Brakes and tires
What gain should your brake controller start at?
Any page that gives you one gain number and stops is selling certainty it does not have. Gain depends on the brake type, the condition of the drums, magnet wear, axle count, how the trailer is loaded and how the tow vehicle brakes behave, and none of that is knowable from two weights.
What there is instead is a repeatable procedure, and the procedure is the real answer. The number below exists so you have somewhere sensible to start, scaled by the ratio between the two weights, because a trailer heavier than the tow vehicle needs its brakes doing more of the work.
A starting point, then go and set it
Start at 6.4, then set it properly at 25 mph with the manual override lever alone.
| Figure | Value |
|---|---|
| Weight ratio | 1.21 |
| Starting gain | 6.4 |
| Usual working range | 5.4 to 7.4 |
| Trailer heavier than the tow vehicle | yes |
Shown with the example figures above. Change any field to run your own numbers.
The working
Rule of thumbratio = loaded trailer weight / loaded tow vehicle weight start = 3.5 + ratio x 2.4 minus 0.6 for 3 or more axles, plus 0.5 for a single axle THEN set it properly at 25 mph with the manual override lever alone
This is a starting point scaled by the weight ratio, not a specification. No formula gets brake gain right. Widely taught towing convention rather than a published specification. It is a good starting point and it is not a rating.
Controllers and breakaway hardware
A proportional controller matches the trailer brakes to how hard you are actually stopping. A breakaway battery that has quietly gone flat gives no warning at all, so a kit with a charge display earns its money.
CURT Echo Kit, Bluetooth Brake Controller with Manual Override Button
$342.90 Published ratingsThe Echo with a physical manual override button included. Sway response depends on being able to apply the trailer brakes alone, instantly, without unlocking a phone, so this is the version worth the extra money.
Best for: Anybody buying an Echo who intends to tow a trailer big enough to sway.
Check price on Amazon
CURT Echo Mobile Bluetooth Trailer Brake Controller, 7-way, 1 to 2 axles
$289.95 Published ratingsPlugs in between the truck and trailer connectors with no wiring at all, and is controlled from a phone. It moves between vehicles in seconds, which is the entire point: a rental truck, a borrowed truck or a second vehicle needs no install.
Check before buying: Manual override lives in the phone app on the base unit, which is not where you want it when a trailer starts to sway. The Echo Kit adds a physical override button and is the version to buy for that reason.
Best for: Towing with a vehicle you do not own, or with more than one vehicle.
Check price on Amazon
Tekonsha Prodigy iD Brake Controller, 1 to 4 axles
$229.99 Published ratingsConfigured from a phone rather than through a two button interface, and it supports four axles, which matters on a triple axle fifth wheel or a heavy equipment trailer.
Best for: A four axle trailer, or somebody who tows several trailers and wants saved profiles.
Check price on Amazon
REDARC Tow-Pro Liberty Electric Trailer Brake Controller, 1 to 2 axles
$190.00 Published ratingsThe control head is a single knob that mounts flush in a blank switch panel, with the electronics hidden behind the dash. On a modern truck with no room under the dash for a brick, this is frequently the only tidy answer.
Best for: A vehicle with no space for a conventional controller, or anybody who does not want a box hanging below the steering column.
Check price on Amazon
Tekonsha Primus IQ Proportional Brake Controller, 1 to 3 axles
$157.99 Published ratingsThe controller the rest of this category gets compared to, and the one a dozen listings on Amazon describe themselves as replacing. Proportional, self levelling so mounting angle does not matter much, and a boost setting for a heavy trailer.
Best for: Almost anybody adding a controller to a truck that does not have one built in.
Check price on Amazon
CURT Venturer Next Electric Trailer Brake Controller, time delay, 1 to 3 axles
$76.11The cheapest controller here from a maker with a service path. It is time delay rather than proportional, which means it ramps to a preset rather than matching how hard you are actually braking. For a light trailer towed occasionally that is an acceptable trade; for a heavy one it is not.
Check before buying: Time delay is a genuine functional step down from proportional. The trailer brakes come on at the same rate whether you are slowing gently or stopping hard.
Best for: A light trailer, towed a few times a year, on a budget.
Check price on AmazonEvery rating shown is the manufacturer's own published figure. The rating on the part you receive is what governs, and your own door jamb sticker governs everything above it.
The procedure that actually sets it
- Find a flat, dry, empty surface. Nothing behind you and nothing to hit. An empty industrial road or a large empty lot. Not a public highway and not in the rain.
- Set the gain to the starting figure. From the result above. It will almost certainly be wrong, and that is fine, because you are about to correct it.
- Roll at about 25 mph. Slow enough to be safe, fast enough that the brakes have something to do.
- Apply the manual override lever ALONE. Foot completely off the vehicle brake pedal. You are testing the trailer brakes by themselves, which is the only way to feel what they are actually doing.
- Raise the gain until they just barely grab, then back it off. You want the point where the trailer noticeably pulls the rig back, just short of locking a wheel. Then reduce slightly so they do not lock.
- Re-check whenever anything changes. A different load, a different trailer, wet weather, or new brake shoes all move the setting. Shoes bed in, so re-check after the first few hundred miles on new ones.
Proportional against time delay
These are two genuinely different products, and the difference shows up worst in an emergency stop.
A proportional controller matches the trailer brakes to how hard the tow vehicle is actually decelerating. A time delay controller ramps to a preset regardless.
Published standard A published, traceable figure: a standards body, a federal regulation or a manufacturer specification states it.
| Type | How it decides | What it feels like | Where it suits |
|---|---|---|---|
| Proportional | Reads actual tow vehicle deceleration with an inertia sensor | Gentle stops stay gentle, hard stops get everything | Anything heavy, or towed often |
| Time delay | Ramps to a preset over a fixed period when the pedal is pressed | Dragging in light braking, not enough in an emergency | A light trailer towed a few times a year |
The gain setting controls the ratio on a proportional controller and the ceiling on a time delay one. Neither is set correctly from a table.
The breakaway system nobody checks
A breakaway switch applies the trailer brakes fully if the trailer separates from the tow vehicle. It runs off a small battery on the trailer, charged through the 7-way connector.
That battery is flat on a great many trailers on the road. A trailer that has sat all winter unplugged has nothing left, and there is no warning of any kind. Test it: pull the pin with the trailer hitched and try to move forward a few feet. The brakes should lock hard. Then push the pin back in.
Check the cable too. It attaches to the tow vehicle, never to a safety chain, because a chain stays with the trailer in a separation and a cable clipped to it does nothing at all.
Frequently asked questions
How do I set trailer brake controller gain?
Roll at about 25 mph on a flat, dry, empty surface and apply the manual override lever alone with your foot off the brake pedal. Raise the gain until the trailer brakes just barely grab, then back it off slightly so they do not lock. No calculation substitutes for that test, because gain depends on brake condition, magnet wear and how the trailer is loaded.
How do I know if the gain is too low?
The rig feels like the tow vehicle is doing all the stopping, stopping distances feel long, and on a descent the tow vehicle brakes get hot and start to fade. You may also feel the trailer pushing the tow vehicle in a hard stop. The override test tells you directly: if pulling the lever at 25 mph barely slows you, the gain is too low.
How do I know if the gain is too high?
The trailer brakes grab, the stop feels jerky, and in the worst case a trailer wheel locks and skids, which flat spots the tire and removes your control over the trailer. On the manual override test at 25 mph, a wheel that locks means back the gain off until it does not.
Does the gain setting change with the load?
Yes, and this is the setting people forget. A trailer loaded for a two week trip needs more gain than the same trailer travelling empty. Wet weather also changes it. Re-run the 25 mph override test whenever the load changes meaningfully, and always after fitting new brake shoes, which bed in over the first few hundred miles.
Is a proportional controller worth it over time delay?
For anything heavy or towed often, yes. A proportional controller matches trailer braking to how hard the tow vehicle is actually decelerating, so gentle stops stay gentle and hard stops get everything. A time delay controller ramps to a preset regardless, which feels like dragging in light braking and like not enough in an emergency stop.
When are trailer brakes required by law?
There is no single federal weight for a light trailer. It is state law and the threshold genuinely varies, commonly between 1,500 and 5,000 lb, with some states using a ratio to the tow vehicle weight instead. Check your own state and every state you drive through, and check the trailer certification label, which frequently requires brakes on its own terms.
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Researched, not professional advice. This page is compiled from published standards, manufacturer towing guides and product specifications, and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are towing convention rather than published standards, and they are labelled that way wherever they appear. Nothing here overrides your own ratings. Work your payload sum before your tow rating, because payload is the limit that actually binds on most half ton trucks and nearly every SUV. Load a conventional trailer to 10 to 15 percent tongue weight and a fifth wheel to 15 to 25 percent pin weight, and never lighter: a tail heavy trailer is what starts sway. Weigh the rig loaded rather than trusting a brochure dry weight. A weight distribution hitch and a set of air bags both restore ride height and control, and neither one raises a single rating. Trailer brakes are required by state law above a threshold that varies by state, and a breakaway battery that has quietly gone flat is the normal condition of most trailers on the road.