What holds true for flying holds true for anything that moves at high speeds. Stopping is not optional. While most RV articles talk about the dynamics of motion or the joys of the destination, few address the principles of going from 60 to 0mph without damage to trailer or occupants.
While Hensley Mfg. put itself on the RV map with the introduction of the Hensley Arrow Advanced Towing System, a product designed for a vehicle in motion, we’ve recently become interested in what happens in those precious few seconds from the moment the driver pounces on the brake pedal to the sigh of relief at the end.
We began our quest with what has become a necessary evil for the trailer enthusiast: the brake controller.
Brake controllers have gone from a simple timing device to pendulums to the modern accelerometer driven devices most of us use today. The overriding theory has always been that you want your trailer brakes to engage at precisely, or slightly ahead, of the tow-vehicle’s brakes. Of course, no one has invented a brake controller that can read minds (yet), so every manufacturer has had to fall back on the one common event that occurs every time a tow vehicle’s brakes are applied: illumination of the brake lights.
Your car or truck’s brake light comes on the moment the brake pedal is pushed, slightly before any brake pressure is actually applied. Brake control manufacturers take advantage of this by tapping into that circuit (called the “Brake Light Wire” by most) and sending a small amount of power to the trailer brakes the moment it’s detected. That’s how your trailer stops “ahead” of the tow vehicle.
After that, the brake controller sends a greater or lesser amount of power to the trailer brakes, depending on the input from the accelerometer, cable to the brake, hydraulic pressure, or pendulum position, depending on which type of brake controller you have.
Brake controllers that tap into the brake line or cable to the brake pedal are the only type that can stop the trailer ahead of the tow vehicle.
Hydraulically controlled brake controllers rely on the brake light signal to make this happen. The signal from the brake line pressure doesn’t go into effect until the towvehicle brakes actuate. Cable type controllers are essentially doing the same thing, except they detect the slight “tug” on the cable instead of detecting the brake light signal. Any brake controller that connects to the brake light circuit can stop the trailer ahead of the tow vehicle.
On most brake controllers, the driver adjusts this initial power output with the GAIN control. That way, the power can be reduced in city driving to keep the trailer from “grabbing” the brakes, resulting in the “bobble head” effect on the tow-vehicle occupants. The safety issue here is that the driver can fail to turn the gain back up for high-speed driving, which can result in an accident in a panic stop situation.
Once the accelerometer or other input device takes over, the power sent to the brakes depends on two factors: the reading from the input device and the gain. In the case of an accelerometer based controller, the deceleration of the tow-vehicle is measured and, depending how rapidly the tow-vehicle is slowing, power is sent to the trailer brakes. Again, this output is limited by the gain setting. This is true of any brake controller, whether it taps into the brake line, cables to the brake pedal, or uses an accelerometer to control power to the trailer brakes. The goal of any of these controllers is to make the trailer brakes work in conjunction with the tow-vehicle brakes.
Myth #2: Proportional braking is the key to smooth trailer braking.
Brake controller manufacturers have been attempting to line up your tow-vehicle brakes to your trailer brakes for decades. The theory is that if both sets of brakes are applied at precisely the same time, smooth braking will be accomplished.
Here’s the problem: the hydraulic disc brakes in your tow-vehicle do not function the same as the electric drum brakes in your trailer. Thus the recent popularity of hydraulic trailer brakes, a very expensive “cure” for the problem. The fact is, electric drum brakes are more efficient at low speeds and hydraulic disc brakes are more efficient at high speeds. Therefore, applying the same amount of braking to both sets of brakes actually exacerbates the problem. It would be like putting a distance runner and a sprinter on the starting line together and expecting them to always finish together, no matter the distance.
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