I am wonder what the weight limits for a d unit is to be legal in all states. From what I can find on the internet I think it is 32,000 lbs, 20,000 lbs on the drive axle and 12,000 lbs on the steerining axle. When I checked on a base plate the rating was 33,000 lbs. The salesman tells me that it is a 33,000 lbs gvw truck. He said I can put 21,000 on the drives and 12,000 on the steering. I can't find anything on the fmcsa website to tell me I can only find info on indiviual states. Could someone clear this up for me. Thanks
First note that weight limits for any kind of truck vary within states, depending on the road you are on. In my home state of Minnesota, for example, the road at the end of our driveway has an axle weight limit of nine tons (18,000 lbs per axle), but in the spring thaw, it is reduced to seven tons (14,000 lbs per axle). Bridge weight limits change as bridge conditions change. On city streets, your truck will be legal on some streets and illegal on others.
For guidance, the front pages of the
Rand McNally Motor Carrier's Road Atlas (available at most truck stops) can be very informative. Study the North American Federal Weight and Size Limits, and the
Bridge Formula Table. These numbers apply in general to roadways that are part of the national network, though states and local jurisdictions can set their own rules.
They are not straight trucks, but there are some big-rigs out there that run legal on a 20,000 lbs. front axle. Our straight truck axle and tires are legal for 14,600 lbs. 20,000 lbs. front axles can be seen on some straight trucks, usually dump trucks and cement mixers that are made to haul a lot of weight.
If we were running a single rear axle, the legal limit would be 20,000 lbs. Running tandems close together as we do, the limit is 17,000 on each, for a total rear-axle weight of 34,000 lbs.
Thus, with 34,000 lbs. capacity in the rear and 14,600 in the front, we can legally drive on most highways at 48,600 lbs. With the truck weighing about 34,000 lbs. with no freight on board (all equipment on board, all tanks full), that leaves us with a theoretical payload of 14,600 lbs.
I say theoretical because the number assumes equal distribution of weight, which in the real world does not generally happen. Freight comes in different shapes and sizes and it is not always possible to equally distribute its weight.
Back to the Minnesota road; are we legal to run our 14,600 lbs. front axle when the axle-weight limit is reduced to 14,000 lbs.? Yes we are. The limit refers to the weight actually transmitted to the ground, and not the weight rating. But that way of determining front axle weight is not the way in all states.
This is a complex subject because a host of jurisdictions make the rules (feds, states, counties, cities, turnpike authorities, port authorities, and more). For every rule, there are several others that may or may not agree.
Our approach was to spec for the national network. We have tandem drive axles, not for the increased payload they provide, but because we wanted the smooth ride they provide. We went with the 14,600 lbs. front axle to make sure we would be legal with our large sleeper, and to have a robust front end that will hold it's alignment and provide an extra measure of safety.
Even when fully loaded, we have never come close to putting 14,600 lbs of weight on the front axle. Loaded or empty, 12,000 lbs is closer to the norm. In fact, when loaded, the front end is generally lighter because of the teeter-totter effect. The rear axles act as a pivot point and the weight in the rear tends to raise weight off the front.
Truck payloads widely vary depending on things like manufacturer's GVWR of each axle, placement of the axles and the number of axles. If you are spec'ing a new truck you have full control over such things. If you are buying a new or used truck off the lot, I would take it to a scale first, to determine what the actual truck weight is and how much of it is on each axle. With that information in hand (on the scale ticket you will receive), you can better estimate how your truck will scale out when loaded.
You are asking very good questions at the right time ... meaning before you buy the truck. There is at least one horror story out there (and true) of a truck that was configured wrong by the dealer but sold in bad faith to an unspecting customers who later learned that the front end was overweight.
