When a motorhome brakes with a flat-towed vehicle behind it, the towed vehicle's own brakes need to engage too — without that, the full stopping weight of both vehicles falls entirely on the motorhome's brake system, which most motorhomes simply aren't equipped to handle safely, especially in an emergency stop. A supplemental braking system solves this by actuating the towed vehicle's brakes proportionally as the motorhome brakes, and it's legally required in most states above certain towed weight thresholds, not just a recommended upgrade.
The Three Main System Types
Mechanical systems use the physical momentum of the towed vehicle pressing forward against the tow bar to activate its brake pedal directly through a cable or rod linkage — no electronics, no separate battery required. Simple and reliable, though generally less precisely proportional than electronic alternatives.
Portable electronic systems use an accelerometer inside the towed vehicle to detect motorhome braking and apply proportional brake pressure through a compact unit that sits on the floor near the brake pedal, removed and stored when not towing. These offer more precise, proportional braking than mechanical systems, at the cost of needing to install and remove the unit each time.
Permanently mounted systems integrate directly into the towed vehicle's brake system and remain installed full time, engaging automatically whenever the vehicle is connected for towing. The most seamless day-to-day experience, at a higher upfront installation cost and complexity.
Our Top Picks
Demco Air Force One
A premium air-actuated system trusted heavily in the specialty flat-tow installation world, offering genuinely proportional braking response with wireless monitoring in the motorhome cab so the driver can confirm the towed vehicle's brakes are engaging correctly in real time.
Highly regarded for reliability by installation professionals · True proportional braking · Wireless cab monitoring included
Premium price and installation complexity · Requires professional installation for most owners
Blue Ox Patriot Radio Frequency
A well-regarded portable system that balances proportional electronic braking against the convenience of not requiring permanent installation. The wireless RF monitor keeps the driver informed of brake activation status without a cable running between vehicles.
No permanent modification to the towed vehicle needed · Proportional response · Trusted, established brand
Requires setup and removal at each hookup/disconnect · Portable units are more exposed to being forgotten or misplaced
Brake Buddy Select 3
A direct competitor to the Blue Ox Patriot in the portable electronic category, similarly well-regarded and often compared head-to-head by flat-tow specialty shops as functionally very close in real-world performance. A solid choice when Blue Ox parts availability or pricing doesn't favor the Patriot specifically.
Proportional braking without permanent installation · Compact and easy to store · Strong reputation among RV specialty installers
Same portability tradeoff as other non-permanent systems · Requires the towed vehicle's battery to stay charged for the system to function
NSA Ready Brake Mechanical System
The straightforward, no-electronics option — a mechanical linkage that pulls the towed vehicle's brake pedal via cable tension whenever the tow bar compresses under motorhome braking. Less proportionally precise than electronic systems, but simple, reliable, and meaningfully less expensive.
No batteries or electronics to fail · Lower price than electronic alternatives · Simple mechanical reliability
Less precisely proportional than electronic systems · Some adjustment tuning needed to get braking feel right
Portable vs Permanent: Which Fits Your Towing Pattern
RVers who flat tow occasionally — a few trips a year — often prefer a portable electronic system precisely because it doesn't require permanent modification to a vehicle that spends most of its time as a regular daily driver. Full-time RVers or anyone who tows the same dedicated toad vehicle constantly get more day-to-day convenience from a permanently mounted system that's always ready without a setup step at every hookup.
Beyond Legal Compliance: Real Safety Benefits
It's worth separating the legal-minimum framing from the actual safety case for supplemental braking, because the two aren't quite the same thing. Even in situations where local law might not strictly require a braking system at your specific towed weight, the practical stopping-distance improvement from engaging the towed vehicle's own brakes is substantial — motorhomes are heavy, and adding an unbraked vehicle's weight to an emergency stop meaningfully extends how far the combined rig travels before stopping. Treating supplemental braking as a safety fundamental rather than a legal checkbox is the more useful mental model.
Testing Your System Before Every Trip
Regardless of which system type you choose, testing brake engagement before setting out — not just at initial installation — is a habit worth building into your pre-trip routine. Most systems have a straightforward test procedure: have a second person watch the towed vehicle's brake lights while you apply the motorhome's brakes at low speed in a parking lot, confirming the towed vehicle's brakes visibly engage each time. A five-minute check before a trip is far preferable to discovering a wiring or connection issue during an actual emergency stop on the highway.
Battery Considerations for Electronic Systems
Portable and permanently mounted electronic braking systems both rely on the towed vehicle's own battery to power the accelerometer and brake actuation — a battery that's died or is disconnected (common on older vehicles with a battery cutoff switch) means the braking system won't function even though the tow bar and physical connection are perfectly fine. A battery charge line, which draws a trickle charge from the motorhome while towing, is a worthwhile add-on that keeps the towed vehicle's battery topped off across a long travel day and avoids this exact failure mode.
Getting Your System Inspected Annually
Beyond pre-trip functional testing, an annual inspection by an RV service center familiar with flat tow systems catches wear that isn't always obvious from a basic brake-light test — worn cables, degraded electrical connections, or a mechanical system that's drifted out of proper adjustment over a season of use. This is a relatively inexpensive service relative to the safety and reliability it confirms, and it's worth budgeting into your annual RV maintenance routine alongside more commonly remembered items like tire and brake inspections on the motorhome itself.
Keep a simple log of when your braking system was last inspected and any parts replaced, the same way you'd track other maintenance milestones — it's a small habit that pays off both for your own peace of mind and for resale value if you eventually sell the equipment or the towed vehicle itself.
None of this needs to be complicated or formal — a simple note in your phone or a maintenance app is enough. The goal is just making sure a working system stays working, rather than discovering a gradual failure only when it matters most.
Supplemental braking is one of those categories where the investment of time and money pays for itself the very first time it's actually needed in an emergency stop — and where you'll never know for certain how many close calls it quietly prevented along the way.
Frequently Asked Questions
Is a supplemental braking system legally required in every state?
No, requirements vary by state and are generally based on the towed vehicle's weight — some states require braking above 1,500 lbs, others have higher thresholds or different rules entirely. Since interstate travel means crossing multiple states' requirements on most trips, equipping for the strictest applicable threshold is the safest approach.
Do mechanical braking systems work as well as electronic ones?
They're generally considered less precisely proportional than electronic systems, since they rely on physical tow bar compression rather than an accelerometer reading actual deceleration force. They're still a legitimate, legal, and reliable braking solution — just a different tradeoff between simplicity and braking precision.
Can I install a supplemental braking system myself?
Portable electronic systems are generally more DIY-friendly since they don't require permanent vehicle modification. Permanently mounted systems, particularly air-actuated systems like the Demco Air Force One, typically require professional installation given the complexity of integrating with the vehicle's brake system.
What happens if my supplemental braking system fails while towing?
This is exactly why wireless in-cab monitoring, offered on several systems in this category, matters — it alerts the driver immediately if the towed vehicle's brakes aren't engaging as expected, rather than discovering a problem only during an emergency stop. Regular pre-trip testing of the braking system is a standard safety habit worth building into your routine.