Truck Axle Weight Distribution on a 53' Trailer

The weigh station is open and your PrePass is blinking red. This is a time when you need your truck axle weight within the legal limits. The fines are steep. You could end up paying thousands of dollars.

In this blog post, we'll cover the basics of truck axle weight distribution and walk through the steps to adjusting axle weight.

Basics of Truck Axle Weight Distribution

The Federal Government regulates axle weight using the Federal Highway Administration's Bridge Formula.

In the United States, your axle weight limits are:

80,000 lbs total gross weight
34,000 lbs drive and tandem axles
20,000 lbs steering axle

While the bridge formula allows a max of 17,000 per axle, a semi rig has 2 drive axles and 2 trailer axles. The truck scales measure double axles as a single unit. Thus, the max is 34,000.

Notice that if you have 34,000 lbs on the drive axles and 34,000 lbs on the trailer tandem axles, that leaves 12,000 lbs for the steer axle. But the Bridge formula allows up to 20,000 lbs on a single steer axle.

At times you may have a heavy load where the steer axle weighs more than 12,000 lbs, but your drive and tandem axles are within legal limits. As long as the steer axle is less than 20,000 and your total weight isn't over 80,000, you're okay.

These weight limits apply when you're driving on the Interstate Highway. Non-Interstate roads in some states may have different weight requirements. You should take state limits into account in your route planning.

If you haul in Canada, they use the metric system. The weight limits there are:

5,500 kg steering axle (12,125 lbs; some provinces vary)
17,000 kg drive and tandem axles (37,479 lbs)

When to Weigh Your Truck Axles

A lot of truckers only weigh their trucks if the bill of lading (BOL) shows the freight weighs 40,000 lbs or more. Although you won't have an overweight problem if the freight is less than 40,000 lbs, keep in mind that shippers can make mistakes. For example:

The loader miscounts the pallets and you have one or more extra
The shipper loaded the wrong product, and it's heavier
The clerk may have entered the wrong weight for the product

Whatever the case, $9 is a drop in the bucket compared to the $2,000 - $3,000 or more you'd pay in fines for an overweight axle.

What's the Best Way to Distribute Axle Weight?

When you can, get the weights of your drive axles and trailer axles nearly equal. This smooths out the ride and helps prevent freight from shifting. It also helps you get good traction.

How To Adjust Tandem Axle Weight

It's best to weigh your axles when you have a full tank of fuel.

If your truck weighs less than 80,000 lbs but you're too heavy on the drive axle or tandem axle, you can adjust the weight distribution by sliding the tandem axle.

Step 1: Unlock the Tandem Axle Slide

On most trailers, you'll find a pull lever near the tandem axles. Major trailer manufacturers place it on the driver's side. Pulling the lever releases the four locking pins that hold the tandem axles in position.

With the locking pins released, you can slide the position of the tandem by moving the tractor while the trailer brake is set. Move forward to position the tandems toward the rear of the trailer. Moving the tractor backward slides the tandems toward the front.

If you're too heavy on the tandem axle, moving the tractor forward will distribute more weight to the drive axles. Moving backward puts more weight on the tandem. Just remember that you move the tractor in the direction you want to increase the weight.

Step 2: Calculate the Distance

You can estimate the amount of weight redistribution by the number of holes in the locking rail. For each hole, you shift approximately 250 lbs of weight. Take the amount you need to redistribute and divide by 250. If there's any remainder, round up to the next whole number. This tells you how many holes you need to slide the tandems.

For example, if you're too heavy on your drive axles by 900 lbs you can calculate like so:

900 / 250 = 3.6

Always round up to the next whole number. In this case, you round up to 4. You need to move the tandems forward 4 holes (by moving the tractor backward).

Keep in mind that it's an estimate. Always reweigh to confirm that you're legal.

Step 3: Slide the Tandem Axle

If you have someone to assist you. They can signal you when the tandems are in position. Make sure they stay clear while you're moving. They can release the lever to lock the pins in place.

A lot of times, you may not have anyone to assist. Mark the hole you want to move to with chalk, pencil, or a piece of tape.

If one or more locking pins won't release, try rocking the tractor back and forth a few times while the trailer brake is set. Sometimes if you're on uneven ground or on an incline, the pins won't release. Move to level ground to adjust the tandems.

Step 4: Lock the Tandem Axle

After adjusting the tandems, make sure the pins lock into the holes. You should have all four in place.

If one pin malfunctions and doesn't lock, you're still legal as long as the other 3 lock in place. Have the defect corrected as soon as you can. If you can't get at least 3 pins to lock, call roadside assist.

How To Adjust the Fifth Wheel

The fifth wheel position distributes the weight between the drive axles and the steer axle. Moving the fifth wheel forward increases the weight on the drive axle. Moving to the rear increases the drive axle weight. The fifth wheel position doesn't significantly affect the weight on the tandems.

You shouldn't need to adjust the fifth wheel very often. Once you've set the ideal position for a heavy load, the same position is ideal for all heavy loads.

If You Need To Return to the Shipper

After you pick up a load, weigh your truck as close to the shipper as you can. If there's a problem, you don't want to make a long trek back.

Some shippers have scales on site. It's convenient, but some experienced drivers recommend that you weigh at a CAT Scale location. CAT guarantees their scales‚Äô accuracy.

State Truck Axle Restrictions

A few states and most Canadian provinces have laws that limit the distance from the kingpin to the rear axle. In most cases, you're allowed a max distance of 41 feet from the kingpin to the center of the tandem axles.

California and Rhode Island measure the max distance from the kingpin to the center of the rear axle. In California, the max distance from the kingpin to the center of the rear axle is 40 feet. Rhode Island's max distance is 41 feet.

You want to make sure your trailer is loaded so that you can set your tandems to the legal distance without being overweight on one of your axles.

Conclusion

Federal highway laws limit the axle weight of commercial vehicles to reduce the wear and tear on roads and bridges. The max gross weight for a vehicle with 5 axles is 80,000 lbs.

The max drive axle weight for the steer axle is 20,000 lbs. The twin axles at the drive and tandem positions can have up to 34,000 lbs each.

States may have stricter weight restrictions on routes other than Interstate.

Some states have restrictions on the length from the kingpin to the tandem axle. Most Canadian provinces do also. California is the most restrictive. If you're going through or into these jurisdictions, you'll need to take their restrictions into account when you distribute axle weight.

April 5, 2021