How it works
A ball mount’s drop (or rise) is the vertical distance between the top of its shank, where it slides into the receiver, and the top of the platform the ball sits on. To tow level, that distance must make up the difference between your receiver and the trailer’s coupler.
Drop needed = (receiver height − expected squat) − coupler height
Negative result = rise needed
If you enter the ball mount you already have, the calculator shows how far off level the coupler will sit and the trailer’s approximate tilt: tilt = atan(height error ÷ distance from ball to trailer axle).
Worked example
Receiver at 20 in, coupler at 16 in with the trailer level, and the truck squats about 1 in when hitched.
- Drop needed: (20 − 1) − 16 = 3 in
- With a 2 in drop mount, the coupler sits 1 in high: within the usual 1 in tolerance.
- With a 6 in drop mount, the coupler would sit 3 in low, which is too much.
Coupler height error and trailer tilt
Tilt for a trailer with its axles 180 in (15 ft) behind the ball.
| Coupler too high or low by | Trailer tilt | Typical result |
|---|---|---|
| 1 in | 0.3° | Level enough |
| 2 in | 0.6° | Noticeable, adjust if you can |
| 3 in | 1.0° | Too much: change the ball mount |
| 4 in | 1.3° | Too much: change the ball mount |
Why level towing matters
On a tandem-axle trailer, tilting the nose down puts more load on the front axle and its tires; tilting it up overloads the rear axle. Tilt also changes tongue weight a little, and a nose-high trailer can feel less stable. On campers, a level trailer keeps the fridge, doors and water tanks working as designed.
Measure again with the trailer loaded, since springs settle under weight. If you use a weight distribution hitch, the head height is set with the bars tensioned; see the weight distribution calculator. Make sure the ball mount’s rating covers your trailer with the hitch class calculator.
Common mistakes
- Measuring to the bottom of the receiver. Use the top inside edge of the opening, the standard reference.
- Measuring on a slope. Driveways tilt; both heights must be taken on level ground.
- Leveling with the trailer empty. Springs compress under load and change the coupler height slightly.
- Forgetting squat. A soft rear suspension can drop the receiver 1–3 in once hitched.