a small hazard I cat imagine there stopping distance being shorter at 50 to 55 than a regular load at 60 to 65 I bet the distance increases
AzIron-There probably is nothing worse to stop than a live load {food grade trailer, especially a milk transport} Those trailers don't have the compartment baffles a fuel tanker would have. For one reason-bacteria. those trailers have to be easy to clean. When a milk transport comes to a stop it will rock/surge back and forth for over a minute. One other thing to go with this thread-Manufacture liability.
I think what you're getting at is say you have a truck that is rated for 22500kg for the roads, manufacturer rating is 24000kg but if you only moved it at 10 mph would it hurt it to load to 28000kg taking out liability, legal limits, etc what is safe for the truck to not be damaged? It would handle much more load then what it is rated for in a situation like that. You don't see it as much, but you still see the odd dump truck on a site with dirt piled in every nook of the box insanely overloaded to proof roll a pad. Or hauling dirt where trucks won't go on a actual road and they are loaded until there is absolutely no room left. Within reason at that slow of speeds, short of hitting some massive holes it's not going to hurt anything. The amount of stress the truck will take at 60 mph hitting a pot hole fully loaded is exponentially greater then a truck even 25% overloaded hitting one at walking speed.
Except frames crack, axle housings crack and springs break. Get the same crap every year from farmers over loading during wheat harvest. Loader till it breaks. The welding shop near me does a monstrous business after harvest. There is no reason to over load a vehicle period not one reason is viable. And if it's on site hauling what is the rush. If the contractor can't bid a job to get done in a reasonable time frame he needs another line of work. Been at this 48 years, owned/ operated also.
The above 2 posts is what I was getting at. Ignoring legalities, liabilities, etc, what safety factor is engineered the truck before you start breaking stuff. I have been told (correctly or not, maybe crane op can help) that lifting chains/slings have a capacity double of the WLL (working load limit)? I didn't know if that same sort of capacity was engineered into trucks. I realise now that there is no simple answer.
Yep Pony ,the safe weight limit(SWL) is half the breaking strain. That's for chains and ropes including SWR Now weight limits. My truck is the same axle configuration as yours and same tyre sizes and spring suspension. The GVM should be 22.5 tons but according to the paperwork from QLD DOT I can go to 26.4 tons. I guess if I got hauled over by the Mermaids they could only fine me on axle limits.
Over here, a twin steer, tandem drive truck has a maximum mandated GVM of 26 ton. The Mercedes Actros I used to drive had a factory gvm of 33 ton. For off-road transport for a short distance I think I had it loaded to around 36 ton.
Dont g err t me started on my days hauling silage and runng manure trucks Now here is one thing that's almost always overlooked is bearing heat about 5 months a year here it can be a major contributor to blow outs weight is friction so hot hubs transfers thru the rims to tires I have seen tires increase about 15 psi due to heat of a hub especially aluminum rims A driver for a local contractor was telling me on there 65 ton lowboy they had to get choosy about hub oil and real choosey about tires and with a gross load the trailer was designed for if over 95 degrees absolutely not more than 50mph or they would eat seal and separate tires
The real problem is fatigue, and how many cycles before failure. Average truck frame {class eight-OTR} is grade 80. Trucks for vocational use in some cases grade 100. Here's one for thought-The king pin on semi trailers was the same material grade for over 80 years under SAE. Not until 8 years ago did SAE change the specifications to a higher grade material. But what ever-load it up till you get caught or your pocket book says no more.
I can recall many years ago some trailers we used for transporting our scraper fleet (D9G/H & 631/641). In all conversations they were referred to as "100 ton trailers" and nobody could figure out why they had so many tyre failure problems, especially if one of them happened to be loaded with two D9's. Turns out that nobody read the plates closely enough. Sure the trailers were rated at 100 tonnes BUT at a maximum speed of 5mph...!! Any speed above that and they were rated at 50 tonnes maximum. As TS said above - "nobody drives the limit"
Class 8 truck 5th wheels is there different weight classes on them ?
Holland weight ratings. http://cdnmedia.endeavorsuite.com/i...8eb4e/Holland Fifth Wheel Selection Guide.pdf
We NEVER move yarders over 35/40mph or when it's over 80*.
100* ambient temp with 14/16 ply 295/75 22.5 tires running at 65 mph will have a psi of 125 to 130 on a set of drives. cold psi 100. Steers inflated cold to 105 psi can reach 135 psi plus. So when they blow it's a really big boom.
The 12.00/20's on the big yarders are at 100# and sounded like the 4th of July when they blew. I prefer to move when cool & wet out. I'm glad I changed them all over to a tubeless radial now.
The less 32 nd's of tread depth the more likely a failure. The higher the ambient temp the road surface temp climbs drastically. A drive tire with 19 32nd's tread depth inflated cold to 100 psi in 100* temps will run at 115 psi. A tire with 7 32nd's will be at 125 plus psi. Too much contact surface and way less air flow through the tread. Recap tires especially-from years of experience I only inflate to a max 93 psi cold and a recap at that psi has about a 80% less chance of exploding. That 8 psi difference on the top end of the scale makes a huge difference.
the first trailer that I towed the 120 on was a 1978 Miller with those charming walking axle beams, and 17.5's that were loaded right to sidewall. We tongue loaded the crap out of it, and still could not keep rubber on it. They spent a fortune getting those beams re-built and new bearings before I joined the company. It still dog-tracked and scrubbed rubber. I had a blowout on I-90 in Issaquah a few miles from the job and limped it there at 25 MPH on 7. That was loud for me, I don't recall if a car was near but that would have been bad! Tire guy fixed it and I got it back to the shop, and I went shopping for the 20 ton we have now with the 22" tires. That Miller had a title problem and I think they scrapped that POS, best thing that could happen IMO.
That’s good info, Truck Shop. That’s been my experience, too. After, talking to lots of folks, my retreader and fleet managers. I go with 95psi cold on caps and by doing so, substantially reduced failures. Plus, I only cap once & after that, I sell the casings. We are seeing 70F temps in Southcentral and I’m noticing a big increase of alligators on the shoulder of the Parks Highway.
I run 60 max, if I see 62 I was a little late on the brake. With the excavator on I run 55 max. If I am holding you up, I suggest you leave home earlier
It's funny how pressure will get you on either end, either high or low pressure. Too low and it's all contact and then a massive sidewall flex heat engine. A low one might not blow first, the dual next to it will fail for picking up the load.
Tires need to be gauge checked every service, anytime a trailer enters the shop even if it was seen the week before-the tires get a walk around. Bumping tires with a bat is really worthless other than it tells most there is some air inside. Checking with gauge is the only way and only takes a few more minutes. Any tire that sticks 80 psi is considered a flat in the shop and 95% of the time there is something in it. One item that tire shops have a tendency to over look on aluminum wheels is the valve stem o-ring. Every time a new tire go's on a wheel the stems are changed, when the stems corrode against the aluminum those will start leaking. Plus shop rule new tires are to be inflated laying down not standing up.
What's the reason for inflating on side?
If tire/wheel are standing the rim has a chance to not seat straight on the bead. Laying flat gravity can't control the rim.
I'm always blown away by how light a lot of other regions run trucks. What we call a tandem here is a single steer axle, and 2 drive axles. Your average tandem here in Ontario is legal for 29,000Kg(63,800lbs). Even that is derating the components as a result of axle weight laws. My steer is rated for 9100kg(20,000lbs) and my drives are 21,000kg(46,000lbs). Tri axles, or twin steers are good for 37,500kg(82,500). And we can then add a two or three axle pup trailer to add another 20-25 ton on that. Rolling down the road weighing in excess of 50 tonnes is par for the course. Probably explains the state of our roads here, but at least we get work done!
You ar getting it done we can do similar here up to 80000 lbs after you get to 64000 on steer and drives with appropriate axels you have to do the rest with pushers or tag axels on dump trucks that's Az follows fed rules for the most part you have to be permitted for no reducible load to haul over 80 thousand and the definition of reducible is less than 8 hours work to remove We just hit our first big heatwave of 110 plus in the afternoon and the tire shops are busy happens every year first big heat and all the tire shops are out of tires by the end of the week you will also see a lot of broke down trucks on side of road something about 110 degrees after that the heat just eats your weak point
I wonder about this. If the same truck is sold in both Australia and Canada, would it be an identical vehicle (apart from left/right hand drive) or built heavier for the higher GVM in Canada? Or do they just stamp the VIN plate with a higher number for different countries?
Axle mass limits for my state.
I know Australian trucks are a fair bit different than us I dont think there is much difference if any between us and Canada trucks
My tandem is good for 48K. I'm OK with that. It is a small box with short boards so I can reach in there with the 35G excavator. I recently purchased the license and downgraded the tonnage from 80K to 72K, because my combo with excavator and buckets is about 67K That leaves me with 5k of leftover bedding capacity. I don't see a future where I have a half bed of bedding gravel and then toss all the buckets in there on top of it.
Then again the manufacturers here are adding drop axles for added weight on truck, last 20yard bed dump I saw new had three drop axles with 17.5's on them in front of 46k tandem set with a 20k steer. May as well go to a trailer at that point as cannot bridge out.
Depends on the state az goes by the fed bridge witch also accounts for so many axels in so many feet I think it's like 6 axels in 29 feet is good to 72000 and 7 axels in in 32 feet is good to 78000 Purpose built dump trucks are highly expensive but can go a lot of places end dumps never will that's another reason transfers were widely popular you have a 10 wheeler truck that can haul 20 ton and fit about anywhere a waste of time for most commercial but residential and landscaping supply there really handy
Is the primary reason our boss had dump trucks. Also has short wb trailers with Bridge law drop axles they routinely haul 25t
I've always liked that idea-Lets install a drop axle or two or three and add more tare weight so we can haul more net weight. Ever look at the trailing arm bushings on one with twin drop's and the scuffed tires. Just more expense, the enemy of good is better. It has to do with Cogsworth Cogs type thinking.
Dump truck kryptonite is weight that's why they have low geared rear ends cheap transmissions and 10 liter motors that are about fried at 350 thousand not that the truck is any better shape at that point sure see a lot of trucks that were not set up right and frame is bent behind the cab
I agree AZ, wrong frame thickness, wrong drive axle housings, wrong suspension and wrong steer axle plus wrong steering gear. But hey they got it on the cheap-they think.
Lifting hardware is rated at a working load limit of 1/5 of test data.(breaking strength) If it has been exceeded at any time that rigging is no longer to be used by the the rule.
I always welcome rain or a least try to move on a cool wet road when moving a heavy load.
Exactly!
I like nice cool wet weather-it causes more boost more power to heat those tires up and dry the road off.
Dense air is fast air.