The Physics Most RV Owners Miss

If you’ve spent any time researching towing, you’ve heard the rule:

“Keep tongue weight between 10–15%.”

It’s good advice. But it’s incomplete.

Many RV owners assume that if their tongue weight is correct, sway shouldn’t happen. Yet properly loaded trailers still experience instability every day.

Why?

Because trailer center of mass and tongue weight stability are only part of the equation.

To truly understand towing balance physics, we have to go deeper.

What Is the Trailer’s Center of Mass?

The center of mass (COM) is the point where the trailer’s weight is evenly distributed in all directions.

In a travel trailer, it shifts depending on:

• Water tank levels
• Cargo placement
• Propane and battery position
• Interior storage

When the center of mass moves rearward, tongue weight decreases.
When it moves forward, tongue weight increases.

This is why loading affects stability.

But center of mass alone does not determine sway behavior.

Tongue Weight: Necessary but Not Sufficient

Proper tongue weight:

• Improves axle loading balance
• Increases downward force at the hitch
• Reduces the likelihood of immediate instability

However, tongue weight is a static measurement.
Sway is a dynamic event.

You can have perfect 12–13% tongue weight and still experience sway under:

• Crosswinds
• Passing trucks
• Emergency maneuvers
• High-speed conditions

Why? Because rotation still occurs at the hitch ball.

Center of Pressure vs. Center of Mass

This is where most discussions stop short.

In motion, aerodynamic forces act on the center of pressure (COP)—not the center of mass.

The center of pressure is the average location where wind forces push against the trailer’s side surface.

In most travel trailers:

• The center of pressure is above the axles.
• It is often slightly rearward relative to the center of mass.

When crosswinds hit:

• Force acts at the center of pressure.
• A moment arm forms between the COP and the hitch pivot.
• Rotational torque develops.

This torque creates yaw—regardless of correct tongue weight.

That’s the missing piece in most towing balance physics discussions.

Moment Arms and Rotational Force

To understand sway, imagine this simplified system:

• The hitch ball acts as a pivot point.
• The wind applies force at a point behind that pivot.
• Distance between force and pivot = moment arm.
• Force × distance = rotational torque.

Even with proper loading, that torque exists.

Tongue weight increases resistance to instability—but it does not eliminate the pivot point itself.

As long as the pivot allows rotation, external forces can create yaw.

Why Properly Loaded Trailers Still Sway

Here’s the critical takeaway:

Loading reduces instability risk.
It does not remove the mechanical condition that allows instability.

If the trailer can pivot freely at the ball:

• Lateral force can create rotation.
• Rotation can create oscillation.
• Oscillation can amplify.

Even perfectly balanced trailers remain vulnerable to dynamic forces.

That’s why so many owners say:

“I’m within all my limits—why is this still happening?”

Because limits manage weight, not geometry.

Load Transfer During Motion

Another overlooked factor is dynamic load transfer.

Under acceleration or braking:

• Weight shifts forward or backward.
• Tongue weight changes temporarily.
• Axle loading changes momentarily.

Under crosswinds:

• Weight shifts side-to-side.
• Tire grip fluctuates.
• Suspension components flex.

These transient shifts can reduce effective stability—even if static measurements are correct.

This is why trailer loading safety is essential—but incomplete.

Why Bigger Trucks Don’t Solve It Either

Many assume upgrading the tow vehicle fixes instability.

While heavier trucks reduce sensitivity, they do not eliminate:

• The pivot point at the hitch.
• The moment arm created by wind forces.
• Rotational torque acting on the trailer.

Stability improves, but the underlying geometry remains unchanged.

The Missing Link: Pivot Geometry

The only way to remove rotational instability entirely is to change the pivot location.

The ProPride 3P® Hitch uses Pivot Point Projection™ to relocate the effective pivot point forward near the tow vehicle’s rear axle.

This eliminates the independent rotation of the trailer at the ball.

When lateral force acts:

• The trailer cannot yaw independently.
• The system behaves as a unified vehicle.
• Rotational torque is neutralized.

Loading still matters—but it is no longer your only defense.

Proper Loading + Proper Geometry = True Stability

Correct tongue weight is essential.
Balanced cargo is critical.
Understanding center of mass is important.

But those factors manage weight distribution—not rotational freedom.

True stability requires:

1. Correct loading practices
2. Proper weight distribution
3. Engineered pivot control

Without geometry control, sway remains possible—even if unlikely under ideal conditions.

Final Takeaway

The common 10–15% tongue weight rule is a starting point—not a solution.

Trailer stability depends on:

• Center of mass
• Center of pressure
• Moment arms
• Rotational torque
• Pivot geometry

Loading improves balance.
Geometry determines whether yaw can occur.

And as long as the trailer can pivot freely at the hitch ball, dynamic forces can create instability.

That’s why proper loading is necessary—but not sufficient.

True sway elimination requires eliminating the pivot that allows it.