Do You Need Supplemental Brakes to Flat Tow? (Straight Answer)

By Jeff McDonough, Founder of TowPro Academy, 10+ years and 250,000+ miles.

Short answer: In many cases, yes. Three places can require brakes on the towed car: your motorhome maker (check its manual), the states and provinces on your route (many require brakes on a towed vehicle above a certain weight, and the rules vary and change), and in some cases your insurer. Even where no rule applies, a supplemental braking system means the car helps you stop instead of pushing the motorhome. Many experienced RVers run one on every trip.

Why a towed car needs its own brakes

Your motorhome’s brakes were sized for the motorhome. Without brakes of its own, the towed car pushes on the motorhome every time you slow down. That means longer stops and more heat in the motorhome’s brakes, especially on long downgrades.

There’s also a detail many people don’t know. Most cars have power brakes: when the engine runs, a booster multiplies the force on the pedal. With the engine off, as it is on a flat tow, that power assist is mostly gone after a press or two. The pedal still works, but it takes far more force. Every supplemental braking system has to deal with this. Some are built to push hard enough without assist. Others supply assist while you tow, for example by creating vacuum for the car’s booster. The system maker will tell you which kind yours is.

Who decides whether you need them?

• Your motorhome maker. Many say a towed vehicle over a certain weight needs its own brakes, and that can apply even where the law doesn’t require them. Look in the towing section of the motorhome or chassis manual.
• Every state and province on your route. Many set a towed-vehicle weight above which brakes are required, and some also require a breakaway system. Published summaries disagree with each other and go out of date, so confirm with the official source. That means each state’s DMV or state police, or the province’s transportation ministry. Write down the date you checked.
• Your equipment and insurance. Tow bar and brake makers have their own requirements. Call your insurance agent to confirm the towed car is covered while it’s being towed.

Your rig has to meet the rules everywhere you drive, not just at home. When in doubt, set up for the strictest rule on the trip. For general towing rules by state (written for trailers, but a useful starting point), see Towing Laws by State, then confirm anything important with the official source.

Portable vs permanent systems

Portable units sit in the driver’s footwell and push the brake pedal with an arm. They cost less to install and can move to your next car, but you set them up every trip, they take up the footwell, and they have to be positioned correctly each time. Permanent systems are installed in the car, often with an actuator on the pedal arm. They’re out of sight and ready whenever you hook up, but they’re installed for one vehicle and take more time and money to fit (Lippert overview of installed vs portable systems).

How systems know when to brake

• Inertia-sensing (proportional): a sensor feels the motorhome slow down and brakes the car to match, lightly in a gentle stop and harder in a hard one. Some also need the motorhome’s brake-light signal.
• Direct: takes a signal from the motorhome’s own brake system, so the car brakes when, and as hard as, the motorhome does. Motorhomes with air brakes and those with hydraulic brakes use different designs.
• Mechanical: when you brake, the car pushes against the tow bar, and that push pulls a cable to its brake pedal. Simple, but it must be installed and adjusted exactly as its maker says.

Match the system to your motorhome first (air vs hydraulic brakes makes a big difference), then to your car. The brake maker should list your car as supported. Ask both your baseplate installer and the brake maker before you buy, and check the car’s manual for notes on electric parking brakes or brake-pedal position while towing.

The brake system is one part of the equipment chain. See how the baseplate and tow bar fit together.

Some vehicles add steps when you use a braking system. The 2026 Bronco, for example, has you pull two fuses: see flat towing a Jeep Wrangler or Ford Bronco.

The breakaway system

Most systems include a breakaway. A cable from the motorhome connects to a switch. If the car ever separates, the cable pulls the switch and the system applies the car’s brakes. Attach the breakaway cable every time, to its own approved point and not to a safety cable. Keep its power supply healthy, and test it the way the maker describes. The idea is the same as on a trailer: see How a Trailer Breakaway Switch Works.

Set it up, test it, and watch the monitor

Follow the maker’s steps for positioning, braking force and calibration. Too little, and the car isn’t helping. Too much, and its brakes drag, heat up and wear. Many systems have a monitor in the motorhome that should come on when you brake and go off when you release. If it stays on when you’re not braking, treat it as a stuck brake and pull over safely. At stops, feel near each wheel without touching it. One wheel much hotter than the others can mean too much braking. At unhook, switch the system off or remove it so it doesn’t drain the battery or press the pedal while you drive.

Common braking mistakes

• Towing without brakes when the motorhome maker or the law requires them.
• Buying a system before confirming it fits both the motorhome and the car.
• Skipping setup and calibration, or setting the force too high or too low.
• Forgetting to switch on a portable unit, or not attaching the breakaway cable.
• Ignoring a monitor that stays on.

FAQ

Is it illegal to flat tow without brakes?

It depends on the towed vehicle’s weight and on each state or province you drive through. Many require brakes above a set weight, and the rules change. Check the official source for every place on your route, and check your motorhome manual, which may be stricter.

Is a portable brake system as good as a permanent one?

Both can do the job when they’re matched to your rig and set up the maker’s way. The trade-off is convenience and cost: portable units move between cars but need setup every trip, while permanent systems are always ready but are installed for one vehicle.

Can a brake system drain my car’s battery?

Yes. Many systems draw power from the towed car’s battery, which isn’t being charged on a flat tow. Some include a charge line from the motorhome. Know where your system gets its power, and follow both the brake maker’s and the car manual’s steps for battery drain.

A brake system that draws power can also drain the toad’s battery; see flat towing battery drain.

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