Truck and weight
Axle Weight Distribution Calculator
Uses static beam reactions between the kingpin and trailer tandem, then transfers kingpin load across the tractor wheelbase. Trailer reaction = cargo weight x cargo CG distance / kingpin-to-tandem span; kingpin reaction is the balance. It follows a cited OpenStax source record captured 2026-08-13.
Model how cargo position changes calculated steer, drive, trailer, and gross axle-group loads.
Enter operating details
Planning result
Enter valid values, then calculate.
- Detail
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Planning boundary: This simplified static-equilibrium estimate does not model suspension behavior or replace an actual scale reading. It does not compare weights with regulations, permits, tire limits, or equipment ratings.
What this calculator returns
This axle weight calculator models how a single combined cargo center of gravity changes steer, drive, and trailer axle-group loads. It is a transparent physics planner for carriers and loading teams. Empty connected axle weights and geometry remain user inputs, and the result reports calculated physical reactions without interpreting legal limits or regulations.
How this is calculated
The trailer is treated as a simply supported beam between the kingpin and trailer axle-group center. Cargo position determines how much cargo reaction transfers to the trailer group and how much transfers through the kingpin.
The cargo portion transferred at the fifth wheel is distributed between steer and drive groups using the tractor wheelbase and fifth-wheel position. Those reactions are added to the entered empty connected axle weights. Gross calculated weight remains the sum of all three groups.
Trailer reaction = cargo weight x cargo CG distance / kingpin-to-tandem span; kingpin reaction is the balance.
Variable definitions
- C
- Cargo weight represented by one combined center of gravity.
- x
- Cargo center-of-gravity distance behind the kingpin.
- L_t
- Distance from kingpin to trailer axle-group center.
- L_w
- Tractor wheelbase from steer axle to drive-group center.
- f
- Fifth-wheel distance ahead of the drive-group center.
Worked example
For 40,000 pounds of cargo centered 20 feet behind the kingpin with a 40-foot kingpin-to-tandem span, half the cargo reaction goes to the trailer group and half goes through the kingpin.
If the fifth wheel is 2 feet ahead of the drives on a 20-foot tractor wheelbase, 10 percent of the kingpin cargo reaction transfers to steer and 90 percent to drives. Those increments are added to the entered empty connected axle values.
How to interpret the result
Move the cargo center rearward to increase trailer reaction and reduce kingpin reaction. Move it forward to do the reverse. The relationship assumes a rigid static model and one combined cargo center.
Treat the output as a loading estimate. Confirm the actual connected vehicle on appropriate scales and use the vehicle manufacturer information for equipment ratings and setup decisions.
Assumptions and limitations
A planning statics model, not a scale ticket, suspension simulation, equipment-rating check, loading plan, or legal-limit comparison.
- It does not model suspension equalization, frame flex, multiple cargo points, liquid surge, dynamic braking, or road grade.
- Empty axle weights must describe the connected tractor and trailer in the same configuration used for the load.
- It does not determine fifth-wheel or tandem notch movement.
- It does not compare the result with legal limits, permits, tire limits, or equipment ratings.
Rules and sources used
Frequently asked questions
Does moving cargo rearward add trailer axle weight?
In this static model, yes. A rearward cargo center increases the trailer-group reaction and reduces load transferred through the kingpin.
Can this replace a certified scale?
No. Use it for planning, then confirm the loaded combination on appropriate scales.
What does gross calculated weight mean?
It is the sum of the entered empty steer, drive, and trailer weights plus the entered cargo weight. It is a physics result, not a legal-limit check.