You’ve got questions. We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we waited until Tuesday to talk about the differences inertia-based and time-based brake controllers.

M.G. Charlotte, NC

Q: I am looking for a good, reliable brake controller for my trailer. Can you provide me with some information about inertia-based and time-based brake controllers? I’m not sure that I understand the difference.

A: Let’s start with inertia-based controllers. Inertia is defined as the resistance of a body in motion (in this case, your trailer) to an opposing force (in this case, braking force). Inertia-based controllers sense and react to the inertia generated from the tow vehicle’s brakes and activate the trailer brakes accordingly. Most inertia-based units use a pendulum to detect the change in inertia, and there are a few units that will allow you to tune the braking rate for a given amount of pendulum movement. With the exception of a full panic stop, inertia-based systems provide a progressive braking action to the trailer.

Time-based controllers use adjustable time settings to activate the trailer brakes. Unlike inertia-based actuators, these controllers offer instant activation of the trailer brakes when the tow vehicle brakes are applied. When you apply the brakes, the time-based controller initiates a time-sequenced progressive activation of the trailer brakes, usually via the brake light circuit. For example; when you hit the brakes, the controller can apply 10 percent of full braking force for the first half-second and then progressively add braking force until full pressure is applied (if necessary). Time intervals are usually programmable and some manufacturers will allow you to program the time interval and the percentage of force applied. This allows you to custom tune your trailer brakes to the trailer load, road conditions, etc.

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Author: Dave Matthews

Dave Matthews was a mechanic for the U.S. Army, a Ford dealership, and served for many years as a fleet mechanic for construction companies. Now a technical content producer at Summit Racing, Dave has spent decades working on everything from military vehicles to high performance race machines.