How it works
Picture the tow vehicle as a beam on two supports, the front and rear axles. Tongue weight hangs off the back, behind the rear axle, so it levers the front up and pushes the rear down. A weight distribution hitch adds a twisting force (a moment) through its spring bars that pushes the front back down and passes part of the load to the trailer axles.
Front load lost (no WD) = T × OH ÷ WB
Bar moment M = R × T × OH × L ÷ (L + OH)
Moved to trailer axles = M ÷ L
Front change = −(1 − R) × T × OH ÷ WB
Rear change = (T − M ÷ L) − front change
T is tongue weight, WB the wheelbase, OH the distance from the rear axle to the ball, L the distance from the ball to the trailer axles and R the share of lost front load you want back. The numbers always add up: front change + rear change + load moved to the trailer equals the tongue weight.
Worked example
800 lb tongue weight, 145 in wheelbase, 48 in from rear axle to ball, trailer axles 200 in behind the ball, 50% restoration.
- Front load lost without WD: 800 × 48 ÷ 145 = 265 lb; rear gains 1,065 lb.
- With bars set for 50%: front loses only 132 lb.
- 77 lb moves to the trailer axles; the rear axle gains 855 lb instead of 1,065 lb.
Axle load changes at 50% restoration
For a 145 in wheelbase, 48 in from the rear axle to the ball and trailer axles 200 in behind the ball.
| Tongue weight | Front lost, no WD | Front lost, with WD | Rear gain, with WD | To trailer axles |
|---|---|---|---|---|
| 500 lb | 166 lb | 83 lb | 534 lb | 48 lb |
| 700 lb | 232 lb | 116 lb | 748 lb | 68 lb |
| 900 lb | 298 lb | 149 lb | 962 lb | 87 lb |
| 1,100 lb | 364 lb | 182 lb | 1,176 lb | 106 lb |
| 1,300 lb | 430 lb | 215 lb | 1,389 lb | 126 lb |
Why the front axle matters
The front tires steer and do much of the braking. When tongue weight lifts the front, steering feels light, headlights point up and the front brakes have less grip to work with. Meanwhile the rear axle can creep past its GAWR. That is why the result checks both axles: a hitch setup is only right when neither axle is over its rating.
A long rear overhang makes everything worse, because the lever is longer. Bumper-mounted hitches and long ball mounts increase the front lift; a short, sturdy ball mount reduces it. You can see the effect by changing the rear-axle-to-ball distance above. For the effect without bars, use the axle load calculator, and check the hitch weight itself with the tongue weight calculator.
Common mistakes
- Over-tightening the bars. Restoring more than 100% unloads the rear axle and can make the rig feel loose.
- Measuring from the wrong points. Use the axle centerlines and the ball center, not the bumper or the end of the trailer.
- Treating it as extra capacity. Weight distribution does not raise the tow rating, payload or GCWR.
- Setting up with an empty trailer. Adjust the hitch with the trailer loaded the way you travel.
- Ignoring sway control. Many weight distribution hitches add friction or cam sway control; it complements, not replaces, correct tongue weight.