I've read many times that exceeding GCVWR is a stopping safety issue.What I'm not understanding is the GCVWR assuming there are NOT electric brakes?Is it assuming trailer brake failure and the vehicle's GCVWR can fully stop both trailer and TV? From my experience, a well tuned brake controller the brakes just feel like stopping without a load at all. So how does exceeding GCVWR cause a safety issue stopping with electric brakes? Just curious, not doing it.

Hypothetically, in a perfect world, the trailer stops itself. But if you’ve towed much, you’d know that isn’t always the case, for various reasons. Additionally, it’s more than just braking ability that go into the combined weight rating.

SAE J2807 tow ratings allow for trailer brakes to be required, for tow ratings over 3,000 pounds. The owner's manual will state the threshold when brakes are required in order to be compliant with this standard. Some vehicles can achieve max tow rating without trailer brakes (Ford Explorer is one example), but modern pickups with their huge numbers absolutely require them.2020 F150 Owner's Manual wrote:"Important: The towing vehicle’s braking system is rated for operation at Gross Vehicle Weight Rating, not at Gross Combined Weight Rating. Separate functional brakes should be used for safe control of towed vehicles and for trailers where the Gross Combined Weight of the towing vehicle plus the trailer exceed the Gross Vehicle Weight Rating of the towing vehicle."FWIW - the actual standard for trailer stopping performance is:The combination is required to stop completely from 20 mph in 80 feet or less. During this stop test, the trailer must remain within an 11.5-foot-wide lane throughout the entire stop. In addition to the active testing, the parking brake must be able to hold the truck and trailer firmly in place both upward and downward on a 12 percent grade when it is at the maximum GCWR.

crasster wrote:I've read many times that exceeding GCVWR is a stopping safety issue.What I'm not understanding is the GCVWR assuming there are NOT electric brakes?Is it assuming trailer brake failure and the vehicle's GCVWR can fully stop both trailer and TV? From my experience, a well tuned brake controller the brakes just feel like stopping without a load at all. So how does exceeding GCVWR cause a safety issue stopping with electric brakes? Just curious, not doing it.Actually. Your tow vehicles brakes are only designed to stop the GVWR of the vehicle. NOT the GCVWR. that is why trailer brakes are required. So your TV can safely stop it's own max weight (GVWR). Anything over that the trailer brakes are supposed to stop. Yes the TV brakes may stop the trailer. Eventually. But not safely, especially in a E stop.

Terryallan wrote:crasster wrote:I've read many times that exceeding GCVWR is a stopping safety issue.What I'm not understanding is the GCVWR assuming there are NOT electric brakes?Is it assuming trailer brake failure and the vehicle's GCVWR can fully stop both trailer and TV? From my experience, a well tuned brake controller the brakes just feel like stopping without a load at all. So how does exceeding GCVWR cause a safety issue stopping with electric brakes? Just curious, not doing it.Actually. Your tow vehicles brakes are only designed to stop the GVWR of the vehicle. NOT the GCVWR. that is why trailer brakes are required. So your TV can safely stop it's own max weight (GVWR). Anything over that the trailer brakes are supposed to stop. Yes the TV brakes may stop the trailer. Eventually. But not safely, especially in a E stop.Okay thank you! I learned something new today. :)

Brakes on any vehicle are sized to the axle their on.A 7000 lb trailer axle = 7000 lb of braking performance.Same with the tow vehicle.A one to DRW with 9900 rawr and 6000 fawr = 15900 lbs of braking performance at a minimum.A triaxle trailer/7k axles = 21000 lb of braking performance.Now add the trucks 15900 lbs of braking performance = 36900 lbs of braking performance.As someone mentioned the trucks brakes stops the truck and the trailer brakes stops the trailer. If they don't then there is a reason why...but its time to get them fixed.

How does GCVWR affect stopping if you have trailer brakes?

Mike134
Explorer
Jan 29, 2020
SAE J2807 tow ratings also include the ability of the tow vehicle to stop the combination with total failure of the trailer brakes
Cummins12V98
Explorer III
Jan 29, 2020
Mike134 wrote:
SAE J2807 tow ratings also include the ability of the tow vehicle to stop the combination with total failure of the trailer brakes

There are multiple braking tests. One is the ability to hold the GCVWR on a specific grade with ONLY the use of the emergency brake.
Mickeyfan0805
Explorer
Jan 29, 2020
Cummins12V98 wrote:
My opinion and experience is they each stop them selves if each are in good shape.

And the other -in an emergency. Brake lines blew on the TV when trying to avoid an idiot who cut me off on the interstate last summer. It was the trailer brakes that got us to safety!
Terryallan
Explorer II
Jan 29, 2020
Mike134 wrote:
SAE J2807 tow ratings also include the ability of the tow vehicle to stop the combination with total failure of the trailer brakes

Yep. but it will take a while
Cummins12V98
Explorer III
Jan 29, 2020
Mickeyfan0805 wrote:
Cummins12V98 wrote:
My opinion and experience is they each stop them selves if each are in good shape.

And the other -in an emergency. Brake lines blew on the TV when trying to avoid an idiot who cut me off on the interstate last summer. It was the trailer brakes that got us to safety!

YIKES!
Terryallan
Explorer II
Jan 29, 2020
Mickeyfan0805 wrote:
Cummins12V98 wrote:
My opinion and experience is they each stop them selves if each are in good shape.

And the other -in an emergency. Brake lines blew on the TV when trying to avoid an idiot who cut me off on the interstate last summer. It was the trailer brakes that got us to safety!

Could you not use your parking / E brake on the truck? Those are operated mechanically. Have a cable that pulls them on.
troubledwaters
Explorer III
Jan 29, 2020
ScottG wrote:
...BTW, I have seen both Ford and GM write about this very subject and they make it clear that the trucks are part of the formula and have a major impact on stopping the trailer. So yes, it is clearly part of the certification or more accurately, it's part of the design criteria.
"Major Impact" - Count me as very skeptical on this. I' love to see one of those write-ups alluded to.
blt2ski
Moderator
Jan 30, 2020
I would suggest you figure out what an LEO/CVEO will test you on if pulled over, at some kind off scale etc.
You will find out, them real cops don't care about your manufactures warranty/weight ratings.
Example, your gcw is the sum of the TV axles, trailer Axel's per federal bridge laws, which usually is higher than manufactures ratings for light duty trucks and trailers that we on this forum drive tow etc.
If you are pulled over. One brake test is "is you trailers battery at 11.6V or higher. If yes, your good. If not, you have a failed brake system. Get new battery, or you will sit there until the trailer battery(s) are charged.
From a stop, enguage manual brake lever, or and or leo will pull e cable from the trailer, put TV in first, with trailer brakes activated, trailer should hold TV. If not, were all the trailer tires locked up? Or some locked, another freewheeling? If all locked up, you have enough torques, low treating etc, no big.
If the trailer moves, a wheel or more moves, you have a ticket for a failed brake system. You might get away with adjusting the brakes, OR you get to tear apart and fix trailer brakes at the pull over site, or get a flatbed tow to a shop to fix trailer
Another field test, you going 20mph, hit manual brake lever, trailer needs to slow truck down or ttoo a stop. Another is all brakes working, you stopping with in XX feet from 10-20 mph.
No test is done to my knowledge, that truck must stop trailer, BUT as noted, trailer may have to stop, hold or equal, the truck. My take, trailer brakes must be stronger than truck.
My 02 from classes out on by a WSP CVE Officer. Commercial or personal use towing here in Washington, require and follow the same rules, laws and field tests.

Marty
valhalla360
Navigator
Jan 30, 2020
I haven't read the SAE but I guarantee they have some fudge factors in their.

It's all well and good to say the trailer stops itself but reality is especially away from commercial operators, that's often not the case.

Plus, just having one operational brake on the trailer and none on the truck...you will likely eventually come to a stop on level ground...but I wouldn't want to try it in real life.
Groover
Explorer II
Jan 30, 2020
ScottG wrote:
The brakes on the vehicle help stop the trailer and this is designed into the vehicle. That's why trucks have such huge brakes for their size. Notice the brakes on trucks have gotten bigger over the years? Not because the trucks themselves are that much heavier, it's because they can tow much more than they used to.
The more weight you add to a given setup, the longer the stopping distance.

I have upgraded brakes on my truck and it stops the whole 17K# load faster.

BTW, I have seen both Ford and GM write about this very subject and they make it clear that the trucks are part of the formula and have a major impact on stopping the trailer. So yes, it is clearly part of the certification or more accurately, it's part of the design criteria.

The big reason that trucks have large brakes for their size is that empty tow vehicles generally have a high power to weight ratio, enabling people to drive faster with or without a trailer. The faster you drive the more brakes you need. You may notice that most performance cars have big brakes even though they have zero rated tow capacity. The big brakes do help stop trailers as an added benefit but the problem with that is then your braking ability is limited to the traction that the truck has. As your trailer get heavier that becomes a bigger and bigger issue. To stop quickly you need every tire on the ground doing all it can to help. If your trailer axles are carrying twice as much weight as the truck axles are and the trailer brakes fail you are going to take at least 3 times farther to stop, no matter how good the truck brakes are. In this case, fade resistant truck brakes will help keep the distance from being more than 3 times as far.

In general, a 7K axle on a trailer does not need to be as large as the brakes on a 7k truck axle because you physically can't do repetitive stops as frequently due to the mass of the trailer slowing your acceleration. The brakes have longer to cool down during the slower acceleration and when you do use them the power produced by engine is split between more brakes.

Good trailer brakes also help prevent jacknife situations.