Proper tongue weight is important, as it can affect how the truck and trailer behave (high tongue weight can cause the tow vehicle to understeer, and it can negatively affect braking performance; a low tongue weight can cause uncontrollable trailer sway).

Ford’s system uses ride height sensors, which are fairly standard parts that you normally find in vehicles equipped with air suspension (the ride height sensors tell the system to stop filling air springs when a desired height has been reached).

The F-150 doesn’t have air suspension, but it does have adaptive damping, which uses ride height sensors to monitor certain vehicle handling characteristics like body roll, and to get an idea of road conditions.

Here, allow Ford to walk you through how it uses ride height sensor input to adjust the suspension:.

You may recall that the Ford Raptor’s ride height sensors allow the truck to detect when the vehicle is in the air, firming up the dampers to prevent the suspension from bottoming-out upon landing.

Plus, thanks to the rotary ride height sensor on the control arm (shown above), the truck can tell when it’s airborne, as both wheels would then be in full rebound.

One end of a skinny pushrod hooks to a bracket hard-mounted to the vehicle’s chassis, while the other end attaches to a lever arm that’s part of a rotary sensor (I’ll guess it’s a potentiometer, of sorts) mounted to a suspension component that moves anytime the wheel travels up and down.

In the case of the 2021 Ford F-150's rear suspension, the ride height sensor is hooked to the frame on one end and to the top of the leaf spring pack on the other (specifically, it fastens to the leaf spring center pins, whose job is to bolt the leafs in a leaf spring pack together, and to locate that spring pack on the axle spring perch so that there’s no relative motion).

This is a little beyond the scope of this article, but I want you to know exactly where this ride height sensor is mounted, so take a look at this image of the rear suspension without the ride height sensor, courtesy of one of Dan Edmunds’ always-excellent suspension deep-dives.

Though I haven’t looked at the leaf pack closely, it’s safe to say the two bolts where the sensor mounts are the center pins that locate the spring to the axle by passing through the main leaf, through the helper spring, through the spacer, and poking down into two holes in the spring perch welded to the axle tube (I’ve added some arrows to Dan’s image):.

Notice how long the rear sensor’s lever arm is (two images above); I’m assuming this has to do with the tremendous suspension travel of that rear suspension, particularly at the point of measurement there at the center of the leaf pack.

As I understand it, the truck above with the rear rotary sensor is not equipped with Ford’s semi-active damping system, so the sensor is an add-on component there specifically for the Onboard Scales and Smart Hitch features.

For vehicles that do have Continuously Controlled Damping (CCD), the sensor that provides rear ride height data is actually linear and built into the damper:.

The front suspension’s rotary sensor doesn’t require as large a lever as the rear sensor on trucks without CCD, because there’s a nice pivot arm (the upper control arm) whose small displacement inboard corresponds to a large wheel displacement farther outboard on the arm where the steering knuckle mounts.

To get from the vertical displacement measurements (which Ford says are accurate to less than a tenth of an inch) that the ride height sensors generate to the weight of the load in the truck, Ford engineers are essentially using Hooke’s law: Force = spring constant * displacement.

Ford is well aware of what the spring constants are at the front and rear of the truck, since these are critical parameters needed to tune a suspension.

Note that, for coil springs, this k-value (the spring constant) is a single number, though for leaf springs, things are a little more complicated, as a suspension engineer told me over email:.

So you can have an instance where the exact same weight in a truck bed gives you two different displacement readings from the ride height sensors (illustrated by A and B above, though the curve above isn’t representative of the system, it’s just there to illustrate a concept).

I would assume that they are recording or tracking the vehicle height sensor position during large payload changes when the truck is at rest.

Finally, there is the error of the actual rotary height level sensor, which is probably at least half of the current F150 error.

Onboard scales with Smart Hitch will cost $650 and will add ride height sensors and a computer

If you want Continuously Controlled Damping (which replaces rear rotary sensors for linear ones), that adds $695