Share:
How It Works
This calculator compares two trailer hitch configurations using static force and moment analysis:
- Weight Carrying (WC): The trailer’s tongue weight transfers entirely to the tow vehicle, creating a moment about the rear axle that reduces front axle load and increases rear axle load.
- Weight Distribution (WD): Spring bars create torque at the hitch ball, redistributing weight from the rear axle to the front axle and trailer axle. This helps keep the vehicle level and within GAWR limits.
The bar chart shows front and rear axle loads for each configuration, with GAWR rating lines so you can see at a glance whether any axle is overloaded.
Example Problem
A pickup truck weighs 4,668 lb with 51.6% on the front axle. Wheelbase is 130 in, rear axle to ball is 65 in. FGAWR = 4,050 lb, RGAWR = 4,800 lb. A 6,000 lb trailer has 20% tongue weight. The WD hitch has 2,000 lb total bar tension and 30 in bar length. Trailer axle to ball is 200 in.
- Vehicle front axle = 4,668 × 0.516 = 2,409 lb; rear = 2,259 lb
- Tongue weight = 6,000 × 0.20 = 1,200 lb; trailer axle = 4,800 lb
- WC front delta = −1,200 × 65 / 130 = −600 lb
- WC rear delta = 1,200 − (−600) = 1,800 lb
- WC front axle = 2,409 − 600 = 1,809 lb; WC rear = 2,259 + 1,800 = 4,059 lb
- WD trailer delta = 30 × 2,000 / 200 = 300 lb
- WD rear delta = −(130 + 65 + 200) × 300 / 130 = −912 lb
- WD front delta = −300 − (−912) = 612 lb
- WD front axle = 1,809 + 612 = 2,421 lb; WD rear = 4,059 − 912 = 3,147 lb
The WD hitch moves about 912 lb off the rear axle and 612 lb to the front, keeping both well within GAWR limits.
Frequently Asked Questions
What is a weight distribution hitch?
A weight distribution hitch uses spring bars (also called torsion bars) to create torque at the hitch ball. This transfers weight from the tow vehicle’s rear axle to the front axle and the trailer’s axle, leveling the vehicle and improving handling.
When do I need a weight distribution hitch?
Most manufacturers recommend a WD hitch when the trailer weighs more than 50% of the tow vehicle’s weight, or when the tongue weight causes the rear to sag noticeably. Many states require WD hitches above certain trailer weights.
What is tongue weight and how much is safe?
Tongue weight is the downward force the trailer coupler exerts on the hitch ball. A safe tongue weight is typically 10–15% of the total trailer weight for conventional hitches. Too little tongue weight can cause trailer sway; too much overloads the rear axle.
What do GVWR, GAWR, and GCWR mean?
GVWR (Gross Vehicle Weight Rating) is the max total weight the vehicle can carry including passengers and cargo. GAWR (Gross Axle Weight Rating) is the max load per axle. GCWR (Gross Combined Weight Rating) is the max combined weight of vehicle plus trailer.
Does a WD hitch reduce tongue weight on the frame?
No. The full tongue weight still rests on the vehicle’s frame. The WD hitch only redistributes the load at the axle level through rotational forces (torque). The GVW of the tow vehicle is the same with or without a WD hitch.
Related Calculators
- Tire Size Comparison Calculator — compare tire dimensions for your tow vehicle.
- Torque Calculator — calculate torque, force, and lever arm.
- Weight Equation Calculator — convert between mass and weight.
- Horsepower Calculator — determine engine power available for towing.
- Mass Unit Converter — convert tow ratings between pounds and kilograms.