Trailer brakes and brake controllers: when states require them and how to set them up
Check brake laws, match a controller to your trailer and set the gain for each load
Safety Behind the Wheel Foundation built this guide from the California Department of Motor Vehicles (DMV) trailer handbook, Federal Motor Carrier Safety Administration (FMCSA) rules, National Highway Traffic Safety Administration (NHTSA) recall guidance, state brake laws and published braking research. Every source is listed at the end.
Why trailer brakes are crash prevention equipment
California’s trailer handbook notes that tow vehicle brakes are usually good. Still, they may lack the strength to safely stop the extra hundreds or thousands of pounds a trailer adds [1]. It also warns that most RVs weigh more than cars and need longer distances to stop [1].
When a trailer has no working brakes, the tow vehicle has to slow both. The trailer keeps pushing forward through the hitch. That can stretch out the stop and make the rig harder to control.
A 2024 study shows what is at stake. Researchers in Slovakia ran braking tests with a car towing a small trailer with an inertia brake [2]. That design works on the same push on the hitch idea as the surge brakes on many U.S. boat trailers [1, 2].
With working trailer brakes, the pair slowed harder and stopped in a shorter distance [2]. When the trailer brakes did not work, the trailer pushed against the car, and the forces on the cargo straps were the highest of any test [2]. The authors added that this brake type often works poorly in real use because its cables and rods are out of adjustment [2].
The tests used one small trailer at low speed, so your numbers will differ. The lesson still applies: trailer brakes add safety only when they are the right type, set up well and kept in good condition [2].
The main kinds of trailer brakes
The brakes on your trailer decide what, if anything, you need in the tow vehicle.
Comparison compiled by Safety Behind the Wheel Foundation
Main types of trailer brakes
| Brake type | How it is applied | Often found on | Needs a controller in the tow vehicle? |
|---|---|---|---|
| Electric | A controller in the tow vehicle sends an electric signal to the trailer brakes [1] | Most travel and fifth wheel trailers [1] | Yes |
| Surge | The trailer’s forward push on the hitch applies them [1] | Boat trailers and folding campers [1] | No |
| Electric over hydraulic | An electric signal runs a pump that powers hydraulic brakes | Some heavier and boat trailers | Yes, one listed for this type |
| Air | Air lines from a truck with air brakes | Large commercial trailers | Part of the truck’s air system |
Electric brakes use small electromagnets inside each brake drum. When power arrives through the trailer wiring, the magnet pulls a lever that presses the brake shoes against the drum. More power means harder braking. No power means no trailer braking, so the wiring and plug matter as much as the brakes.
Surge brakes have a sliding actuator built into the coupler, the part that fits over the hitch ball. As the tow vehicle slows, the trailer moves forward and compresses it, which applies the trailer brakes [1]. Backing up pushes the same way, so many surge systems have a reverse lockout. Learn how yours works before your first trip.
Electric over hydraulic systems turn a controller’s electric signal into hydraulic pressure. Not every controller can run them, so check that the controller’s instructions list this brake type.
When the law requires trailer brakes
There is no single U.S. weight at which every personal trailer needs brakes. Each state writes its own rule, and states measure weight in different ways.
Some states count gross weight, which California’s handbook defines as the vehicle plus its load [1]. Ohio uses empty weight for most trailers [6]. Minnesota also compares the trailer with the tow vehicle [4]. Read your state’s wording closely, because the same trailer can pass one test and fail another.
Comparison compiled by Safety Behind the Wheel Foundation
Trailer brake rules in five states
| State | When brakes are required | Other rules worth knowing |
|---|---|---|
| Washington | Brakes on all wheels, but trailers of 3,000 lb gross or less may skip them if conditions are met, such as weighing no more than 40% of the tow vehicle [3] | Over 3,000 lb, brakes must apply on breakaway and hold at least 15 minutes. One control must work all service brakes [3] |
| Minnesota | Gross vehicle weight of 3,000 lb or more, or a gross weight above the tow vehicle’s empty weight [4] | Surge brakes count. Over 3,000 lb, brakes must stop and hold a trailer that breaks loose [4] |
| Florida | Brakes on all wheels, with a similar 3,000 lb and 40% exception [5] | Over 3,000 lb, brakes on all wheels must apply on breakaway and hold at least 15 minutes [5] |
| Ohio | Most trailers with an empty weight of 2,000 lb or more [6] | The driver must be able to apply them from the cab. Boat trailers of 3,000 lb or more built since 2008 need surge or electric brakes on two wheels [6] |
| California | Travel and camp trailers of 1,500 lb gross or more, per the DMV’s trailer handbook [1] | Breakaway switches are required on any trailer of 1,500 lb gross or more built after 1955 [1] |
In Great Britain, a trailer that weighs over 750 kg (about 1,650 pounds) when loaded must have a working brake system [7]. British rules also call for a breakaway cable or a backup coupling [7].
Plan for the strictest rule on your route, since a trailer that is legal at home may need brakes in the next state. Weigh the trailer loaded at a public scale rather than guessing. Also read the tow vehicle’s owner’s manual, which may call for trailer brakes at a lower weight than the law does. Breakaway systems, which apply the trailer brakes if the trailer comes loose, have their own companion guide.
Towing for work: federal rules for commercial rigs
Contractors, landscapers and other trades often tow heavy trailers. Federal motor carrier rules cover a commercial motor vehicle used in interstate commerce. That includes a vehicle or combination with a weight rating, or an actual weight, of 10,001 pounds or more [8].
Under those rules, every commercial motor vehicle must have brakes on all wheels [9]. Trailers of 3,000 pounds or less are excepted when their axle weight stays within 40% of the tow vehicle’s axle weights [9]. All brakes on a vehicle must be capable of working at all times [10].
Surge brakes are allowed only within limits. A trailer rated up to 12,000 pounds may use them if its rating is no more than 1.75 times the tow vehicle’s rating [10]. Heavier trailers, up to 20,000 pounds, are held to 1.25 times [10].
The rules expect one control to apply all service brakes in the combination, and they allow an extra control just for the trailer brakes [11]. A controller’s manual lever fills that role on many work rigs.
Stopping power and load security go together. Federal cargo rules plan for hard stops that throw cargo forward with a force of 0.8 g [12]. In the test above, strap forces rose most when the trailer brakes failed [2].
How a brake controller works
Some state laws expect the driver to run the trailer brakes from the driver’s seat. Ohio says trailer brakes must be designed for the driver to apply from the cab, with the rearmost brakes coming on in step with the tow vehicle’s [6]. Washington requires one control to work all service brakes [3].
For electric brakes, that control is the brake controller. California’s handbook explains that it links the two braking systems so they work together when you press the brake pedal [1].
Comparison compiled by Safety Behind the Wheel Foundation
Types of brake controllers
| Controller type | How it sets braking power | Good to know |
|---|---|---|
| Time delayed | Ramps up power over a set time once you press the pedal | Gives about the same output for a gentle or hard stop |
| Proportional | A motion sensor reads how fast the tow vehicle is slowing and matches it | Smoother stops. Some must be mounted at a set angle |
| Factory built in | Part of the tow vehicle and its dashboard | Check the owner’s manual for the brake types it supports |
Two settings matter most. Gain is the top amount of power the controller will send to the trailer brakes. Some controllers also offer a boost setting that adds a little extra braking at the start of a stop for heavy loads.
Controllers also have a hand lever or button that applies only the trailer brakes [1]. You will use it to set up the controller and, at times, while driving.
Choosing a matched setup
A controller and brakes are only as good as their match. Start with the trailer. Find out its brake type and how many brakes it has, since a tandem axle trailer may have four. The controller must be rated for that number.
Next, check the tow vehicle. Its manual lists towing limits and may say when trailer brakes are needed. Some vehicles have a factory controller or a plug in point for one under the dash.
Buy from sellers who can answer technical questions. Good choices include truck and trailer equipment suppliers, the vehicle dealer’s parts department, trailer and RV dealers, and distributors of rated towing equipment. Unless you are trained in vehicle wiring, have a towing systems technician install it. Wiring and the trailer plug have a companion guide.
Setting up and testing a brake controller
Always follow the controller maker’s instructions first. The routine below shows the general order of a careful setup.
- Load the trailer the way you plan to tow it. Gain set for an empty trailer can be wrong once it is full.
- Hitch up fully. Latch the coupler, cross the safety chains, attach the breakaway cable and connect the plug.
- Check the controller’s display or light. It should show that the trailer brakes are connected.
- For a proportional unit, confirm it is mounted at the angle its instructions require.
- Start with the gain at the setting the instructions suggest for your trailer weight.
- In a dry, level, empty paved lot, drive slowly in a straight line and squeeze the manual lever all the way.
- The trailer brakes should grab firmly. If the trailer wheels lock or skid, turn the gain down. If you barely feel the trailer slowing, turn it up and try again.
- Now test with the brake pedal. A good stop feels like one smooth vehicle, with no shove from behind and no tug at the hitch.
- Write down the gain for each kind of load, and reset it whenever the load changes.
Surge brakes need a different check. Look at the fluid level in the actuator, make sure it slides freely and learn the reverse lockout. Then make a few slow stops in an empty lot to feel the brakes engage.
Using trailer brakes on the road
Good brakes do not cancel the extra weight. Leave much more space ahead than usual, because RVs need longer distances to stop [1].
On long downhill grades, use lower gears as your main way to control speed and save the brakes [1]. Safety Behind the Wheel Foundation gives everyone who tows the same advice. Brakes can fade, or lose grip, when they overheat from long use [1].
Sway is a side to side motion that can grow quickly. California’s handbook says a squeeze of the controller’s hand lever, which brakes the trailer alone, can help settle a trailer that is starting to sway [1]. Use a steady squeeze and avoid sudden steering. Once safely stopped, check whether the load has shifted [1]. Sway control equipment has its own companion guide.
If the controller warns that the trailer is not connected, you have lost trailer braking. Pull over when it is safe and do not continue until it is fixed. Never count on the manual lever to hold a parked rig. Use the parking brake and wheel chocks.
Maintenance and common mistakes
California’s handbook says trailer brakes must always be properly adjusted [1]. The Slovak test found that poorly adjusted cables and rods often weaken inertia brakes [2]. Brakes that feel fine in town may fall short in a hard stop.
Follow the trailer maker’s brake service schedule. A careful inspection looks at shoes, drums, magnets or hydraulic parts, bearings and wiring. Boat trailers dipped in salt water need extra attention to rust. After a collision, a curb strike or a breakaway, have the brakes and controller checked before you tow again.
Check for recalls, too. NHTSA lets you search vehicles, tires and other equipment for safety recalls and sign up for alerts [13]. Search for your trailer and controller, not just your truck.
Frequently asked questions
Does my small utility trailer need brakes?
It depends on its weight and your state’s rule. Many light utility trailers come without brakes. In the states reviewed here, the trigger runs from 1,500 to 3,000 pounds, and Ohio counts empty weight for most trailers [1, 3, 4, 5, 6]. Weigh the trailer loaded, then check your state’s vehicle code or DMV handbook and the rules of every state you will cross. If the tow vehicle’s manual calls for trailer brakes at a lower weight, follow it.
Can I use any brake controller with any trailer?
No. The controller must match the brake type and the number of brakes. Electric over hydraulic systems need a controller that lists them in its instructions. Surge brakes do not use a controller at all. Bring the trailer’s details to a qualified seller or installer and ask them to confirm the match before you buy.
Do surge brakes need a controller?
No. Surge brakes apply themselves when the trailer pushes forward on the hitch as you slow down [1]. They still need care: learn the reverse lockout, check the fluid and keep the actuator moving freely. Minnesota accepts surge brakes as meeting its trailer brake rule [4]. For commercial rigs, federal rules limit surge brakes by weight [10].
What should I do if my trailer brakes lock up or feel weak?
If the trailer wheels lock or skid, the gain is likely too high for the load or the road. If the trailer shoves the tow vehicle, the gain may be too low or the brakes may need work. Retest in an empty lot. If the problem stays, have a trailer brake technician inspect the brakes, wiring and controller. Poor adjustment is a common cause [1, 2].
If I tow for my business, do federal rules apply?
They may. Federal motor carrier rules cover vehicles used in interstate commerce with a weight rating or weight of 10,001 pounds or more [8]. That can include a truck and trailer together. Those rules require brakes on all wheels, with a narrow exception for light trailers [9]. Ask your state’s motor carrier office or FMCSA how the rules apply to your work.
The bottom line
Recommendation from Safety Behind the Wheel Foundation
Safety Behind the Wheel Foundation urges everyone who tows a heavy trailer to match, set and test its brakes before the trip. Trailer brakes help a heavy rig stop in a controlled, predictable way. Learn the rule in every state on your route, then match the controller to the trailer’s brake type and number of brakes. Set the gain with the trailer loaded, test it in an empty lot and reset it when the load changes.
Treat the brakes as safety equipment, not a one time install. Keep them adjusted, inspect them on schedule and check for recalls. A well matched system protects your family, your cargo and everyone sharing the road.
Related articles
Sources and further reading
- 1California Department of Motor Vehicles. Recreational Vehicles and Trailers Handbook (DL 648). Revised November 2011; accessed October 2026. dmv.ca.gov/…/recreational-vehicles-trailers-handboo…
- 2Synák F, Jakubovičová L. Assessing the risks arising from a trailer connected behind a passenger car. Scientific Reports, 14:21937 (via PubMed). Published September 20, 2024. Data year: 2024 (experimental measurements). [https://pubmed.ncbi.nlm.nih.gov/39304691/](https://pubmed.ncbi.nlm.nih.gov/39304691/) (DOI [https://doi.org/10.1038/s41598-024-73107-2](https://doi.org/10.1038/s41598-024-73107-2)) doi.org/10.1038/s41598-024-73107-2
- 3Washington State Legislature. RCW 46.37.340, Braking equipment required. Last amended 2016 (2016 c 22 s 5); accessed October 2026. app.leg.wa.gov/rcw/default.aspx?cite=46.37.340
- 4Minnesota Office of the Revisor of Statutes. 2025 Minnesota Statutes, Section 169.67, Brakes (subdivision 3). 2025 edition. revisor.mn.gov/statutes/cite/169.67
- 5The Florida Senate. The 2025 Florida Statutes, Section 316.261, Brake equipment required. 2025 edition. flsenate.gov/Laws/Statutes/2025/316.261
- 6Ohio Revised Code. Section 4513.20, Brake equipment for vehicles. Effective June 30, 2007; accessed October 2026. codes.ohio.gov/ohio-revised-code/section-4513.20
- 7GOV.UK. Towing with a car: Trailers, caravans and towing equipment. Updated September 17, 2026. gov.uk/…/trailer-and-towing-equipment
- 8Electronic Code of Federal Regulations (eCFR). 49 CFR 390.5, Definitions (commercial motor vehicle). Up to date as of October 2, 2026. ecfr.gov/…/section-390.5
- 9Electronic Code of Federal Regulations (eCFR). 49 CFR 393.42, Brakes required on all wheels. Up to date as of October 1, 2026. ecfr.gov/…/section-393.42
- 10Electronic Code of Federal Regulations (eCFR). 49 CFR 393.48, Brakes to be operative. Up to date as of September 29, 2026. ecfr.gov/…/section-393.48
- 11Electronic Code of Federal Regulations (eCFR). 49 CFR 393.49, Control valves for brakes. Up to date as of October 2, 2026. ecfr.gov/…/section-393.49
- 12Federal Motor Carrier Safety Administration (FMCSA). Cargo Securement Rules. Last updated March 3, 2014. fmcsa.dot.gov/…/cargo-securement-rules
- 13National Highway Traffic Safety Administration (NHTSA). Check for Recalls: Vehicle, Car Seat, Tire, Equipment. No update date shown; accessed October 2026. nhtsa.gov/recalls
This article reflects the safety priorities of safe towing and trailer braking equipment. It is general education, not legal, insurance or mechanical advice. Trailer laws and handbooks change, so verify current rules with your state DMV, legislature or vehicle code. For your own rig, read your tow vehicle and trailer manuals and have a qualified towing or trailer shop inspect and set up your brakes. Reviewed October 2026.
Cite this article: Safety Behind the Wheel Foundation. “Trailer brakes and brake controllers: when states require them and how to set them up.” drivewithcare.org, https://drivewithcare.org/trailer-brakes-brake-controller-setup/. Reviewed October 2026.
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