This week I’ll discuss adjusting the weight on your tractor and trailer axles. You will find yourself adjusting your axles frequently and since it’s your responsibility to make sure your weights are legal, this is important to understand.
One tip I can give is that with light loads it’s a good idea to slide the trailer axles all the way forward. It makes it a lot easier on turns. It’s not required. It’s just a matter of preference.
Making Sure Your Axle Weights Are Legal
When you pick up a heavy load, the best advice I can give you is to not trust the weight the customer puts on the Bill of Lading. Here is an example of why you shouldn’t.
I picked up a load someplace in the middle of nowhere Kansas once. The nearest truck stop with a scale was 35 miles away. When I pulled away from the dock and started down the road the truck was struggling more than I had ever seen it do before as far as picking up speed and getting up some of the hills. The load felt really heavy, certainly a lot heavier than the 35,000 pounds that the shipper had written on the BOL.
I finally got to the truck stop, scaled the load and found my gross weight to be 85,000 pounds. That means, since my empty truck and trailer weighed 35,000, give or take a few hundred, the load was actually a 50,000-pound load, 15,000 pounds more than what was on the BOL.
I had to take the load back and have some of the freight removed, even though the shipper was upset about doing it, but they load a lot of trucks out there every day so I’m pretty sure they knew what they did and hoped I was a new driver who wouldn’t come back. But, the driver is responsible for the legality of the weight so there was no way I was going to take that load overweight.
Some shippers have their own scale but I wouldn’t trust it completely. Who knows how long it’s been since it’s been checked or how accurate it is. You really want to use a certified scale at a truck stop.
To be on the safe side, anything you pick up that says 35,000 pounds or more, scale it. As you gain experience you will be able to tell by the feel if you are heavy or not but sometimes a heavy load is loaded so well it feels lighter than it actually is and a light load may be loaded in such a way that it feels a lot heavier than it actually is. I know of one shipper I went to that made a 25,000 lb load feel like 50,000.
Once you scale, you may need to adjust the axles on the trailer to get your weights correct. Here is what the maximum legal weights are for your axles.:
- Steer axles: 12,000
- Drive axles (axles on the back of the tractor): 34,000
- Trailer axles: 34,000
Our maximum gross weight allowed is 80,000 pounds.
The trailer has axles that can be slid. Look under the trailer around the wheels you will see the locking pins that project through the trailer rails directly under the floor of the trailer. On the driver side, near the front wheels of the trailer, you will see either a handle or air valve to pull
which will pull those pins in so the axles can be slid. Once you do that it’s time to get in the truck and slide them.
Ideally, you want your drive axles and trailer axles to weigh about the same for better handling.
Sliding The Axles
Here are how the weights change when sliding the axles.
If you slide the trailer axles back toward the rear this will make the trailer axles lighter while adding weight to the tractor drive axles. Slide them forward, more weight is added to the trailer and less to the tractor.
So, the next question is how far to slide them, one way or the other.
The rails on the trailer have a line of holes. You will notice some trailers have the holes close, others have them spread farther apart. If you don’t have two different kinds of trailers to compare, measure the distance between the holes with your fingers. If your fingers are a few inches apart, those are the “close” holes, as I called them. If you have to spread your fingers really wide, those are the “far” holes.
If you look at the two images you can see the difference between the “close” and “far” holes. See the rail guide underneath the holes? In the image just above this paragraph, you can see the guide covers the distance of two holes. In the bottom image, it can fit in a space between two holes.
The reason this is important is that the distance between the holes determines how much weight will be shifted with each hole. The “close” holes will be approximately 250-350 pounds per hole, depending on how the freight is loaded. The “far” holes will adjust approximately 450-550 pounds per hole.
So let’s use an example.
The scale ticket gives us a reading as follows :
- Steer: 12,000
- Drive: 35,000
- Trailer: 33,000
We are 1,000 pounds over on the drive axles but 1,000 pounds light on the trailer. This means we have to add weight to the trailer and take it off of the drives. So let’s do it.
Make sure to lock your trailer brakes before sliding. If you have an air valve to release the pins you won’t be able to pull it unless the trailer brakes are already locked.
The holes on the trailer are “close” holes. I start by figuring it will be about 250 pounds per hole. I want to get the drive axles at or under 34,000. So, 250 lbs. x 4 = 1,000 lbs.
I want to slide the trailer axles forward 4 holes. Make sure after sliding you lock the pins back in the holes. If you have a handle you will need to release the handle. If you have an air valve, you will push the trailer air valve from in the cab of your tractor. After locking the pins back make sure to rock the trailer back and forth to secure the pins the get out and look to make sure all of them are locked in place. If you used the air release valve in the cab to lock the pins again, make sure you pull the valve back out to lock the trailer before rocking it.
The new scale ticket should look something like this:
If you have the “far” holes you would slide two holes, 500 lb x 2= 1,000 lb.
The “far”, “close” hole term is my personal term, just to let you know.
When sliding you will not have to move the truck very far, it’s just a matter of inches. At first, it will be a little difficult but with practice and time you will be able to figure it out and it will become much easier and quicker. You could ask someone who is close by to let you know when the pins are lined up.
Another option is to get yourself a “stop bar” which you can place in the holes in front or behind of the holes you want the axles to go into. This will stop your axles where you want them to be.
It’s really not as difficult to adjust weight as it may appear. Ask your trainer to let you practice, even with lighter loads.
Adjusting The Fifth Wheel
Another way to adjust axle weight is by sliding the fifth wheel, the place the trailer attaches to the tractor. Some tractors have this option, some don’t. It depends on the company you work for.
Personally, I hated doing this. Each truck I would get I would find the “sweet spot” for the fifth wheel where the need for this rarely came up. Each truck had a different fifth wheel rail configuration so none of the sweet spots were the same.
However, sometimes the trailer is loaded in such a way that your gross weight is legal, your trailer weight is barely legal but you can’t add any more to that, but your drive axles are overweight. Beer loads were good for this. This is when your fifth wheel comes into play. Adjusting it shifts weight between your drive axles and the steer axle. It will have little to no effect on the trailer axles.
There will either be a handle at the fifth wheel to pull to release the lock pins or you may be lucky and have an air release switch in your tractor. There aren’t that many holes in the fifth wheel rail but it can make a pretty big difference in the weights. You will want to lower the landing gear to remove some of the weight from the fifth wheel. If you don’t it is REALLY hard to slide and could cause some damage.
Sliding the fifth wheel forward will add weight to the steer axles. Sliding it toward the rear will add weight to the drive axles. It can seem confusing because one would think that sliding it forward would put more of the trailer weight on the drive axles since more of the nose of the trailer is across them, but it actually moves the weight to the steer axles.
When you get a truck, experiment with the first few heavy loads you get to find the sweet spot for the fifth wheel. If you aren’t having any problems with the steer axles being over 12,000 lbs and you can get your drive axles legal just with moving the trailer axles, your fifth wheel is probably fine where it is. If you find yourself having to constantly adjust it, work on finding the ideal location because the need to adjust it should happen rarely once you have it set there.
Bridge Laws And Axle Distance
This is another reason you will have to adjust your trailer axles. It can get really tricky if you have a heavy load that requires your axles to be a certain distance back but it will make the axle distance an illegal distance in one or more of the states you’ll be traveling through since each state has its own bridge law regulation.
When that situation arises you will have to contact your dispatch to find out how they want you to handle it.
What this is about is that states put a limit on how far back your trailer axles can be on a 53-foot trailer. The measurements are from the kingpin to some point on your trailer tandems.
For example, some states may measure from the kingpin to the center of the axle GROUP. Others may measure from the kingpin to the center of the REAR axle. Some have no limit. It’s the driver’s responsibility to know the law for each state and a trucker’s atlas gives you a good reference guide. It has all the information you need regarding weight and distance in the front section. You can ask your company if they have a chart you can have. Here is a link that can give you an idea of how this works.
Make sure to ask your trainer to explain the laws. It is very important.
I can’t cover every scenario here but it is very important for a driver to know this. Make sure you have your trainer work with you on all of this. Have the trainer show you where they have their fifth wheel set and if the truck you get has the same setup as their truck you can set it before you leave on your first trip. You will need to be hooked to a trailer to slide the fifth wheel.
All of this can sound pretty daunting but it won’t take long before you understand it.
Feel free to leave comments or further suggestions.
Next time, the article will discuss a very important issue, driving with heavy loads.
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