GCWR

The OP is trying to add the tractor's GVWR plus the trailer's GVWR for some reason. Don't do that.

You can only put on the road a tractor + trailer + load that weigh equal or less than ANY truck or trailer's lowest GVWR in the combination. If the tractor's GVWR is 80k & the trailer's GVWR is 50k, then you can only go down the road at 50k or less, not 130k. You do not add the individual GVWRs.

 

Everything depends on two factors: the legal federal limit and the rating of the axles.

While it is easy to understand, you are making it out as really complicated when it is not.

The federal limit is 40,000 per unit or 80,000 live weight on all the axles.

So you have five axles on an average truck, the steers are the one with the lowest rating, 12,000lbs to 18,000lbs - the latter is not common on road trucks.

The tandems on both the truck and trailer are rated for 34,000lbs.

So you can plate our truck for 100k, but it won't be legal because of the limitations of the axles and it could be a case of a hefty fine and OOS.

To recap, an average truck has these ratings, which are absolute max and can not be exceeded by regulation.

• Steering axle: 12,000 pounds

• Tandem drive axles: 34,000 pounds

• Tandem trailer axles: 34,000 pounds

• Total truck and trailer gross weight: 80,000lbs.

If you add an axle to the truck or trailer, you may not get the full 17,000lbs of the axle's capacity because of the bridge laws, which is another long discussion in itself. You may end up with 12,000lbs capacity.

 

Adding an extra axle only adds 9k capacity. Regardless of whether it's a drop axle. Or a full fledged axle.

In states that play by federal rules.

 

Your asking the wrong person. But a tridem is only good for 43.5k. federally speaking.

Isn't Florida the only state allowing 20k?

 

That's how they get 40K on a spread. 2 x 20K per axle.

 

You Can run regular axles too with non divisible loads.

 

Florida has that kingpin law like Tennessee and Connecticut. But Florida allows 44k on the trailer tandems.

 

Also the lowest rated item can change thing, like tires on your steers, tires rated 12K when installed on a 29K axle lower your capacity, but installing 20k tires on a 12K axle its still 12K. Lowest rating wins.