Weight distribution and adding another axle question

I know and understand the 12/34/34 balance on a 5 axle (3 truck, 2 trailer trailer length 53') configuration....

WITW does extra axles do to the weight limit / distribution? Say your truck has 4 axles and your trailer also has 4, whether or not the axles contact the pavement.....

I read somewhere that Volvo has a configuration on their new trucks that will automatically raise/lower the 3rd axle depending on what kind of weight is on the 5th wheel?

Not that I would ever need to know the answer, just curious....

 

Ok. Supposing your tractor has 4 axles and the trailer has four. Assuming a total of 8 including steers.

https://www.trucking.org/ATA Docs/W...n the Compilation of Size and Weight Laws.pdf

Page 21.

Assuming the group is no more three axles plus steer (Keep in mind 12 thousand for steer axle) the group being three axles 12 feet wheelbase to accomodate the necessary driveshafting, suspension, and so on for the group of three drives your weight allowance is going to be 45000

So the tractor 12 thousand plus 45 thousand will come out to a total tractor gross of 57000

Now for the trailer.

You talked about a 4 axle group. You probably accept that these will fit into a 16 foot wheelbase back there as a group. So thus: 52500 Pounds allowable.

And that's it.

57000 Tractor and 52500 trailer = 109500 Grossweight.

But hold on there a second.

At this point I personally am finished with this topic. There is a reason I avoid playing around with the particulars of this topic. Uncle Sam has a rule for weights, so do the states.

Now all I can do is allow the Heavy Haul People to start working over your question. They will know way more about this than I do.

For practical purposes if I had a 20 foot seacan container on a tri axle trailer chassis, the legal limit is 42000 pounds for the group similar to the 34000 pound tandem axle rule. However since it is a heavy ball bearing loaded seacan going to europe it's probably going to scale in excess of 65000 pounds for the box making a mockery of weights. You follow me?

 

8 axle combinations ("maxi's") can scale 105 in most Westerns states (Oregon, as usual being the eccentric child on the short bus...). A 15' tri scales 43,500, I forget what a quad scales. Lift as many axles as you can when empty to reduce drag. A lot of those rigs are belly dumps for walking floor trailers that haul commodities.

 

Quad is 52,500
Oregon bridge is roughly 102,500. With a 53 foot trailer. Could go up or down depending on bridge.

There's a lot of 53 flats with quad's.

 

4 5 and 6 axle flats are pretty common in Canada. It's apples and oranges though. The allowable weights are much more and some of the lift axles are self steering. I can take a standard tractor with tandem drives and a tridem trailer and run somewhere in the neighbourhood of 105,000 all day long. US? Beyond a 12-34-34 or 12-34-40 for a 10-1 spread I'm a little lost without research. I've ran almost as many permitted as non permitted or light loads in the states so I never honestly had too many worries about weights.

 

14/44/44=102,000. 12' spread on my tractor and the trailer allows for 45,000 but Oregon wont let me bridge that much gross.

 

This will give you a little insight into the Washington extended weight permits. http://www.wsdot.wa.gov/NR/rdonlyres/DF443726-F00D-48BA-A562-8A22F172F254/0/legalweigtchart.pdf

 

When you add axles, the axle rating is trumped by the states bridge laws which can limit the additional capacity as low as 4000 lbs,

 

Oregon is the only state with a lower bridge.

The rest of the north westerners have the same national bridge weights.

 

Anyone seen a trailer with 4 axles total either 2+2 or 1+3 with a 8' spread between groupings? I'm running into needing a permit for every haul and that is going to equal 300+ permits a year (most hauls are 20 miles one way). I have 7 axles now, running 12, 42, 51 lbs per grouping. I cant get my non-divisable load further forward and i am expected to get a permit for 3,000 over on the third axle per trip. If I had 4 axles on the trailer with 8' between, I could get a yearly permit for 129,000 gvw. What is it called having this configuration? I have been searching dual tandem trailer but not getting much on 4 axles.