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What Is a Supplemental Braking System?

Blue Ox Patriot

A supplemental braking system is a unique mechanism designed to brake your vehicle for you as you tow it. There are different designs, each with their own benefits, but the basic concept is the same - apply the brakes on your towed vehicle (dinghy) at the same time as you apply them in your motor home.

Reasons for Supplemental Braking

  1. Safety
    • By using an auxiliary braking system you will achieve a safer, more controlled towing experience. The danger of having thousands of pounds at your rear will be gone.
  2. Less stress on both vehicles
    • Your motor home, typically, is not designed to stop the extra weight of a vehicle being towed behind it. Even if the braking capacity of your motor home is greater than the weight of your dinghy, your motor home's brakes will be significantly stressed when attempting to brake that heft from behind.
    • Your towed vehicle's tires, wheels and chassis may be stressed as well if a supplemental braking system is not used. With no functional brakes, the car relies solely on the force exerted from your motor home, which shoves back on the car, not directly stopping it so much as keeping it from moving forward by exerting excessive pressure on the front of the car.
  3. Maintenance of motor home warranty
    • Motor home manufacturers place a limit on the weight that can be towed without the aid of supplemental brakes. If you exceed that recommended weight, not only do you run the risk of damaging your motor home, you are also likely to face liability issues. You may find your warranty void if you do not adhere to the manufacturer's specifications regarding the use of brakes on dinghies over a certain weight.
  4. Longer-lasting, better-functioning tow bar
    • Panicked stops without supplemental brakes are the leading cause of tow system failure. Without a braking system in place, you are far more likely to end up in a jackknife situation. This occurs when the force of your dinghy is simply too much for your tow bar to handle. By using a supplemental braking system, you ensure that your dinghy will brake along with your RV, limiting the force exerted by it and, therefore, limiting the stress on your tow bar.
  5. It's the law
    • Nearly every state and Canadian province requires supplemental brakes on towed vehicles over a certain weight, in the same way that they require brakes on trailers of a certain weight.

Compare the Different Systems

Can it...Portable Pre-Set SystemsPortable Proportional SystemsDirect SystemsVacuum-Assist Systems
Be switched between different towed vehicles?YesYesYesNo
Be monitored from my motor home?YesYesYesYes
Activate the brakes in a breakaway situation?YesYesYesYes
Brake in proportion to my motor home?NoYesYesNo
Work with continuous power-assist brakes?NoEvenBrake - No
The Patriot - Yes
With purchase of brake pressure reducer (RM-900002)
Be installed quickly and easily?YesYesNo
Installation requires an advanced mechanical background
Installation requires an advanced mechanical background
Be easily and acurately adjusted?Somewhat
Switch between 3 basic levels
Fine-tune adjustment
Adjustment is not necessary
Fine-tune adjustment

Go to Choosing a System for more help in picking the supplemental braking system that best suits your needs.

Types of Supplemental Braking Systems

Pre-Set Systems

The most basic type of auxiliary braking system is a portable, electric brake controller that applies the towed vehicle brakes upon receiving a signal from the RV that its brakes have been applied. Roadmaster's 9700 is an example of this type of system.

Roadmaster 9700

How It Works:



Proportional Systems

Perhaps the most popular towing braking systems, proportional devices are designed to brake your dinghy with the same intensity that you use to brake your RV. This way you get heavy-duty emergency braking, general everyday braking or slow-to-an-idle braking in one system with little manual adjustment necessary. Examples include Roadmaster's Even Brake and Blue Ox's Patriot systems.

Roadmaster Even Brake

How It Works:



Direct Systems

Direct systems have a much more involved installation process than most other systems, but they deliver superior braking as a result. Like basic proportional systems, direct systems offer everything from emergency braking to slow-to-an-idle action, yet they have a far better response time and require no manual adjustment. Direct systems tap into your tow vehicle's brakes to sense when and how you apply the pedal so that the actuator in the dinghy can replicate that same timing and pressure. Roadmaster's BrakeMaster is an example of this type of system.

Roadmaster BrakeMaster

How It Works:



Vacuum-Assist Systems

With a vacuum-assist system - also known as an active system - your dinghy's brake pedal will be depressed with the same intensity as you would use if you were behind its wheel at the time. This is made possible by activating the power-assist function of your towed vehicle's brakes.

The power-assist feature in your vehicle multiplies the force you place on the brake pedal for effective stopping action. This was developed to make braking easier for you, the driver. Without vacuum-assist technology, you would have to strain to apply enough pressure to your vehicle's brake pedal for adequate stopping. The development of this technology allows anyone to safely drive a vehicle without having to worry about whether he or she is strong enough to effectively stop the car.

Typically, the power-assist feature does not function when your vehicle's engine is off, as is the case when the car is being towed. This is why the first supplemental braking systems that were created were designed to work with a "dead pedal." - a brake pedal without active vacuum assist.

Active braking systems tap into a separate vacuum source to achieve power-assisted braking capability in the dinghy. As a result, your dinghy's brake pedal will be depressed with a fraction of the pressure that is typically used by supplemental braking systems. Because the amount of pressure that is applied with other systems is excessive under normal circumstances, continuous use of these systems can be harmful to your vehicle. If you do not properly set the intensity, or if the system is not adequately positioned, that extreme pressure can damage your vehicle's firewall or other brake components.

Blue Ox ToadStop II

How It Works:



Choosing a System

If you're going to be traveling through multiple states and want to be certain to adhere to each of their laws, or if you are concerned about having a system in place for safety reasons, then any supplemental braking system should do. If, however, you have other towing-related concerns that may influence your decision, then perhaps the following guidelines can help.

If you rarely tow your car but want to be prepared for those times that you do...

Maybe you're not as concerned with having all the bells and whistles, but you do need a system in place. The most economical option is a device that activates your dinghy's brakes with a predetermined intensity. Roadmaster's 9700 controller is a basic, pre-set system that should fit your purposes.

If you intend to drive on mountains or uneven terrain...

You're going to want more control than a basic system offers. Because you will be on an incline, you will need a system that can sense the braking action of your motor home. This way the dinghy will only brake slightly if you are climbing a hill and will stop with greater intensity if you are heading down one. Either a proportional system or a direct system, therefore, is recommended, because both systems will brake your dinghy in proportion to your motor home's braking.

If you're planning a long trip...

The more time you spend behind the wheel, the more control you're going to want for your towing system. Peace of mind comes from having a dependable braking system that not only works consistently, but smoothly. Vacuum-assist systems are designed to brake your dinghy as you would if you were driving it at the time. The result is smooth, even braking that is less stressful on your car.

If you tow multiple cars at different times you might switch between towing...

Several auxiliary braking systems are portable and can be easily moved from vehicle to vehicle. Most pre-set system and proportional system can be easily switched between vehicles.

If you want a do-it-yourself system...

pre-set system and most basic proportional system are relatively simple to install. Both direct and vacuum-assist systems, however, require extensive mechanical knowledge and time. That being said, almost every auxiliary braking system, following the initial installation, can be easily removed for everyday driving and quickly re-installed for towing.

If you have a vehicle with active or continuous power-assist brakes, such as a Hummer or a hybrid...

Vehicles with this feature have brakes that continue to operate normally when the engine is off. Because the vacuum-assist function is still working when these cars are in the tow position, most systems will automatically apply too much pressure to the brake pedal, because they are designed to work with "dead" pedals.

If you have a heavy-duty vehicle to tow...

The heavier your dinghy is, the more exact you'll want your braking to be. A direct system would be best for this because these systems are the most responsive to your tow vehicle's braking. The BrakeMaster, for example, can sense when and how you brake in your RV with greater accuracy than other proportional systems.

If you tow often and you are concerned about the possible wear and tear on your towed vehicle...

Vacuum-assist systems are designed to apply your dinghy's brakes as you would if you were behind its wheel at the time. By activating the power-assist function that your vehicle's brakes normally have, you can achieve adequate braking with a normal amount of pressure. This will eliminate any concerns about damage that can be caused by a system that applies excessive pressure to work with a "dead pedal."

Questions and Comments about this Article

Have a dump trailer with an automotive battery (located on the trailer) for raising and lowering the dump trailer - if installing a brake breakaway system can this battery be used instead of the smaller battery that comes with the kit?
Etrailer Expert
Reply from Les D.

@Tom your brake-away system can use any battery source that can lock the brakes and hold them fully engaged for a minimum of 15 minutes.

Reply from Tom

@LesD Thank you for the information - it confirms my thoughts.

Angela B.
I think I would go with the vacuum-assist system



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